ZOONOMIA; OR, THE LAWS OF ORGANIC LIFE. VOL. I. _By ERASMUS DARWIN, M. D. F. R. S. _ AUTHOR OF THE BOTANIC GARDEN. * * * * * Principiò coelum, ac terras, camposque liquentes, Lucentemque globum lunæ, titaniaque astra, Spiritus intùs alit, totamque infusa per artus Mens agitat molem, et magno se corpore miscet. --VIRG. Æn. Vi. Earth, on whose lap a thousand nations tread, And Ocean, brooding his prolific bed, Night's changeful orb, blue pole, and silvery zones, Where other worlds encircle other suns, One Mind inhabits, one diffusive Soul Wields the large limbs, and mingles with the whole. * * * * * _THE SECOND EDITION, CORRECTED. _ * * * * * LONDON:PRINTED FOR. J. JOHNSON, IN ST. PAUL'S CHURCH-YARD. 1796. Entered at Stationers' Hall. * * * * * DEDICATION. To the candid and ingenious Members of the College of Physicians, of theRoyal Philosophical Society, of the Two Universities, and to all those, whostudy the Operations of the Mind as a Science, or who practice Medicine asa Profession, the subsequent Work is, with great respect, inscribed by theAuthor, DERBY, May 1, 1794. CONTENTS. _Preface. _ SECT. I. _Of Motion. _ II. _Explanations and Definitions. _ III. _The Motions of the Retina demonstrated by Experiments. _ IV. _Laws of Animal Causation. _ V. _Of the four Faculties or Motions of the Sensorium. _ VI. _Of the four Classes of Fibrous Motions. _ VII. _Of Irritative Motions. _ VIII. _Of Sensitive Motions. _ IX. _Of Voluntary Motions. _ X. _Of Associate Motions. _ XI. _Additional Observations on the Sensorial Powers. _ XII. _Of Stimulus, Sensorial Exertion, and Fibrous Contraction. _ XIII. _Of Vegetable Animation. _ XIV. _Of the Production of Ideas. _ XV. _Of the Classes of Ideas. _ XVI. _Of Instinct. _ XVII. _The Catenation of Animal Motions. _ XVIII. _Of Sleep. _ XIX. _Of Reverie. _ XX. _Of Vertigo. _ XXI. _Of Drunkenness. _ XXII. _Of Propensity to Motion. Repetition. Imitation. _ XXIII. _Of the Circulatory System. _ XXIV. _Of the Secretion of Saliva, and of Tears. And of the Lacrymal Sack. _ XXV. _Of the Stomach and Intestines. _ XXVI. _Of the Capillary Glands, and of the Membranes. _ XXVII. _Of Hemorrhages. _ XXVIII. _The Paralysis of the Lacteals. _ XXIX. _The Retrograde Motions of the Absorbent Vessels. _ XXX. _The Paralysis of the Liver. _ XXXI. _Of Temperaments. _ XXXII. _Diseases of Irritation. _ XXXIII. ---- _of Sensation. _ XXXIV. ---- _of Volition. _ XXXV. ---- _of Relation. _ XXXVI. _The Periods of Diseases. _ XXXVII. _Of Digestion, Secretion, Nutrition. _ XXXVIII. _Of the Oxygenation of the Blood in the Lungs and Placenta. _ XXXIX. _Of Generation. _ XL. _Of Ocular Spectra. _ * * * * * TO ERASMUS DARWIN, ON HIS WORK INTITLED ZOONOMIA, _By DEWHURST BILSBORROW. _ * * * * * HAIL TO THE BARD! who sung, from Chaos hurl'd How suns and planets form'd the whirling world; How sphere on sphere Earth's hidden strata bend, And caves of rock her central fires defend; Where gems new-born their twinkling eyes unfold, 5 And young ores shoot in arborescent gold. How the fair Flower, by Zephyr woo'd, unfurls Its panting leaves, and waves its azure curls; Or spreads in gay undress its lucid form To meet the sun, and shuts it to the storm; 10 While in green veins impassion'd eddies move, And Beauty kindles into life and love. How the first embryon-fibre, sphere, or cube, Lives in new forms, --a line, --a ring, --a tube; Closed in the womb with limbs unfinish'd laves, 15 Sips with rude mouth the salutary waves; Seeks round its cell the sanguine streams, that pass, And drinks with crimson gills the vital gas; Weaves with soft threads the blue meandering vein, The heart's red concave, and the silver brain; 20 Leads the long nerve, expands the impatient sense, And clothes in silken skin the nascent Ens. Erewhile, emerging from its liquid bed, It lifts in gelid air its nodding head; The lights first dawn with trembling eyelid hails, 25 With lungs untaught arrests the balmy gales; Tries its new tongue in tones unknown, and hears The strange vibrations with unpractised ears; Seeks with spread hands the bosom's velvet orbs. With closing lips the milky fount absorbs; 30 And, as compress'd the dulcet streams distil, Drinks warmth and fragrance from the living rill;-- Eyes with mute rapture every waving line, Prints with adoring kiss the Paphian shrine, And learns erelong, the perfect form confess'd, 35 Ideal Beauty from its mother's breast. Now in strong lines, with bolder tints design'd, You sketch ideas, and portray the mind; Teach how fine atoms of impinging light To ceaseless change the visual sense excite; 40 While the bright lens collects the rays, that swerve, And bends their focus on the moving nerve. How thoughts to thoughts are link'd with viewless chains, Tribes leading tribes, and trains pursuing trains; With shadowy trident how Volition guides, 45 Surge after surge, his intellectual tides; Or, Queen of Sleep, Imagination roves With frantic Sorrows, or delirious Loves. Go on, O FRIEND! explore with eagle-eye; Where wrapp'd in night retiring Causes lie: 50 Trace their slight bands, their secret haunts betray, And give new wonders to the beam of day; Till, link by link with step aspiring trod, You climb from NATURE to the throne of GOD. --So saw the Patriarch with admiring eyes 55 From earth to heaven a golden ladder rise; Involv'd in clouds the mystic scale ascends, And brutes and angels crowd the distant ends. TRIN. COL. CAMBRIDGE, _Jan. _ 1, 1794. * * * * * REFERENCES TO THE WORK. _Botanic Garden. _ Part I. Line 1. Canto I. L. 105. ---- 3. ---- IV. L. 402. ---- 4. ---- I. L. 140. ---- 5. ---- III. L. 401. ---- 8. ---- IV. L. 452. ---- 9. ---- I. L. 14. _Zoonomia. _ ---- 12. Sect. XIII. ---- 13. ---- XXXIX. 4. 1. ---- 18. ---- XVI. 2. And XXXVIII. ---- 26. ---- XVI. 4. ---- 30. ---- XVI. 4. ---- 36. ---- XVI. 6. ---- 38. ---- III. And VII. ---- 43. ---- X. ---- 44. ---- XVIII. 17. ---- 45. ---- XVII. 3. 7. ---- 47. ---- XVIII. 8. ---- 50. ---- XXXIX. 4. 8. ---- 51. ---- XXXIX the Motto. ---- 54. ---- XXXIX. 8. * * * * * PREFACE. * * * * * The purport of the following pages is an endeavour to reduce the factsbelonging to ANIMAL LIFE into classes, orders, genera, and species; and, bycomparing them with each other, to unravel the theory of diseases. Ithappened, perhaps unfortunately for the inquirers into the knowledge ofdiseases, that other sciences had received improvement previous to theirown; whence, instead of comparing the properties belonging to animatednature with each other, they, idly ingenious, busied themselves inattempting to explain the laws of life by those of mechanism and chemistry;they considered the body as an hydraulic machine, and the fluids as passingthrough a series of chemical changes, forgetting that animation was itsessential characteristic. The great CREATOR of all things has infinitely diversified the works of hishands, but has at the same time stamped a certain similitude on thefeatures of nature, that demonstrates to us, that _the whole is one familyof one parent_. On this similitude is founded all rational analogy; which, so long as it is concerned in comparing the essential properties of bodies, leads us to many and important discoveries; but when with licentiousactivity it links together objects, otherwise discordant, by some fancifulsimilitude; it may indeed collect ornaments for wit and poetry, butphilosophy and truth recoil from its combinations. The want of a theory, deduced from such strict analogy, to conduct thepractice of medicine is lamented by its professors; for, as a great numberof unconnected facts are difficult to be acquired, and to be reasoned from, the art of medicine is in many instances less efficacious under thedirection of its wisest practitioners; and by that busy crowd, who eitherboldly wade in darkness, or are led into endless error by the glare offalse theory, it is daily practised to the destruction of thousands; add tothis the unceasing injury which accrues to the public by the perpetualadvertisements of pretended nostrums; the minds of the indolent becomesuperstitiously fearful of diseases, which they do not labour under; andthus become the daily prey of some crafty empyric. A theory founded upon nature, that should bind together the scattered factsof medical knowledge, and converge into one point of view the laws oforganic life, would thus on many accounts contribute to the interest ofsociety. It would capacitate men of moderate abilities to practise the artof healing with real advantage to the public; it would enable every one ofliterary acquirements to distinguish the genuine disciples of medicine fromthose of boastful effrontery, or of wily address; and would teach mankindin some important situations the _knowledge of themselves_. There are some modern practitioners, who declaim against medical theory ingeneral, not considering that to think is to theorize; and that no one candirect a method of cure to a person labouring under disease withoutthinking, that is, without theorizing; and happy therefore is the patient, whose physician possesses the best theory. The words idea, perception, sensation, recollection, suggestion, andassociation, are each of them used in this treatise in a more limited sensethan in the writers of metaphysic. The author was in doubt, whether heshould rather have substituted new words instead of them; but was at lengthof opinion, that new definitions of words already in use would be lessburthensome to the memory of the reader. A great part of this work has lain by the writer above twenty years, assome of his friends can testify: he had hoped by frequent revision to havemade it more worthy the acceptance of the public; this however his otherperpetual occupations have in part prevented, and may continue to prevent, as long as he may be capable of revising it; he therefore begs of thecandid reader to accept of it in its present state, and to excuse anyinaccuracies of expression, or of conclusion, into which the intricacy ofhis subject, the general imperfection of language, or the frailty he has incommon with other men, may have betrayed him; and from which he has not thevanity to believe this treatise to be exempt. * * * * * ZOONOMIA. * * * * * SECT. I. OF MOTION. The whole of nature may be supposed to consist of two essences orsubstances; one of which may be termed spirit, and the other matter. Theformer of these possesses the power to commence or produce motion, and thelatter to receive and communicate it. So that motion, considered as acause, immediately precedes every effect; and, considered as an effect, itimmediately succeeds every cause. The MOTIONS OF MATTER may be divided into two kinds, primary and secondary. The secondary motions are those, which are given to or received from othermatter in motion. Their laws have been successfully investigated byphilosophers in their treatises on mechanic powers. These motions aredistinguished by this circumstance, that the velocity multiplied into thequantity of matter of the body acted upon is equal to the velocitymultiplied into the quantity of matter of the acting body. The primary motions of matter may be divided into three classes, thosebelonging to gravitation, to chemistry, and to life; and each class has itspeculiar laws. Though these three classes include the motions of solid, liquid, and aerial bodies; there is nevertheless a fourth division ofmotions; I mean those of the supposed ethereal fluids of magnetism, electricity, heat, and light; whose properties are not so well investigatedas to be classed with sufficient accuracy. _1st. _ The gravitating motions include the annual and diurnal rotation ofthe earth and planets, the flux and reflux of the ocean, the descent ofheavy bodies, and other phænomena of gravitation. The unparalleled sagacityof the great NEWTON has deduced the laws of this class of motions from thesimple principle of the general attraction of matter. These motions aredistinguished by their tendency to or from the centers of the sun orplanets. _2d. _ The chemical class of motions includes all the various appearances ofchemistry. Many of the facts, which belong to these branches of science, are nicely ascertained, and elegantly classed; but their laws have not yetbeen developed from such simple principles as those above-mentioned; thoughit is probable, that they depend on the specific attractions belonging tothe particles of bodies, or to the difference of the quantity of attractionbelonging to the sides and angles of those particles. The chemical motionsare distinguished by their being generally attended with an evidentdecomposition or new combination of the active materials. _3d. _ The third class includes all the motions of the animal and vegetableworld; as well those of the vessels, which circulate their juices, and ofthe muscles, which perform their locomotion, as those of the organs ofsense, which constitute their ideas. This last class of motion is the subject of the following pages; which, though conscious of their many imperfections, I hope may give some pleasureto the patient reader, and contribute something to the knowledge and to thecure of diseases. * * * * * SECT. II. EXPLANATIONS AND DEFINITIONS. I. _Outline of the animal economy. _--II. 1. _Of the sensorium. _ 2. _Of the brain and nervous medulla. _ 3. _A nerve. _ 4. _A muscular fibre. _ 5. _The immediate organs of sense. _ 6. _The external organs of sense. _ 7. _An idea or sensual motion. _ 8. _Perception. _ 9. _Sensation. _ 10. _Recollection and suggestion. _ 11. _Habit, causation, association, catenation. _ 12. _Reflex ideas. _ 13. _Stimulus defined. _ * * * * * As some explanations and definitions will be necessary in the prosecution of the work, the reader is troubled with them in this place, and is intreated to keep them in his mind as he proceeds, and to take them for granted, till an apt opportunity occurs to evince their truth; to which I shall premise a very short outline of the animal economy. * * * * * I. --1. The nervous system has its origin from the brain, and is distributedto every part of the body. Those nerves, which serve the senses, principally arise from that part of the brain, which is lodged in the head;and those, which serve the purposes of muscular motion, principally arisefrom that part of the brain, which is lodged in the neck and back, andwhich is erroneously called the spinal marrow. The ultimate fibrils ofthese nerves terminate in the immediate organs of sense and muscularfibres, and if a ligature be put on any part of their passage from the heador spine, all motion and perception cease in the parts beneath theligature. 2. The longitudinal muscular fibres compose the locomotive muscles, whosecontractions move the bones of the limbs and trunk, to which theirextremities are attached. The annular or spiral muscular fibres compose thevascular muscles, which constitute the intestinal canal, the arteries, veins, glands, and absorbent vessels. 3. The immediate organs of sense, as the retina of the eye, probablyconsist of moving fibrils, with a power of contraction similar to that ofthe larger muscles above described. 4. The cellular membrane consists of cells, which resemble those of asponge, communicating with each other, and connecting together all theother parts of the body. 5. The arterial system consists of the aortal and the pulmonary artery, which are attended through their whole course with their correspondentveins. The pulmonary artery receives the blood from the right chamber ofthe heart, and carries it to the minute extensive ramifications of thelungs, where it is exposed to the action of the air on a surface equal tothat of the whole external skin, through the thin moist coats of thosevessels, which are spread on the air-cells, which constitute the minuteterminal ramifications of the wind-pipe. Here the blood changes its colourfrom a dark red to a bright scarlet. It is then collected by the branchesof the pulmonary vein, and conveyed to the left chamber of the heart. 6. The aorta is another large artery, which receives the blood from theleft chamber of the heart, after it has been thus aerated in the lungs, andconveys it by ascending and descending branches to every other part of thesystem; the extremities of this artery terminate either in glands, as thesalivary glands, lacrymal glands, &c. Or in capillary vessels, which areprobably less involuted glands; in these some fluid, as saliva, tears, perspiration, are separated from the blood; and the remainder of the bloodis absorbed or drank up by branches of veins correspondent to the branchesof the artery; which are furnished with valves to prevent its return; andis thus carried back, after having again changed its colour to a dark red, to the right chamber of the heart. The circulation of the blood in theliver differs from this general system; for the veins which drink up therefluent blood from those arteries, which are spread on the bowels andmesentery, unite into a trunk in the liver, and form a kind of artery, which is branched into the whole substance of the liver, and is called thevena portarum; and from which the bile is separated by the numerous hepaticglands, which constitute that viscus. 7. The glands may be divided into three systems, the convoluted glands, such as those above described, which separate bile, tears, saliva, &c. Secondly, the glands without convolution, as the capillary vessels, whichunite the terminations of the arteries and veins; and separate both themucus, which lubricates the cellular membrane, and the perspirable matter, which preserves the skin moist and flexible. And thirdly, the wholeabsorbent system, consisting of the lacteals, which open their mouths intothe stomach and intestines, and of the lymphatics, which open their mouthson the external surface of the body, and on the internal linings of all thecells of the cellular membrane, and other cavities of the body. These lacteal and lymphatic vessels are furnished with numerous valves toprevent the return of the fluids, which they absorb, and terminate inglands, called lymphatic glands, and may hence be considered as long necksor mouths belonging to these glands. To these they convey the chyle andmucus, with a part of the perspirable matter, and atmospheric moisture; allwhich, after having passed through these glands, and having suffered somechange in them, are carried forward into the blood, and supply perpetualnourishment to the system, or replace its hourly waste. 8. The stomach and intestinal canal have a constant vermicular motion, which carries forwards their contents, after the lacteals have drank up thechyle from them; and which is excited into action by the stimulus of thealiment we swallow, but which becomes occasionally inverted or retrograde, as in vomiting, and in the iliac passion. II. 1. The word _sensorium_ in the following pages is designed to expressnot only the medullary part of the brain, spinal marrow, nerves, organs ofsense, and of the muscles; but also at the same time that living principle, or spirit of animation, which resides throughout the body, without beingcognizable to our senses, except by its effects. The changes whichoccasionally take place in the sensorium, as during the exertions ofvolition, or the sensations of pleasure or pain, are termed _sensorialmotions_. 2. The similarity of the texture of the brain to that of the pancreas, andsome other glands of the body, has induced the inquirers into this subjectto believe, that a fluid, perhaps much more subtile than the electric aura, is separated from the blood by that organ for the purposes of motion andsensation. When we recollect, that the electric fluid itself is actuallyaccumulated and given out voluntarily by the torpedo and the gymnotuselectricus, that an electric shock will frequently stimulate into motion aparalytic limb, and lastly that it needs no perceptible tubes to convey it, this opinion seems not without probability; and the singular figure of thebrain and nervous system seems well adapted to distribute it over everypart of the body. For the medullary substance of the brain not only occupies the cavities ofthe head and spine, but passes along the innumerable ramifications of thenerves to the various muscles and organs of sense. In these it lays asideits coverings, and is intermixed with the slender fibres, which constitutethose muscles and organs of sense. Thus all these distant ramifications ofthe sensorium are united at one of their extremities, that is, in the headand spine; and thus these central parts of the sensorium constitute acommunication between all the organs of sense and muscles. 3. A _nerve_ is a continuation of the medullary substance of the brain fromthe head or spine towards the other parts of the body, wrapped in itsproper membrane. 4. The _muscular fibres_ are moving organs intermixed with that medullarysubstance, which is continued along the nerves, as mentioned above. Theyare indued with the power of contraction, and are again elongated either byantagonist muscles, by circulating fluids, or by elastic ligaments. So themuscles on one side of the forearm bend the fingers by means of theirtendons, and those on the other side of the fore-arm extend them again. Thearteries are distended by the circulating blood; and in the necks ofquadrupeds there is a strong elastic ligament, which assists the muscles, which elevate the head, to keep it in its horizontal position, and to raiseit after it has been depressed. 5. The _immediate organs of sense_ consist in like manner of moving fibresenveloped in the medullary substance above mentioned; and are erroneouslysupposed to be simply an expansion of the nervous medulla, as the retina ofthe eye, and the rete mucosum of the skin, which are the immediate organsof vision, and of touch. Hence when we speak of the contractions of thefibrous parts of the body, we shall mean both the contractions of themuscles, and those of the immediate organs of sense. These _fibrousmotions_ are thus distinguished from the _sensorial motions_ abovementioned. 6. The _external organs_ of sense are the coverings of the immediate organsof sense, and are mechanically adapted for the reception or transmission ofpeculiar bodies, or of their qualities, as the cornea and humours of theeye, the tympanum of the ear, the cuticle of the finders and tongue. 7. The word _idea_ has various meanings in the writers of metaphysic: it ishere used simply for those notions of external things, which our organs ofsense bring us acquainted with originally; and is defined a contraction, ormotion, or configuration, of the fibres, which constitute the immediateorgan of sense; which will be explained at large in another part of thework. Synonymous with the word idea, we shall sometimes use the words_sensual motion_ in contradistinction to _muscular motion_. 8. The word _perception_ includes both the action of the organ of sense inconsequence of the impact of external objects, and our attention to thataction; that is, it expresses both the motion of the organ of sense, oridea, and the pain or pleasure that succeeds or accompanies it. 9. The pleasure or pain which necessarily accompanies all those perceptionsor ideas which we attend to, either gradually subsides, or is succeeded byother fibrous motions. In the latter case it is termed _sensation_, asexplained in Sect. V. 2, and VI. 2. --The reader is intreated to keep thisin his mind, that through all this treatise the word sensation is used toexpress pleasure or pain only in its active state, by whatever means it isintroduced into the system, without any reference to the stimulation ofexternal objects. 10. The vulgar use of the word _memory_ is too unlimited for our purpose:those ideas which we voluntarily recall are here termed ideas of_recollection_, as when we will to repeat the alphabet backwards. And thoseideas which are suggested to us by preceding ideas are here termed ideas of_suggestion_, as whilst we repeat the alphabet in the usual order; when byhabits previously acquired B is suggested by A, and C by B, without anyeffort of deliberation. 11. The word _association_ properly signifies a society or convention ofthings in some respects similar to each other. We never say in commonlanguage, that the effect is associated with the cause, though theynecessarily accompany or succeed each other. Thus the contractions of ourmuscles and organs of sense may be said to be associated together, butcannot with propriety be said to be associated with irritations, or withvolition, or with sensation; because they are caused by them, as mentionedin Sect. IV. When fibrous contractions succeed other fibrous contractions, the connection is termed _association_; when fibrous contractions succeedsensorial motions, the connection is termed _causation_; when fibrous andsensorial motions reciprocally introduce each other in progressive trainsor tribes, it is termed _catenation_ of animal motions. All theseconnections are said to be produced by _habit_; that is, by frequentrepetition. 12. It may be proper to observe, that by the unavoidable idiom of ourlanguage the ideas of perception, of recollection, or of imagination, inthe plural number signify the ideas belonging to perception, torecollection, or to imagination; whilst the idea of perception, ofrecollection, or of imagination, in the singular number is used for what istermed "a reflex idea of any of those operations of the sensorium. " 13. By the word _stimulus_ is not only meant the application of externalbodies to our organs of sense and muscular fibres, which excites intoaction the sensorial power termed irritation; but also pleasure or pain, when they excite into action the sensorial power termed sensation; anddesire or aversion, when they excite into action the power of volition; andlastly, the fibrous contractions which precede association; as is furtherexplained in Sect. XII. 2. 1. * * * * * SECT. III. THE MOTIONS OF THE RETINA DEMONSTRATED BY EXPERIMENTS. I. _Of animal motions and of ideas. _ II. _The fibrous structure of the retina. _ III. _The activity of the retina in vision. _ 1. _Rays of light have no momentum. _ 2. _Objects long viewed become fainter. _ 3. _Spectra of black objects become luminous. _ 4. _Varying spectra from gyration. _ 5. _From long inspection of various colours. _ IV. _Motions of the organs of sense constitute ideas. _ 1. _Light from pressing the eye-ball, and sound from the pulsation of the carotid artery. _ 2. _Ideas in sleep mistaken for perceptions. _ 3. _Ideas of imagination produce pain and sickness like sensations. _ 4. _When the organ of sense is destroyed, the ideas belonging to that sense perish. _ V. _Analogy between muscular motions and sensual motions, or ideas. _ 1. _They are both originally excited by irritations. _ 2. _And associated together in the same manner. _ 3. _Both act in nearly the same times. _ 4. _Are alike strengthened or fatigued by exercise. _ 5. _Are alike painful from inflammation. _ 6. _Are alike benumbed by compression. _ 7. _Are alike liable to paralysis. _ 8. _To convulsion. _ 9. _To the influence of old age. _--VI. _Objections answered. _ 1. _Why we cannot invent new ideas. _ 2. _If ideas resemble external objects. _ 3. _Of the imagined sensation in an amputated limb. _ 4. _Abstract ideas. _--VII. _What are ideas, if they are not animal motions?_ Before the great variety of animal motions can be duly arranged intonatural classes and orders, it is necessary to smooth the way to this yetunconquered field of science, by removing some obstacles which thwart ourpassage. I. To demonstrate that the retina and other immediate organs ofsense possess a power of motion, and that these motions constitute ourideas, according to the fifth and seventh of the preceding assertions, claims our first attention. Animal motions are distinguished from the communicated motions, mentionedin the first section, as they have no mechanical proportion to their cause;for the goad of a spur on the skin of a horse shall induce him to move aload of hay. They differ from the gravitating motions there mentioned asthey are exerted with equal facility in all directions, and they differfrom the chemical class of motions, because no apparent decompositions ornew combinations are produced in the moving materials. Hence, when we say animal motion is excited by irritation, we do not meanthat the motion bears any proportion to the mechanical impulse of thestimulus; nor that it is affected by the general gravitation of the twobodies; nor by their chemical properties, but solely that certain animalfibres are excited into action by something external to the moving organ. In this sense the stimulus of the blood produces the contractions of theheart; and the substances we take into our stomach and bowels stimulatethem to perform their necessary functions. The rays of light excite theretina into animal motion by their stimulus; at the same time that thoserays of light themselves are physically converged to a focus by theinactive humours of the eye. The vibrations of the air stimulate theauditory nerve into animal action; while it is probable that the tympanumof the ear at the same time undergoes a mechanical vibration. To render this circumstance more easy to be comprehended, _motion may bedefined to be a variation of figure_; for the whole universe may beconsidered as one thing possessing a certain figure; the motions of any ofits parts are a variation of this figure of the whole: this definition ofmotion will be further explained in Section XIV. 2. 2. On the production ofideas. Now the motions of an organ of sense are a succession of configurations ofthat organ; these configurations succeed each other quicker or slower; andwhatever configuration of this organ of sense, that is, whatever portion ofthe motion of it is, or has usually been, attended to, constitutes an idea. Hence the configuration is not to be considered as an effect of the motionof the organ, but rather as a part or temporary termination of it; andthat, whether a pause succeeds it, or a new configuration immediately takesplace. Thus when a succession of moving objects are presented to our view, the ideas of trumpets, horns, lords and ladies, trains and canopies, areconfigurations, that is, parts or links of the successive motions of theorgan of vision. [Illustration: Plate I. ] These motions or configurations of the organs of sense differ from thesensorial motions to be described hereafter, as they appear to be simplycontractions of the fibrous extremities of those organs, and in thatrespect exactly resemble the motions or contractions of the larger muscles, as appears from the following experiment. Place a circular piece of redsilk about an inch in diameter on a sheet of white paper in a strong light, as in Plate I. --look for a minute on this area, or till the eye becomessomewhat fatigued, and then, gently closing your eyes, and shading themwith your hand, a circular green area of the same apparent diameter becomesvisible in the closed eye. This green area is the colour reverse to the redarea, which had been previously inspected, as explained in the experimentson ocular spectra at the end of the work, and in Botanical Garden, P. 1. Additional note, No. 1. Hence it appears, that a part of the retina, whichhad been fatigued by contraction in one direction, relieves itself byexerting the antagonist fibres, and producing a contraction in an oppositedirection, as is common in the exertions of our muscles. Thus when we aretired with long action of our arms in one direction, as in holding a bridleon a journey, we occasionally throw them into an opposite position torelieve the fatigued muscles. Mr. Locke has defined an idea to be "whatever is present to the mind;" butthis would include the exertions of volition, and the sensations ofpleasure and pain, as well as those operations of our system, whichacquaint us with external objects; and is therefore too unlimited for ourpurpose. Mr. Lock seems to have fallen into a further error, by conceiving, that the mind could form a general or abstract idea by its own operation, which was the copy of no particular perception; as of a triangle ingeneral, that was neither acute, obtuse, nor right angled. The ingeniousDr. Berkley and Mr. Hume have demonstrated, that such general ideas have noexistence in nature, not even in the mind of their celebrated inventor. Weshall therefore take for granted at present, that our recollection orimagination of external objects consists of a partial repetition of theperceptions, which were excited by those external objects, at the time webecame acquainted with them; and that our reflex ideas of the operations ofour minds are partial repetitions of those operations. II. The following article evinces that the organ of vision consists of afibrous part as well as of the nervous medulla, like other white muscles;and hence, as it resembles the muscular parts of the body in its structure, we may conclude, that it must resemble them in possessing a power of beingexcited into animal motion. --The subsequent experiments on the optic nerve, and on the colours remaining in the eye, are copied from a paper on ocularspectra published in the seventy-sixth volume of the Philos. Trans. By Dr. R. Darwin of Shrewsbury; which, as I shall have frequent occasion to referto, is reprinted in this work, Sect. XL. The retina of an ox's eye wassuspended in a glass of warm water, and forcibly torn in a few places; theedges of these parts appeared jagged and hairy, and did not contract andbecome smooth like simple mucus, when it is distended till it breaks; whichevinced that it consisted of fibres. This fibrous construction became stillmore distinct to the light by adding some caustic alcali to the water; asthe adhering mucus was first eroded, and the hair-like fibres remainedfloating in the vessel. Nor does the degree of transparency of the retinainvalidate this evidence of its fibrous structure, since Leeuwenhoek hasshewn, that the crystalline humour itself consists of fibres. Arc. Nat. V. I. 70. Hence it appears, that as the muscles consist of larger fibres intermixedwith a smaller quantity of nervous medulla, the organ of vision consists ofa greater quantity of nervous medulla intermixed with smaller fibres. It isprobable that the locomotive muscles of microscopic animals may havegreater tenuity than these of the retina; and there is reason to concludefrom analogy, that the other immediate organs of sense, as the portiomollis of the auditory nerve, and the rete mucosum of the skin, possess asimilarity of structure with the retina, and a similar power of beingexcited into animal motion. III. The subsequent articles shew, that neither mechanical impressions, norchemical combinations of light, but that the animal activity of the retinaconstitutes vision. 1. Much has been conjectured by philosophers about the momentum of the raysof light; to subject this to experiment a very light horizontal balance wasconstructed by Mr. Michel, with about an inch square of thin leaf-coppersuspended at each end of it, as described in Dr. Priestley's History ofLight and Colours. The focus of a very large convex mirror was thrown byDr. Powel, in his lectures on experimental philosophy, in my presence, onone wing of this delicate balance, and it receded from the light; thrown onthe other wing, it approached towards the light, and this repeatedly; sothat no sensible impulse could be observed, but what might well be ascribedto the ascent of heated air. Whence it is reasonable to conclude, that the light of the day must be muchtoo weak in its dilute state to make any mechanical impression on sotenacious a substance as the retina of the eye. --Add to this, that as theretina is nearly transparent, it could therefore make less resistance tothe mechanical impulse of light; which, according, to the observationsrelated by Mr. Melvil in the Edinburgh Literary Essays, only communicatesheat, and should therefore only communicate momentum, where it isobstructed, reflected, or refracted. --From whence also may be collected thefinal cause of this degree of transparency of the retina, viz. Left by thefocus of stronger lights, heat and pain should have been produced in theretina, instead of that stimulus which excites it into animal motion. 2. On looking long on an area of scarlet silk of about an inch in diameterlaid on white paper, as in Plate I. The scarlet colour becomes fainter, till at length it entirely vanishes, though the eye is kept uniformly andsteadily upon it. Now if the change or motion of the retina was amechanical impression, or a chemical tinge of coloured light, theperception would every minute become stronger and stronger, --whereas inthis experiment it becomes every instant weaker and weaker. The samecircumstance obtains in the continued application of sound, or of sapidbodies, or of odorous ones, or of tangible ones, to their adapted organs ofsense. [Illustration: Plate II. ] Thus when a circular coin, as a shilling, is pressed on the palm of thehand, the sense of touch is mechanically compressed; but it is the stimulusof this pressure that excites the organ of touch into animal action, whichconstitutes the perception of hardness and of figure; for in some minutesthe perception ceases, though the mechanical pressure of the objectremains. 3. Make with ink on white paper a very black spot about half an inch indiameter, with a tail about an inch in length, so as to resemble a tadpole, as in Plate II. ; look steadfastly for a minute on the center of this spot, and, on moving the eye a little, the figure of the tadpole will be seen onthe white part of the paper; which figure of the tadpole will appear moreluminous than the other part of the white paper; which can only beexplained by supposing that a part of the retina, on which the tadpole wasdelineated, to have become more sensible to light than the other parts ofit, which were exposed to the white paper; and not from any idea ofmechanical impression or chemical combination of light with the retina. 4. When any one turns round rapidly, till he becomes dizzy, and falls uponthe ground, the spectra of the ambient objects continue to presentthemselves in rotation, and he seems to behold the objects still in motion. Now if these spectra were impressions on a passive organ, they either mustcontinue as they were received last, or not continue at all. 5. Place a piece of red silk about an inch in diameter on a sheet of whitepaper in a strong light, as in Plate I; look steadily upon it from thedistance of about half a yard for a minute; then closing your eye-lids, cover them with your hands and handkerchief, and a green spectrum will beseen in your eyes resembling in form the piece of red silk. After someseconds of time the spectrum will disappear, and in a few more seconds willreappear; and thus alternately three or four times, if the experiment bewell made, till at length it vanishes entirely. [Illustration: Plate III. ] 6. Place a circular piece of white paper, about four inches in diameter, inthe sunshine, cover the center of this with a circular piece of black silk, about three inches in diameter; and the center of the black silk with acircle of pink silk, about two inches in diameter; and the center of thepink silk with a circle of yellow silk, about one inch in diameter; and thecenter of this with a circle of blue silk, about half an inch in diameter;make a small spot with ink in the center of the blue silk, as in PlateIII. ; look steadily for a minute on this central spot, and then closingyour eyes, and applying your hand at about an inch distance before them, soas to prevent too much or too little light from passing through theeye-lids, and you will see the most beautiful circles of colours thatimagination can conceive; which are most resembled by the coloursoccasioned by pouring a drop or two of oil on a still lake in a bright day. But these circular irises of colours are not only different from thecolours of the silks above mentioned, but are at the same time perpetuallychanging as long as they exist. From all these experiments it appears, that these spectra in the eye arenot owing to the mechanical impulse of light impressed on the retina; norto its chemical combination with that organ; nor to the absorption andemission of light, as is supposed, perhaps erroneously, to take place incalcined shells and other phosphorescent bodies, after having been exposedto the light: for in all these cases the spectra in the eye should eitherremain of the same colour, or gradually decay, when the object iswithdrawn; and neither their evanescence during the presence of theirobject, as in the second experiment, nor their change from dark toluminous, as in the third experiment, nor their rotation, as in the fourthexperiment, nor the alternate presence and evanescence of them, as in thefifth experiment, nor the perpetual change of colours of them, as in thelast experiment, could exist. IV. The subsequent articles shew, that these animal motions orconfigurations of our organs of sense constitute our ideas. 1. If any one in the dark presses the ball of his eye, by applying hisfinger to the external corner of it, a luminous appearance is observed; andby a smart stroke on the eye great slashes of fire are perceived. (Newton'sOptics. ) So that when the arteries, that are near the auditory nerve, makestronger pulsations than usual, as in some fevers, an undulating sound isexcited in the ears. Hence it is not the presence of the light and sound, but the motions of the organ, that are immediately necessary to constitutethe perception or idea of light and sound. 2. During the time of sleep, or in delirium, the ideas of imagination aremistaken for the perceptions of external objects; whence it appears, thatthese ideas of imagination, are no other than a reiteration of thosemotions of the organs of sense, which were originally excited by thestimulus of external objects: and in our waking hours the simple ideas, that we call up by recollection or by imagination, as the colour of red, orthe smell of a rose, are exact resemblances of the same simple ideas fromperception; and in consequence must be a repetition of those very motions. 3. The disagreeable sensation called the tooth-edge is originally excitedby the painful jarring of the teeth in biting the edge of the glass, orporcelain cup, in which our food was given us in our infancy, as is furtherexplained in the Section XVI. 10, on Instinct. --This disagreeable sensationis afterwards excitable not only by a repetition of the sound, that wasthen produced, but by imagination alone, as I have myself frequentlyexperienced; in this case the idea of biting a china cup, when I imagine itvery distinctly, or when I see another person bite a cup or glass, excitesan actual pain in the nerves of my teeth. So that this idea and pain seemto be nothing more than the reiterated motions of those nerves, that wereformerly so disagreeably affected. Other ideas that are excited by imagination or recollection in manyinstances produce similar effects on the constitution, as our perceptionshad formerly produced, and are therefore undoubtedly a repetition of thesame motions. A story which the celebrated Baron Van Swieton relates ofhimself is to this purpose. He was present when the putrid carcase of adead dog exploded with prodigious stench; and some years afterwards, accidentally riding along the same road, he was thrown into the samesickness and vomiting by the idea of the stench, as he had beforeexperienced from the perception of it. 4. Where the organ of sense is totally destroyed, the ideas which werereceived by that organ seem to perish along with it, as well as the powerof perception. Of this a satisfactory instance has fallen under myobservation. A gentleman about sixty years of age had been totally deaf fornear thirty years: he appeared to be a man of good understanding, andamused himself with reading, and by conversing either by the use of thepen, or by signs made with his fingers, to represent letters. I observedthat he had so far forgot the pronunciation of the language, that when heattempted to speak, none of his words had distinct articulation, though hisrelations could sometimes understand his meaning. But, which is much to thepoint, he assured me, that in his dreams he always imagined that peopleconversed with him by signs or writing, and never that he heard any onespeak to him. From hence it appears, that with the perceptions of sounds hehas also lost the ideas of them; though the organs of speech still retainsomewhat of their usual habits of articulation. This observation may throw some light on the medical treatment of deafpeople; as it may be learnt from their dreams whether the auditory nerve beparalytic, or their deafness be owing to some defect of the external organ. It rarely happens that the immediate organ of vision is perfectlydestroyed. The most frequent causes of blindness are occasioned by defectsof the external organ, as in cataracts and obfuscations of the cornea. ButI have had the opportunity of conversing with two men, who had been someyears blind; one of them had a complete gutta serena, and the other hadlost the whole substance of his eyes. They both told me that they did notremember to have ever dreamt of visible objects, since the total loss oftheir sight. V. Another method of discovering that our ideas are animal motions of theorgans of sense, is from considering the great analogy they bear to themotions of the larger muscles of the body. In the following articles itwill appear that they are originally excited into action by the irritationof external objects like our muscles; are associated together like ourmuscular motions; act in similar time with them; are fatigued by continuedexertion like them; and that the organs of sense are subject toinflammation, numbness, palsy, convulsion, and the defects of old age, inthe same manner as the muscular fibres. 1. All our perceptions or ideas of external objects are universally allowedto have been originally excited by the stimulus of those external objects;and it will be shewn in a succeeding section, that it is probable that allour muscular motions, as well those that are become voluntary as those ofthe heart and glandular system, were originally in like manner excited bythe stimulus of something external to the organ of motion. 2. Our ideas are also associated together after their production preciselyin the same manner as our muscular motions; which will likewise be fullyexplained in the succeeding section. 3. The time taken up in performing an idea is likewise much the same asthat taken up in performing a muscular motion. A musician can press thekeys of an harpsichord with his fingers in the order of a tune he has beenaccustomed to play, in as little time as he can run over those notes in hismind. So we many times in an hour cover our eye-balls with our eye-lidswithout perceiving that we are in the dark; hence the perception or idea oflight is not changed for that of darkness in so small a time as thetwinkling of an eye; so that in this case the muscular motion of theeye-lid is performed quicker than the perception of light can be changedfor that of darkness. --So if a fire-stick be whirled round in the dark, aluminous circle appears to the observer; if it be whirled somewhat slower, this circle becomes interrupted in one part; and then the time taken up insuch a revolution of the stick is the same that the observer uses inchanging his ideas: thus the [Greek: dolikoskoton enkos] of Homer, the longshadow of the flying javelin, is elegantly designed to give us an idea ofits velocity, and not of its length. 4. The fatigue that follows a continued attention of the mind to one objectis relieved by changing the subject of our thoughts; as the continuedmovement of one limb is relieved by moving another in its stead. Whereas adue exercise of the faculties of the mind strengthens and improves thosefaculties, whether of imagination or recollection; as the exercise of ourlimbs in dancing or fencing increases the strength and agility of themuscles thus employed. 5. If the muscles of any limb are inflamed, they do not move without pain;so when the retina is inflamed, its motions also are painful. Hence lightis as intolerable in this kind of ophthalmia, as pressure is to the fingerin the paronychia. In this disease the patients frequently dream of havingtheir eyes painfully dazzled; hence the idea of strong light is painful aswell as the reality. The first of these facts evinces that our perceptionsare motions of the organs of sense; and the latter, that our imaginationsare also motions of the same organs. 6. The organs of sense, like the moving muscles, are liable to becomebenumbed, or less sensible, from compression. Thus, if any person on alight day looks on a white wall, he may perceive the ramifications of theoptic artery, at every pulsation of it, represented by darker branches onthe white wall; which is evidently owing to its compressing the retinaduring the diastole of the artery. Savage Nosolog. 7. The organs of sense and the moving muscles are alike liable to beaffected with palsy, as in the gutta serena, and in some cases of deafness;and one side of the face has sometimes lost its power of sensation, butretained its power of motion; other parts of the body have lost theirmotions but retained their sensation, as in the common hemiplagia; and inother instances both these powers have perished together. 8. In some convulsive diseases a delirium or insanity supervenes, and theconvulsions cease; and conversely the convulsions shall supervene, and thedelirium cease. Of this I have been a witness many times in a day in theparoxysms of violent epilepsies; which evinces that one kind of delirium isa convulsion of the organs of sense, and that our ideas are the motions ofthese organs: the subsequent cases will illustrate this observation. Miss G----, a fair young lady, with light eyes and hair, was seized withmost violent convulsions of her limbs, with outrageous hiccough, and mostvehement efforts to vomit: after near an hour was elapsed this tragedyceased, and a calm talkative delirium supervened for about another hour;and these relieved each other at intervals during the greatest part ofthree or four days. After having carefully considered this disease, Ithought the convulsions of her ideas less dangerous than those of hermuscles; and having in vain attempted to make any opiate continue in herstomach, an ounce of laudanum was rubbed along the spine of her back, and adram of it was used as an enema; by this medicine a kind of drunkendelirium was continued many hours; and when it ceased the convulsions didnot return; and the lady continued well many years, except some lighterrelapses, which were relieved in the same manner. Miss H----, an accomplished young lady, with light eyes and hair, wasseized with convulsions of her limbs, with hiccough, and efforts to vomit, more violent than words can express; these continued near an hour, and weresucceeded with a cataleptic spasm of one arm, with the hand applied to herhead; and after about twenty minutes these spasms ceased, and a talkativereverie supervened for near an other hour, from which no violence, which itwas proper to use, could awaken her. These periods of convulsions, first ofthe muscles, and then of the ideas, returned twice a day for several weeks;and were at length removed by great doses of opium, after a great varietyof other medicines and applications had been in vain experienced. This ladywas subject to frequent relapses, once or twice a year for many years, andwas as frequently relieved by the same method. Miss W----, an elegant young lady, with black eyes and hair, had sometimesa violent pain of her side, at other times a most painful strangury, whichwere every day succeeded by delirium; which gave a temporary relief to thepainful spasms. After the vain exhibition of variety of medicines andapplications by different physicians, for more than a twelvemonth, she wasdirected to take some doses of opium, which were gradually increased, bywhich a drunken delirium was kept up for a day or two, and the painsprevented from returning. A flesh diet, with a little wine or beer, insteadof the low regimen she had previously used, in a few weeks completelyestablished her health; which, except a few relapses, has continued formany years. 9. Lastly, as we advance in life all the parts of the body become morerigid, and are rendered less susceptible of new habits of motion, thoughthey retain those that were before established. This is sensibly observedby those who apply themselves late in life to music, fencing, or any of themechanic arts. In the same manner many elderly people retain the ideas theyhad learned early in life, but find great difficulty in acquiring newtrains of memory; insomuch that in extreme old age we frequently see aforgetfulness of the business of yesterday, and at the same time acircumstantial remembrance of the amusements of their youth; till at lengththe ideas of recollection and activity of the body gradually ceasetogether, --such is the condition of humanity!--and nothing remains but thevital motions and sensations. VI. 1. In opposition to this doctrine of the production of our ideas, itmay be asked, if some of our ideas, like other animal motions, arevoluntary, why can we not invent new ones, that have not been received byperception? The answer will be better understood after having perused thesucceeding section, where it will be explained, that the muscular motionslikewise are originally excited by the stimulus of bodies external to themoving organ; and that the will has only the power of repeating the motionsthus excited. 2. Another objector may ask, Can the motion of an organ of sense resemblean odour or a colour? To which I can only answer, that it has not beendemonstrated that any of our ideas resemble the objects that excite them;it has generally been believed that they do not; but this shall bediscussed at large in Sect. XIV. 3. There is another objection that at first view would seem less easy tosurmount. After the amputation, of a foot or a finger, it has frequentlyhappened, that an injury being offered to the stump of the amputated limb, whether from cold air, too great pressure, or other accidents, the patienthas complained, of a sensation of pain in the foot or finger, that was cutoff. Does not this evince that all our ideas are excited in the brain, andnot in the organs of sense? This objection is answered, by observing thatour ideas of the shape, place, and solidity of our limbs, are acquired byour organs of touch and of sight, which are situated in our fingers andeyes, and not by any sensations in the limb itself. In this case the pain or sensation, which formerly has arisen in the footor toes, and been propagated along the nerves to the central part of thesensorium, was at the same time accompanied with a visible idea of theshape and place, and with a tangible idea of the solidity of the affectedlimb: now when these nerves are afterwards affected by any injury done tothe remaining stump with a similar degree or kind of pain, the ideas of theshape, place, or solidity of the lost limb, return by association; as theseideas belong to the organs of sight and touch, on which they were firstexcited. 4. If you wonder what organs of sense can be excited into motion, when youcall up the ideas of wisdom or benevolence, which Mr. Locke has termedabstracted ideas; I ask you by what organs of sense you first becameacquainted with these ideas? And the answer will be reciprocal; for it iscertain that all our ideas were originally acquired by our organs of sense;for whatever excites our perception must be external to the organ thatperceives it, and we have no other inlets to knowledge but by ourperceptions: as will be further explained in Section XIV. And XV. On theProductions and Classes of Ideas. VII. If our recollection or imagination be not a repetition of animalmovements, I ask, in my turn, What is it? You tell me it consists of imagesor pictures of things. Where is this extensive canvas hung up? or where arethe numerous receptacles in which those are deposited? or to what else inthe animal system have they any similitude? That pleasing picture of objects, represented in miniature on the retina ofthe eye, seems to have given rise to this illusive oratory! It was forgotthat this representation belongs rather to the laws of light, than to thoseof life; and may with equal elegance be seen in the camera obscura as inthe eye; and that the picture vanishes for ever, when the object iswithdrawn. * * * * * SECT. IV. LAWS OF ANIMAL CAUSATION. I. The fibres, which constitute the muscles and organs of sense, possess apower of contraction. The circumstances attending the exertion of thispower of CONTRACTION constitute the laws of animal motion, as thecircumstances attending the exertion of the power of ATTRACTION constitutethe laws of motion of inanimate matter. II. The spirit of animation is the immediate cause of the contraction ofanimal fibres, it resides in the brain and nerves, and is liable to generalor partial diminution or accumulation. III. The stimulus of bodies external to the moving organ is the remotecause of the original contractions of animal fibres. IV. A certain quantity of stimulus produces irritation, which is anexertion of the spirit of animation exciting the fibres into contraction. V. A certain quantity of contraction of animal fibres, if it be perceivedat all, produces pleasure; a greater or less quantity of contraction, if itbe perceived at all, produces pain; these constitute sensation. VI. A certain quantity of sensation produces desire or aversion; theseconstitute volition. VII. All animal motions which have occurred at the same time, or inimmediate succession, become so connected, that when one of them isreproduced, the other has a tendency to accompany or succeed it. Whenfibrous contractions succeed or accompany other fibrous contractions, theconnection is termed association; when fibrous contractions succeedsensorial motions, the connexion is termed causation; when fibrous andsensorial motions reciprocally introduce each other, it is termedcatenation of animal motions. All these connections are said to be producedby habit, that is, by frequent repetition. These laws of animal causationwill be evinced by numerous facts, which occur in our daily exertions; andwill afterwards be employed to explain the more recondite phænomena of theproduction, growth, diseases, and decay of the animal system. * * * * * SECT. V. OF THE FOUR FACULTIES OR MOTIONS OF THE SENSORIUM. 1. _Four sensorial powers. _ 2. _Irritation, sensation, volition, association defined. _ 3. _Sensorial motions distinguished from fibrous motions. _ 1. The spirit of animation has four different modes of action, or in otherwords the animal sensorium possesses four different faculties, which areoccasionally exerted, and cause all the contractions of the fibrous partsof the body. These are the faculty of causing fibrous contractions inconsequence of the irritations excited by external bodies, in consequenceof the sensations of pleasure or pain, in consequence of volition, and inconsequence of the associations of fibrous contractions with other fibrouscontractions, which precede or accompany them. These four faculties of the sensorium during their inactive state aretermed irritability, sensibility, voluntarity, and associability; in theiractive state they are termed as above, irritation, sensation, volition, association. 2. IRRITATION is an exertion or change of some extreme part of thesensorium residing in the muscles or organs of sense, in consequence of theappulses of external bodies. SENSATION is an exertion or change of the central parts of the sensorium, or of the whole of it, _beginning_ at some of those extreme parts of it, which reside in the muscles or organs of sense. VOLITION is an exertion or change of the central parts of the sensorium, orof the whole of it, _terminating_ in some of those extreme parts of it, which reside in the muscles or organs of sense. ASSOCIATION is an exertion or change of some extreme part of the sensoriumresiding in the muscles or organs of sense, in consequence of someantecedent or attendant fibrous contractions. 3. These four faculties of the animal sensorium may at the time of theirexertions be termed motions without impropriety of language; for we cannotpass from a state of insensibility or inaction to a state of sensibility orof exertion without some change of the sensorium, and every change includesmotion. We shall therefore sometimes term the above described faculties_sensorial motions_ to distinguish them from _fibrous motions_; whichlatter expression includes the motions of the muscles and organs of sense. The active motions of the fibres, whether those of the muscles or organs ofsense, are probably simple contractions; the fibres being again elongatedby antagonist muscles, by circulating fluids, or sometimes by elasticligaments, as in the necks of quadrupeds. The sensorial motions, whichconstitute the sensations of pleasure or pain, and which constitutevolition, and which cause the fibrous contractions in consequence ofirritation or of association, are not here supposed to be fluctuations orrefluctuations of the spirit of animation; nor are they supposed to bevibrations or revibrations, nor condensations or equilibrations of it; butto be changes or motions of it peculiar to life. * * * * * SECT. VI. OF THE FOUR CLASSES OF FIBROUS MOTIONS. I. _Origin of fibrous contractions. _ II. _Distribution of them into four classes, irritative motions, sensitive motions, voluntary motions, and associate motions, defined. _ I. All the fibrous contractions of animal bodies originate from thesensorium, and resolve themselves into four classes, correspondent with thefour powers or motions of the sensorium above described, and from whichthey have their causation. 1. These fibrous contractions were originally caused by the irritationsexcited by objects, which are external to the moving organ. As thepulsations of the heart are owing to the irritations excited by thestimulus of the blood; and the ideas of perception are owing to theirritations excited by external bodies. 2. But as painful or pleasurable sensations frequently accompanied thoseirritations, by habit these fibrous contractions became causeable by thesensations, and the irritations ceased to be necessary to their production. As the secretion of tears in grief is caused by the sensation of pain; andthe ideas of imagination, as in dreams or delirium, are excited by thepleasure or pain, with which they were formerly accompanied. 3. But as the efforts of the will frequently accompanied these painful orpleasureable sensations, by habit the fibrous contractions became causableby volition; and both the irritations and sensations ceased to be necessaryto their production. As the deliberate locomotions of the body, and theideas of recollection, as when we will to repeat the alphabet backwards. 4. But as many of these fibrous contractions frequently accompanied otherfibrous contractions, by habit they became causable by their associationswith them; and the irritations, sensations, and volition, ceased to benecessary to their production. As the actions of the muscles of the lowerlimbs in fencing are associated with those of the arms; and the ideas ofsuggestion are associated with other ideas, which precede or accompanythem; as in repeating carelessly the alphabet in its usual order afterhaving began it. II. We shall give the following names to these four classes of fibrousmotions, and subjoin their definitions. 1. Irritative motions. That exertion or change of the sensorium, which iscaused by the appulses of external bodies, either simply subsides, or issucceeded by sensation, or it produces fibrous motions; it is termedirritation, and irritative motions are those contractions of the muscularfibres, or of the organs of sense, that are immediately consequent to thisexertion or change of the sensorium. 2. Sensitive motions. That exertion or change of the sensorium, whichconstitutes pleasure or pain, either simply subsides, or is succeeded byvolition, or it produces fibrous motions; it is termed sensation, and thesensitive motions are those contractions of the muscular fibres, or of theorgans of sense, that are immediately consequent to this exertion or changeof the sensorium. 3. Voluntary motions. That exertion or change of the sensorium, whichconstitutes desire or aversion, either simply subsides, or is succeeded byfibrous motions; it is then termed volition, and voluntary motions arethose contractions of the muscular fibres, or of the organs of sense, thatare immediately consequent to this exertion or change of the sensorium. 4. Associate motions. That exertion or change of the sensorium, whichaccompanies fibrous motions, either simply subsides, or is succeeded bysensation or volition, or it produces other fibrous motions; it is thentermed association, and the associate motions are those contractions of themuscular fibres, or of the organs of sense, that are immediately consequentto this exertion or change of the sensorium. * * * * * SECT. VII. OF IRRITATIVE MOTIONS. I. 1. _Some muscular motions are excited by perpetual irritations. _ 2. _Others more frequently by sensations. _ 3. _Others by volition. Case of involuntary stretchings in paralytic limbs. _ 4. _Some sensual motions are excited by perpetual irritations. _ 5. _Others more frequently by sensation or volition. _ II. 1. _Muscular motions excited by perpetual irritations occasionally become obedient sensation and to volition. _ 2. _And the sensual motions. _ III. 1. _Other muscular motions are associated with the irritative ones. _ 2. _And other ideas with irritative ones. Of letters, language, hieroglyphics. Irritative ideas exist without our attention to them. _ I. 1. Many of our muscular motions are excited by perpetual irritations, asthose of the heart and arterial system by the circumfluent blood. Manyother of them are excited by intermitted irritations, as those of thestomach and bowels by the aliment we swallow; of the bile-ducts by thebile; of the kidneys, pancreas, and many other glands, by the peculiarfluids they separate from the blood; and those of the lacteal and otherabsorbent vessels by the chyle, lymph, and moisture of the atmosphere. These motions are accelerated or retarded, as their correspondentirritations are increased or diminished, without our attention orconsciousness, in the same manner as the various secretions of fruit, gum, resin, wax, and, honey, are produced in the vegetable world, and as thejuices of the earth and the moisture of the atmosphere are absorbed bytheir roots and foliage. 2. Other muscular motions, that are most frequently connected with oursensations, as those of the sphincters of the bladder and anus, and themusculi erectores penis, were originally excited into motion by irritation, for young children make water, and have other evacuations without attentionto these circumstances; "et primis etiam ab incunabulis tenduntur sæpiuspuerorum penes, amore nondum expergefacto. " So the nipples of young womenare liable to become turgid by irritation, long before they are in asituation to be excited by the pleasure of giving milk to the lips of achild. 3. The contractions of the larger muscles of our bodies, that are mostfrequently connected with volition, were originally excited into action byinternal irritations: as appears from the stretching or yawning of allanimals after long sleep. In the beginning of some fevers this irritationof the muscles produces perpetual stretching and yawning; in other periodsof fever an universal restlessness arises from the same cause, the patientchanging the attitude of his body every minute. The repeated struggles ofthe foetus in the uterus must be owing to this internal irritation: for thefoetus can have no other inducement to move its limbs but the tædium orirksomeness of a continued posture. The following case evinces, that the motions of stretching the limbs aftera continued attitude are not always owing to the power of the will. Mr. Dean, a mason, of Austry in Leicestershire, had the spine of the thirdvertebra of the back enlarged; in some weeks his lower extremities becamefeeble, and at length quite paralytic: neither the pain of blisters, theheat of fomentations, nor the utmost efforts of the will could produce theleast motion in these limbs; yet twice or thrice a day for many months hisfeet, legs, and thighs, were affected for many minutes with forceablestretchings, attended with the sensation of fatigue; and he at lengthrecovered the use of his limbs, though the spine continued protuberant. Thesame circumstance is frequently seen in a less degree in the commonhemiplagia; and when this happens, I have believed repeated and strongshocks of electricity to have been of great advantage. 4. In like manner the various organs of sense are originally excited intomotion by various external stimuli adapted to this purpose, which motionsare termed perceptions or ideas; and many of these motions during ourwaking hours are excited by perpetual irritation, as those of the organs ofhearing and of touch. The former by the constant low indistinct noises thatmurmur around us, and the latter by the weight of our bodies on the partswhich support them; and by the unceasing variations of the heat, moisture, and pressure of the atmosphere; and these sensual motions, precisely as themuscular ones above mentioned, obey their correspondent irritations withoutour attention or consciousness. 5. Other classes of our ideas are more frequently excited by our sensationsof pleasure or pain, and others by volition: but that these have all beenoriginally excited by stimuli from external objects, and only vary in theircombinations or reparations, has been fully evinced by Mr. Locke: and areby him termed the ideas of perception in contradistinction to those, whichhe calls the ideas of reflection. II. 1. These muscular motions, that are excited by perpetual irritation, are nevertheless occasionally excitable by the sensations of pleasure orpain, or by volition; as appears by the palpitation of the heart from fear, the increased secretion of saliva at the sight of agreeable food, and theglow on the skin of those who are ashamed. There is an instance told in thePhilosophical Transactions of a man, who could for a time stop the motionof his heart when he pleased; and Mr. D. Has often told me, be could so farincrease the peristaltic motion of his bowels by voluntary efforts, as toproduce an evacuation by stool at any time in half an hour. 2. In like manner the sensual motions, or ideas, that are excited byperpetual irritation, are nevertheless occasionally excited by sensation orvolition; as in the night, when we listen under the influence of fear, orfrom voluntary attention, the motions excited in the organ of hearing bythe whispering of the air in our room, the pulsation of our own arteries, or the faint beating of a distant watch, become objects of perception. III. 1. Innumerable trains or tribes of other motions are associated withthese muscular motions which are excited by irritation; as by the stimulusof the blood in the right chamber of the heart, the lungs are induced toexpand themselves; and the pectoral and intercostal muscles, and thediaphragm, act at the same time by their associations with them. And whenthe pharinx is irritated by agreeable food, the muscles of deglutition arebrought into action by association. Thus when a greater light falls on theeye, the iris is brought into action without our attention; and the ciliaryprocess, when the focus is formed before or behind the retina, by theirassociations with the increased irritative motions of the organ of vision. Many common actions of life are produced in a similar manner. If a flysettle on my forehead, whilst I am intent on my present occupation, Idislodge it with my finger, without exciting my attention or breaking thetrain of my ideas. 2. In like manner the irritative ideas suggest to us many other trains ortribes of ideas that are associated with them. On this kind of connection, language, letters, hieroglyphics, and every kind of symbol, depend. Thesymbols themselves produce irritative ideas, or sensual motions, which wedo not attend to; and other ideas, that are succeeded by sensation, areexcited by their association with them. And as these irritative ideas makeup a part of the chain of our waking thoughts, introducing other ideas thatengage our attention, though themselves are unattended to, we find it verydifficult to investigate by what steps many of our hourly trains of ideasgain their admittance. It may appear paradoxical, that ideas can exist, and not be attended to;but all our perceptions are ideas excited by irritation, and succeeded bysensation. Now when these ideas excited by irritation give us neitherpleasure nor pain, we cease to attend to them. Thus whilst I am walkingthrough that grove before my window, I do not run against the trees or thebenches, though my thoughts are strenuously exerted on some other object. This leads us to a distinct knowledge of irritative ideas, for the idea ofthe tree or bench, which I avoid, exists on my retina, and induces byassociation the action of certain locomotive muscles; though neither itselfnor the actions of those muscles engage my attention. Thus whilst we are conversing on this subject, the tone, note, andarticulation of every individual word forms its correspondent irritativeidea on the organ of hearing; but we only attend to the associated ideas, that are attached by habit to these irritative ones, and are succeeded bysensation; thus when we read the words "PRINTING-PRESS" we do not attend tothe shape, size, or existence of the letters which compose these words, though each of them excites a correspondent irritative motion of our organof vision, but they introduce by association our idea of the most useful ofmodern inventions; the capacious reservoir of human knowledge, whosebranching streams diffuse sciences, arts, and morality, through all nationsand all ages. * * * * * SECT. VIII. OF SENSITIVE MOTIONS. I. 1. _Sensitive muscular motions were originally excited into action by irritation. _ 2. _And sensitive sensual motions, ideas of imagination, dreams. _ II. 1. _Sensitive muscular motions are occasionally obedient to volition. _ 2. _And sensitive sensual motions. _ III. 1. _Other muscular motions are associated with the sensitive ones. _ 2. _And other sensual motions. _ I. 1. Many of the motions of our muscles, that are excited into action byirritation, are at the same time accompanied with painful or pleasurablesensations; and at length become by habit causable by the sensations. Thusthe motions of the sphincters of the bladder and anus were originallyexcited into action by irritation; for young children give no attention tothese evacuations; but as soon as they become sensible of the inconvenienceof obeying these irritations, they suffer the water or excrement toaccumulate, till it disagreeably affects them; and the action of thosesphincters is then in consequence of this disagreeable sensation. So thesecretion of saliva, which in young children is copiously produced byirritation, and drops from their mouths, is frequently attended with theagreeable sensation produced by the mastication of tasteful food;, till atlength the sight of such food to a hungry person excites into action thesesalival glands; as is seen in the slavering of hungry dogs. The motions of those muscles, which are affected by lascivious ideas, andthose which are exerted in smiling, weeping, starting from fear, andwinking at the approach of danger to the eye, and at times the actions ofevery large muscle of the body become causable by our sensations. And allthese motions are performed with strength and velocity in proportion to theenergy of the sensation that excites them, and the quantity of sensorialpower. 2. Many of the motions of our organs of sense, or ideas, that wereoriginally excited into action by irritation, become in like manner morefrequently causable by our sensations of pleasure or pain. These motionsare then termed the ideas of imagination, and make up all the scenery andtransactions of our dreams. Thus when any painful or pleasurable sensationspossess us, as of love, anger, fear; whether in our sleep or waking hours, the ideas, that have been formerly excited by the objects of thesesensations, now vividly recur before us by their connection with thesesensations themselves. So the fair smiling virgin, that excited your loveby her presence, whenever that sensation recurs, rises before you inimagination; and that with all the pleasing circumstances, that had beforeengaged your attention. And in sleep, when you dream under the influence offear, all the robbers, fires, and precipices, that you formerly have seenor heard of, arise before you with terrible vivacity. All these sensualmotions, like the muscular ones above mentioned, are performed withstrength and velocity in proportion to the energy of the sensation ofpleasure or pain, which excites them, and the quantity of sensorial power. II. 1. Many of these muscular motions above described, that are mostfrequently excited by our sensations, are nevertheless occasionallycausable by volition; for we can smile or frown spontaneously, can makewater before the quantity or acrimony of the urine produces a disagreeablesensation, and can voluntarily masticate a nauseous drug, or swallow abitter draught, though our sensation would strongly dissuade us. 2. In like manner the sensual motions, or ideas, that are most frequentlyexcited by our sensations, are nevertheless occasionally causeable byvolition, as we can spontaneously call up our last night's dream before us, tracing it industriously step by step through all its variety of sceneryand transaction; or can voluntarily examine or repeat the ideas, that havebeen excited by out disgust or admiration. III. 1. Innumerable trains or tribes of motions are associated with thesesensitive muscular motions above mentioned; as when a drop of water fallinginto the wind-pipe disagreeably affects the air-vessels of the lungs, theyare excited into violent action; and with these sensitive motions areassociated the actions of the pectoral and intercostal muscles, and thediaphragm; till by their united and repeated succussions the drop isreturned through the larinx. The same occurs when any thing disagreeablyaffects the nostrils, or the stomach, or the uterus; variety of muscles areexcited by association into forcible action, not to be suppressed by theutmost efforts of the will; as in sneezing, vomiting, and parturition. 2. In like manner with these sensitive sensual motions, or ideas ofimagination, are associated many other trains or tribes of ideas, which bysome writers of metaphysics have been classed under the terms ofresemblance, causation, and contiguity; and will be more fully treated ofhereafter. * * * * * SECT. IX. OF VOLUNTARY MOTIONS. I. 1. _Voluntary muscular motions are originally excited by irritations. _ 2. _And voluntary ideas. Of reason. _ II. 1. _Voluntary muscular motions are occasionally causable by sensations. _ 2. _And voluntary ideas. _ III. 1. _Voluntary muscular motions are occasionally obedient to irritations. _ 2. _And voluntary ideas. _ IV. 1. _Voluntary muscular motions are associated with other muscular motions. _ 2. _And voluntary ideas. _ When pleasure or pain affect the animal system, many of its motions bothmuscular and sensual are brought into action; as was shewn in the precedingsection, and were called sensitive motions. The general tendency of thesemotions is to arrest and to possess the pleasure, or to dislodge or avoidthe pain: but if this cannot immediately be accomplished, desire oraversion are produced, and the motions in consequence of this new facultyof the sensorium are called voluntary. I. 1. Those muscles of the body that are attached to bones, have in generaltheir principal connections with volition, as I move my pen or raise mybody. These motions were originally excited by irritation, as was explainedin the section on that subject, afterwards the sensations of pleasure orpain, that accompanied the motions thus excited, induced a repetition ofthem; and at length many of them were voluntarily practised in successionor in combination for the common purposes of life, as in learning to walk, or to speak; and are performed with strength and velocity in proportion tothe energy of the volition, that excites them, and the quantity ofsensorial power. 2. Another great class of voluntary motions consists of the ideas ofrecollection. We will to repeat a certain train of ideas, as of thealphabet backwards; and if any ideas, that do not belong to this intendedtrain, intrude themselves by other connections, we will to reject them, andvoluntarily persist in the determined train. So at my approach to a housewhich I have but once visited, and that at the distance of many months, Iwill to recollect the names of the numerous family I expect to see there, and I do recollect them. On this voluntary recollection of ideas our faculty of reason depends, asit enables us to acquire an idea of the dissimilitude of any two ideas. Thus if you voluntarily produce the idea of a right-angled triangle, andthen of a square; and after having excited these ideas repeatedly, youexcite the idea of their difference, which is that of another right-angledtriangle inverted over the former; you are said to reason upon thissubject, or to compare your ideas. These ideas of recollection, like the muscular motions above mentioned, were originally excited by the irritation of external bodies, and weretermed ideas of perception: afterwards the pleasure or pain, thataccompanied these motions, induced a repetition of them in the absence ofthe external body, by which they were first excited; and then they weretermed ideas of imagination. At length they become voluntarily practised insuccession or in combination for the common purposes of life; as when wemake ourselves masters of the history of mankind, or of the sciences theyhave investigated; and are then called ideas of recollection; and areperformed with strength and velocity in proportion to the energy of thevolition that excites them, and the quantity of sensorial power. II. 1. The muscular motions above described, that are most frequentlyobedient to the will are nevertheless occasionally causable by painful orpleasurable sensation, as in the starting from fear, and the contraction ofthe calf of the leg in the cramp. 2. In like manner the sensual motions, or ideas, that are most frequentlyconnected with volition, are nevertheless occasionally causable by painfulor pleasurable sensation. As the histories of men, or the description ofplaces, which we have voluntarily taken pains to remember, sometimes occurto us in our dreams. III. 1. The muscular motions that are generally subservient to volition, are also occasionally causable by irritation, as in stretching the limbsafter sleep, and yawning. In this manner a contraction of the arm isproduced by passing the electric fluid from the Leyden phial along itsmuscles; and that even though the limb is paralytic. The sudden motion ofthe arm produces a disagreeable sensation in the joint, but the musclesseem to be brought into action simply by irritation. 2. The ideas, that are generally subservient to the will, are in likemanner occasionally excited by irritation; as when we view again an object, we have before well studied, and often recollected. IV. 1. Innumerable trains or tribes of motions are associated with thesevoluntary muscular motions above mentioned; as when I will to extend my armto a distant object, some other muscles are brought into action, andpreserve the balance of my body. And when I wish to perform any steadyexertion, as in threading a needle, or chopping with an ax, the pectoralmuscles are at the same time brought into action to preserve the trunk ofthe body motionless, and we cease to respire for a time. 2. In like manner the voluntary sensual motions, or ideas of recollection, are associated with many other trains or tribes of ideas. As when Ivoluntarily recollect a gothic window, that I saw some time ago, the wholefront of the cathedral occurs to me at the same time. * * * * * SECT. X. OF ASSOCIATE MOTIONS. I. 1. _Many muscular motions excited by irritations in trains or tribes become associated. _ 2. _And many ideas. _ II. 1. _Many sensitive muscular motions become associated. _ 2. _And many sensitive ideas. _ III. 1. _Many voluntary muscular motions become associated. _ 2. _And then become obedient to sensation or irritation. _ 3. _And many voluntary ideas become associated. _ All the fibrous motions, whether muscular or sensual, which are frequentlybrought into action together, either in combined tribes, or in successivetrains, become so connected by habit, that when one of them is reproducedthe others have a tendency to succeed or accompany it. I. 1. Many of our muscular motions were originally excited in successivetrains, as the contractions of the auricles and of the ventricles of theheart; and others in combined tribes, as the various divisions of themuscles which compose the calf of the leg, which were originally irritatedinto synchronous action by the tædium or irksomeness of a continuedposture. By frequent repetitions these motions acquire associations, whichcontinue during our lives, and even after the destruction of the greatestpart of the sensorium; for the heart of a viper or frog will continue topulsate long after it is taken from the body; and when it has entirelyceased to move, if any part of it is goaded with a pin, the whole heartwill again renew its pulsations. This kind of connection we shall termirritative association, to distinguish it from sensitive and voluntaryassociations. 2. In like manner many of our ideas are originally excited in tribes; asall the objects of sight, after we become so well acquainted with the lawsof vision, as to distinguish figure and distance as well as colour; or intrains, as while we pass along the objects that surround us. The tribesthus received by irritation become associated by habit, and have beentermed complex ideas by the writers of metaphysics, as this book, or thatorange. The trains have received no particular name, but these are alikeassociations of ideas, and frequently continue during our lives. So thetaste of a pine-apple, though we eat it blindfold, recalls the colour andshape of it; and we can scarcely think on solidity without figure. II. 1. By the various efforts of our sensations to acquire or avoid theirobjects, many muscles are daily brought into successive or synchronousactions; these become associated by habit, and are then excited togetherwith great facility, and in many instances gain indissoluble connections. So the play of puppies and kittens is a representation of their mode offighting or of taking their prey; and the motions of the muscles necessaryfor those purposes become associated by habit, and gain a great adroitnessof action by these early repetitions: so the motions of the abdominalmuscles, which were originally brought into concurrent action, with theprotrusive motion of the rectum or bladder by sensation, become soconjoined with them by habit, that they not only easily obey thesesensations occasioned by the stimulus of the excrement and urine, but arebrought into violent and unrestrainable action in the strangury andtenesmus. This kind of connection we shall term sensitive association. 2. So many of our ideas, that have been excited together or in successionby our sensations, gain synchronous or successive associations, that aresometimes indissoluble but with life. Hence the idea of an inhuman ordishonourable action perpetually calls up before us the idea of the wretchthat was guilty of it. And hence those unconquerable antipathies areformed, which some people have to the sight of peculiar kinds of food, ofwhich in their infancy they have eaten to excess or by constraint. III. 1. In learning any mechanic art, as music, dancing, or the use of thesword, we teach many of our muscles to act together or in succession byrepeated voluntary efforts; which by habit become formed into tribes ortrains of association, and serve all our purposes with great facility, andin some instances acquire an indissoluble union. These motions aregradually formed into a habit of acting together by a multitude ofrepetitions, whilst they are yet separately causable by the will, as isevident from the long time that is taken up by children in learning to walkand to speak; and is experienced by every one, when he first attempts toskate upon the ice or to swim: these we shall term voluntary associations. 2. All these muscular movements, when they are thus associated into tribesor trains, become afterwards not only obedient to volition, but to thesensations and irritations; and the same movement composes a part of manydifferent tribes or trains of motion. Thus a single muscle, when it acts inconsort with its neighbours on one side, assists to move the limb in onedirection; and in another, when, it acts with those in its neighbourhood onthe other side; and in other directions, when it acts separately or jointlywith those that lie immediately under or above it; and all these with equalfacility after their associations have been well established. The facility, with which each muscle changes from one associated tribe toanother, and that either backwards or forwards, is well observable in themuscles of the arm in moving the windlass of an air-pump; and the slownessof those muscular movements, that have not been associated by habit, may beexperienced by any one, who shall attempt to saw the air quickperpendicularly with one hand, and horizontally with the other at the sametime. 3. In learning every kind of science we voluntarily associate many tribesand trains of ideas, which afterwards are ready for all the purposes eitherof volition, sensation, or irritation; and in some instances acquireindissoluble habits of acting together, so as to affect our reasoning, andinfluence our actions. Hence the necessity of a good education. These associate ideas are gradually formed into habits of acting togetherby frequent repetition, while they are yet separately obedient to the will;as is evident from the difficulty we experience in gaining so exact an ideaof the front of St. Paul's church, as to be able to delineate it withaccuracy, or in recollecting a poem of a few pages. And these ideas, thus associated into tribes, not only make up the parts ofthe trains of volition, sensation, and irritation; but the same ideacomposes a part of many different tribes and trains of ideas. So the simpleidea of whiteness composes a part of the complex idea of snow, milk, ivory;and the complex idea of the letter A composes a part of the severalassociated trains of ideas that make up the variety of words, in which thisletter enters. The numerous trains of these associated ideas are divided by Mr. Hume intothree classes, which he has termed contiguity, causation, and resemblance. Nor should we wonder to find them thus connected together, since it is thebusiness of our lives to dispose them into those three classes; and webecome valuable to ourselves and our friends, as we succeed in it. Thosewho have combined an extensive class of ideas by the contiguity of time orplace, are men learned in the history of mankind, and of the sciences theyhave cultivated. Those who have connected a great class of ideas ofresemblances, possess the source of the ornaments of poetry and oratory, and of all rational analogy. While those who have connected great classesof ideas of causation, are furnished with the powers of producing effects. These are the men of active wisdom, who lead armies to victory, andkingdoms to prosperity; or discover and improve the sciences, whichmeliorate and adorn the condition of humanity. * * * * * SECT. XI. ADDITIONAL OBSERVATIONS ON THE SENSORIAL POWERS. I. _Stimulation is of various kinds adapted to the organs of sense, to the muscles, to hollow membranes, and glands. Some objects irritate our senses by repeated impulses. _ II. 1. _Sensation and volition frequently affect the whole sensorium. _ 2. _Emotions, passions, appetites. _ 3. _Origin of desire and aversion. Criterion of voluntary actions, difference of brutes and men. _ 4. _Sensibility and voluntarity. _ III. _Associations formed before nativity, irritative motions mistaken for officiated ones. _ _Irritation. _ I. The various organs of sense require various kinds of stimulation toexcite them into action; the particles of light penetrate the cornea andhumours of the eye, and then irritate the naked retina; rapid particles, dissolved or diffused in water or saliva, and odorous ones, mixed orcombined with the air, irritate the extremities of the nerves of taste andsmell; which either penetrate, or are expanded on the membranes of thetongue and nostrils; the auditory nerves are stimulated by the vibrationsof the atmosphere communicated by means of the tympanum and of the fluid, whether of air or of water, behind it; and the nerves of touch by thehardness of surrounding bodies, though the cuticle is interposed betweenthese bodies and the medulla of the nerve. As the nerves of the senses have each their appropriated objects, whichstimulate them into activity; so the muscular fibres, which are theterminations of other sets of nerves, have their peculiar objects, whichexcite them into action; the longitudinal muscles are stimulated intocontraction by extension, whence the stretching or pandiculation after along continued posture, during which they have been kept in a state ofextension; and the hollow muscles are excited into action by distention, asthose of the rectum and bladder are induced to protrude their contents fromtheir sense of the distention rather than of the acrimony of thosecontents. There are other objects adapted to stimulate the nerves, which terminate invariety of membranes, and those especially which form the terminations ofcanals; thus the preparations of mercury particularly affect the salivaryglands, ipecacuanha the stomach, aloe the sphincter of the anus, cantharides that of the bladder, and lastly every gland of the body appearsto be indued with a kind of taste, by which it selects or forms each itspeculiar fluid from the blood; and by which it is irritated into activity. Many of these external properties of bodies, which stimulate our organs ofsense, do not seem to effect this by a single impulse, but by repeatedimpulses; as the nerve of the ear is probably not excitable by a singlevibration of air, nor the optic nerve by a single particle of light; whichcircumstance produces some analogy between those two senses, at the sametime the solidity of bodies is perceived by a single application of a solidbody to the nerves of touch, and that even through the cuticle; and we areprobably possessed of a peculiar sense to distinguish the nice degrees ofheat and cold. The senses of touch and of hearing acquaint us with the mechanical impactand vibration of bodies, those of smell and taste seem to acquaint us withsome of their chemical properties, while the sense of vision and of heatacquaint us with the existence of their peculiar fluids. _Sensation and Volition. _ II. Many motions are produced by pleasure or pain, and that even incontradiction to the power of volition, as in laughing, or in thestrangury; but as no name has been given to pleasure or pain, at the timeit is exerted so as to cause fibrous motions, we have used the termsensation for this purpose; and mean it to bear the same analogy topleasure and pain, that the word volition does to desire and aversion. 1. It was mentioned in the fifth Section, that, what we have termedsensation is a motion of the central parts, or of the whole sensorium, _beginning_ at some of the extremities of it. This appears first, becauseour pains and pleasures are always caused by our ideas or muscular motions, which are the motions of the extremities of the sensorium. And, secondly, because the sensation of pleasure or pain frequently continues some timeafter the ideas or muscular motions which excited it have ceased: for weoften feel a glow of pleasure from an agreeable reverie, for many minutesafter the ideas, that were the subject of it, have escaped our memory; andfrequently experience a dejection of spirits without being able to assignthe cause of it but by much recollection. When the sensorial faculty of desire or aversion is exerted so as to causefibrous motions, it is termed volition; which is said in Sect. V. To be amotion of the central parts, or of the whole sensorium, _terminating_ insome of the extremities of it. This appears, first, because our desires andaversions always terminate in recollecting and comparing our ideas, or inexerting our muscles; which are the motions of the extremities of thesensorium. And, secondly, because desire or aversion begins, and frequentlycontinues for a time in the central parts of the sensorium, before it ispeculiarly exerted at the extremities of it; for we sometimes feel desireor aversion without immediately knowing their objects, and in consequencewithout immediately exerting any of our muscular or sensual motions toattain them: as in the beginning of the passion of love, and perhaps ofhunger, or in the ennui of indolent people. Though sensation and volition begin or terminate at the extremities orcentral parts of the sensorium, yet the whole of it is frequentlyinfluenced by the exertion of these faculties, as appears from theireffects on the external habit: for the whole skin is reddened by shame, andan universal trembling is produced by fear: and every muscle of the body isagitated in angry people by the desire of revenge. There is another very curious circumstance, which shews that sensation andvolition are movements of the sensorium in contrary directions; that is, that volition begins at the central parts of it, and proceeds to theextremities; and that sensation begins at the extremities, and proceeds tothe central parts: I mean that these two sensorial faculties cannot bestrongly exerted at the same time; for when we exert our volition strongly, we do not attend to pleasure or pain; and conversely, when we are stronglyaffected with the sensation of pleasure or pain, we use no volition. Aswill be further explained in Section XVIII. On sleep, and Section XXXIV. Onvolition. 2. All our emotions and passions seem to arise out of the exertions ofthese two faculties of the animal sensorium. Pride, hope, joy, are thenames of particular pleasures: shame, despair, sorrow, are the names ofpeculiar pains: and love, ambition, avarice, of particular desires: hatred, disgust, fear, anxiety, of particular aversions. Whilst the passion ofanger includes the pain from a recent injury, and the aversion to theadversary that occasioned it. And compassion is the pain we experience atthe sight of misery, and the desire of relieving it. There is another tribe of desires, which are commonly termed appetites, andare the immediate consequences of the absence of some irritative motions. Those, which arise from defect of internal irritations, have proper namesconferred upon them, as hunger, thirst, lust, and the desire of air, whenour respiration is impaired by noxious vapours; and of warmth, when we areexposed to too great a degree of cold. But those, whose stimuli areexternal to the body, are named from the objects, which are by natureconstituted to excite them; these desires originate from our pastexperience of the pleasurable sensations they occasion, as the smell of anhyacinth, or the taste of a pine-apple. Whence it appears, that our pleasures and pains are at least as various andas numerous as our irritations; and that our desires and aversions must beas numerous as our pleasures and pains. And that as sensation is here usedas a general term for our numerous pleasures and pains, when they producethe contractions of our fibres; so volition is the general name for ourdesires and aversions, when they produce fibrous contractions. Thus when amotion of the central parts, or of the whole sensorium, terminates in theexertion of our muscles, it is generally called voluntary action; when itterminates in the exertion of our ideas, it is termed recollection, reasoning, determining. 3. As the sensations of pleasure and pain are originally introduced by theirritations of external objects: so our desires and aversions areoriginally introduced by those sensations; for when the objects of ourpleasures or pains are at a distance, and we cannot instantaneously possessthe one, or avoid the other, then desire or aversion is produced, and avoluntary exertion of our ideas or muscles succeeds. The pain of hunger excites you to look out for food, the tree, that shadesyou, presents its odoriferous fruit before your eyes, you approach, pluck, and eat. The various movements of walking to the tree, gathering the fruit, andmasticating it, are associated motions introduced by their connection withsensation; but if from the uncommon height of the tree, the fruit beinaccessible, and you are prevented from quickly possessing the intendedpleasure, desire is produced. The consequence of this desire is, first, adeliberation about the means to gain the object of pleasure in process oftime, as it cannot be procured immediately; and, secondly, the muscularaction necessary for this purpose. You voluntarily call up all your ideas of causation, that are related tothe effect you desire, and voluntarily examine and compare them, and atlength determine whether to ascend the tree, or to gather stones from theneighbouring brook, is easier to practise, or more promising of success;and, finally, you gather the stones, and repeatedly fling them to dislodgethe fruit. Hence then we gain a criterion to distinguish voluntary acts or thoughtsfrom those caused by sensation. As the former are always employed about the_means_ to acquire pleasurable objects, or the _means_ to avoid painfulones; while the latter are employed in the possession of those, which arealready in our power. Hence the activity of this power of volition produces the great differencebetween the human and the brute creation. The ideas and the actions ofbrutes are almost perpetually employed about their present pleasures, ortheir present pains; and, except in the few instances which are mentionedin Section XVI, on instinct, they seldom busy themselves about the means ofprocuring future bliss, or of avoiding future misery; so that the acquiringof languages, the making of tools, and labouring for money, which are allonly the means to procure pleasures; and the praying to the Deity, asanother means to procure happiness, are characteristic of human nature. 4. As there are many diseases produced by the quantity of the sensation ofpain or pleasure being too great or too little; so are there diseasesproduced by the susceptibility of the constitution to motions causable bythese sensations being too dull or too vivid. This susceptibility of thesystem to sensitive motions is termed sensibility, to distinguish it fromsensation, which is the actual existence or exertion of pain or pleasure. Other classes of diseases are owing to the excessive promptitude, orsluggishness of the constitution to voluntary exertions, as well as to thequantity of desire or of aversion. This susceptibility of the system tovoluntary motions is termed voluntarity, to distinguish it from volition, which is the exertion of desire or aversion; these diseases will be treatedof at length in the progress of the work. _Association. _ III. 1. It is not easy to assign a cause, why those animal movements, thathave once occurred in succession, or in combination, should afterwards havea tendency to succeed or accompany each other. It is a property ofanimation, and distinguishes this order of being from the other productionsof nature. When a child first wrote the word man, it was distinguished in his mindinto three letters, and those letters into many parts of letters; but byrepeated use the word man becomes to his hand in writing it, as to hisorgans of speech in pronouncing it, but one movement without anydeliberation, or sensation, or irritation, interposed between the parts ofit. And as many separate motions of our muscles thus become united, andform, as it were, one motion; so each separate motion before such union maybe conceived to consist of many parts or spaces moved through; and perhapseven the individual fibres of our muscles have thus gradually been broughtto act in concert, which habits began to be acquired as early as the veryformation of the moving organs, long before the nativity of the animal; asexplained in the Section XVI. 2. On instinct. 2. There are many motions of the body, belonging to the irritative class, which might by a hasty observer be mistaken for associated ones; as theperistaltic motion of the stomach and intestines, and the contractions ofthe heart and arteries, might be supposed to be associated with theirritative motions of their nerves of sense, rather than to be excited bythe irritation of their muscular fibres by the distention, acrimony, ormomentum of the blood. So the distention or elongation of muscles byobjects external to them irritates them into contraction, though thecuticle or other parts may intervene between the stimulating body and thecontracting muscle. Thus a horse voids his excrement when its weight orbulk irritates the rectum or sphincter ani. These muscles act from theirritation of distention, when he excludes his excrement, but the musclesof the abdomen and diaphragm are brought into motion by association withthose of the sphincter and rectum. * * * * * SECT. XII. OF STIMULUS, SENSORIAL EXERTION, AND FIBROUS CONTRACTION. I. Of fibrous contraction. 1. _Two particles of a fibre cannot approach without the intervention of something, as in magnetism, electricity, elasticity. Spirit of life is not electric ether. Galvani's experiments. _ 2. _Contraction of a fibre. _ 3. _Relaxation succeeds. _ 4. _Successive contractions, with intervals. Quick pulse from debility, from paucity of blood. Weak contractions performed in less time, and with shorter intervals. _ 5. _Last situation of the fibres continues after contraction. _ 6. _Contraction greater than usual induces pleasure or pain. _ 7. _Mobility of the fibres uniform. Quantity of sensorial power fluctuates. Constitutes excitability. _ II. Of sensorial exertion. 1. _Animal motion includes stimulus, sensorial power, and contractile fibres. The sensorial faculties act separately or conjointly. Stimulus of four kinds. Strength and weakness defined. Sensorial power perpetually exhausted and renewed. Weakness from defect of stimulus. From defect of sensorial power, the direct and indirect debility of Dr. Brown. Why we become warm in Buxton bath after a time, and see well after a time in a darkish room. Fibres may act violently, or with their whole force, and yet feebly. Great exertion in inflammation explained. Great muscular force of some insane people. _ 2. _Occasional accumulation of sensorial power in muscles subject to constant stimulus. In animals sleeping in winter. In eggs, seeds, schirrous tumours, tendons, bones. _ 3. _Great exertion introduces pleasure or pain. Inflammation. Libration of the system between torpor and activity. Fever-fits. _ 4. _Desire and aversion introduced. Excess of volition cures fevers. _ III. Of repeated stimulus. 1. _A stimulus repeated too frequently looses effect. As opium, wine, grief. Hence old age. Opium and aloes in small doses. _ 2. _A stimulus not repeated too frequently does not lose effect. Perpetual movement of the vital organs. _ 3. _A stimulus repeated at uniform times produces greater effect. Irritation combined with association. _ 4. _A stimulus repeated frequently and uniformly may be withdrawn, and the action of the organ will continue. Hence the bark cures agues, and strengthens weak constitutions. _ 5. _Defect of stimulus repeated at certain intervals causes fever-fits. _ 6. _Stimulus long applied ceases to act a second time. _ 7. _If a stimulus excites sensation in an organ not usually excited into sensation, inflammation is produced. _ IV. Of stimulus greater than natural. 1. _A stimulus greater than natural diminishes the quantity of sensorial power in general. _ 2. _In particular organs. _ 3. _Induces the organ into spasmodic actions. _ 4. _Induces the antagonist fibres into action. _ 5. _Induces the organ into convulsive or fixed spasms. _ 6. _Produces paralysis of the organ. _ V. Of stimulus less than natural. 1. _Stimulus less than natural occasions accumulation of sensorial power in general. _ 2. _In particular organs, flushing of the face in a frosty morning. In fibres subject to perpetual stimulus only. Quantity of sensorial power inversely as the stimulus. _ 3. _Induces pain. As of cold, hunger, head-ach. _ 4. _Induces more feeble and frequent contraction. As in low fevers. Which are frequently owing to deficiency of sensorial power rather than to deficiency of stimulus. _ 5. _Inverts successive trains of motion. Inverts ideas. _ 6. _Induces paralysis and death. _ VI. Cure of increased exertion. 1. _Natural cure of exhaustion of sensorial power. _ 2. _Decrease the irritations. Venesection. Cold. Abstinence. _ 3. _Prevent the previous cold fit. Opium. Bark. Warmth. Anger. Surprise. _ 4. _Excite some other part of the system. Opium and warm bath relieve pains both from defect and from excess of stimulus. _ 5. _First increase the stimulus above, and then decrease it beneath the natural quantity. _ VII. Cure of decreased exertion. 1. _Natural cure by accumulation of sensorial power. Ague-fits. Syncope. _ 2. _Increase the stimulation, by wine, opium, given so as not to intoxicate. Cheerful ideas. _ 3. _Change the kinds of stimulus. _ 4. _Stimulate the associated organs. Blisters of use in heart-burn, and cold extremities. _ 5. _Decrease the stimulation for a time, cold bath. _ 6. _Decrease the stimulation below natural, and then increase it above natural. Bark after emetics. Opium after venesection. Practice of Sydenham in chlorosis. _ 7. _Prevent unnecessary expenditure of sensorial power. Decumbent posture, silence, darkness. Pulse quickened by rising out of bed. _ 8. _To the greatest degree of quiescence apply the least stimulus. Otherwise paralysis or inflammation of the organ ensues. Gin, wine, blisters, destroy by too great stimulation in fevers with debility. Intoxication in the slightest degree succeeded by debility. Golden rule for determining the best degree of stimulus in low fevers. Another golden rule for determining the quantity of spirit which those, who are debilitated by drinking it, may safely omit. _ I. _Of fibrous contraction. _ 1. If two particles of iron lie near each other without motion, andafterwards approach each other; it is reasonable to conclude that somethingbesides the iron particles is the cause of their approximation; thisinvisible something is termed magnetism. In the same manner, if theparticles, which compose an animal muscle, do not touch each other in therelaxed state of the muscle, and are brought into contact during thecontraction of the muscle, it is reasonable to conclude, that some otheragent is the cause of this new approximation. For nothing can act, where itdoes not exist; for to act includes to exist; and therefore the particlesof the muscular fibre (which in its state of relaxation are supposed not totouch) cannot affect each other without the influence of some intermediateagent; this agent is here termed the spirit of animation, or sensorialpower, but may with equal propriety be termed the power, which causescontraction; or may be called by any other name, which the reader maychoose to affix to it. The contraction of a muscular fibre may be compared to the followingelectric experiment, which is here mentioned not as a philosophicalanalogy, but as an illustration or simile to facilitate the conception of adifficult subject. Let twenty very small Leyden phials properly coated behung in a row by fine silk threads at a small distance from each other; letthe internal charge of one phial be positive, and of the other negativealternately, if a communication be made from the internal surface of thefirst to the external surface of the last in the row, they will all of theminstantly approach each other, and thus shorten a line that might connectthem like a muscular fibre. See Botanic Garden, p. 1. Canto I. 1. 202, noteon Gymnotus. The attractions of electricity or of magnetism do not apply philosophicallyto the illustration of the contraction of animal fibres, since the force ofthose attractions increases in some proportion inversely as the distance, but in muscular motion there appears no difference in velocity or strengthduring the beginning or end of the contraction, but what may be clearlyascribed to the varying mechanic advantage in the approximation of one boneto another. Nor can muscular motion be assimilated with greaterplausibility to the attraction of cohesion or elasticity; for in bending asteel spring, as a small sword, a less force is required to bend it thefirst inch than the second; and the second than the third; the particles ofsteel on the convex side of the bent spring endeavouring to restorethemselves more powerfully the further they are drawn from each other. SeeBotanic Garden, P. I. Addit. Note XVIII. I am aware that this may be explained another way, by supposing theelasticity of the spring to depend more on the compression of the particleson the concave side than on the extension of them on the convex side; andby supposing the elasticity of the elastic gum to depend more on theresistance to the lateral compression of its particles than to thelongitudinal extension of them. Nevertheless in muscular contraction, asabove observed, there appears no difference in the velocity or force of itat its commencement or at its termination; from whence we must concludethat animal contraction is governed by laws of its own, and not by those ofmechanics, chemistry, magnetism, or electricity. On these accounts I do not think the experiments conclusive, which werelately published by Galvani, Volta, and others, to shew a similitudebetween the spirit of animation, which contracts the muscular fibres, andthe electric fluid. Since the electric fluid may act only as a more potentstimulus exciting the muscular fibres into action, and not by supplyingthem with a new quantity of the spirit of life. Thus in a recent hemiplegiaI have frequently observed, when the patient yawned and stretched himself, that the paralytic limbs moved also, though they were totally disobedientto the will. And when he was electrified by passing shocks from theaffected hand to the affected foot, a motion of the paralytic limbs wasalso produced. Now as in the act of yawning the muscles of the paralyticlimbs were excited into action by the stimulus of the irksomeness of acontinued posture, and not by any additional quantity of the spirit oflife; so we may conclude, that the passage of the electric fluid, whichproduced a similar effect, acted only as a stimulus, and not by supplyingany addition of sensorial power. If nevertheless this theory should ever become established, a stimulus mustbe called an eductor of vital ether; which stimulus may consist ofsensation or volition, as in the electric eel, as well as in the appulsesof external bodies; and by drawing off the charges of vital fluid mayoccasion the contraction or motions of the muscular fibres, and organs ofsense. 2. The immediate effect of the action of the spirit of animation orsensorial power on the fibrous parts of the body, whether it acts in themode of irritation, sensation, volition, or association, is a contractionof the animal fibre, according to the second law of animal causation. Sect. IV. Thus the stimulus of the blood induces the contraction of the heart;the agreeable taste of a strawberry produces the contraction of the musclesof deglutition; the effort of the will contracts the muscles, which movethe limbs in walking; and by association other muscles of the trunk arebrought into contraction to preserve the balance of the body. The fibrousextremities of the organs of sense have been shewn, by the ocular spectrain Sect. III. To suffer similar contraction by each of the above modes ofexcitation; and by their configurations to constitute our ideas. 3. After animal fibres have for some time been excited into contraction, arelaxation succeeds, even though the exciting cause continues to act. Inrespect to the irritative motions this is exemplified in the peristalticcontractions of the bowels; which cease and are renewed alternately, thoughthe stimulus of the aliment continues to be uniformly applied; in thesensitive motions, as in strangury, tenesmus, and parturition, thealternate contractions and relaxations of the muscles exist, though thestimulus is perpetual. In our voluntary exertions it is experienced, as noone can hang long by the hands, however vehemently he wills so to do; andin the associate motions the constant change of our attitudes evinces thenecessity of relaxation to those muscles, which have been long in action. This relaxation of a muscle after its contraction, even though the stimuluscontinues to be applied, appears to arise from the expenditure ordiminution of the spirit of animation previously resident in the muscle, according to the second law of animal causation in Sect. IV. In thoseconstitutions, which are termed weak, the spirit of animation becomessooner exhausted, and tremulous motions are produced, as in the hands ofinfirm people, when they lift a cup to their mouths. This quickerexhaustion of the spirit of animation is probably owing to a less quantityof it residing in the acting fibres, which therefore more frequentlyrequire a supply from the nerves, which belong to them. 4. If the sensorial power continues to act, whether it acts in the mode ofirritation, sensation, volition, or association, a new contraction of theanimal fibre succeeds after a certain interval; which interval is ofshorter continuance in weak people than in strong ones. This is exemplifiedin the shaking of the hands of weak people, when they attempt to write. Ina manuscript epistle of one of my correspondents, which is written in asmall hand, I observed from four to six zigzags in the perpendicular strokeof every letter, which shews that both the contractions of the fingers, andintervals between them, must have been performed in very short periods oftime. The times of contraction of the muscles of enfeebled people being less, andthe intervals between those contractions being less also, accounts for thequick pulse in fevers with debility, and in dying animals. The shortness ofthe intervals between one contraction and another in weak constitutions, isprobably owing to the general deficiency of the quantity of the spirit ofanimation, and that therefore there is a less quantity of it to be receivedat each interval of the activity of the fibres. Hence in repeated motions, as of the fingers in performing on the harpsichord, it would at first sightappear, that swiftness and strength were incompatible; nevertheless thesingle contraction of a muscle is performed with greater velocity as wellas with greater force by vigorous constitutions, as in throwing a javelin. There is however another circumstance, which may often contribute to causethe quickness of the pulse in nervous fevers, as in animals bleeding todeath in the slaughter-house; which is the deficient quantity of blood;whence the heart is but half distended, and in consequence soonercontracts. See Sect. XXXII. 2. 1. For we must not confound frequency of repetition with quickness of motion, or the number of pulsations with the velocity, with which the fibres, whichconstitute the coats of the arteries, contract themselves. For where thefrequency of the pulsations is but seventy-five in a minute, as in health;the contracting fibres, which constitute the sides of the arteries, maymove through a greater space in a given time, than where the frequency ofpulsation is one hundred and fifty in a minute, as in some fevers withgreat debility. For if in those fevers the arteries do not expandthemselves in their diastole to more than half the usual diameter of theirdiastole in health, the fibres which constitute their coats, will movethrough a less space in a minute than in health, though they make twopulsations for one. Suppose the diameter of the artery during its systole to be one line, andthat the diameter of the same artery during its diastole is in health isfour lines, and in a fever with, great debility only two lines. It follows, that the arterial fibres contract in health from a circle of twelve linesin circumference to a circle of three lines in circumference, that is theymove through a space of nine lines in length. While the arterial fibres inthe fever with debility would twice contract from a circle of six lines toa circle of three lines; that is while they move through a space equal tosix lines. Hence though the frequency of pulsation in fever be greater astwo to one, yet the velocity of contraction in health is greater as nine tosix, or as three to two. On the contrary in inflammatory diseases with strength, as in the pleurisy, the velocity of the contracting sides of the arteries is much greater thanin health, for if we suppose the number of pulsations in a pleurisy to behalf as much more than in health, that is as one hundred and twenty toeighty, (which is about what generally happens in inflammatory diseases)and if the diameter of the artery in diastole be one third greater than inhealth, which I believe is near the truth, the result will be, that thevelocity of the contractile sides of the arteries will be in a pleurisy astwo and a half to one, compared to the velocity of their contraction in astate of health, for if the circumference of the systole of the artery bethree lines, and the diastole in health be twelve lines in circumference, and in a pleurisy eighteen lines; and secondly, if the artery pulsatesthrice in the diseased state for twice in the healthy one, it follows, thatthe velocity of contraction in the diseased state to that in the healthystate will be forty-five to eighteen, or as two and a half to one. From hence it would appear, that if we had a criterion to determine thevelocity of the arterial contractions, it would at the same time give ustheir strength, and thus be of more service in distinguishing diseases, than the knowledge of their frequency. As such a criterion cannot be had, the frequency of pulsation, the age of the patient being allowed for, willin some measure assist us to distinguish arterial strength from arterialdebility, since in inflammatory diseases with strength the frequency seldomexceeds one hundred and eighteen or one hundred and twenty pulsations in aminute; unless under peculiar circumstance, as the great additional stimuliof wine or of external heat. 5. After a muscle or organ of sense has been excited into contraction, andthe sensorial power ceases to act, the last situation or configuration ofit continues; unless it be disturbed by the action of some antagonistfibres, or other extraneous power. Thus in weak or languid people, whereverthey throw their limbs on their bed or sofa, there they lie, till anotherexertion changes their attitude; hence one kind of ocular spectra seems tobe produced after looking at bright objects; thus when a fire-stick iswhirled round in the night, there appears in the eye a complete circle offire; the action or configuration of one part of the retina not ceasingbefore the return of the whirling fire. Thus if any one looks at the setting sun for a short time, and then covershis closed eyes with his hand, he will for many seconds of time perceivethe image of the sun on his retina. A similar image of all other bodieswould remain some time in the eye, but is effaced by the eternal change ofthe motions of the extremity of this nerve in our attention to otherobjects. See Sect. XVIII. 5. On Sleep. Hence the dark spots, and otherocular spectra, are more frequently attended to, and remain longer in theeyes of weak people, as after violent exercise, intoxication, or want ofsleep. 6. A contraction of the fibres somewhat greater than usual introducespleasurable sensation into the system, according to the fourth law ofanimal causation. Hence the pleasure in the beginning of drunkenness isowing to the increased action of the system from the stimulus of vinousspirit or of opium. If the contractions be still greater in energy orduration, painful sensations are introduced, as in consequence of greatheat, or caustic applications, or fatigue. If any part of the system, which is used to perpetual activity, as thestomach, or heart, or the fine vessels of the skin, acts for a time withless energy, another kind of painful sensation ensues, which is calledhunger, or faintness, or cold. This occurs in a less degree in thelocomotive muscles, and is called wearysomeness. In the two former kinds ofsensation there is an expenditure of sensorial power, in these latter thereis an accumulation of it. 7. We have used the words exertion of sensorial power as a general term toexpress either irritation, sensation, volition, or association; that is, toexpress the activity or motion of the spirit of animation, at the time itproduces the contractions of the fibrous parts of the system. It may besupposed that there may exist a greater or less mobility of the fibrousparts of our system, or a propensity to be stimulated into contraction bythe greater or less quantity or energy of the spirit of animation; and thathence if the exertion of the sensorial power be in its natural state, andthe mobility of the fibres be increased, the same quantity of fibrouscontraction will be caused, as if the mobility of the fibres continues inits natural state, and the sensorial exertion be increased. Thus it may be conceived, that in diseases accompanied with strength, as ininflammatory fevers with arterial strength, that the cause of greaterfibrous contraction, may exist in the increased mobility of the fibres, whose contractions are thence both more forceable and more frequent. Andthat in diseases attended with debility, as in nervous fevers, where thefibrous contractions are weaker, and more frequent, it may be conceivedthat the cause consists in a decrease of mobility of the fibres; and thatthose weak constitutions, which are attended with cold extremities andlarge pupils of the eyes, may possess less mobility of the contractilefibres, as well as less quantity of exertion of the spirit of animation. In answer to this mode of reasoning it may be sufficient to observe, thatthe contractile fibres consist of inert matter, and when the sensorialpower is withdrawn, as in death, they possess no power of motion at all, but remain in their last state, whether of contraction or relaxation, andmust thence derive the whole of this property from the spirit of animation. At the same time it is not improbable, that the moving fibres of strongpeople may possess a capability of receiving or containing a greaterquantity of the spirit of animation than those of weak people. In every contraction of a fibre there is an expenditure of the sensorialpower, or spirit of animation; and where the exertion of this sensorialpower has been for some time increased, and the muscles or organs of sensehave in consequence acted with greater energy, its propensity to activityis proportionally lessened; which is to be ascribed to the exhaustion ordiminution of its quantity. On the contrary, where there has been lessfibrous contraction than usual for a certain time, the sensorial power orspirit of animation becomes accumulated in the inactive part of the system. Hence vigour succeeds rest, and hence the propensity to action of all ourorgans of sense and muscles is in a state of perpetual fluctuation. Theirritability for instance of the retina, that is, its quantity of sensorialpower, varies every moment according to the brightness or obscurity of theobject last beheld compared with the present one. The same occurs to oursense of heat, and to every part of our system, which is capable of beingexcited into action. When this variation of the exertion of the sensorial power becomes much andpermanently above or beneath the natural quantity, it becomes a disease. Ifthe irritative motions be too great or too little, it shews that thestimulus of external things affect this sensorial power too violently ortoo inertly. If the sensitive motions be too great or too little, the causearises from the deficient or exuberant quantity of sensation produced inconsequence of the motions of the muscular fibres or organs of sense; ifthe voluntary actions are diseased the cause is to be looked for in thequantity of volition produced in consequence of the desire or aversionoccasioned by the painful or pleasurable sensations above mentioned. Andthe diseases of associations probably depend on the greater or lessquantity of the other three sensorial powers by which they were formed. From whence it appears that the propensity to action, whether it be calledirritability, sensibility, voluntarity, or associability, is only anothermode of expression for the quantity of sensorial power residing in theorgan to be excited. And that on the contrary the words inirritability andinsensibility, together with inaptitude to voluntary and associate motions, are synonymous with deficiency of the quantity of sensorial power, or ofthe spirit of animation, residing in the organs to be excited. II. _Of sensorial Exertion. _ 1. There are three circumstances to be attended to in the production ofanimal motions, 1st. The stimulus. 2d. The sensorial power. 3d. Thecontractile fibre. 1st. A stimulus, external to the organ, originallyinduces into action the sensorial faculty termed irritation; this producesthe contraction of the fibres, which, if it be perceived at all, introducespleasure or pain; which in their active state are termed sensation; whichis another sensorial faculty, and occasionally produces contraction of thefibres; this pleasure or pain is therefore to be considered as anotherstimulus, which may either act alone or in conjunction with the formerfaculty of the sensorium termed irritation. This new stimulus of pleasure or pain either induces into action thesensorial faculty termed sensation, which then produces the contraction ofthe fibres; or it introduces desire or aversion, which excite into actionanother sensorial faculty, termed volition, and may therefore be consideredas another stimulus, which either alone or in conjunction with one or bothof the two former faculties of the sensorium produces the contraction ofanimal fibres. There is another sensorial power, that of association, whichperpetually, in conjunction with one or more of the above, and frequentlysingly, produces the contraction of animal fibres, and which is itselfexcited into action by the previous motions of contracting fibres. Now as the sensorial power, termed irritation, residing in any particularfibres, is excited into exertion by the stimulus of external bodies actingon those fibres; the sensorial power, termed sensation, residing in anyparticular fibres is excited into exertion by the stimulus of pleasure orpain acting on those fibres; the sensorial power, termed volition, residingin any particular fibres is excited into exertion by the stimulus of desireor aversion; and the sensorial power, termed association, residing in anyparticular fibres, is excited into action by the stimulus of other fibrousmotions, which had frequently preceded them. The word stimulus maytherefore be used without impropriety of language, for any of these fourcauses, which excite the four sensorial powers into exertion. For thoughthe immediate cause of volition has generally been termed _a motive_; andthat of irritation only has generally obtained the name of _stimulus_; yetas the immediate cause, which excites the sensorial powers of sensation, orof association into exertion, have obtained no general name, we shall usethe word stimulus for them all. Hence the quantity of motion produced in any particular part of the animalsystem will be as the quantity of stimulus and the quantity of sensorialpower, or spirit of animation, residing in the contracting fibres. Whereboth these quantities are great, _strength_ is produced, when that word isapplied to the motions of animal bodies. Where either of them is deficient, _weakness_ is produced, as applied to the motions of animal bodies. Now as the sensorial power, or spirit of animation, is perpetuallyexhausted by the expenditure of it in fibrous contractions, and isperpetually renewed by the secretion or production of it in the brain andspinal marrow, the quantity of animal strength must be in a perpetual stateof fluctuation on this account; and if to this be added the unceasingvariation of all the four kinds of stimulus above described, which producethe exertions of the sensorial powers, the ceaseless vicissitude of animalstrength becomes easily comprehended. If the quantity of sensorial power remains the same, and the quantity ofstimulus be lessened, a weakness of the fibrous contractions ensues, whichmay be denominated _debility from defect of stimulus_. If the quantity ofstimulus remains the same, and the quantity of sensorial power be lessened, another kind of weakness ensues, which may be termed _debility from defectof sensorial power_; the former of these is called by Dr. Brown, in hisElements of Medicine, direct debility, and the latter indirect debility. The coincidence of some parts of this work with correspondent deductions inthe Brunonian Elementa Medicina, a work (with some exceptions) of greatgenius, must be considered as confirmations of the truth of the theory, asthey were probably arrived at by different trains of reasoning. Thus in those who have been exposed to cold and hunger there is adeficiency of stimulus. While in nervous fever there is a deficiency ofsensorial power. And in habitual drunkards, in a morning before their usualpotation, there is a deficiency both of stimulus and of sensorial power. While, on the other hand, in the beginning of intoxication there is anexcess of stimulus; in the hot-ach, after the hands have been immersed insnow, there is a redundancy of sensorial power; and in inflammatorydiseases with arterial strength, there is an excess of both. Hence if the sensorial power be lessened, while the quantity of stimulusremains the same as in nervous fever, the frequency of repetition of thearterial contractions may continue, but their force in respect to removingobstacles, as in promoting the circulation of the blood, or the velocity ofeach contraction, will be diminished, that is, the animal strength will belessened. And secondly, if the quantity of sensorial power be lessened, andthe stimulus be increased to a certain degree, as in giving opium innervous fevers, the arterial contractions may be performed more frequentlythan natural, yet with less strength. And thirdly, if the sensorial power continues the same in respect toquantity, and the stimulus be somewhat diminished, as in going into adarkish room, or into a coldish bath, suppose of about eighty degrees ofheat, as Buxton-bath, a temporary weakness of the affected fibres isinduced, till an accumulation of sensorial power gradually succeeds, andcounterbalances the deficiency of stimulus, and then the bath ceases tofeel cold, and the room ceases to appear dark; because the fibres of thesubcutaneous vessels, or of the organs of sense, act with their usualenergy. A set of muscular fibres may thus be stimulated into violent exertion, thatis, they may act frequently, and with their whole sensorial power, but maynevertheless not act strongly; because the quantity of their sensorialpower was originally small, or was previously exhausted. Hence a stimulusmay be great, and the irritation in consequence act with its full force, asin the hot paroxysms of nervous fever; but if the sensorial power, termedirritation, be small in quantity, the force of the fibrous contractions, and the times of their continuance in their contracted state, will beproportionally small. In the same manner in the hot paroxysm of putrid fevers, which are shewn inSect. XXXIII. To be inflammatory fevers with arterial debility, thesensorial power termed sensation is exerted with great activity, yet thefibrous contractions, which produce the circulation of the blood, areperformed without strength, because the quantity of sensorial power thenresiding in that part of the system is small. Thus in irritative fever with arterial strength, that is, with excess ofspirit of animation, the quantity of exertion during the hot part of theparoxysm is to be estimated from the quantity of stimulus, and the quantityof sensorial power. While in sensitive (or inflammatory) fever witharterial strength, that is, with excess of spirit of animation, the violentand forcible actions of the vascular system during the hot part of theparoxysm are induced by the exertions of two sensorial powers, which areexcited by two kinds of stimulus. These are the sensorial power ofirritation excited by the stimulus of bodies external to the moving fibres, and the sensorial power of sensation excited by the pain in consequence ofthe increased contractions of those moving fibres. And in insane people in some cases the force of their muscular actions willbe in proportion to the quantity of sensorial power, which they possess, and the quantity of the stimulus of desire or aversion, which excites theirvolition into action. At the same time in other cases the stimulus of painor pleasure, and the stimulus of external bodies, may excite into actionthe sensorial powers of sensation and irritation, and thus add greaterforce to their muscular actions. 2. The application of the stimulus, whether that stimulus be some qualityof external bodies, or pleasure or pain, or desire or aversion, or a linkof association, excites the correspondent sensorial power into action, andthis causes the contraction of the fibre. On the contraction of the fibre apart of the spirit of animation becomes expended, and the fibre ceases tocontract, though the stimulus continues to be applied; till in a certaintime the fibre having received a supply of sensorial power is ready tocontract again, if the stimulus continues to be applied. If the stimulus onthe contrary be withdrawn, the same quantity of quiescent sensorial powerbecomes resident in the fibre as before its contraction; as appears fromthe readiness for action of the large locomotive muscles of the body in ashort time after common exertion. But in those muscular fibres, which are subject to constant stimulus, asthe arteries, glands, and capillary vessels, another phenomenon occurs, iftheir accustomed stimulus be withdrawn; which is, that the sensorial powerbecomes accumulated in the contractile fibres, owing to the want of itsbeing perpetually expended, or carried away, by their usual unremittedcontractions. And on this account those muscular fibres become afterwardsexcitable into their natural actions by a much weaker stimulus; or intounnatural violence of action by their accustomed stimulus, as is seen inthe hot fits of intermittent fevers, which are in consequence of theprevious cold ones. Thus the minute vessels of the skin are constantlystimulated by the fluid matter of heat; if the quantity of this stimulus ofheat be a while diminished, as in covering the hands with snow, the vesselscease to act, as appears from the paleness of the skin; if this coldapplication of snow be continued but a short time, the sensorial power, which had habitually been supplied to the fibres, becomes now accumulatedin them, owing to the want of its being expended by their accustomedcontractions. And thence a less stimulus of heat will now excite them intoviolent contractions. If the quiescence of fibres, which had previously been subject to perpetualstimulus, continues a longer time; or their accustomed stimulus be morecompletely withdrawn; the accumulation of sensorial power becomes stillgreater, as in those exposed to cold and hunger; pain is produced, and theorgan gradually dies from the chemical changes, which take place in it; orit is at a great distance of time restored to action by stimulus appliedwith great caution in small quantity, as happens to some larger animals andto many insects, which during the winter months lie benumbed with cold, andare said to sleep, and to persons apparently drowned, or apparently frozento death. Snails have been said to revive by throwing them into water afterhaving been many years shut up in the cabinets of the curious; and eggs andseeds in general are restored to life after many months of torpor by thestimulus of warmth and moisture. The inflammation of schirrous tumours, which have long existed in a stateof inaction, is a process of this kind; as well as the sensibility acquiredby inflamed tendons and bones, which had at their formation a similarsensibility, which had so long lain dormant in their uninflamed state. 3. If after long quiescence from defect of stimulus the fibres, which hadpreviously been habituated to perpetual stimulus, are again exposed to buttheir usual quantity of it; as in those who have suffered the extremes ofcold or hunger; a violent exertion of the affected organ commences, owing, as above explained, to the great accumulation of sensorial power. Thisviolent exertion not only diminishes the accumulated spirit of animation, but at the same time induces pleasure or pain into the system, which, whether it be succeeded by inflammation or not, becomes an additionalstimulus, and acting along with the former one, produces still greaterexertions; and thus reduces the sensorial power in the contracting fibresbeneath its natural quantity. When the spirit of animation is thus exhausted by useless exertions, theorgan becomes torpid or unexcitable into action, and a second fit ofquiescence succeeds that of abundant activity. During this second fit ofquiescence the sensorial power becomes again accumulated, and another fitof exertion follows in train. These vicissitudes of exertion and inertionof the arterial system constitute the paroxysms of remittent fevers; orintermittent ones, when there is an interval of the natural action of thearteries between the exacerbations. In these paroxysms of fevers, which consist of the libration of thearterial system between the extremes of exertion and quiescence, either thefits become less and less violent from the contractile fibres becomingcoming less excitable to the stimulus by habit, that is, by becomingaccustomed to it, as explained below XII. 3. 1. Or the whole sensorialpower becomes exhausted, and the arteries cease to beat, and the patientdies in the cold part of the paroxysm. Or secondly, so much pain isintroduced into the system by the violent contractions of the fibres, thatinflammation arises, which prevents future cold fits by expending a part ofthe sensorial power in the extension of old vessels or the production ofnew ones; and thus preventing the too great accumulation or exertion of itin other parts of the system; or which by the great increase of stimulusexcites into great action the whole glandular system as well as thearterial, and thence a greater quantity of sensorial power is produced inthe brain, and thus its exhaustion in any peculiar part of the systemceases to be affected. 4. Or thirdly, in consequence of the painful or pleasurable sensation abovementioned, desire and aversion are introduced, and inordinate volitionsucceeds; which by its own exertions expends so much of the spirit ofanimation, that the two other sensorial faculties, or irritation andsensation, act so much more feebly; that the paroxysms of fever, or thatlibration between the extremes of exertion and inactivity of the arterialsystem, gradually subsides. On this account a temporary insanity is afavourable sign in fevers, as I have had some opportunities of observing. III. _Of repeated Stimulus. _ 1. When a stimulus is repeated more frequently than the expenditure ofsensorial power can be renewed in the acting organ, the effect of thestimulus becomes gradually diminished. Thus if two grains of opium beswallowed by a person unused to so strong a stimulus, all the vascularsystems in the body act with greater energy, all the secretions and theabsorption from those secreted fluids are increased in quantity; andpleasure or pain are introduced into the system, which adds an additionalstimulus to that already too great. After some hours the sensorial powerbecomes diminished in quantity, expended by the great activity of thesystem; and thence, when the stimulus of the opium is withdrawn, the fibreswill not obey their usual degree of natural stimulus, and a consequenttorpor or quiescence succeeds, as is experienced by drunkards, who on theday after a great excess of spirituous potation feel indigestion, head-ach, and general debility. In this fit of torpor or quiescence of a part or of the whole of thesystem, an accumulation of the sensorial power in the affected fibres isformed, and occasions a second paroxysm of exertion by the application onlyof the natural stimulus, and thus a libration of the sensorial exertionbetween one excess and the other continues for two or three days, where thestimulus was violent in degree; and for weeks in some fevers, from thestimulus of contagious matter. But if a second dose of opium be exhibited before the fibres have regainedtheir natural quantity of sensorial power, its effect will be much lessthan the former, because the spirit of animation or sensorial power is inpart exhausted by the previous excess of exertion. Hence all medicinesrepeated too frequently gradually lose their effect, as opium and wine. Many things of disagreeable taste at first cease to be disagreeable byfrequent repetition, as tobacco; grief and pain gradually diminish, and atlength cease altogether, and hence life itself becomes tolerable. Besides the temporary diminution of the spirit of animation or sensorialpower, which is naturally stationary or resident in every living fibre, bya single exhibition of a powerful stimulus, the contractile fibresthemselves, by the perpetual application of a new quantity of stimulus, before they have regained their natural quantity of sensorial power, appearto suffer in their capability of receiving so much as the natural quantityof sensorial power; and hence a permanent deficiency of spirit of animationtakes place, however long the stimulus may have been withdrawn. On thiscause depends the permanent debility of those, who have been addicted tointoxication, the general weakness of old age, and the natural debility orinirritability of those, who have pale skins and large pupils of theireyes. There is a curious phenomenon belongs to this place, which has alwaysappeared difficult of solution; and that is, that opium or aloes may beexhibited in small doses at first, and gradually increased to very largeones without producing stupor or diarrhoea. In this case, though the opiumand aloes are given in such small doses as not to produce intoxication orcatharsis, yet they are exhibited in quantities sufficient in some degreeto exhaust the sensorial power, and hence a stronger and a stronger dose isrequired; otherwise the medicine would soon cease to act at all. On the contrary, if the opium or aloes be exhibited in a large dose atfirst, so as to produce intoxication or diarrhoea; after a few repetitionsthe quantity of either of them may be diminished, and they will stillproduce this effect. For the more powerful stimulus dissevers theprogressive catenations of animal motions, described in Sect. XVII. Andintroduces a new link between them; whence every repetition strengthensthis new association or catenation, and the stimulus may be graduallydecreased, or be nearly withdrawn, and yet the effect shall continue;because the sensorial power of association or catenation being united withthe stimulus, increases in energy with every repetition of the catenatedcircle; and it is by these means that all the irritative associations ofmotions are originally produced. 2. When a stimulus is repeated at such distant intervals of time, that thenatural quantity of sensorial power becomes completely restored in theacting fibres, it will act with the same energy as when first applied. Hence those who have lately accustomed themselves to large doses of opiumby beginning with small ones, and gradually increasing them, and repeatingthem frequently, as mentioned in the preceding paragraph; if they intermitthe use of it for a few days only, must begin again with as small doses asthey took at first, otherwise they will experience the inconveniences ofintoxication. On this circumstance depend the constant unfailing effects of the variouskinds of stimulus, which excite into action all the vascular systems in thebody; the arterial, venous, absorbent, and glandular vessels, are broughtinto perpetual unwearied action by the fluids, which are adapted tostimulate them; but these have the sensorial power of association added tothat of irritation, and even in some degree that of sensation, and even ofvolition, as will be spoken of in their places; and life itself is thuscarried on by the production of sensorial power being equal to its waste orexpenditure in the perpetual movement of the vascular organization. 3. When a stimulus is repeated at uniform intervals of time with suchdistances between them, that the expenditure of sensorial power in theacting fibres becomes completely renewed, the effect is produced withgreater facility or energy. For the sensorial power of association iscombined with the sensorial power of irritation, or, in common language, the acquired habit assists the power of the stimulus. This circumstance not only obtains in the annual and diurnal catenations ofanimal motions explained in Sect. XXXVI. But in every less circle ofactions or ideas, as in the burthen of a song, or the iterations of adance; and constitutes the pleasure we receive from repetition andimitation; as treated of in Sect. XXII. 2. 4. When a stimulus has been many times repeated at uniform intervals, so asto produce the complete action of the organ, it may then be graduallydiminished, or totally withdrawn, and the action of the organ willcontinue. For the sensorial power of association becomes united with thatof irritation, and by frequent repetition becomes at length of sufficientenergy to carry on the new link in the circle of actions, without theirritation which at first introduced it. Hence, when the bark is given at stated intervals for the cure ofintermittent fevers, if sixty grains of it be given every three hours forthe twenty-four hours preceding the expected paroxysm, so as to stimulatethe defective part of the system into action, and by that means to preventthe torpor or quiescence of the fibres, which constitutes the cold fit;much less than half the quantity, given before the time at which anotherparoxysm of quiescence would have taken place, will be sufficient toprevent it; because now the sensorial power, termed association, acts in atwofold manner. First, in respect to the period of the catenation in whichthe cold fit was produced, which is now dissevered by the stronger stimulusof the first doses of the bark; and, secondly, because each dose of barkbeing repeated at periodical times, has its effect increased by thesensorial faculty of association being combined with that of irritation. Now, when sixty grains of Peruvian bark are taken twice a day, suppose atten o'clock and at six, for a fortnight, the irritation excited by thisadditional stimulus becomes a part of the diurnal circle of actions, andwill at length carry on the increased action of the system without theassistance of the stimulus of the bark. On this theory the bittermedicines, chalybeates, and opiates in appropriated doses, exhibited for afortnight, give permanent strength to pale feeble children, and other weakconstitutions. 5. When a defect of stimulus, as of heat, recurs at certain diurnalintervals, which induces some torpor or quiescence of a part of the system, the diurnal catenation of actions becomes disordered, and a new associationwith this link of torpid action is formed; on the next period the quantityof quiescence will be increased, suppose the same defect of stimulus torecur, because now the new association conspires with the defectiveirritation in introducing the torpid action of this part of the diurnalcatenation. In this manner many fever-fits commence, where the patient isfor some days indisposed at certain hours, before the cold paroxysm offever is completely formed. See Sect. XVII. 3. 3. On Catenation of AnimalMotions. 6. If a stimulus, which at first excited the affected organ into so greatexertion as to produce sensation, be continued for a certain time, it willcease to produce sensation both then and when repeated, though theirritative motions in consequence of it may continue or be re-excited. Many catenations of irritative motions were at first succeeded bysensation, as the apparent motions of objects when we walk past them, andprobably the vital motions themselves in the early state of our existence. But as those sensations were followed by no movements of the system inconsequence of them, they gradually ceased to be produced, not being joinedto any succeeding link of catenation. Hence contagious matter, which hasfor some weeks stimulated the system into great and permanent sensation, ceases afterwards to produce general sensation, or inflammation, though itmay still induce topical irritations. See Sect. XXXIII. 2. 8. XIX. 9. Our absorbent system then seems to receive those contagious matters, whichit has before experienced, in the same manner as it imbibes common moistureor other fluids; that is, without being thrown into so violent action as toproduce sensation; the consequence of which is an increase of daily energyor activity, till inflammation and its consequences succeed. 7. If a stimulus excites an organ into such violent contractions as toproduce sensation, the motions of which organ had not usually producedsensation, this new sensorial power, added to the irritation occasioned bythe stimulus, increases the activity of the organ. And if this activity becatenated with the diurnal circle of actions, an increasing inflammation isproduced; as in the evening paroxysms of small-pox, and other fevers withinflammation. And hence schirrous tumours, tendons and membranes, andprobably the arteries themselves become inflamed, when they are stronglystimulated. IV. _Of Stimulus greater than natural. _ 1. A quantity of stimulus greater than natural, producing an increasedexertion of sensorial power, whether that exertion be in the mode ofirritation, sensation, volition, or association, diminishes the generalquantity of it. This fact is observable in the progress of intoxication, asthe increased quantity or energy of the irritative motions, owing to thestimulus of vinous spirit, introduces much pleasurable sensation into thesystem, and much exertion of muscular or sensual motions in consequence ofthis increased sensation; the voluntary motions, and even the associateones, become much impaired or diminished; and delirium and staggeringsucceed. See Sect. XXI. On Drunkenness. And hence the great prostration ofthe strength of the locomotive muscles in some fevers, is owing to theexhaustion of sensorial power by the increased action of the arterialsystem. In like manner a stimulus greater than natural, applied to a part of thesystem, increases the exertion of sensorial power in that part, anddiminishes it in some other part. As in the commencement of scarlet fever, it is usual to see great redness and heat on the faces and breasts ofchildren, while at the same time their feet are colder than natural;partial heats are observable in other fevers with debility, and aregenerally attended with torpor or quiescence of some other part of thesystem. But these partial exertions of sensorial power are sometimesattended with increased partial exertions in other parts of the system, which sympathize with them, as the flushing of the face after a full meal. Both these therefore are to be ascribed to sympathetic associations, explained in Sect. XXXV. And not to general exhaustion or accumulation ofsensorial power. 2. A quantity of stimulus greater than natural, producing an increasedexertion of sensorial power in any particular organ, diminishes thequantity of it in that organ. This appears from the contractions of animalfibres being not so easily excited by a less stimulus after the organ hasbeen subjected to a greater. Thus after looking at any luminous object of asmall size, as at the setting sun, for a short time, so as not much tofatigue the eye, this part of the retina becomes less sensible to smallerquantities of light; hence when the eyes are turned on other less luminousparts of the sky, a dark spot is seen resembling the shape of the sun, orother luminous object which we last behold. See Sect. XL. No. 2. Thus we are some time before we can distinguish objects in an obscure roomafter coming from bright day-light, though the iris presently contractsitself. We are not able to hear weak sounds after loud ones. And thestomachs of those who have been much habituated to the stronger stimulus offermented or spirituous liquors, are not excited into due action by weakerones. 3. A quantity of stimulus something greater than the last mentioned, orlonger continued, induces the organ into spasmodic action, which ceases andrecurs alternately. Thus on looking for a time on the setting sun, so asnot greatly to fatigue the sight, a yellow spectrum is seen when the eyesare closed and covered, which continues for a time, and then disappears andrecurs repeatedly before it entirely vanishes. See Sect. XL. No. 5. Thusthe action of vomiting ceases and is renewed by intervals, although theemetic drug is thrown up with the first effort. A tenesmus continues byintervals some time after the exclusion of acrid excrement; and thepulsations of the heart of a viper are said to continue some time after itis cleared from its blood. In these cases the violent contractions of the fibres produce painaccording to law 4; and this pain constitutes an additional kind orquantity of excitement, which again induces the fibres into contraction, and which painful excitement is again renewed, and again inducescontractions of the fibres with gradually diminishing effect. 4. A quantity of stimulus greater than that last mentioned, or longercontinued, induces the antagonist muscles into spasmodic action. This isbeautifully illustrated by the ocular spectra described in Sect. XL. No. 6. To which the reader is referred. From those experiments there is reason toconclude that the fatigued part of the retina throws itself into a contrarymode of action like oscitation or pandiculation, as soon as the stimulus, which has fatigued it, is withdrawn; but that it still remains liable to beexcited into action by any other colours except the colour with which ithas been fatigued. Thus the yawning and stretching the limbs after acontinued action or attitude seems occasioned by the antagonist musclesbeing stimulated by their extension during the contractions of those inaction, or in the situation in which that action last left them. 5. A quantity of stimulus greater than the last, or longer continued, induces variety of convulsions or fixed spasms either of the affected organor of the moving fibres in the other parts of the body. In respect to thespectra in the eye, this is well illustrated in No. 7 and 8, of Sect. XL. Epileptic convulsions, as the emprosthotonos and opisthotonos, with thecramp of the calf of the leg, locked jaw, and other cataleptic fits, appearto originate from pain, as some of these patients scream aloud before theconvulsion takes place; which seems at first to be an effort to relievepainful sensation, and afterwards an effort to prevent it. In these cases the violent contractions of the fibres produce so much pain, as to constitute a perpetual excitement; and that in so great a degree asto allow but small intervals of relaxation of the contracting fibres as inconvulsions, or no intervals at all as in fixed spasms. 6. A quantity of stimulus greater than the last, or longer continued, produces a paralysis of the organ. In many cases this paralysis is only atemporary effect, as on looking long on a small area of bright red silkplaced on a sheet of white paper on the floor in a strong light, the redsilk gradually becomes paler, and at length disappears; which evinces thata part of the retina, by being violently excited, becomes for a timeunaffected by the stimulus of that colour. Thus cathartic medicines, opiates, poisons, contagious matter, cease to influence our system after ithas been habituated to the use of them, except by the exhibition ofincreased quantities of them; our fibres not only become unaffected bystimuli, by which they have previously been violently irritated, as by thematter of the small-pox or measles; but they also become unaffected bysensation, where the violent exertions, which disabled them, were inconsequence of too great quantity of sensation. And lastly the fibres, which become disobedient to volition, are probably disabled by their tooviolent exertions in consequence of too great a quantity of volition. After every exertion of our fibres a temporary paralysis succeeds, whencethe intervals of all muscular contractions, as mentioned in No. 3 and 4 ofthis Section; the immediate cause of these more permanent kinds ofparalysis is probably owing in the same manner to the too great exhaustionof the spirit of animation in the affected part; so that a strongerstimulus is required, or one of a different kind from that, whichoccasioned those too violent contractions, to again excite the affectedorgan into activity; and if a stronger stimulus could be applied, it mustagain induce paralysis. For these powerful stimuli excite pain at the same time, that they produceirritation; and this pain not only excites fibrous motions by its stimulus, but it also produces volition; and thus all these stimuli acting at thesame time, and sometimes with the addition of their associations, produceso great exertion as to expend the whole of the sensorial power in theaffected fibres. V. _Of Stimulus less than natural. _ 1. A quantity of stimulus less than natural, producing a decreased exertionof sensorial power, occasions an accumulation of the general quantity ofit. This circumstance is observable in the hemiplagia, in which thepatients are perpetually moving the muscles, which are unaffected. On thisaccount we awake with greater vigour after sleep, because during so manyhours, the great usual expenditure of sensorial power in the performance ofvoluntary actions, and in the exertions of our organs of sense, inconsequence of the irritations occasioned by external objects had beensuspended, and a consequent accumulation had taken place. In like manner the exertion of the sensorial power less than natural in onepart of the system, is liable to produce an increase of the exertion of itin some other part. Thus by the action of vomiting, in which the naturalexertion of the motions of the stomach are destroyed or diminished, anincreased absorption of the pulmonary and cellular lymphatics is produced, as is known by the increased absorption of the fluid deposited in them indropsical cases. But these partial quiescences of sensorial power are alsosometimes attended with other partial quiescences, which sympathize withthem, as cold and pale extremities from hunger. These therefore are to beascribed to the associations of sympathy explained in Sect. XXXV. And notto the general accumulation of sensorial power. 2. A quantity of stimulus less than natural, applied to fibres previouslyaccustomed to perpetual stimulus, is succeeded by accumulation of sensorialpower in the affected organ. The truth of this proposition is evinced, because a stimulus less than natural, if it be somewhat greater than thatabove mentioned, will excite the organ so circumstanced into violentactivity. Thus on a frosty day with wind, the face of a person exposed tothe wind is at first pale and shrunk; but on turning the face from thewind, it becomes soon of a glow with warmth and flushing. The glow of theskin in emerging from the cold-bath is owing to the same cause. It does not appear, that an accumulation of sensorial power above thenatural quantity is acquired by those muscles, which are not subject toperpetual stimulus, as the locomotive muscles: these, after the greatestfatigue, only acquire by rest their usual aptitude to motion; whereas thevascular system, as the heart and arteries, after a short quiescence, arethrown into violent action by their natural quantity of stimulus. Nevertheless by this accumulation of sensorial power during the applicationof decreased stimulus, and by the exhaustion of it during the action ofincreased stimulus, it is wisely provided, that the actions of the vascularmuscles and organs of sense are not much deranged by small variations ofstimulus; as the quantity of sensorial power becomes in some measureinversely as the quantity of stimulus. 3. A quantity of stimulus less than that mentioned above, and continued forsome time, induces pain in the affected organ, as the pain of cold in thehands, when they are immersed in snow, is owing to a deficiency of thestimulation of heat. Hunger is a pain from the deficiency of thestimulation of food. Pain in the back at the commencement of ague-fits, andthe head-achs which attend feeble people, are pains from defect ofstimulus, and are hence relieved by opium, essential oils, spirit of wine. As the pains, which originate from defect of stimulus, only occur in thoseparts of the system, which have been previously subjected to perpetualstimulus; and as an accumulation of sensorial power is produced in thequiescent organ along with the pain, as in cold or hunger, there is reasonto believe, that the pain is owing to the accumulation of sensorial power. For, in the locomotive muscles, in the retina of the eye, and other organsof senses, no pain occurs from the absence of stimulus, nor any greataccumulation of sensorial power beyond their natural quantity, since theseorgans have not been used to a perpetual supply of it. There is indeed agreater accumulation occurs in the organ of vision after its quiescence, because it is subject to more constant stimulus. 4. A certain quantity of stimulus less than natural induces the movingorgan into feebler and more frequent contractions, as mentioned in No. I. 4. Of this Section. For each contraction moving through a less space, orwith less force, that is, with less expenditure of the spirit of animation, is sooner relaxed, and the spirit of animation derived at each intervalinto the acting fibres being less, these intervals likewise become shorter. Hence the tremours of the hands of people accustomed to vinous spirit, tillthey take their usual stimulus; hence the quick pulse in fevers attendedwith debility, which is greater than in fevers attended with strength; inthe latter the pulse seldom beats above 120 times in a minute, in theformer it frequently exceeds 140. It must be observed, that in this and the two following articles thedecreased action of the system is probably more frequently occasioned bydeficiency in the quantity of sensorial power, than in the quantity ofstimulus. Thus those feeble constitutions which have large pupils of theireyes, and all who labour under nervous fevers, seem to owe their want ofnatural quantity of activity in the system to the deficiency of sensorialpower; since, as far as can be seen, they frequently possess the naturalquantity of stimulus. 5. A certain quantity of stimulus, less than that above mentioned, invertsthe order of successive fibrous contractions; as in vomiting the vermicularmotions of the stomach and duodenum are inverted, and their contentsejected, which is probably owing to the exhaustion of the spirit ofanimation in the acting muscles by a previous excessive stimulus, as by theroot of ipecacuanha, and the consequent defect of sensorial power. The sameretrograde motions affect the whole intestinal canal in ileus; and theoesophagus in globus hystericus. See this further explained in Sect. XXIX. No. 11. On Retrograde Motions. I must observe, also, that something similar happens in the production ofour ideas, or sensual motions, when they are too weakly excited; when anyone is thinking intensely about one thing, and carelessly conversing aboutanother, he is liable to use the word of a contrary meaning to that whichhe designed, as cold weather for hot weather, summer for winter. 6. A certain quantity of stimulus, less than that above mentioned, issucceeded by paralysis, first of the voluntary and sensitive motions, andafterwards of those of irritation, and of association, which constitutesdeath. VI. _Cure of increased Exertion. _ 1. The cure, which nature has provided for the increased exertion of anypart of the system, consists in the consequent expenditure of the sensorialpower. But as a greater torpor follows this exhaustion of sensorial power, as explained in the next paragraph, and a greater exertion succeeds thistorpor, the constitution frequently sinks under these increasing librationsbetween exertion and quiescence; till at length complete quiescence, thatis, death, closes the scene. For, during the great exertion of the system in the hot fit of fever, anincrease of stimulus is produced from the greater momentum of the blood, the greater distention of the heart and arteries, and the increasedproduction of heat, by the violent actions of the system occasioned by thisaugmentation of stimulus, the sensorial power becomes diminished in a fewhours much beneath its natural quantity, the vessels at length cease toobey even these great degrees of stimulus, as shewn in Sect. XL. 9. 1. Anda torpor of the whole or of a part of the system ensues. Now as this second cold fit commences with a greater deficiency ofsensorial power, it is also attended with a greater deficiency of stimulusthan in the preceding cold fit, that is, with less momentum of blood, lessdistention of the heart. On this account the second cold fit becomes moreviolent and of longer duration than the first; and as a greateraccumulation of sensorial power must be produced before the system ofvessels will again obey the diminished stimulus, it follows, that thesecond hot fit of fever will be more violent than the former one. And thatunless some other causes counteract either the violent exertions in the hotfit, or the great torpor in the cold fit, life will at length beextinguished by the expenditure of the whole of the sensorial power. Andfrom hence it appears, that the true means of curing fevers must be such asdecrease the action of the system in the hot fit, and increase it in thecold fit; that is, such as prevent the too great diminution of sensorialpower in the hot fit, and the too great accumulation of it in the cold one. 2. Where the exertion of the sensorial powers is much increased, as in thehot fits of fever or inflammation, the following are the usual means ofrelieving it. Decrease the irritations by blood-letting, and otherevacuations; by cold water taken into the stomach, or injected as an enema, or used externally; by cold air breathed into the lungs, and diffused overthe skin; with food of less stimulus than the patient has been accustomedto. 3. As a cold fit, or paroxysm of inactivity of some parts of the system, generally precedes the hot fit, or paroxysm of exertion, by which thesensorial power becomes accumulated, this cold paroxysm should be preventedby stimulant medicines and diet, as wine, opium, bark, warmth, cheerfulness, anger, surprise. 4. Excite into greater action some other part of the system, by which meansthe spirit of animation may be in part expended, and thence the inordinateactions of the diseased part may be lessened. Hence when a part of the skinacts violently, as of the face in the eruption of the small-pox, if thefeet be cold they should be covered. Hence the use of a blister appliednear a topical inflammation. Hence opium and warm bath relieve pains bothfrom excess and defect of stimulus. 5. First increase the general stimulation above its natural quantity, whichmay in some degree exhaust the spirit of animation, and then decrease thestimulation beneath its natural quantity. Hence after sudorific medicinesand warm air, the application of refrigerants may have greater effect, ifthey could be administered without danger of producing too great torpor ofsome part of the system; as frequently happens to people in health fromcoming out of a warm room into the cold air, by which a topicalinflammation in consequence of torpor of the mucous membrane of the nostrilis produced, and is termed a cold in the head. VII. _Cure of decreased Exertion. _ 1. Where the exertion of the sensorial powers is much decreased, as in thecold fits of fever, a gradual accumulation of the spirit of animation takesplace; as occurs in all cases where inactivity or torpor of a part of thesystem exists; this accumulation of sensorial power increases, till stimuliless than natural are sufficient to throw it into action, then the cold fitceases; and from the action of the natural stimuli a hot one succeeds withincreased activity of the whole system. So in fainting fits, or syncope, there is a temporary deficiency ofsensorial exertion, and a consequent quiescence of a great part of thesystem. This quiescence continues, till the sensorial power becomes againaccumulated in the torpid organs; and then the usual diurnal stimuli excitethe revivescent parts again into action; but as this kind of quiescencecontinues but a short time compared to the cold paroxysm of an ague, andless affects the circulatory system, a less superabundancy of exertionsucceeds in the organs previously torpid, and a less excess of arterialactivity. See Sect. XXXIV. 1. 6. 2. In the diseases occasioned by a defect of sensorial exertion, as in coldfits of ague, hysteric complaint, and nervous fever, the following meansare those commonly used. 1. Increase the stimulation above its naturalquantity for some weeks, till a new habit of more energetic contraction ofthe fibres is established. This is to be done by wine, opium, bark, steel, given at exact periods, and in appropriate quantities; for if thesemedicines be given in such quantity, as to induce the least degree ofintoxication, a debility succeeds from the useless exhaustion of spirit ofanimation in consequence of too great exertion of the muscles or organs ofsense. To these irritative stimuli should be added the sensitive ones ofcheerful ideas, hope, affection. 3. Change the kinds of stimulus. The habits acquired by the constitutiondepend on such nice circumstances, that when one kind of stimulus ceases toexcite the sensorial power into the quantity of exertion necessary tohealth, it is often sufficient to change the stimulus for anotherapparently similar in quantity and quality. Thus when wine ceases tostimulate the constitution, opium in appropriate doses supplies the defect;and the contrary. This is also observed in the effects of catharticmedicines, when one loses its power, another, apparently less efficacious, will succeed. Hence a change of diet, drink, and stimulating medicines, isoften advantageous in diseases of debility. 4. Stimulate the organs, whose motions are associated with the torpid partsof the system. The actions of the minute vessels of the various parts ofthe external skin are not only associated with each other, but are stronglyassociated with those of some of the internal membranes, and particularlyof the stomach. Hence when the exertion of the stomach is less thannatural, and indigestion and heartburn succeed, nothing so certainlyremoves these symptoms as the stimulus of a blister on the back. Thecoldness of the extremities, as of the nose, ears, or fingers, are hencethe best indication for the successful application of blisters. 5. Decrease the stimulus for a time. By lessening the quantity of heat fora minute or two by going into the cold bath, a great accumulation ofsensorial power is produced; for not only the minute vessels of the wholeexternal skin for a time become inactive, as appears by their paleness; butthe minute vessels of the lungs lose much of their activity also by concertwith those of the skin, as appears from the difficulty of breathing atfirst going into cold water. On emerging from the bath the sensorial poweris thrown into great exertion by the stimulus of the common degree of thewarmth of the atmosphere, and a great production of animal heat is theconsequence. The longer a person continues in the cold bath the greatermust be the present inertion of a great part of the system, and inconsequence a greater accumulation of sensorial power. Whence M. Pomèrecommends some melancholy patients to be kept from two to six hours inspring-water, and in baths still colder. 6. Decrease the stimulus for a time below the natural, and then increase itabove natural. The effect of this process, improperly used, is seen ingiving much food, or applying much warmth, to those who have beenpreviously exposed to great hunger, or to great cold. The accumulatedsensorial power is thrown into so violent exertion, that inflammations andmortifications supervene, and death closes the catastrophe. In manydiseases this method is the most successful; hence the bark in aguesproduces more certain effect after the previous exhibition of emetics. Indiseases attended with violent pain, opium has double the effect, ifvenesection and a cathartic have been previously used. On this seems tohave been founded the successful practice of Sydenham, who used venesectionand a cathartic in chlorosis before the exhibition of the bark, steel, andopiates. 7. Prevent any unnecessary expenditure of sensorial power. Hence in feverswith debility, a decumbent posture is preferred, with silence, littlelight, and such a quantity of heat as may prevent any chill sensation, orany coldness of the extremities. The pulse of patients in fevers withdebility increases in frequency above ten pulsations in a minute on theirrising out of bed. For the expenditure of sensorial power to preserve anerect posture of the body adds to the general deficiency of it, and thusaffects the circulation. 8. The longer in time and the greater in degree the quiescence or inertionof an organ has been, so that it still retains life or excitability, theless stimulus should at first be applied to it. The quantity of stimulationis a matter of great nicety to determine, where the torpor or quiescence ofthe fibres has been experienced in a great degree, or for a considerabletime, as in cold fits of the ague, in continued fevers with great debility, or in people famished at sea, or perishing with cold. In the two lastcases, very minute quantities of food should be first supplied, and veryfew additional degrees of heat. In the two former cases, but littlestimulus of wine or medicine, above what they had been lately accustomedto, should be exhibited, and this at frequent and stated intervals, so thatthe effect of one quantity may be observed before the exhibition ofanother. If these circumstances are not attended to, as the sensorial power becomesaccumulated in the quiescent fibres, an inordinate exertion takes place bythe increase of stimulus acting on the accumulated quantity of sensorialpower, and either the paralysis, or death of the contractile fibres ensues, from the total expenditure of the sensorial power in the affected organ, owing to this increase of exertion, like the debility after intoxication. Or, secondly, the violent exertions above mentioned produce painfulsensation, which becomes a new stimulus, and by thus producinginflammation, and increasing the activity of the fibres already too great, sooner exhausts the whole of the sensorial power in the acting organ, andmortification, that is, the death of the part, supervenes. Hence there have been many instances of people, whose limbs have been longbenumbed by exposure to cold, who have lost them by mortification on theirbeing too hastily brought to the fire; and of others, who were nearlyfamished at sea, who have died soon after having taken not more than anusual meal of food. I have heard of two well-attested instances of patientsin the cold fit of ague, who have died from the exhibition of gin andvinegar, by the inflammation which ensued. And in many fevers attended withdebility, the unlimited use of wine, and the wanton application ofblisters, I believe, has destroyed numbers by the debility consequent totoo great stimulation, that is, by the exhaustion of the sensorial power byits inordinate exertion. Wherever the least degree of intoxication exists, a proportional debilityis the consequence; but there is a golden rule by which the necessary anduseful quantity of stimulus in fevers with debility may be ascertained. When wine or beer are exhibited either alone or diluted with water, if thepulse becomes slower the stimulus is of a proper quantity; and should berepeated every two or three hours, or when the pulse again becomes quicker. In the chronical debility brought on by drinking spirituous or fermentedliquors, there is another golden rule by which I have successfully directedthe quantity of spirit which they may safely lessen, for there is no othermeans by which they can recover their health. It should be premised, thatwhere the power of digestion in these patients is totally destroyed, thereis not much reason to expect a return to healthful vigour. I have directed several of these patients to omit one fourth part of thequantity of vinous spirit they have been lately accustomed to, and if in afortnight their appetite increases, they are advised to omit another fourthpart; but if they perceive that their digestion becomes impaired from thewant of this quantity of spirituous potation, they are advised to continueas they are, and rather bear the ills they have, than risk the encounter ofgreater. At the same time flesh-meat with or without spice is recommended, with Peruvian bark and steel in small quantities between their meals, andhalf a grain of opium or a grain, with five or eight grains of rhubarb atnight. * * * * * SECT. XIII. OF VEGETABLE ANIMATION. I. 1. _Vegetables are irritable; mimosa, dionæa muscipula. Vegetable secretions. _ 2. _Vegetable buds are inferior animals, are liable to greater or less irritability. _ II. _Stamens and pistils of plants shew marks of sensibility. _ III. _Vegetables possess some degree of volition. _ IV. _Motions of plants are associated like those of animals. _ V. 1. _Vegetable structure like that of animals, their anthers and stigmas are living creatures. Male-flowers of Vallisneria. _ 2. _Whether vegetables, possess ideas? They have organs of sense as of touch and smell, and ideas of external things?_ I. 1. The fibres of the vegetable world, as well as those of the animal, are excitable into a variety of motion by irritations of external objects. This appears particularly in the mimosa or sensitive plant, whose leavescontract on the slightest injury; the dionæa muscipula, which was latelybrought over from the marshes of America, presents us with another curiousinstance of vegetable irritability; its leaves are armed with spines ontheir upper edge, and are spread on the ground around the stem; when aninsect creeps on any of them in its passage to the flower or seed, the leafshuts up like a steel rat-trap, and destroys its enemy. See Botanic Garden, Part II. Note on Silene. The various secretions of vegetables, as of odour, fruit, gum, resin, wax, honey, seem brought about in the same manner as in the glands of animals;the tasteless moisture of the earth is converted by the hop-plant into abitter juice; as by the caterpillar in the nut-shell the sweet kernel isconverted into a bitter powder. While the power of absorption in the rootsand barks of vegetables is excited into action by the fluids applied totheir mouths like the lacteals and lymphatics of animals. 2. The individuals of the vegetable world may be considered as inferior orless perfect animals; a tree is a congeries of many living buds, and inthis respect resembles the branches of coralline, which are a congeries ofa multitude of animals. Each of these buds of a tree has its proper leavesor petals for lungs, produces its viviparous or its oviparous offspring inbuds or seeds; has its own roots, which extending down the stem of the treeare interwoven with the roots of the other buds, and form the bark, whichis the only living part of the stem, is annually renewed, and issuperinduced upon the former bark, which then dies, and with its stagnatedjuices gradually hardening into wood forms the concentric circles, which wesee in blocks of timber. The following circumstances evince the individuality of the buds of trees. First, there are many trees, whose whole internal wood is perished, and yetthe branches are vegete and healthy. Secondly, the fibres of the barks oftrees are chiefly longitudinal, resembling roots, as is beautifully seen inthose prepared barks, that were lately brought from Otaheita. Thirdly, inhorizontal wounds of the bark of trees, the fibres of the upper lip arealways elongated downwards like roots, but those of the lower lip do notapproach to meet them. Fourthly, if you wrap wet moss round any joint of avine, or cover it with moist earth, roots will shoot out from it. Fifthly, by the inoculation or engrafting of trees many fruits are produced from onestem. Sixthly, a new tree is produced from a branch plucked from an oldone, and set in the ground. Whence it appears that the buds of deciduoustrees are so many annual plants, that the bark is a contexture of the rootsof each individual bud; and that the internal wood is of no other use butto support them in the air, and that thus they resemble the animal world intheir individuality. The irritability of plants, like that of animals, appears liable to beincreased or decreased by habit; for those trees or shrubs, which arebrought from a colder climate to a warmer, put out their leaves andblossoms a fortnight sooner than the indigenous ones. Professor Kalm, in his Travels in New York, observes that the apple-treesbrought from England blossom a fortnight sooner than the native ones. Inour country the shrubs, that are brought a degree or two from the north, are observed to flourish better than those, which come from the south. TheSiberian barley and cabbage are said to grow larger in this climate thanthe similar more southern vegetables. And our hoards of roots, as ofpotatoes and onions, germinate with less heat in spring, after they havebeen accustomed to the winter's cold, than in autumn after the summer'sheat. II. The stamens and pistils of flowers shew evident marks of sensibility, not only from many of the stamens and some pistils approaching towards eachother at the season of impregnation, but from many of them closing theirpetals and calyxes during the cold parts of the day. For this cannot beascribed to irritation, because cold means a defect of the stimulus ofheat; but as the want of accustomed stimuli produces pain, as in coldness, hunger, and thirst of animals, these motions of vegetables in closing uptheir flowers must be ascribed to the disgreeable sensation, and not to theirritation of cold. Others close up their leaves during darkness, which, like the former, cannot be owing to irritation, as the irritating materialis withdrawn. The approach of the anthers in many flowers to the stigmas, and of thepistils of some flowers to the anthers, must be ascribed to the passion oflove, and hence belongs to sensation, not to irritation. III. That the vegetable world possesses some degree of voluntary powers, appears from their necessity to sleep, which we have shewn in Sect. XVIII. To consist in the temporary abolition of voluntary power. This voluntarypower seems to be exerted in the circular movement of the tendrils ofvines, and other climbing vegetables; or in the efforts to turn the uppersurface of their leaves, or their flowers to the light. IV. The associations of fibrous motions are observable in the vegetableworld, as well as in the animal. The divisions of the leaves of thesensitive plant have been accustomed to contract at the same time from theabsence of light; hence if by any other circumstance, as a slight stroke orinjury, one division is irritated into contraction, the neighbouring onescontract also, from their motions being associated with those of theirritated part. So the various stamina of the class of syngenesia have beenaccustomed to contract together in the evening, and thence if you stimulateone of them with a pin, according to the experiment of M. Colvolo, they allcontract from their acquired associations. To evince that the collapsing of the sensitive plant is not owing to anymechanical vibrations propagated along the whole branch, when a single leafis struck with the finger, a leaf of it was slit with sharp scissors, andsome seconds of time passed before the plant seemed sensible of the injury;and then the whole branch collapsed as far as the principal stem: thisexperiment was repeated several times with the least possible impulse tothe plant. V. 1. For the numerous circumstances in which vegetable buds are analogousto animals, the reader is referred to the additional notes at the end ofthe Botanic Garden, Part I. It is there shewn, that the roots of vegetablesresemble the lacteal system of animals; the sap-vessels in the earlyspring, before their leaves expand, are analogous to the placental vesselsof the foetus; that the leaves of land-plants resemble lungs, and those ofaquatic plants the gills of fish; that there are other systems of vesselsresembling the vena portarum of quadrupeds, or the aorta of fish; that thedigestive power of vegetables is similar to that of animals converting thefluids, which they absorb, into sugar; that their seeds resemble the eggsof animals, and their buds and bulbs their viviparous offspring. And, lastly, that the anthers and stigmas are real animals, attached indeed totheir parent tree like polypi or coral insects, but capable of spontaneousmotion; that they are affected with the passion of love, and furnished withpowers of reproducing their species, and are fed with honey like the mothsand butterflies, which plunder their nectaries. See Botanic Garden, Part I. Add. Note XXXIX. The male flowers of vallisneria approach still nearer to apparentanimality, as they detach themselves from the parent plant, and float onthe surface of the water to the female ones. Botanic Garden, Part II. Art. Vallisneria. Other flowers of the classes of monecia and diecia, andpolygamia, discharge the fecundating farina, which floating in the air iscarried to the stigma of the female flowers, and that at considerabledistances. Can this be effected by any specific attraction? or, like thediffusion of the odorous particles of flowers, is it left to the currentsof winds, and the accidental miscarriages of it counteracted by thequantity of its production? 2. This leads us to a curious enquiry, whether vegetables have ideas ofexternal things? As all our ideas are originally received by our senses, the question may be changed to, whether vegetables possess any organs ofsense? Certain it is, that they possess a sense of heat and cold, anotherof moisture and dryness, and another of light and darkness; for they closetheir petals occasionally from the presence of cold, moisture, or darkness. And it has been already shewn, that these actions cannot be performedsimply from irritation, because cold and darkness are negative quantities, and on that account sensation or volition are implied, and in consequence asensorium or union of their nerves. So when we go into the light, wecontract the iris; not from any stimulus of the light on the fine musclesof the iris, but from its motions being associated with the sensation oftoo much light on the retina: which could not take place without asensorium or center of union of the nerves of the iris with those ofvision. See Botanic Garden, Part I. Canto 3. L. 440. Note. Besides these organs of sense, which distinguish cold, moisture, anddarkness, the leaves of mimosa, and of dionæa, and of drosera, and thestamens of many flowers, as of the berbery, and the numerous class ofsyngenesia, are sensible to mechanic impact, that is, they possess a senseof touch, as well as a common sensorium; by the medium of which theirmuscles are excited into action. Lastly, in many flowers the anthers, whenmature, approach the stigma, in others the female organ approaches to themale. In a plant of collinsonia, a branch of which is now before me, thetwo yellow stamens are about three eights of an inch high, and diverge fromeach other, at an angle of about fifteen degrees, the purple style is halfan inch high, and in some flowers is now applied to the stamen on the righthand, and in others to that of the left; and will, I suppose, change placeto-morrow in those, where the anthers have not yet effused their powder. I ask, by what means are the anthers in many flowers, and stigmas in otherflowers, directed to find their paramours? How do either of them know, thatthe other exists in their vicinity? Is this curious kind of storge producedby mechanic attraction, or by the sensation of love? The latter opinion issupported by the strongest analogy, because a reproduction of the speciesis the consequence; and then another organ of sense must be wanted todirect these vegetable amourettes to find each other, one probablyanalogous to our sense of smell, which in the animal world directs thenew-born infant to its source of nourishment, and they may thus possess afaculty of perceiving as well as of producing odours. Thus, besides a kind of taste at the extremities of their roots, similar tothat of the extremities of our lacteal vessels, for the purpose ofselecting their proper food: and besides different kinds of irritabilityresiding in the various glands, which separate honey, wax, resin, and otherjuices from their blood; vegetable life seems to possess an organ of senseto distinguish the variations of heat, another to distinguish the varyingdegrees of moisture, another of light, another of touch, and probablyanother analogous to our sense of smell. To these must be added theindubitable evidence of their passion of love, and I think we may trulyconclude, that they are furnished with a common sensorium belonging to eachbud and that they must occasionally repeat those perceptions either intheir dreams or waking hours, and consequently possess ideas of so many ofthe properties of the external world, and of their own existence. * * * * * SECT. XIV. OF THE PRODUCTION OF IDEAS. I. _Of material and immaterial beings. Doctrine of St. Paul. _ II. 1. _Of the sense of touch. Of solidity. _ 2. _Of figure. Motion. Time. Place. Space. Number. _ 3. _Of the penetrability of matter. _ 4. _Spirit of animation possesses solidity, figure, visibility, &c. Of Spirits and angels. _ 5. _The existence of external things. _ III. _Of vision. _ IV. _Of hearing. _ V. _Of smell and taste. _ VI. _Of the organ of sense by which we perceive heat and cold, not by the sense of touch. _ VII. _Of the sense of extension, the whole of the locomotive muscles may be considered as one organ of sense. _ VIII. _Of the senses of hunger, thirst, want of fresh air, suckling children, and lust. _ IX. _Of many other organs of sense belonging to the glands. Of painful sensations from the excess of light, pressure, heat, itching, caustics, and electricity. _ I. Philosophers have been much perplexed to understand, in what manner webecome acquainted with the external world; insomuch that Dr. Berkly evendoubted its existence, from having observed (as he thought) that none ofour ideas resemble their correspondent objects. Mr. Hume asserts, that ourbelief depends on the greater distinctness or energy of our ideas fromperception; and Mr. Reid has lately contended, that our belief of externalobjects is an innate principle necessarily joined with our perceptions. So true is the observation of the famous Malbranch, "that our senses arenot given us to discover the essences of things, but to acquaint us withthe means of preserving our existence, " (L. I. Ch. V. ) a melancholyreflection to philosophers! Some philosophers have divided all created beings into material andimmaterial: the former including all that part of being, which obeys themechanic laws of action and reaction, but which can begin no motion ofitself; the other is the cause of all motion, and is either termed thepower of gravity, or of specific attraction, or the spirit of animation. This immaterial agent is supposed to exist in or with matter, but to bequite distinct from it, and to be equally capable of existence, after thematter, which now possesses it, is decomposed. Nor is this theory ill supported by analogy, since heat, electricity, andmagnetism, can be given to or taken from a piece of iron; and musttherefore exist, whether separated from the metal, or combined with it. From a parity of reasoning, the spirit of animation, would appear to becapable of existing as well separately from the body as with it. I beg to be understood, that I do not wish to dispute about words, and amready to allow, that the powers of gravity, specific attraction, electricity, magnetism, and even the spirit of animation, may consist ofmatter of a finer kind; and to believe, with St. Paul and Malbranch, thatthe ultimate cause only of all motion is immaterial, that is God. St. Paulsays, "in him we live and move, and have our being;" and, in the 15thchapter to the Corinthians, distinguishes between the psyche or livingspirit, and the pneuma or reviving spirit. By the words spirit of animationor sensorial power, I mean only that animal life, which mankind possessesin common with brutes, and in some degree even with vegetables, and leavethe consideration of the immortal part of us, which is the object ofreligion, to those who treat of revelation. II. 1. _Of the Sense of Touch. _ The first idea we become acquainted with, are those of the sense of touch;for the foetus must experience some varieties of agitation, and exert somemuscular action, in the womb; and may with great probability be supposedthus to gain some ideas of its own figure, of that of the uterus, and ofthe tenacity of the fluid, that surrounds it, (as appears from the factsmentioned in the succeeding Section upon Instinct. ) Many of the organs of sense are confined to a small part of the body, asthe nostrils, ear, or eye, whilst the sense of touch is diffused over thewhole skin, but exists with a more exquisite degree of delicacy at theextremities of the fingers and thumbs, and in the lips. The sense of touchis thus very commodiously disposed for the purpose of encompassing smallerbodies, and for adapting itself to the inequalities of larger ones. Thefigure of small bodies seems to be learnt by children by their lips as muchas by their fingers; on which account they put every new object to theirmouths, when they are satiated with food, as well as when they are hungry. And puppies seem to learn their ideas of figure principally by the lips intheir mode of play. We acquire our tangible ideas of objects either by the simple pressure ofthis organ of touch against a solid body, or by moving our organ of touchalong the surface of it. In the former case we learn the length and breadthof the object by the quantity of our organ of touch, that is impressed byit: in the latter case we learn the length and breadth of objects by thecontinuance of their pressure on our moving organ of touch. It is hence, that we are very slow in acquiring our tangible ideas, andvery slow in recollecting them; for if I now think of the tangible idea ofa cube, that is, if I think of its figure, and of the solidity of everypart of that figure, I must conceive myself as passing my fingers over it, and seem in some measure to feel the idea, as I formerly did theimpression, at the ends of them, and am thus very slow in distinctlyrecollecting it. When a body compresses any part of our sense of touch, what happens? First, this part of our sensorium undergoes a mechanical compression, which istermed a stimulus; secondly, an idea, or contraction of a part of the organof sense is excited; thirdly, a motion of the central parts, or of thewhole sensorium, which is termed sensation, is produced; and these threeconstitute the perception of solidity. 2. _Of Figure, Motion, Time, Place, Space, Number. _ No one will deny, that the medulla of the brain and nerves has a certainfigure; which, as it is diffused through nearly the whole of the body, musthave nearly the figure of that body. Now it follows, that the spirit ofanimation, or living principle, as it occupies this medulla, and no otherpart, (which is evinced by a great variety of cruel experiments on livinganimals, ) it follows, that this spirit of animation has also the samefigure as the medulla above described. I appeal to common sense! the spiritof animation acts, Where does it act? It acts wherever there is the medullaabove mentioned; and that whether the limb is yet joined to a livinganimal, or whether it be recently detached from it; as the heart of a viperor frog will renew its contractions, when pricked with a pin, for manyminutes of time after its exsection from the body. --Does it act any whereelse?--No; then it certainly exists in this part of space, and no whereelse; that is, it hath figure; namely, the figure of the nervous system, which is nearly the figure of the body. When the idea of solidity isexcited, as above explained, a part of the extensive organ of touch iscompressed by some external body, and this part of the sensorium socompressed exactly resembles _in figure_ the figure of the body thatcompressed it. Hence, when we acquire the idea of solidity, we acquire atthe same time the idea of FIGURE; and this idea of figure, or motion of _apart_ of the organ of touch, exactly resembles _in its figure_ the figureof the body that occasions it; and thus exactly acquaints us with thisproperty of the external world. Now, as the whole universe with all its parts possesses a certain form orfigure, if any part of it moves, that form or figure of the whole isvaried: hence, as MOTION is no other than a perpetual variation of figure, our idea of motion is also a real resemblance of the motion that producedit. It may be said in objection to this definition of motion, that an ivoryglobe may revolve on its axis, and that here will be a motion withoutchange of figure. But the figure of the particle _x_ on one side of thisglobe is not the _same_ figure as the figure of _y_ on the other side, anymore than the particles themselves are the same, though they are _similar_figures; and hence they cannot change place with each other withoutdisturbing or changing the figure of the whole. Our idea of TIME is from the same source, but is more abstracted, as itincludes only the comparative velocities of these variations of figure;hence if it be asked, How long was this book in printing? it may beanswered, Whilst the sun was passing through Aries. Our idea of PLACE includes only the figure of a group of bodies, not thefigures of the bodies themselves. If it be asked where is Nottinghamshire, the answer is, it is surrounded by Derbyshire, Lincolnshire andLeicestershire; hence place is our idea of the figure of one bodysurrounded by the figures of other bodies. The idea of SPACE is a more abstracted idea of place excluding the group ofbodies. The idea of NUMBER includes only the particular arrangements, ordistributions of a group of bodies, and is therefore only a more abstractedidea of the parts of the figure of the group of bodies; thus when I sayEngland is divided into forty counties, I only speak of certain divisionsof its figure. Hence arises the certainty of the mathematical sciences, as they explainthese properties of bodies, which are exactly resembled by our ideas ofthem, whilst we are obliged to collect almost all our other knowledge fromexperiment; that is, by observing the effects exerted by one body uponanother. 3. _Of the Penetrability of Matter. _ The impossibility of two bodies existing together in the same space cannotbe deduced from our idea of solidity, or of figure. As soon as we perceivethe motions of objects that surround us, and learn that we possess a powerto move our own bodies, we experience, that those objects, which excite inus the idea of solidity and of figure, oppose this voluntary movement ofour own organs; as whilst I endeavour to compress between my hands an ivoryball into a spheroid. And we are hence taught by experience, that our ownbody and those, which we touch, cannot exist in the same part of space. But this by no means demonstrates, that no two bodies can exist together inthe same part of space. Galilæo in the preface to his works seems to be ofopinion, that matter is not impenetrable; Mr. Michel, and Mr. Boscowich inhis Theoria. Philos. Natur. Have espoused this hypothesis: which has beenlately published by Dr. Priestley, to whom the world is much indebted forso many important discoveries in science. (Hist. Of Light and Colours, p. 391. ) The uninterrupted passage of light through transparent bodies, of theelectric æther through metallic and aqueous bodies, and of the magneticeffluvia through all bodies, would seem to give some probability to thisopinion. Hence it appears, that beings may exist without possessing theproperty of solidity, as well as they can exist without possessing theproperties, which excite our smell or taste, and can thence occupy spacewithout detruding other bodies from it; but we cannot become acquaintedwith such beings by our sense of touch, any more than we can with odours orflavours without our senses of smell and taste. But that any being can exist without existing in space, is to my ideasutterly incomprehensible. My appeal is to common sense. _To be_ implies awhen and a where; the one is comparing it with the motions of other beings, and the other with their situations. If there was but one object, as the whole creation may be considered as oneobject, then I cannot ask where it exists? for there are no other objectsto compare its situation with. Hence if any one denies, that a being existsin space, he denies, that there are any other beings but that one; for toanswer the question, "Where does it exist?" is only to mention thesituation of the objects that surround it. In the same manner if it be asked--"When does a being exist?" The answeronly specifies the successive motions either of itself, or of other bodies;hence to say, a body exists not in time, is to say, that there is, or was, no motion in the world. 4. _Of the Spirit of Animation. _ But though there may exist beings in the universe, that have not theproperty of solidity; that is, which can possess any part of space, at thesame time that it is occupied by other bodies; yet there may be otherbeings, that can assume this property of solidity, or disrobe themselves ofit occasionally, as we are taught of spirits, and of angels; and it wouldseem, that THE SPIRIT OF ANIMATION must be endued with this property, otherwise how could it occasionally give motion to the limbs ofanimals?--or be itself stimulated into motion by the obtrusions ofsurrounding bodies, as of light, or odour? If the spirit of animation was always necessarily penetrable, it could notinfluence or be influenced by the solidity of common matter; they wouldexist together, but could not detrude each other from the part of space, where they exist; that is, they could not communicate motion to each other. _No two things can influence or affect each other, which have not someproperty common to both of them_; for to influence or affect another bodyis to give or communicate some property to it, that it had not before; buthow can one body give that to another, which it does not possessitself?--The words imply, that they must agree in having the power orfaculty of possessing some common property. Thus if one body removesanother from the part of space, that it possesses, it must have the powerof occupying that space itself: and if one body communicates heat or motionto another, it follows, that they have alike the property of possessingheat or motion. Hence the spirit of animation at the time it communicates or receivesmotion from solid bodies, must itself possess some property of solidity. And in consequence at the time it receives other kinds of motion fromlight, it must possess that property, which light possesses, to communicatethat kind of motion; and for which no language has a name, unless it may betermed Visibility. And at the time it is stimulated into other kinds ofanimal motion by the particles of sapid and odorous bodies affecting thesenses of taste and smell, it must resemble these particles of flavour, andof odour, in possessing some similar or correspondent property; and forwhich language has no name, unless we may use the words Saporosity andOdorosity for those common properties, which are possessed by our organs oftaste and smell, and by the particles of sapid and odorous bodies; as thewords Tangibility and Audibility may express the common property possessedby our organs of touch, and of hearing, and by the solid bodies, or theirvibrations, which affect those organs. 5. Finally, though the figures of bodies are in truth resembled by thefigure of the part of the organ of touch, which is stimulated into motion;and that organ resembles the solid body, which stimulates it, in itsproperty of solidity; and though the sense of hearing resembles thevibrations of external bodies in its capability of being stimulated intomotion by those vibrations; and though our other organs of sense resemblethe bodies, that stimulate them, in their capability of being stimulated bythem; and we hence become acquainted with these properties of the externalworld; yet as we can repeat all these motions of our organs of sense by theefforts of volition, or in consequence of the sensation of pleasure orpain, or by their association with other fibrous motions, as happens in ourreveries or in sleep, there would still appear to be some difficulty indemonstrating the existence of any thing external to us. In our dreams we cannot determine this circumstance, because our power ofvolition is suspended, and the stimuli of external objects are excluded;but in our waking hours we can compare our ideas belonging to one sensewith those belonging to another, and can thus distinguish the ideasoccasioned by irritation from those excited by sensation, volition, orassociation. Thus if the idea of the sweetness of sugar should be excitedin our dreams, the whiteness and hardness of it occur at the same time byassociation; and we believe a material lump of sugar present before us. Butif, in our waking hours, the idea of the sweetness of sugar occurs to us, the stimuli of surrounding objects, as the edge of the table, on which wepress, or green colour of the grass, on which we tread, prevent the otherideas of the hardness and whiteness of the sugar from being exerted byassociation. Or if they should occur, we voluntarily compare them with theirritative ideas of the table or grass above mentioned, and detect theirfallacy. We can thus distinguish the ideas caused by the stimuli ofexternal objects from those, which are introduced by association, sensation, or volition; and during our waking hours can thus acquire aknowledge of the external world. Which nevertheless we cannot do in ourdreams, because we have neither perceptions of external bodies, nor thepower of volition to enable us to compare them with the ideas ofimagination. III. _Of Vision. _ Our eyes observe a difference of colour, or of shade, in the prominencesand depressions of objects, and that those shades uniformly vary, when thesense of touch observes any variation. Hence when the retina becomesstimulated by colours or shades of light in a certain form, as in acircular spot; we know by experience, that this is a sign, that a tangiblebody is before us; and that its figure is resembled by the miniature figureof the part of the organ of vision, that is thus stimulated. Here whilst the stimulated part of the retina resembles exactly the visiblefigure of the whole in miniature, the various kinds of stimuli fromdifferent colours mark the visible figures of the minuter parts; and byhabit we instantly recall the tangible figures. Thus when a tree is the object of sight, a part of the retina resembling aflat branching figure is stimulated by various shades of colours; but it isby suggestion, that the gibbosity of the tree, and the moss, that fringesits trunk, appear before us. These are ideas of suggestion, which we feelor attend to, associated with the motions of the retina, or irritativeideas, which we do not attend to. So that though our visible ideas resemble in miniature the outline of thefigure of coloured bodies, in other respects they serve only as a language, which by acquired associations introduce the tangible ideas of bodies. Hence it is, that this sense is so readily deceived by the art of thepainter to our amusement and instruction. The reader will find much verycurious knowledge on this subject in Bishop Berkley's Essay on Vision, awork of great ingenuity. The immediate object however of the sense of vision is light; this fluid, though its velocity is so great, appears to have no perceptible mechanicalimpulse, as was mentioned in the third Section, but seems to stimulate theretina into animal motion by its transmission through this part of thesensorium: for though the eyes of cats or other animals appear luminous inobscure places; yet it is probable, that none of the light, which falls onthe retina, is reflected from it, but adheres to or enters into combinationwith the choroide coat behind it. The combination of the particles of light with opake bodies, and thereforewith the choroide coat of the eye, is evinced from the heat, which is givenout, as in other chemical combinations. For the sunbeams communicate noheat in their passage through transparent bodies, with which they do notcombine, as the air continues cool even in the focus of the largestburning-glasses, which in a moment vitrifies a particle of opaque matter. IV. _Of the Organ of Hearing. _ It is generally believed, that the tympanum of the ear vibratesmechanically, when exposed to audible sounds, like the strings of onemusical instrument, when the same notes are struck upon another. Nor isthis opinion improbable, as the muscles and cartilages of the larynx areemployed in producing variety of tones by mechanical vibration: so themuscles and bones of the ear seem adapted to increase or diminish thetension of the tympanum for the purposes of similar mechanical vibrations. But it appears from dissection, that the tympanum is not the immediateorgan of hearing, but that like the humours and cornea of the eye, it isonly of use to prepare the object for the immediate organ. For the portiomollis of the auditory nerve is not spread upon the tympanum, but upon thevestibulum, and cochlea, and semicircular canals of the ear; while betweenthe tympanum and the expansion of the auditory nerve the cavity is said byDr. Cotunnus and Dr. Meckel to be filled with water; as they had frequentlyobserved by freezing the heads of dead animals before they dissected them;and water being a more dense fluid than air is much better adapted to thepropagation of vibrations. We may add, that even the external opening ofthe ear is not absolutely necessary for the perception of sound: for somepeople, who from these defects would have been completely deaf, havedistinguished acute or grave sounds by the tremours of a stick held betweentheir teeth propagated along the bones of the head, (Haller. Phys. T. V. P. 295). Hence it appears, that the immediate organ of hearing is not affected bythe particles of the air themselves, but is stimulated into animal motionby the vibrations of them. And it is probable from the loose bones, whichare found in the heads of some fishes, that the vibrations of water aresensible to the inhabitants of that element by a similar organ. The motions of the atmosphere, which we become acquainted with by the senseof touch, are combined with its solidity, weight, or vis intertiæ; whereasthose, that are perceived by this organ, depend alone on its elasticity. But though the vibration of the air is the immediate object of the sense ofhearing, yet the ideas, we receive by this sense, like those received fromlight, are only as a language, which by acquired associations acquaints uswith those motions of tangible bodies, which depend on their elasticity;and which we had before learned by our sense of touch. V. _Of Smell and of Taste. _ The objects of smell are dissolved in the fluid atmosphere, and those oftaste in the saliva, or other aqueous fluid, for the better diffusing themon their respective organs, which seem to be stimulated into animal motionperhaps by the chemical affinities of these particles, which constitute thesapidity and odorosity of bodies with the nerves of sense, which perceivethem. Mr. Volta has lately observed a curious circumstance relative to our senseof taste. If a bit of clean lead and a bit of clean silver be separatelyapplied to the tongue and palate no taste is perceived; but by applyingthem in contact in respect to the parts out of the mouth, and nearly so inrespect to the parts, which are immediately applied to the tongue andpalate, a saline or acidulous taste is perceived, as of a fluid like astream of electricity passing from one of them to the other. This newapplication of the sense of taste deserves further investigation, as it mayacquaint us with new properties of matter. From the experiments above mentioned of Galvani, Volta, Fowler, and others, it appears, that a plate of zinc and a plate of silver have greater effectthan lead and silver. If one edge of a plate of silver about the size ofhalf a crown-piece be placed upon the tongue, and one edge of a plate ofzinc about the same size beneath the tongue, and if their opposite edgesare then brought into contact before the point of the tongue, a taste isperceived at the moment of their coming into contact; secondly, if one ofthe above plates be put between the upper lip and the gum of thefore-teeth, and the other be placed under the tongue, and their exterioredges be then brought into contact in a darkish room, a flash of light isperceived in the eyes. These effects I imagine only shew the sensibility of our nerves of sense tovery small quantities of the electric fluid, as it passes through them; forI suppose these sensations are occasioned by slight electric shocksproduced in the following manner. By the experiments published by Mr. Bennet, with his ingenious doubler of electricity, which is the greatestdiscovery made in that science since the coated jar, and the eduction oflightning from the skies, it appears that zinc was always found minus, andsilver was always found plus, when both of them were in their separatestate. Hence, when they are placed in the manner above described, as soonas their exterior edges come nearly into contact, so near as to have anextremely thin plate of air between them, that plate of air becomes chargedin the same manner as a plate of coated glass; and is at the same instantdischarged through the nerves of taste or of sight, and gives thesensations, as above described, of light or of saporocity; and only shewsthe great sensibility of these organs of sense to the stimulus of theelectric fluid in suddenly passing through them. VI. _Of the Sense of Heat. _ There are many experiments in chemical writers, that evince the existenceof heat as a fluid element, which covers and pervades all bodies, and isattracted by the solutions of some of them, and is detruded from thecombination of others. Thus from the combinations of metals with acids, andfrom those combinations of animal fluids, which are termed secretions, thisfluid matter of heat is given out amongst the neighbouring bodies; and inthe solutions of salts in water, or of water in air, it is absorbed fromthe bodies, that surround them; whilst in its facility in passing throughmetallic bodies, and its difficulty in pervading resins and glass, itresembles the properties of the electric aura; and is like that excited byfriction, and seems like that to gravitate amongst other bodies in itsuncombined state, and to find its equilibrium. There is no circumstance of more consequence in the animal economy than adue proportion of this fluid of heat; for the digestion of our nutriment inthe stomach and bowels, and the proper qualities of all our secretedfluids, as they are produced or prepared partly by animal and partly bychemical processes, depend much on the quantity of heat; the excess ofwhich, or its deficiency, alike gives us pain, and induces us to avoid thecircumstances that occasion them. And in this the perception of heatessentially differs from the perceptions of the sense of touch, as wereceive pain from too great pressure of solid bodies, but none from theabsence of it. It is hence probable, that nature has provided us with a setof nerves for the perception of this fluid, which anatomists have not yetattended to. There may be some difficulty in the proof of this assertion; if we look ata hot fire, we experience no pain of the optic nerve, though the heat alongwith the light must be concentrated upon it. Nor does warm water or warmoil poured into the ear give pain to the organ of hearing; and hence asthese organs of sense do not perceive small excesses or deficiences ofheat; and as heat has no greater analogy to the solidity or to the figuresof bodies, than it has to their colours or vibrations; there seems nosufficient reason for our ascribing the perception of heat and cold to thesense of touch; to which it has generally been attributed, either becauseit is diffused beneath the whole skin like the sense of touch, or owing tothe inaccuracy of our observations, or the defect of our languages. There is another circumstance would induce us to believe, that theperceptions of heat and cold do not belong to the organ of touch; since theteeth, which are the least adapted for the perceptions of solidity orfigure, are the most sensible to heat or cold; whence we are forewarnedfrom swallowing those materials, whose degree of coldness or of heat wouldinjure our stomachs. The following is an extract from a letter of Dr. R. W. Darwin, ofShrewsbury, when he was a student at Edinburgh. "I made an experimentyesterday in our hospital, which much favours your opinion, that thesensation of heat and of touch depend on different sets of nerves. A manwho had lately recovered from a fever, and was still weak, was seized withviolent cramps in his legs and feet; which were removed by opiates, exceptthat one of his feet remained insensible. Mr. Ewart pricked him with a pinin five or six places, and the patient declared he did not feel it in theleast, nor was he sensible of a very smart pinch. I then held a red-hotpoker at some distance, and brought it gradually nearer till it came withinthree inches, when he asserted that he felt it quite distinctly. I supposesome violent irritation on the nerves of touch had caused the cramps, andhad left them paralytic; while the nerves of heat, having suffered noincreased stimulus, retained their irritability. " Add to this, that the lungs, though easily stimulated into inflammation, are not sensible to heat. See Class. III. 1. 1. 10. VII. _Of the Sense of Extension. _ The organ of touch is properly the sense of pressure, but the muscularfibres themselves constitute the organ of sense, that feels extension. Thesense of pressure is always attended with the ideas of the figure andsolidity of the object, neither of which accompany our perception ofextension. The whole set of muscles, whether they are hollow ones, as theheart, arteries, and intestines, or longitudinal ones attached to bones, contract themselves, whenever they are stimulated by forcible elongation;and it is observable, that the white muscles, which constitute the arterialsystem, seem to be excited into contraction from no other kinds ofstimulus, according to the experiments of Haller. And hence the violentpain in some inflammations, as in the paronychia, obtains immediate reliefby cutting the membrane, that was stretched by the tumour of the subjacentparts. Hence the whole muscular system may be considered as one organ of sense, and the various attitudes of the body, as ideas belonging to this organ, ofmany of which we are hourly conscious, while many others, like theirritative ideas of the other senses, are performed without our attention. When the muscles of the heart cease to act, the refluent blood againdistends or elongates them; and thus irritated they contract as before. Thesame happens to the arterial system, and I suppose to the capillaries, intestines, and various glands of the body. When the quantity of urine, or of excrement, distends the bladder, orrectum, those parts contract, and exclude their contents, and many othermuscles by association act along with them; but if these evacuations arenot soon complied with, pain is produced by a little further extension ofthe muscular fibres: a similar pain is caused in the muscles, when a limbis much extended for the reduction of dislocated bones; and in thepunishment of the rack: and in the painful cramps of the calf of the leg, or of other muscles, for a greater degree of contraction of a muscle, thanthe movement of the two bones, to which its ends are affixed, will admitof, must give similar pain to that, which is produced by extending itbeyond its due length. And the pain from punctures or incisions arises fromthe distention of the fibres, as the knife passes through them; for itnearly ceases as soon as the division is completed. All these motions of the muscles, that are thus naturally excited by thestimulus of distending bodies, are also liable to be called into strongaction by their catenation, with the irritations or sensations produced bythe momentum of the progressive particles of blood in the arteries, as ininflammatory fevers, or by acrid substances on other sensible organs, as inthe strangury, or tenesmus, or cholera. We shall conclude this account of the sense of extension by observing, thatthe want of its object is attended with a disagreeable sensation, as wellas the excess of it. In those hollow muscles, which have been accustomed toit, this disagreeable sensation is called faintness, emptiness, andsinking; and, when it arises to a certain degree, is attended with syncope, or a total quiescence of all motions, but the internal irritative ones, ashappens from sudden loss of blood, or in the operation of tapping in thedropsy. VIII. _Of the Appetites of Hunger, Thirst, Heat, Extension, the want offresh Air, animal Love, and the Suckling of Children. _ Hunger is most probably perceived by those numerous ramifications of nervesthat are seen about the upper opening of the stomach; and thirst by thenerves about the fauces, and the top of the gula. The ideas of these sensesare few in the generality of mankind, but are more numerous in those, whoby disease, or indulgence, desire particular kinds of foods or liquids. A sense of heat has already been spoken of, which may with propriety becalled an appetite, as we painfully desire it, when it is deficient inquantity. The sense of extension may be ranked amongst these appetites, since thedeficiency of its object gives disagreeable sensation; when this happens inthe arterial system, it is called faintness, and seems to bear some analogyto hunger and to cold; which like it are attended with emptiness of a partof the vascular system. The sense of want of fresh air has not been attended to, but is as distinctas the others, and the first perhaps that we experience after our nativity;from the want of the object of this sense many diseases are produced, asthe jail-fever, plague, and other epidemic maladies. Animal love is anotherappetite, which occurs later in life, and the females of lactiferousanimals have another natural inlet of pleasure or pain from the sucklingtheir offspring. The want of which either owing to the death of theirprogeny, or to the fashion of their country, has been fatal to many of thesex. The males have also pectoral glands, which are frequently turgid witha thin milk at their nativity, and are furnished with nipples, which erecton titillation like those of the female; but which seem now to be of nofurther use, owing perhaps to some change which these animals haveundergone in the gradual progression of the formation of the earth, and ofall that it inhabit. These seven last mentioned senses may properly be termed appetites, as theydiffer from those of touch, sight, hearing, taste, and smell, in thisrespect; that they are affected with pain as well by the defect of theirobjects as by the excess of them, which is not so in the latter. Thus coldand hunger give us pain, as well as an excess of heat or satiety; but it isnot so with darkness and silence. IX. Before we conclude this Section on the organs of sense, we mustobserve, that, as far as we know, there are many more senses, than havebeen here mentioned, as every gland seems to be influenced to separate fromthe blood, or to absorb from the cavities of the body, or from theatmosphere, its appropriated fluid, by the stimulus of that fluid on theliving gland; and not by mechanical capillary absorption, nor by chemicalaffinity. Hence it appears, that each of these glands must have a peculiarorgan to perceive these irritations, but as these irritations are notsucceeded by sensation, they have not acquired the names of senses. However when these glands are excited into motions stronger than usual, either by the acrimony of their fluids, or by their own irritability beingmuch increased, then the sensation of pain is produced in them as in allthe other senses of the body; and these pains are all of different kinds, and hence the glands at this time really become each a different organ ofsense, though these different kinds of pain have acquired no names. Thus a great excess of light does not give the idea of light but of pain;as in forcibly opening the eye when it is much inflamed. The great excessof pressure or distention, as when the point of a pin is pressed upon ourskin, produces pain, (and when this pain of the sense of distention isslighter, it is termed itching, or tickling), without any idea of solidityor of figure: an excess of heat produces smarting, of cold another kind ofpain; it is probable by this sense of heat the pain produced by causticbodies is perceived, and of electricity, as all these are fluids, thatpermeate, distend, or decompose the parts that feel them. * * * * * SECT. XV. OF THE CLASSES OF IDEAS. I. 1. _Ideas received in tribes. _ 2. _We combine them further, or abstract from these tribes. _ 3. _Complex ideas. _ 4. _Compounded ideas. _ 5. _Simple ideas, modes, substances, relations, general ideas. _ 6. _Ideas of reflexion. _ 7. _Memory and imagination imperfectly defined. Ideal presence. Memorandum-rings. _ II. 1. _Irritative ideas. Perception. _ 2. _Sensitive ideas, imagination. _ 3. _Voluntary ideas, recollection. _ 4. _Associated ideas, suggestion. _ III. 1. _Definitions of perception, memory. _ 2. _Reasoning, judgment, doubting, distinguishing, comparing. _ 3. _Invention. _ 4. _Consciousness. _ 5. _Identity. _ 6. _Lapse of time. _ 7. _Free-will. _ I. 1. As the constituent elements of the material world are onlyperceptible to our organs of sense in a state of combination; it follows, that the ideas or sensual motions excited by them, are never receivedsingly, but ever with a greater or less degree of combination. So thecolours of bodies or their hardnesses occur with their figures: every smelland taste has its degree of pungency as well as its peculiar flavour: andeach note in music is combined with the tone of some instrument. It appearsfrom hence, that we can be sensible of a number of ideas at the same time, such as the whiteness, hardness, and coldness, of a snow-ball, and canexperience at the same time many irritative ideas of surrounding bodies, which we do not attend to, as mentioned in Section VII. 3. 2. But thoseideas which belong to the same sense, seem to be more easily combined intosynchronous tribes, than those which were not received by the same sense, as we can more easily think of the whiteness and figure of a lump of sugarat the same time, than the whiteness and sweetness of it. 2. As these ideas, or sensual motions, are thus excited with greater orless degrees of combination; so we have a power, when we repeat them eitherby our volition or sensation, to increase or diminish this degree ofcombination, that is, to form compounded ideas from those, which were moresimple; and abstract ones from those, which were more complex, when theywere first excited; that is, we can repeat a part or the whole of thosesensual motions, which did constitute our ideas of perception; and therepetition of which now constitutes our ideas of recollection, or ofimagination. 3. Those ideas, which we repeat without change of the quantity of thatcombination, with which we first received them, are called complex ideas, as when you recollect Westminster Abbey, or the planet Saturn: but it mustbe observed, that these complex ideas, thus re-excited by volition, sensation, or association, are seldom perfect copies of their correspondentperceptions, except in our dreams, where other external objects do notdetract our attention. 4. Those ideas, which are more complex than the natural objects that firstexcited them, have been called compounded ideas, as when we think of asphinx, or griffin. 5. And those that are less complex than the correspondent natural objects, have been termed abstracted ideas: thus sweetness, and whiteness, andsolidity, are received at the same time from a lump of sugar, yet I canrecollect any of these qualities without thinking of the others, that wereexcited along with them. When ideas are so far abstracted as in the above example, they have beentermed simple by the writers of metaphysics, and seem indeed to be morecomplete repetitions of the ideas or sensual motions, originally excited byexternal objects. Other classes of these ideas, where the abstraction has not been so great, have been termed, by Mr. Locke, modes, substances, and relations, but theyseem only to differ in their degree of abstraction from the complex ideasthat were at first excited; for as these complex or natural ideas arethemselves imperfect copies of their correspondent perceptions, so theseabstract or general ideas are only still more imperfect copies of the sameperceptions. Thus when I have seen an object but once, as a rhinoceros, myabstract idea of this animal is the same as my complex one. I may thinkmore or less distinctly of a rhinoceros, but it is the very rhinoceros thatI saw, or some part or property of him, which recurs to my mind. But when any class of complex objects becomes the subject of conversation, of which I have seen many individuals, as a castle or an army, someproperty or circumstance belonging to it is peculiarly alluded to; and thenI feel in my own mind, that my abstract idea of this complex object is onlyan idea of that part, property, or attitude of it, that employs the presentconversation, and varies with every sentence that is spoken concerning it. So if any one should say, "one may sit upon a horse safer than on a camel, "my abstract idea of the two animals includes only an outline of the levelback of the one, and the gibbosity on the back of the other. What noise isthat in the street?--Some horses trotting over the pavement. Here my ideaof the horses includes principally the shape and motion of their legs. Soalso the abstract ideas of goodness and courage are still more imperfectrepresentations of the objects they were received from; for here weabstract the material parts, and recollect only the qualities. Thus we abstract so much from some of our complex ideas, that at length itbecomes difficult to determine of what perception they partake; and in manyinstances our idea seems to be no other than of the sound or letters of theword, that stands for the collective tribe, of which we are said to have anabstracted idea, as noun, verb, chimæra, apparition. 6. Ideas have been divided into those of perception and those ofreflection, but as whatever is perceived must be external to the organ thatperceives it, all our ideas must originally be ideas of perception. 7. Others have divided our ideas into those of memory, and those ofimagination; they have said that a recollection of ideas in the order theywere received constitutes memory, and without that order imagination; butall the ideas of imagination, excepting the few that are termed simpleideas, are parts of trains or tribes in the order they were received; as ifI think of a sphinx, or a griffin, the fair face, bosom, wings, claws, tail, are all complex ideas in the order they were received: and it behovesthe writers, who adhere to this definition, to determine, how small thetrains must be, that shall be called imagination; and how great those, thatshall be called memory. Others have thought that the ideas of memory have a greater vivacity thanthose of imagination: but the ideas of a person in sleep, or in a wakingreverie, where the trains connected with sensation are uninterrupted, aremore vivid and distinct than those of memory, so that they cannot bedistinguished by this criterion. The very ingenious author of the Elements of Criticism has described whathe conceives to be a species of memory, and calls it ideal presence; butthe instances he produces are the reveries of sensation, and are thereforein truth connections of the imagination, though they are recalled in theorder they were received. The ideas connected by association are in common discourse attributed tomemory, as we talk of memorandum-rings, and tie a knot on our handkerchiefsto bring something into our minds at a distance of time. And a school-boy, who can repeat a thousand unmeaning lines in Lilly's Grammar, is said tohave a good memory. But these have been already shewn to belong to theclass of association; and are termed ideas of suggestion. II. Lastly, the method already explained of classing ideas into thoseexcited by irritation, sensation, volition, or association, we hope will befound more convenient both for explaining the operations of the mind, andfor comparing them with those of the body; and for the illustration and thecure of the diseases of both, and which we shall here recapitulate. 1. Irritative ideas are those, which are preceded by irritation, which isexcited by objects external to the organs of sense: as the idea of thattree, which either I attend to, or which I shun in walking near it withoutattention. In the former case it is termed perception, in the latter it istermed simply an irritative idea. 2. Sensitive ideas are those, which are preceded by the sensation ofpleasure or pain; as the ideas, which constitute our dreams or reveries, this is called imagination. 3. Voluntary ideas are those, which are preceded by voluntary exertion, aswhen I repeat the alphabet backwards: this is called recollection. 4. Associate ideas are those, which are preceded by other ideas or muscularmotions, as when we think over or repeat the alphabet by rote in its usualorder; or sing a tune we are accustomed to; this is called suggestion. III. 1. Perceptions signify those ideas, which are preceded by irritationand succeeded by the sensation of pleasure or pain, for whatever excitesour attention interests us; that is, it is accompanied with, pleasure orpain; however slight may be the degree or quantity of either of them. The word memory includes two classes of ideas, either those which, arepreceded by voluntary exertion, or those which are suggested by theirassociations with other ideas. 2. Reasoning is that operation of the sensorium, by which we excite two ormany tribes of ideas; and then re-excite the ideas, in which they differ, or correspond. If we determine this difference, it is called judgment; ifwe in vain endeavour to determine it, it is called doubting. If we re-excited the ideas, in which they differ, it is calleddistinguishing. If we re-excite those in which they correspond, it iscalled comparing. 3. Invention is an operation of the sensorium, by which we voluntarilycontinue to excite one train of ideas, suppose the design of raising waterby a machine; and at the same time attend to all other ideas, which areconnected with this by every kind of catenation; and combine or separatethem voluntarily for the purpose of obtaining some end. For we can create nothing new, we can only combine or separate the ideas, which we have already received by our perceptions: thus if I wish torepresent a monster, I call to my mind the ideas of every thingdisagreeable and horrible, and combine the nastiness and gluttony of a hog, the stupidity and obstinacy of an ass, with the fur and awkwardness of abear, and call the new combination Caliban. Yet such a monster may exist innature, as all his attributes are parts of nature. So when I wish torepresent every thing, that is excellent, and amiable; when I combinebenevolence with cheerfulness, wisdom, knowledge, taste, wit, beauty ofperson, and elegance of manners, and associate them in one lady as apattern to the world, it is called invention; yet such a person mayexist, --such a person does exist!--It is ---- ----, who is as much amonster as Caliban. 4. In respect to consciousness, we are only conscious of our existence, when we think about it; as we only perceive the lapse of time, when weattend to it; when we are busied about other objects, neither the lapse oftime nor the consciousness of our own existence can occupy our attention. Hence, when we think of our own existence, we only excite abstracted orreflex ideas (as they are termed), of our principal pleasures or pains, ofour desires or aversions, or of the figure, solidity, colour, or otherproperties of our bodies, and call that act of the sensorium aconsciousness of our existence. Some philosopher, I believe it is DesCartes, has said, "I think, therefore I exist. " But this is not rightreasoning, because thinking is a mode of existence; and it is thence onlysaying, "I exist, therefore I exist. " For there are three modes ofexistence, or in the language of grammarians three kinds of verbs. First, simply I am, or exist. Secondly, I am acting, or exist in a state ofactivity, as I move. Thirdly, I am suffering, or exist in a state of beingacted upon, as I am moved. The when, and the where, as applicable to thisexistence, depends on the successive motions of our own or of other bodies;and on their respective situations, as spoken of Sect. XIV. 2. 5. 5. Our identity is known by our acquired habits or catenated trains ofideas and muscular motions; and perhaps, when we compare infancy with oldage, in those alone can our identity be supposed to exist. For what else isthere of similitude between the first speck of living entity and the matureman?--every deduction of reasoning, every sentiment or passion, with everyfibre of the corporeal part of our system, has been subject almost toannual mutation; while some catenations alone of our ideas and muscularactions have continued in part unchanged. By the facility, with which we can in our waking hours voluntarily producecertain successive trains of ideas, we know by experience, that we havebefore reproduced them; that is, we are conscious of a time of ourexistence previous to the present time; that is, of our identity now andheretofore. It is these habits of action, these catenations of ideas andmuscular motions, which begin with life, and only terminate with it; andwhich we can in some measure deliver to our posterity; as explained inSect. XXXIX. 6. When the progressive motions of external bodies make a part of ourpresent catenation of ideas, we attend to the lapse of time; which appearsthe longer, the more frequently we thus attend to it; as when we expectsomething at a certain hour, which much interests us, whether it be anagreeable or disagreeable event; or when we count the passing seconds on astop-watch. When an idea of our own person, or a reflex idea of our pleasures andpains, desires and aversions, makes a part of this catenation, it is termedconsciousness; and if this idea of consciousness makes a part of acatenation, which we excite by recollection, and know by the facility withwhich we excite it, that we have before experienced it, it is calledidentity, as explained above. 7. In respect to freewill, it is certain, that we cannot will to think of anew train of ideas, without previously thinking of the first link of it; asI cannot will to think of a black swan, without previously thinking of ablack swan. But if I now think of a tail, I can voluntarily recollect allanimals, which have tails; my will is so far free, that I can pursue theideas linked to this idea of tail, as far as my knowledge of the subjectextends; but to will without motive is to will without desire or aversion;which is as absurd as to feel without pleasure or pain; they are bothsolecisms in the terms. So far are we governed by the catenations ofmotions, which affect both the body and the mind of man, and which beginwith our irritability, and end with it. * * * * * SECT. XVI. OF INSTINCT. Haud equidem credo, quia sit divinitus illis Ingenium, aut rerum fato prudentia major. --Virg. Georg. L. I. 415. I. _Instinctive actions defined. Of connate passions. _ II. _Of the sensations and motions of the foetus in the womb. _ III. _Some animals are more perfectly formed than others before nativity. Of learning to walk. _ IV. _Of the swallowing, breathing, sucking, pecking, and lapping of young animals. _ V. _Of the sense of smell, and its uses to animals. Why cats do not eat their kittens. _ VI. _Of the accuracy of sight in mankind, and their sense of beauty. Of the sense of touch in elephants, monkies, beavers, men. _ VII. _Of natural language. _ VIII. _The origin of natural language;_ 1. _the language of fear;_ 2. _of grief;_ 3. _of tender pleasure;_ 4. _of serene pleasure;_ 5. _of anger;_ 6. _of attention. _ IX. _Artificial language of turkies, hens, ducklings, wagtails, cuckoos, rabbits, dogs, and nightingales. _ X. _Of music; of tooth-edge; of a good ear; of architecture. _ XI. _Of acquired knowledge; of foxes, rooks, fieldfares, lapwings, dogs, cats, horses, crows, and pelicans. _ XII. _Of birds of passage, dormice, snakes, bats, swallows, quails, ringdoves, stare, chaffinch, hoopoe, chatterer, hawfinch, crossbill, rails and cranes. _ XIII. _Of birds nests; of the cuckoo; of swallows nests; of the taylor bird. _ XIV. _Of the old soldier; of haddocks, cods, and dog fish; of the remora; of crabs, herrings, and salmon. _ XV. _Of spiders, caterpillars, ants, and the ichneumon. _ XVI. 1. _Of locusts, gnats;_ 2. _bees;_ 3. _dormice, flies, worms, ants, and wasps. _ XVII. _Of the faculty that distinguishes man from the brutes. _ I. All those internal motions of animal bodies, which contribute to digesttheir aliment, produce their secretions, repair their injuries, or increasetheir growth, are performed without our attention or consciousness. Theyexist as well in our sleep, as in our waking hours, as well in the foetusduring the time of gestation, as in the infant after nativity, and proceedwith equal regularity in the vegetable as in the animal system. Thesemotions have been shewn in a former part of this work to depend on theirritations of peculiar fluids, and as they have never been classed amongstthe instinctive actions of animals, are precluded from our presentdisquisition. But all those actions of men or animals, that are attended withconsciousness, and seem neither to have been directed by their appetites, taught by their experience, nor deduced from observation or tradition, havebeen referred to the power of instinct. And this power has been explainedto be a _divine something_, a kind of inspiration; whilst the poor animal, that possesses it, has been thought little better than _a machine_! The _irksomeness_, that attends a continued attitude of the body, or the_pains_, that we receive from heat, cold, hunger, or other injuriouscircumstances, excite us to _general locomotion_: and our senses are soformed and constituted by the hand of nature, that certain objects presentus with pleasure, others with pain, and we are induced to approach andembrace these, to avoid and abhor those, as such sensations direct us. Thus the palates of some animals are gratefully affected by the masticationof fruits, others of grains, and others of flesh; and they are thenceinstigated to attain, and to consume those materials; and are furnishedwith powers of muscular motion, and of digestion proper for such purposes. These _sensations_ and _desires_ constitute a part of our system, as our_muscles_ and _bones_ constitute another part: and hence they may alike betermed _natural_ or _connate_; but neither of them can properly be termed_instinctive_: as the word instinct in its usual acceptation refers only tothe _actions_ of animals, as above explained: the origin of these _actions_is the subject of our present enquiry. The reader is intreated carefully to attend to this definition of_instinctive actions_, lest by using the word instinct without adjoiningany accurate idea to it, he may not only include the natural desires oflove and hunger, and the natural sensations of pain or pleasure, but thefigure and contexture of the body, and the faculty of reason itself underthis general term. II. We experience some sensations, and perform some actions before ournativity; the sensations of cold and warmth, agitation and rest, fulnessand inanition, are instances of the former; and the repeated struggles ofthe limbs of the foetus, which begin about the middle of gestation, andthose motions by which it frequently wraps the umbilical chord around itsneck or body, and even sometimes ties it on a knot; are instances of thelatter. Smellie's Midwifery, (Vol. I. P. 182. ) By a due attention to these circumstances many of the actions of younganimals, which at first sight seemed only referable to an inexplicableinstinct, will appear to have been acquired like all other animal actions, that are attended with consciousness, _by the repeated efforts of ourmuscles under the conduct of our sensations or desires_. The chick in the shell begins to move its feet and legs on the sixth day ofincubation (Mattreican, p. 138); or on the seventh day, (Langley);afterwards they are seen to move themselves gently in the liquid thatsurrounds them, and to open and shut their mouths, (Harvei, de Generat. P. 62, and 197. Form de Poulet. Ii. P. 129). Puppies before the membranes arebroken, that involve them, are seen to move themselves, to put out theirtongues, and to open and shut their mouths, (Harvey, Gipson, Riolan, Haller). And calves lick themselves and swallow many of their hairs beforetheir nativity: which however puppies do not, (Swammerden, p. 319. FlemyngPhil. Trans. Ann. 1755. 42). And towards the end of gestation, the foetusof all animals are proved to drink part of the liquid in which they swim, (Haller. Physiol. T. 8. 204). The white of egg is found in the mouth andgizzard of the chick, and is nearly or quite consumed before it is hatched, (Harvie de Generat. 58). And the liquor amnii is found in the mouth andstomach of the human foetus, and of calves; and how else should thatexcrement be produced in the intestines of all animals, which is voided ingreat quantity soon after their birth; (Gipson, Med. Essays, Edinb. V. I. 13. Halleri Physiolog. T. 3. P. 318. And T. 8). In the stomach of a calfthe quantity of this liquid amounted to about three pints, and the hairsamongst it were of the same colour with those on its skin, (Blasii Anat. Animal, p. M. 122). These facts are attested by many other writers ofcredit, besides those above mentioned. III. It has been deemed a surprising instance of instinct, that calves andchickens should be able to walk by a few efforts almost immediately aftertheir nativity: whilst the human infant in those countries where he is notincumbered with clothes, as in India, is five or six months, and in ourclimate almost a twelvemonth, before he can safely stand upon his feet. The struggles of all animals in the womb must resemble their mode ofswimming, as by this kind of motion they can best change their attitude inwater. But the swimming of the calf and chicken resembles their manner ofwalking, which they have thus in part acquired before their nativity, andhence accomplish it afterwards with very few efforts, whilst the swimmingof the human creature resembles that of the frog, and totally differs fromhis mode of walking. There is another circumstance to be attended to in this affair, that notonly the growth of those peculiar parts of animals, which are first wantedto secure their subsistence, are in general furthest advanced before theirnativity: but some animals come into the world more completely formedthroughout their whole system than others: and are thence much forwarder inall their habits of motion. Thus the colt, and the lamb, are much moreperfect animals than the blind puppy, and the naked rabbit; and the chickof the pheasant, and the partridge, has more perfect plumage, and moreperfect eyes, as well as greater aptitude to locomotion, than the callownestlings of the dove, and of the wren. The parents of the former only findit necessary to shew them their food, and to teach them to take it up;whilst those of the latter are obliged for many days to obtrude it intotheir gaping mouths. IV. From the facts mentioned in No. 2. Of this Section, it is evinced thatthe foetus learns to swallow before its nativity; for it is seen to openits mouth, and its stomach is found filled with the liquid that surroundsit. It opens its mouth, either instigated by hunger, or by the irksomenessof a continued attitude of the muscles of its face; the liquor amnii, inwhich it swims, is agreeable to its palate, as it consists of a nourishingmaterial, (Haller Phys. T. 8. P. 204). It is tempted to experience itstaste further in the mouth, and by a few efforts learns to swallow, in thesame manner as we learn all other animal actions, which are attended withconsciousness, _by the repeated efforts of our muscles under the conduct ofour sensations or volitions_. The inspiration of air into the lungs is so totally different from that ofswallowing a fluid in which we are immersed, that it cannot be acquiredbefore our nativity. But at this time, when the circulation of the blood isno longer continued through the placenta, that suffocating sensation, whichwe feel about the precordia, when we are in want of fresh air, disagreeablyaffects the infant: and all the muscles of the body are excited into actionto relieve this oppression; those of the breast, ribs, and diaphragm arefound to answer this purpose, and thus respiration is discovered, and iscontinued throughout our lives, as often as the oppression begins to recur. Many infants, both of the human creature, and of quadrupeds, struggle for aminute after they are born before they begin to breathe, (Haller Phys. T. 8. P. 400. Ib pt. 2. P. 1). Mr. Buffon thinks the action of the dry airupon the nerves of smell of new-born animals, by producing an endeavour tosneeze, may contribute to induce this first inspiration, and that therarefaction of the air by the warmth of the lungs contributes to induceexpiration, (Hist. Nat. Tom. 4. P. 174). Which latter it may effect byproducing a disagreeable sensation by its delay, and a consequent effort torelieve it. Many children sneeze before they respire, but not all, as faras I have observed, or can learn from others. At length, by the direction of its sense of smell, or by the officious careof its mother, the young animal approaches the odoriferous rill of itsfuture nourishment, already experienced to swallow. But in the act ofswallowing, it is necessary nearly to close the mouth, whether the creaturebe immersed in the fluid it is about to drink, or not: hence, when thechild first attempts to suck, it does not slightly compress the nipplebetween its lips, and suck as an adult person would do, by absorbing themilk; but it takes the whole nipple into its mouth for this purpose, compresses it between its gums, and thus repeatedly chewing (as it were)the nipple, presses out the milk, exactly in the same manner as it is drawnfrom the teats of cows by the hands of the milkmaid. The celebrated Harveyobserves, that the foetus in the womb must have sucked in a part of itsnourishment, because it knows how to suck the minute it is born, as any onemay experience by putting a finger between its lips, and because in a fewdays it forgets this art of sucking, and cannot without some difficultyagain acquire it, (Exercit. De Gener. Anim. 48). The same observation ismade by Hippocrates. A little further experience teaches the young animal to suck by absorption, as well as by compression; that is, to open the chest as in the beginningof respiration, and thus to rarefy the air in the mouth, that the pressureof the denser external atmosphere may contribute to force out the milk. The chick yet in the shell has learnt to drink by swallowing a part of thewhite of the egg for its food; but not having experienced how to take upand swallow solid seeds, or grains, is either taught by the felicitousindustry of its mother; or by many repeated attempts is enabled at lengthto distinguish and to swallow this kind of nutriment. And puppies, though they know how to suck like other animals from theirprevious experience in swallowing, and in respiration; yet are they long inacquiring the art of lapping with their tongues, which from the flaccidityof their cheeks, and length of their mouths, is afterwards a moreconvenient way for them to take in water. V. The senses of smell and taste in many other animals greatly excel thoseof mankind, for in civilized society, as our victuals are generallyprepared by others, and are adulterated with salt, spice, oil, andempyreuma, we do not hesitate about eating whatever is set before us, andneglect to cultivate these senses: whereas other animals try every morselby the smell, before they take it into their mouths, and by the tastebefore they swallow it: and are led not only each to his proper nourishmentby this organ of sense, but it also at a maturer age directs them in thegratification of their appetite of love. Which may be further understood byconsidering the sympathies of these parts described in Class IV. 2. 1. 7. While the human animal is directed to the object of his love by his senseof beauty, as mentioned in No. VI. Of this Section. Thus Virgil. Georg. III. 250. Nonne vides, ut tota tremor pertentat equorum Corpora, si tantum notas odor attulit auras? Nonne canis nidum veneris nasutus odore Quærit, et erranti trahitur sublambere linguâ? Respuit at gustum cupidus, labiisque retractis Elevat os, trepidansque novis impellitur æstris Inserit et vivum felici vomere semen. -- Quam tenui filo cæcos adnectit amores Docta Venus, vitæque monet renovare favillam!--ANON. The following curious experiment is related by Galen. "On dissecting a goatgreat with young I found a brisk embryon, and having detached it from thematrix, and snatching it away before it saw its dam, I brought it into acertain room, where there were many vessels, some filled with wine, otherswith oil, some with honey, others with milk, or some other liquor; and inothers were grains and fruits; we first observed the young animal get uponits feet, and walk; then it shook itself, and afterwards scratched its sidewith one of its feet: then we saw it smelling to every one of these things, that were set in the room; and when it had smelt to them all, it drank upthe milk. " L. 6. De locis. Cap. 6. Parturient quadrupeds, as cats, and bitches, and sows, are led by theirsense of smell to eat the placenta as other common food; why then do theynot devour their whole progeny, as is represented in an antient emblem ofTIME? This is said sometimes to happen in the unnatural state in which weconfine sows; and indeed nature would seem to have endangered her offspringin this nice circumstance! But at this time the stimulus of the milk in thetumid teats of the mother excites her to look out for, and to desire someunknown circumstance to relieve her. At the same time the smell of the milkattracts the exertions of the young animals towards its source, and thusthe delighted mother discovers a new appetite, as mentioned in Sect. XIV. 8. And her little progeny are led to receive and to communicate pleasure bythis most beautiful contrivance. VI. But though the human species in some of their sensations are muchinferior to other animals, yet the accuracy of the sense of touch, whichthey possess in so eminent a degree, gives them a great superiority ofunderstanding; as is well observed by the ingenious Mr. Buffon. Theextremities of other animals terminate in horns, and hoofs, and claws, veryunfit for the sensation of touch; whilst the human hand is finely adaptedto encompass its object with this organ of sense. The elephant is indeed endued with a fine sense of feeling at the extremityof his proboscis, and hence has acquired much more accurate ideas of touchand of sight than most other creatures. The two following instances of thesagacity of these animals may entertain the reader, as they were told me bysome gentlemen of distinct observation, and undoubted veracity, who hadbeen much conversant with our eastern settlements. First, the elephantsthat are used to carry the baggage of our armies, are put each under thecare of one of the natives of Indostan, and whilst himself and his wife gointo the woods to collect leaves and branches of trees for his food, theyfix him to the ground by a length of chain, and frequently leave a childyet unable to walk, under his protection: and the intelligent animal notonly defends it, but as it creeps about, when it arrives near the extremityof his chain, he wraps his trunk gently round its body, and brings it againinto the centre of his circle. Secondly, the traitor elephants are taughtto walk on a narrow path between two pit-falls, which are covered withturf, and then to go into the woods, and to seduce the wild elephants tocome that way, who fall into these wells, whilst he passes safe betweenthem: and it is universally observed, that those wild elephants that escapethe snare, pursue the traitor with the utmost vehemence, and if they canovertake him, which sometimes happens, they always beat him to death. The monkey has a hand well enough adapted for the sense of touch, whichcontributes to his great facility of imitation; but in taking objects withhis hands, as a stick or an apple, he puts his thumb on the same side ofthem with his fingers, instead of counteracting the pressure of his fingerswith it: from this neglect he is much slower in acquiring the figures ofobjects, as he is less able to determine the distances or diameters oftheir parts, or to distinguish their vis inertiæ from their hardness. Helvetius adds, that the shortness of his life, his being fugitive beforemankind, and his not inhabiting all climates, combine to prevent hisimprovement. (De l'Esprit. T. 1. P. ) There is however at this time an oldmonkey shewn in Exeter Change, London, who having lost his teeth, when nutsare given him, takes a stone into his hand, and cracks them with it one byone; thus using tools to effect his purpose like mankind. The beaver is another animal that makes much use of his hands, and if wemay credit the reports of travellers, is possessed of amazing ingenuity. This however, M. Buffon affirms, is only where they exist in large numbers, and in countries thinly peopled with men; while in France in their solitarystate they shew no uncommon ingenuity. Indeed all the quadrupeds, that have collar-bones, (claviculæ) use theirfore-limbs in some measure as we use our hands, as the cat, squirrel, tyger, bear and lion; and as they exercise the sense of touch moreuniversally than other animals, so are they more sagacious in watching andsurprising their prey. All those birds, that use their claws for hands, asthe hawk, parrot, and cuckoo, appear to be more docile and intelligent;though the gregarious tribes of birds have more acquired knowledge. Now as the images, that are painted on the retina of the eye, are no otherthan signs, which recall to our imaginations the objects we had beforeexamined by the organ of touch, as is fully demonstrated by Dr. Berkley inhis treatise on vision; it follows that the human creature has greatly moreaccurate and distinct sense of vision than that of any other animal. Whenceas he advances to maturity he gradually acquires a sense of female beauty, which at this time directs him to the object of his new passion. Sentimental love, as distinguished from the animal passion of that name, with which it is frequently accompanied, consists in the desire orsensation of beholding, embracing, and saluting a beautiful object. The characteristic of beauty therefore is that it is the object of love;and though many other objects are in common language called beautiful, yetthey are only called so metaphorically, and ought to be termed agreeable. AGrecian temple may give us the pleasurable idea of sublimity, a Gothictemple may give us the pleasurable idea of variety, and a modern house thepleasurable idea of utility; music and poetry may inspire our love byassociation of ideas; but none of these, except metaphorically, can betermed beautiful; as we have no wish to embrace or salute them. Our perception of beauty consists in our recognition by the sense of visionof those objects, first, which have before inspired our love by thepleasure, which they have afforded to many of our senses: as to our senseof warmth, of touch, of smell, of taste, hunger and thirst; and, secondly, which bear any analogy of form to such objects. When the babe, soon after it is born into this cold world, is applied toits mother's bosom; its sense of perceiving warmth is first agreeablyaffected; next its sense of smell is delighted with the odour of her milk;then its taste is gratified by the flavour of it: afterwards the appetitesof hunger and of thirst afford pleasure by the possession of their objects, and by the subsequent digestion of the aliment; and, lastly, the sense oftouch is delighted by the softness and smoothness of the milky fountain, the source of such variety of happiness. All these various kinds of pleasure at length become associated with theform of the mother's breast; which the infant embraces with its hands, presses with its lips, and watches with its eyes; and thus acquires moreaccurate ideas of the form of its mother's bosom, than of the odour andflavour or warmth, which it perceives by its other senses. And hence at ourmaturer years, when any object of vision is presented to us, which by itswaving or spiral lines bears any similitude to the form of the femalebosom, whether it be found in a landscape with soft gradations of risingand descending surface, or in the forms of some antique vases, or in otherworks of the pencil or the chissel, we feel a general glow of delight, which seems to influence all our senses; and, if the object be not toolarge, we experience an attraction to embrace it with our arms, and tosalute it with our lips, as we did in our early infancy the bosom of ourmother. And thus we find, according to the ingenious idea of Hogarth, thatthe waving lines of beauty were originally taken from the temple of Venus. This animal attraction is love; which is a sensation, when the object ispresent; and a desire, when it is absent. Which constitutes the purestsource of human felicity, the cordial drop in the otherwise vapid cup oflife, and which overpays mankind for the care and labour, which areattached to the pre-eminence of his situation above other animals. It should have been observed, that colour as well as form sometimes entersinto our idea of a beautiful object, as a good complexion for instance, because a fine or fair colour is in general a sign of health, and conveysto us an idea of the warmth of the object; and a pale countenance on thecontrary gives an idea of its being cold to the touch. It was before remarked, that young animals use their lips to distinguishthe forms of things, as well as their fingers, and hence we learn theorigin of our inclination to salute beautiful objects with our lips. For adefinition of Grace, see Class III. 1. 2. 4. VII. There are two ways by which we become acquainted with the passions ofothers: first, by having observed the effects of them, as of fear or anger, on our own bodies, we know at sight when others are under the influence ofthese affections. So when two cocks are preparing to fight, each feels thefeathers rise round his own neck, and knows from the same sign thedisposition of his adversary: and children long before they can speak, orunderstand the language of their parents, may be frightened by an angrycountenance, or soothed by smiles and blandishments. Secondly, when we put ourselves into the attitude that any passionnaturally occasions, we soon in some degree acquire that passion; hencewhen those that scold indulge themselves in loud oaths, and violent actionsof the arms, they increase their anger by the mode of expressingthemselves: and on the contrary the counterfeited smile of pleasure indisagreeable company soon brings along with it a portion of the reality, asis well illustrated by Mr. Burke. (Essay on the Sublime and Beautiful. ) This latter method of entering into the passions of others is rendered ofvery extensive use by the pleasure we take in imitation, which is every daypresented before our eyes, in the actions of children, and indeed in allthe customs and fashions of the world. From this our aptitude to imitation, arises what is generally understood by the word sympathy so well explainedby Dr. Smith of Glasgow. Thus the appearance of a cheerful countenancegives us pleasure, and of a melancholy one makes us sorrowful. Yawning andsometimes vomiting are thus propagated by sympathy, and some people ofdelicate fibres, at the presence of a spectacle of misery, have felt painin the same parts of their own bodies, that were diseased or mangled in theother. Amongst the writers of antiquity Aristotle thought this aptitude toimitation an essential property of the human species, and calls man animitative animal. [Greek: To zôon mimômenon]. These then are the natural signs by which we understand each other, and onthis slender basis is built all human language. For without some naturalsigns, no artificial ones could have been invented or understood, as isvery ingeniously observed by Dr. Reid. (Inquiry into the Human Mind. ) VIII. The origin of this universal language is a subject of the highestcuriosity, the knowledge of which has always been thought utterlyinaccessible. A part of which we shall however here attempt. Light, sound, and odours, are unknown to the foetus in the womb, which, except the few sensations and motions already mentioned, sleeps away itstime insensible of the busy world. But the moment he arrives into day, hebegins to experience many vivid pains and pleasures; these are at the sametime attended with certain muscular motions, and from this their early, andindividual association, they acquire habits of occurring together, that areafterwards indissoluble. 1. _Of Fear. _ As soon as the young animal is born, the first important sensations, thatoccur to him, are occasioned by the oppression about his precordia for wantof respiration, and by his sudden transition from ninety-eight degrees ofheat into so cold a climate. --He trembles, that is, he exerts alternatelyall the muscles of his body, to enfranchise himself from the oppressionabout his bosom, and begins to breathe with frequent and shortrespirations; at the same time the cold contracts his red skin, graduallyturning it pale; the contents of the bladder and of the bowels areevacuated: and from the experience of these first disagreeable sensationsthe passion of fear is excited, which is no other than the expectation ofdisagreeable sensations. This early association of motions and sensationspersists throughout life; the passion of fear produces a cold and paleskin, with tremblings, quick respiration, and an evacuation of the bladderand bowels, and thus constitutes the natural or universal language of thispassion. On observing a Canary bird this morning, January 28, 1772, at the house ofMr. Harvey, near Tutbury, in Derbyshire, I was told it always fainted away, when its cage was cleaned, and desired to see the experiment. The cagebeing taken from the ceiling, and its bottom drawn out, the bird began totremble, and turned quite white about the root of his bill: he then openedhis mouth as if for breath, and respired quick, stood straighter up on hisperch, hung his wings, spread his tail, closed his eyes, and appeared quitestiff and cataleptic for near half an hour, and at length with muchtrembling and deep respirations came gradually to himself. 2. _Of Grief. _ That the internal membrane of the nostrils may be kept always moist, forthe better perception of odours, there are two canals, that conduct thetears after they have done their office in moistening and cleaning the ballof the eye into a sack, which is called the lacrymal sack; and from whichthere is a duct, that opens into the nostrils: the aperture of this duct isformed of exquisite sensibility, and when it is stimulated by odorousparticles, or by the dryness or coldness of the air, the sack contractsitself, and pours more of its contained moisture on the organ of smell. Bythis contrivance the organ is rendered more fit for perceiving such odours, and is preserved from being injured by those that are more strong orcorrosive. Many other receptacles of peculiar fluids disgorge theircontents, when the ends of their ducts are stimulated; as the gall bladder, when the contents of the duodenum stimulate the extremity of the commonbile duct: and the salivary glands, when the termination of their ducts inthe mouth are excited by the stimulus of the food we masticate. Atquevesiculæ seminales suum exprimunt fluidum glande penis fricatâ. The coldness and dryness of the atmosphere, compared with the warmth andmoisture, which the new-born infant had just before experienced, disagreeably affects the aperture of this lacrymal sack: the tears, thatare contained in this sack, are poured into the nostrils, and a furthersupply is secreted by the lacrymal glands, and diffused upon the eye-balls;as is very visible in the eyes and nostrils of children soon after theirnativity. The same happens to us at our maturer age, for in severe frostyweather, snivelling and tears are produced by the coldness and dryness ofthe air. But the lacrymal glands, which separate the tears from the blood, aresituated on the upper external part of the globes of each eye; and, when agreater quantity of tears are wanted, we contract the forehead, and bringdown the eye-brows, and use many other distortions of the face, to compressthese glands. Now as the suffocating sensation, that produces respiration, is removedalmost as soon as perceived, and does not recur again: this disagreeableirritation of the lacrymal ducts, as it must frequently recur, till thetender organ becomes used to variety of odours, is one of the first painsthat is repeatedly attended to: and hence throughout our infancy, and inmany people throughout their lives, all disagreeable sensations areattended with snivelling at the nose, a profusion of tears, and somepeculiar distortions of countenance: according to the laws of earlyassociation before mentioned, which constitutes the natural or universallanguage of grief. You may assure yourself of the truth of this observation, if you willattend to what passes, when you read a distressful tale alone; before thetears overflow your eyes, you will invariably feel a titillation at thatextremity of the lacrymal duct, which terminates in the nostril, then thecompression of the eyes succeeds, and the profusion of tears. Linnæus asserts, that the female bear sheds tears in grief; the same hasbeen said of the hind, and some other animals. 3. _Of Tender Pleasure. _ The first most lively impression of pleasure, that the infant enjoys afterits nativity, is excited by the odour of its mother's milk. The organ ofsmell is irritated by this perfume, and the lacrymal sack empties itselfinto the nostrils, as before explained, and an increase of tears is pouredinto the eyes. Any one may observe this, when very young infants are aboutto suck; for at those early periods of life, the sensation affects theorgan of smell, much more powerfully, than after the repeated habits ofsmelling has inured it to odours of common strength: and in our adultyears, the stronger smells, though they are at the same time agreeable tous, as of volatile spirits, continue to produce an increased secretion oftears. This pleasing sensation of smell is followed by the early affection of theinfant to the mother that suckles it, and hence the tender feelings ofgratitude and love, as well as of hopeless grief, are ever after joinedwith the titillation of the extremity of the lacrymal ducts, and aprofusion of tears. Nor is it singular, that the lacrymal sack should be influenced by pleasingideas, as the sight of agreeable food produces the same effect on thesalivary glands. Ac dum vidimus insomniis lascivæ puellæ simulacrumtenditur penis. Lambs shake or wriggle their tails, at the time when they first suck, toget free of the hard excrement, which had been long lodged in their bowels. Hence this becomes afterwards a mark of pleasure in them, and in dogs, andother tailed animals. But cats gently extend and contract their paws whenthey are pleased, and purr by drawing in their breath, both which resembletheir manner of sucking, and thus become their language of pleasure, forthese animals having collar-bones use their paws like hands when they suck, which dogs and sheep do not. 4. _Of Serene Pleasure. _ In the action of sucking, the lips of the infant are closed around thenipple of its mother, till he has filled his stomach, and the pleasureoccasioned by the stimulus of this grateful food succeeds. Then thesphincter of the mouth, fatigued by the continued action of sucking, isrelaxed; and the antagonist muscles of the face gently acting, produce thesmile of pleasure: as cannot but be seen by all who are conversant withchildren. Hence this smile during our lives is associated with gentle pleasure; it isvisible in kittens, and puppies, when they are played with, and tickled;but more particularly marks the human features. For in children thisexpression of pleasure is much encouraged, by their imitation of theirparents, or friends; who generally address them with a smiling countenance:and hence some nations are more remarkable for the gaiety, and others forthe gravity of their looks. 5. _Of Anger. _ The actions that constitute the mode of fighting, are the immediatelanguage of anger in all animals; and a preparation for these actions isthe natural language of threatening. Hence the human creature clenches hisfist, and sternly surveys his adversary, as if meditating where to make theattack; the ram, and the bull, draws himself some steps backwards, andlevels his horns; and the horse, as he most frequently fights by strikingwith his hinder feet, turns his heels to his foe, and bends back his ears, to listen out the place of his adversary, that the threatened blow may notbe ineffectual. 6. _Of Attention. _ The eye takes in at once but half our horizon, and that only in the day, and our smell informs us of no very distant objects, hence we confideprincipally in the organ of hearing to apprize us of danger: when we hearany the smallest sound, that we cannot immediately account for, our fearsare alarmed, we suspend our steps, hold every muscle still, open our mouthsa little, erect our ears, and listen to gain further information: and thisby habit becomes the general language of attention to objects of sight, aswell as of hearing; and even to the successive trains of our ideas. The natural language of violent pain, which is expressed by writhing thebody, grinning, and screaming; and that of tumultuous pleasure, expressedin loud laughter; belong to Section XXXIV. On Diseases from Volition. IX. It must have already appeared to the reader, that all other animals, aswell as man, are possessed of this natural language of the passions, expressed in signs or tones; and we shall endeavour to evince, that thoseanimals, which have preserved themselves from being enslaved by mankind, and are associated in flocks, are also possessed of some artificiallanguage, and of some traditional knowledge. The mother-turkey, when she eyes a kite hovering high in air, has eitherseen her own parents thrown into fear at his presence, or has byobservation been acquainted with his dangerous designs upon her young. Shebecomes agitated with fear, and uses the natural language of that passion, her young ones catch the fear by imitation, and in an instant concealthemselves in the grass. At the same time that she shews her fears by her gesture and deportment, she uses a certain exclamation, Koe-ut, Koe-ut, and the young onesafterwards know, when they hear this note, though they do not see theirdam, that the presence of their adversary is denounced, and hide themselvesas before. The wild tribes of birds have very frequent opportunities of knowing theirenemies, by observing the destruction they make among their progeny, ofwhich every year but a small part escapes to maturity: but to our domesticbirds these opportunities so rarely occur, that their knowledge of theirdistant enemies must frequently be delivered by tradition in the mannerabove explained, through many generations. This note of danger, as well as the other notes of the mother-turkey, whenshe calls her flock to their food, or to sleep under her wings, appears tobe an artificial language, both as expressed by the mother, and asunderstood by the progeny. For a hen teaches this language with equal easeto the ducklings, she has hatched from suppositious eggs, and educates asher own offspring: and the wagtails, or hedge-sparrows, learn it from theyoung cuckoo their softer nursling, and supply him with food long after hecan fly about, whenever they hear his cuckooing, which Linnæus tells us, ishis call of hunger, (Syst. Nat. ) And all our domestic animals are readilytaught to come to us for food, when we use one tone of voice, and to flyfrom our anger, when we use another. Rabbits, as they cannot easily articulate sounds, and are formed intosocieties, that live under ground, have a very different method of givingalarm. When danger is threatened, they thump on the ground with one oftheir hinder feet, and produce a sound, that can be heard a great way byanimals near the surface of the earth, which would seem to be an artificialsign both from its singularity and its aptness to the situation of theanimal. The rabbits on the island of Sor, near Senegal, have white flesh, and arewell tasted, but do not burrow in the earth, so that we may suspect theirdigging themselves houses in this cold climate is an acquired art, as wellas their note of alarm, (Adanson's Voyage to Senegal). The barking of dogs is another curious note of alarm, and would seem to bean acquired language, rather than a natural sign: for "in the island ofJuan Fernandes, the dogs did not attempt to bark, till some European dogswere put among them, and then they gradually begun to imitate them, but ina strange manner at first, as if they were learning a thing that was notnatural to them, " (Voyage to South America by Don G. Juan, and Don Ant. DeUlloa. B. 2. C. 4). Linnæus also observes, that the dogs of South America do not bark atstrangers, (Syst. Nat. ) And the European dogs, that have been carried toGuinea, are said in three or four generations to cease to bark, and onlyhowl, like the dogs that are natives of that coast, (World Displayed, Vol. XVII. P. 26. ) A circumstance not dissimilar to this, and equally curious, is mentioned byKircherus, de Musurgia, in his Chapter de Lusciniis, "That the youngnightingales, that are hatched under other birds, never sing till they areinstructed by the company of other nightingales. " And Jonston affirms, thatthe nightingales that visit Scotland, have not the same harmony as those ofItaly, (Pennant's Zoology, octavo, p. 255); which would lead us to suspectthat the singing of birds, like human music, is an artificial languagerather than a natural expression of passion. X. Our music like our language, is perhaps entirely constituted ofartificial tones, which by habit suggest certain agreeable passions. Forthe same combination of notes and tones do not excite devotion, love, orpoetic melancholy in a native of Indostan and of Europe. And "theHighlander has the same warlike ideas annexed to the sound of a bagpipe (aninstrument which an Englishman derides), as the Englishman has to that of atrumpet or fife, " (Dr. Brown's Union of Poetry and Music, p. 58. ) So "themusic of the Turks is very different from the Italian, and the people ofFez and Morocco have again a different kind, which to us appears very roughand horrid, but is highly pleasing to them, " (L'Arte Armoniaca a GiorgioAntoniotto). Hence we see why the Italian opera does not delight anuntutored Englishman; and why those, who are unaccustomed to music, aremore pleased with a tune, the second or third time they hear it, than thefirst. For then the same melodious train of sounds excites the melancholy, they had learned from the song; or the same vivid combination of themrecalls all the mirthful ideas of the dance and company. Even the sounds, that were once disagreeable to us, may by habit beassociated with other ideas, so as to become agreeable. Father Lasitau, inhis account of the Iroquois, says "the music and dance of those Americans, have something in them extremely barbarous, which at first disgusts. Wegrow reconciled to them by degrees, and in the end partake of them withpleasure, the savages themselves are fond of them to distraction, " (Moeursdes Savages, Tom. Ii. ) There are indeed a few sounds, that we very generally associate withagreeable ideas, as the whistling of birds, or purring of animals, that aredelighted; and some others, that we as generally associate withdisagreeable ideas, as the cries of animals in pain, the hiss of some ofthem in anger, and the midnight howl of beasts of prey. Yet we receive noterrible or sublime ideas from the lowing of a cow, or the braying of anass. Which evinces, that these emotions are owing to previous associations. So if the rumbling of a carriage in the street be for a moment mistaken forthunder, we receive a sublime sensation, which ceases as soon as we know itis the noise of a coach and six. There are other disagreeable sounds, that are said to set the teeth onedge; which, as they have always been thought a necessary effect of certaindiscordant notes, become a proper subject of our enquiry. Every one in hischildhood has repeatedly bit a part of the glass or earthen vessel, inwhich his food has been given him, and has thence had a very disagreeablesensation in the teeth, which sensation was designed by nature to preventus from exerting them on objects harder than themselves. The jarring soundproduced between the cup and the teeth is always attendant on thisdisagreeable sensation: and ever after when such a sound is accidentallyproduced by the conflict of two hard bodies, we feel by association ofideas the concomitant disagreeable sensation in our teeth. Others have in their infancy frequently held the corner of a silkhandkerchief in their mouth, or the end of the velvet cape of their coat, whilst their companions in play have plucked it from them, and have givenanother disagreeable sensation to their teeth, which has afterwardsrecurred on touching those materials. And the sight of a knife drawn alonga china plate, though no sound is excited by it, and even the imaginationof such a knife and plate so scraped together, I know by repeatedexperience will produce the same disagreeable sensation of the teeth. These circumstances indisputably prove, that this sensation of thetooth-edge is owing to associated ideas; as it is equally excitable bysight, touch, hearing, or imagination. In respect to the artificial proportions of sound excited by musicalinstruments, those, who have early in life associated them with agreeableideas, and have nicely attended to distinguish them from each other, aresaid to have a good ear, in that country where such proportions are infashion: and not from any superior perfection in the organ of hearing, orany intuitive sympathy between certain sounds and passions. I have observed a child to be exquisitely delighted with music, and whocould with great facility learn to sing any tune that he heard distinctly, and yet whole organ of hearing was so imperfect, that it was necessary tospeak louder to him in common conversation than to others. Our music, like our architecture, seems to have no foundation in nature, they are both arts purely of human creation, as they imitate nothing. Andthe professors of them have only classed those circumstances, that are mostagreeable to the accidental taste of their age, or country; and have calledit Proportion. But this proportion must always fluctuate, as it rests onthe caprices, that are introduced into our minds by our various modes ofeducation. And these fluctuations of taste must become more frequent in thepresent age, where mankind have enfranchised themselves from the blindobedience to the rules of antiquity in perhaps every science, but that ofarchitecture. See Sect. XII. 7. 3. XI. There are many articles of knowledge, which the animals in cultivatedcountries seem to learn very early in their lives, either from each other, or from experience, or observation: one of the most general of these is toavoid mankind. There is so great a resemblance in the natural language ofthe passions of all animals, that we generally know, when they are in apacific, or in a malevolent humour, they have the same knowledge of us; andhence we can scold them from us by some tones and gestures, and couldpossibly attract them to us by others, if they were not already apprized ofour general malevolence towards them. Mr. Gmelin, Professor at Petersburg, assures us, that in his journey into Siberia, undertaken by order of theEmpress of Russia, he saw foxes, that expressed no fear of himself orcompanions, but permitted him to come quite near them, having never seenthe human creature before. And Mr. Bongainville relates, that at hisarrival at the Malouine, or Falkland's Islands, which were not inhabited bymen, all the animals came about himself and his people; the fowls settlingupon their heads and shoulders, and the quadrupeds running about theirfeet. From the difficulty of acquiring the confidence of old animals, andthe ease of taming young ones, it appears that the fear, they all conceiveat the sight of mankind, is an acquired article of knowledge. This knowledge is more nicely understood by rooks, who are formed intosocieties, and build, as it were, cities over our heads; they evidentlydistinguish, that the danger is greater when a man is armed with a gun. Every one has seen this, who in the spring of the year has walked under arookery with a gun in his hand: the inhabitants of the trees rise on theirwings, and scream to the unfledged young to shrink into their nests fromthe sight of the enemy. The vulgar observing this circumstance so uniformlyto occur, assert that rooks can smell gun-powder. The fieldfares, (turdus pilarus) which breed in Norway, and come hither inthe cold season for our winter berries; as they are associated in flocks, and are in a foreign country, have evident marks of keeping a kind ofwatch, to remark and announce the appearance of danger. On approaching atree, that is covered with them, they continue fearless till one at theextremity of the bush rising on his wings gives a loud and peculiar note ofalarm, when they all immediately fly, except one other, who continues tillyou approach still nearer, to certify as it were the reality of the danger, and then he also flies off repeating the note of alarm. And in the woods about Senegal there is a bird called uett-uett by thenegroes, and squallers by the French, which, as soon as they see a man, setup a loud scream, and keep flying round him, as if their intent was to warnother birds, which upon hearing the cry immediately take wing. These birdsare the bane of sportsmen, and frequently put me into a passion, andobliged me to shoot them, (Adanson's Voyage to Senegal, 78). For the sameintent the lesser birds of our climate seem to fly after a hawk, cuckoo, orowl, and scream to prevent their companions from being surprised by thegeneral enemies of themselves, or of their eggs and progeny. But the lapwing, (charadrius pluvialis Lin. ) when her unfledged offspringrun about the marshes, where they were hatched, not only gives the note ofalarm at the approach of men or dogs, that her young may concealthemselves; but flying and screaming near the adversary, she appears morefelicitous and impatient, as he recedes from her family, and thusendeavours to mislead him, and frequently succeeds in her design. Theselast instances are so apposite to the situation, rather than to the naturesof the creatures, that use them; and are so similar to the actions of menin the same circumstances, that we cannot but believe, that they proceedfrom a similar principle. Miss M. E. Jacson acquainted me, that she witnessed this autumn an agreeableinstance of sagacity in a little bird, which seemed to use the means toobtain an end; the bird repeatedly hopped upon a poppy-stem, and shook thehead with its bill, till many seeds were scattered, then it settled on theground, and eat the seeds, and again repeated the same management. Sept. 1, 1794. On the northern coast of Ireland a friend of mine saw above a hundred crowsat once preying upon muscles; each crow took a muscle up into the airtwenty or forty yards high, and let it fall on the stones, and thus bybreaking the shell, got possession of the animal. --A certain philosopher (Ithink it was Anaxagoras) walking along the sea-shore to gather shells, oneof these unlucky birds mistaking his bald head for a stone, dropped ashell-fish upon it, and killed at once a philosopher and an oyster. Our domestic animals, that have some liberty, are also possessed of somepeculiar traditional knowledge: dogs and cats have been forced into eachother's society, though naturally animals of a very different kind, andhave hence learned from each other to eat dog's grass (agrostis canina)when they are sick, to promote vomiting. I have seen a cat mistake theblade of barley for this grass, which evinces it is an acquired knowledge. They have also learnt of each other to cover their excrement andurine;--about a spoonful of water was spilt upon my hearth from thetea-kettle, and I observed a kitten cover it with ashes. Hence this mustalso be an acquired art, as the creature mistook the application of it. To preserve their fur clean, and especially their whiskers, cats wash theirfaces, and generally quite behind their ears, every time they eat. As theycannot lick those places with their tongues, they first wet the inside ofthe leg with saliva, and then repeatedly wash their faces with it, whichmust originally be an effect of reasoning, because a means is used toproduce an effect; and seems afterwards to be taught or acquired byimitation, like the greatest part of human arts. These animals seem to possess something like an additional sense by meansof their whiskers; which have perhaps some analogy to the antennæ of mothsand butterflies. The whiskers of cats consist not only of the long hairs ontheir upper lips, but they have also four or five long hairs standing upfrom each eyebrow, and also two or three on each cheek; all which, when theanimal erects them, make with their points so many parts of the peripheryof a circle, of an extent at least equal to the circumference of any partof their own bodies. With this instrument, I conceive, by a littleexperience, they can at once determine, whether any aperture amongst hedgesor shrubs, in which animals of this genus live in their wild state, islarge enough to admit their bodies; which to them is a matter of thegreatest consequence, whether pursuing or pursued. They have likewise apower of erecting and bringing forward the whiskers on their lips; whichprobably is for the purpose of feeling, whether a dark hole be furtherpermeable. The antennæ, or horns, of butterflies and moths, who have awkward wings, the minute feathers of which are very liable to injury, serve, I suppose, asimilar purpose of measuring, as they fly or creep amongst the leaves ofplants and trees, whither their wings can pass without touching them. Mr. Leonard, a very intelligent friend of mine, saw a cat catch a trout bydarting upon it in a deep clear water at the mill at Weaford, nearLichfield. The cat belonged to Mr. Stanley, who had often seen her catchfish in the same manner in summer, when the mill-pool was drawn so low, that the fish could be seen. I have heard of other cats taking fish inshallow water, as they stood on the bank. This seems a natural art oftaking their prey in cats, which their acquired delicacy by domesticationhas in general prevented them from using, though their desire of eatingfish continues in its original strength. Mr. White, in his ingenious History of Selbourn, was witness to a cat'ssuckling a young hare, which followed her about the garden, and camejumping to her call of affection. At Elford, near Lichfield, the Rev. Mr. Sawley had taken the young ones out of a hare, which was shot; they werealive, and the cat, who had just lost her own kittens, carried them away, as it was supposed, to eat them; but it presently appeared, that it wasaffection not hunger which incited her, as she suckled them, and broughtthem up as their mother. Other instances of the mistaken application of what has been termedinstinct may be observed in flies in the night, who mistaking a candle forday-light, approach and perish in the flame. So the putrid smell of thestapelia, or carrion-flower, allures the large flesh-fly to deposit itsyoung worms on its beautiful petals, which perish there for want ofnourishment. This therefore cannot be a necessary instinct, because thecreature mistakes the application of it. Though in this country horses shew little vestiges of policy, yet in thedeserts of Tartary, and Siberia, when hunted by the Tartars they are seento form a kind of community, set watches to prevent their being surprised, and have commanders, who direct, and hasten their flight, Origin ofLanguage, Vol. I. P. 212. In this country, where four or five horses travelin a line, the first always points his ears forward, and the last pointshis backward, while the intermediate ones seem quite careless in thisrespect; which seems a part of policy to prevent surprise. As all animalsdepend most on the ear to apprize them of the approach of danger, the eyetaking in only half the horizon at once, and horses possess a great nicetyof this sense; as appears from their mode of fighting mentioned No. 8. 5. Of this Section, as well as by common observation. There are some parts of a horse, which he cannot conveniently rub, whenthey itch, as about the shoulder, which he can neither bite with his teeth, nor scratch with his hind foot; when this part itches, he goes to anotherhorse, and gently bites him in the part which he wishes to be bitten, whichis immediately done by his intelligent friend. I once observed a young foalthus bite its large mother, who did not choose to drop the grass she had inher mouth, and rubbed her nose against the foal's neck instead of bitingit; which evinces that she knew the design of her progeny, and was notgoverned by a necessary instinct to bite where she was bitten. Many of our shrubs, which would otherwise afford an agreeable food tohorses, are armed with thorns or prickles, which secure them from thoseanimals; as the holly, hawthorn, gooseberry, gorse. In the extensivemoorlands of Staffordshire, the horses have learnt to stamp upon agorse-bush with one of their fore-feet for a minute together, and when thepoints are broken, they eat it without injury. The horses in the new forestin Hampshire are affirmed to do the same by Mr. Gilpin. Forest Scenery, II. 251, and 112. Which is an art other horses in the fertile parts of thecountry do not possess, and prick their mouths till they bleed, if they areinduced by hunger or caprice to attempt eating gorse. Swine have a sense of touch as well as of smell at the end of their nose, which they use as a hand, both to root up the soil, and to turn over andexamine objects of food, somewhat like the proboscis of an elephant. Asthey require shelter from the cold in this climate, they have learnt tocollect straw in their mouths to make their nest, when the wind blows cold;and to call their companions by repeated cries to assist in the work, andadd to their warmth by their numerous bedfellows. Hence these animals, which are esteemed so unclean, have also learned never to befoul theirdens, where they have liberty, with their own excrement; an art, which cowsand horses, which have open hovels to run into, have never acquired. I haveobserved great sagacity in swine; but the short lives we allow them, andtheir general confinement, prevents their improvement, which might probablybe otherwise greater than that of dogs. Instances of the sagacity and knowledge of animals are very numerous toevery observer, and their docility in learning various arts from mankind, evinces that they may learn similar arts from their own species, and thusbe possessed of much acquired and traditional knowledge. A dog whose natural prey is sheep, is taught by mankind, not only to leavethem unmolested, but to guard them; and to hunt, to set, or to destroyother kinds of animals, as birds, or vermin; and in some countries to catchfish, in others to find truffles, and to practise a great variety oftricks; is it more surprising that the crows should teach each other, thatthe hawk can catch less birds, by the superior swiftness of his wing, andif two of them follow him, till he succeeds in his design, that they can byforce share a part of the capture? This I have formerly observed withattention and astonishment. There is one kind of pelican mentioned by Mr. Osbeck, one of Linnæus'stravelling pupils (the pelicanus aquilus), whose food is fish; and which ittakes from other birds, because it is not formed to catch them itself;hence it is called by the English a Man-of-war-bird, Voyage to China, p. 88. There are many other interesting anecdotes of the pelican andcormorant, collected from authors of the best authority, in a well-managedNatural History for Children, published by Mr. Galton. Johnson. London. And the following narration from the very accurate Mons. Adanson, in hisVoyage to Senegal, may gain credit with the reader: as his employment inthis country was solely to make observations in natural history. On theriver Niger, in his road to the island Griel, he saw a great number ofpelicans, or wide throats. "They moved with great state like swans upon thewater, and are the largest bird next to the ostrich; the bill of the one Ikilled was upwards of a foot and half long, and the bag fastened underneathit held two and twenty pints of water. They swim in flocks, and form alarge circle, which they contract afterwards, driving the fish before themwith their legs: when they see the fish in sufficient number confined inthis space, they plunge their bill wide open into the water, and shut itagain with great quickness. They thus get fish into their throat-bag, whichthey eat afterwards on shore at their leisure. " P. 247. XII. The knowledge and language of those birds, that frequently changetheir climate with the seasons, is still more extensive: as they performthese migrations in large societies, and are less subject to the power ofman, than the resident tribes of birds. They are said to follow a leaderduring the day, who is occasionally changed, and to keep a continual cryduring the night to keep themselves together. It is probable that theseemigrations were at first undertaken as accident directed, by the moreadventurous of their species, and learned from one another like thediscoveries of mankind in navigation. The following circumstances stronglysupport this opinion. 1. Nature has provided these animals, in the climates where they areproduced, with another resource: when the season becomes too cold for theirconstitutions, or the food they were supported with ceases to be supplied, I mean that of sleeping. Dormice, snakes, and bats, have not the means ofchanging their country; the two former from the want of wings, and thelatter from his being not able to bear the light of the day. Hence theseanimals are obliged to make use of this resource, and sleep during thewinter. And those swallows that have been hatched too late in the year toacquire their full strength of pinion, or that have been maimed by accidentor disease, have been frequently found in the hollows of rocks on the seacoasts, and even under water in this torpid state, from which they havebeen revived by the warmth of a fire. This torpid state of swallows istestified by innumerable evidences both of antient and modern names. Aristotle speaking of the swallows says, "They pass into warmer climates inwinter, if such places are at no great distance; if they are, they burythemselves in the climates where they dwell, " (8. Hist. C. 16. See alsoDerham's Phys. Theol. V. Ii. P. 177. ) Hence their emigrations cannot depend on a _necessary_ instinct, as theemigrations themselves are not _necessary_. 2. When the weather becomes cold, the swallows in the neighbourhoodassemble in large flocks; that is, the unexperienced attend those that havebefore experienced the journey they are about to undertake: they are thenseen some time to hover on the coast, till there is calm whether, or awind, that suits the direction of their flight. Other birds of passage havebeen drowned by thousands in the sea, or have settled on ships quiteexhausted with fatigue. And others, either by mistaking their course, or bydistress of weather, have arrived in countries where they were never seenbefore: and thus are evidently subject to the same hazards that the humanspecies undergo, in the execution of their artificial purposes. 3. The same birds are emigrant from some countries and not so from others:the swallows were seen at Goree in January by an ingenious philosopher ofmy acquaintance, and he was told that they continued there all the year; asthe warmth of the climate was at all seasons sufficient for their ownconstitutions, and for the production of the flies that supply them withnourishment. Herodotus says, that in Libya, about the springs of the Nile, the swallows continue all the year. (L. 2. ) Quails (tetrao corturnix, Lin. ) are birds of passage from the coast ofBarbary to Italy, and have frequently settled in large shoals on shipsfatigued with their flight. (Ray, Wisdom of God, p. 129. Derham. Physic. Theol. V. Ii. P. 178, ) Dr. Ruffel, in his History of Aleppo, observes thatthe swallows visit that country about the end of February, and havinghatched their young disappear about the end of July; and returning againabout the beginning of October, continue about a fortnight, and then againdisappear. (P. 70. ) When my late friend Dr. Chambres, of Derby, was on the island of Caprea inthe bay of Naples, he was informed that great flights of quails annuallysettle on that island about the beginning of May, in their passage fromAfrica to Europe. And that they always come when the south-east wind blows, are fatigued when they rest on this island, and are taken in such amazingquantities and sold to the Continent, that the inhabitants pay the bishophis stipend out of the profits arising from the sale of them. The flights of these birds across the Mediterranean are recorded near threethousand years ago. "There went forth a wind from the Lord and broughtquails from the sea, and let them fall upon the camp, a day's journey roundabout it, and they were two cubits above the earth, " (Numbers, chap. Ii. Ver. 31. ) In our country, Mr. Pennant informs us, that some quails migrate, andothers only remove from the internal parts of the island to the coasts, (Zoology, octavo, 210. ) Some of the ringdoves and stares breed here, othersmigrate, (ibid. 510, ii. ) And the slender billed small birds do not allquit these kingdoms in the winter, though the difficulty of procuring theworms and insects, that they feed on, supplies the same reason formigration to them all, (ibid. 511. ) Linnæus has observed, that in Sweden the female chaffinches quit thatcountry in September, migrating into Holland, and leave their mates behindtill their return in spring. Hence he has called them Fringilla cælebs, (Amæn. Acad. Ii. 42. Iv. 595. ) Now in our climate both sexes of them areperennial birds. And Mr. Pennant observes that the hoopoe, chatterer, hawfinch, and crossbill, migrate into England so rarely, and at suchuncertain times, as not to deserve to be ranked among our birds of passage, (ibid. 511. ) The water fowl, as geese and ducks, are better adapted for long migrations, than the other tribes of birds, as, when the weather is calm, they can notonly rest themselves, or sleep upon the ocean, but possibly procure somekind of food from it. Hence in Siberia, as soon as the lakes are frozen, the water fowl, whichare very numerous, all disappear, and are supposed to fly to warmerclimates, except the rail, which, from its inability for long flights, probably sleeps, like our bat, in their winter. The following account fromthe Journey of Professor Gmelin, may entertain the reader. "In theneighbourhood of Krasnoiark, amongst many other emigrant water fowls, weobserved a great number of rails, which when pursued never took flight, butendeavoured to escape by running. We enquired how these birds, that couldnot fly, could retire into other countries in the winter, and were told, both by the Tartars and Assanians, that they well knew those birds couldnot alone pass into other countries: but when the cranes (les grues) retirein autumn, each one takes a rail (un rale) upon his back, and carries himto a warmer climate. " _Recapitulation. _ 1. All birds of passage can exist in the climates, where they are produced. 2. They are subject in their migrations to the same accidents anddifficulties, that mankind are subject to in navigation. 3. The same species of birds migrate from some countries, and are residentin others. From all these circumstances it appears that the migrations of birds arenot produced by a necessary instinct, but are accidental improvements, likethe arts among mankind, taught by their cotemporaries, or delivered bytradition from one generation of them to another. XIII. In that season of the year which supplies the nourishment proper forthe expected brood, the birds enter into a contract of marriage, and withjoint labour construct a bed for the reception of their offspring. Theirchoice of the proper season, their contracts of marriage, and theregularity with which they construct their nests, have in all ages excitedthe admiration of naturalists; and have always been attributed to the powerof instinct, which, like the occult qualities of the antient philosophers, prevented all further enquiry. We shall consider them in their order. _Their Choice of the Season. _ Our domestic birds, that are plentifully supplied throughout the year withtheir adapted food, and are covered with houses from the inclemency of theweather, lay their eggs at any season: which evinces that the spring of theyear is not pointed out to them by a necessary instinct. Whilst the wild tribes of birds choose this time of the year from theiracquired knowledge, that the mild temperature of the air is more convenientfor hatching their eggs, and is soon likely to supply that kind ofnourishment, that is wanted for their young. If the genial warmth of the spring produced the passion of love, as itexpands the foliage of trees, all other animals should feel its influenceas well as birds: but, the viviparous creatures, as they suckle theiryoung, that is, as they previously digest the natural food, that it maybetter suit the tender stomachs of their offspring, experience theinfluence of this passion at all seasons of the year, as cats and bitches. The graminivorous animals indeed generally produce their young about thetime when grass is supplied in the greatest plenty, but this is without anydegree of exactness, as appears from our cows, sheep, and hares, and may bea part of the traditional knowledge, which they learn from the example oftheir parents. _Their Contracts of Marriage. _ Their mutual passion, and the acquired knowledge, that their joint labouris necessary to procure sustenance for their numerous family, induces thewild birds to enter into a contract of marriage, which does not howevertake place among the ducks, geese, and fowls, that are provided with theirdaily food from our barns. An ingenious philosopher has lately denied, that animals can enter intocontracts, and thinks this an essential difference between them and thehuman creature:--but does not daily observation convince us, that they formcontracts of friendship with each other, and with mankind? When puppies andkittens play together, is there not a tacit contract, that they will nothurt each other? And does not your favorite dog expect you should give himhis daily food, for his services and attention to you? And thus barters hislove for your protection? In the same manner that all contracts are madeamongst men, that do not understand each others arbitrary language. _Construction of their Nests. _ 1. They seem to be instructed how to build their nests from theirobservation of that, in which they were educated, and from their knowledgeof those things, that are most agreeable to their touch in respect: towarmth, cleanliness, and stability. They choose their situations from theirideas of safety from their enemies, and of shelter from the weather. Nor isthe colour of their nests a circumstance unthought of; the finches, thatbuild in green hedges, cover their habitations with green moss; the swallowor martin, that builds against rocks and houses, covers her's with clay, whilst the lark chooses vegetable straw nearly of the colour of the groundshe inhabits: by this contrivance, they are all less liable to bediscovered by their adversaries. 2. Nor are the nests of the same species of birds constructed always of thesame materials, nor in the same form; which is another circumstance thatascertains, that they are led by observation. In the trees before Mr. Levet's house in Lichfield, there are annuallynests built by sparrows, a bird which usually builds under the tiles ofhouses, or the thatch of barns. Not finding such convenient situations fortheir nests, they build a covered nest bigger than a man's head, with anopening like a mouth at the side, resembling that of a magpie, except thatit is built with straw and hay, and lined with feathers, and so nicelymanaged as to be a defence against both wind and rain. The following extract from a Letter of the Rev. Mr. J. Darwin, of CarletonScroop in Lincolnshire, authenticates a curious fact of this kind. "When Imentioned to you the circumstance of crows or rooks building in the spireof Welbourn church, you expressed a desire of being well informed of thecertainty of the fact. Welbourn is situated in the road from Grantham toLincoln on the Cliff row; I yesterday took a ride thither, and enquired ofthe rector, Mr. Ridgehill, whether the report was true, that rooks built inthe spire of his church. He assured me it was true, and that they had doneso time immemorial, as his parishioners affirmed. There was a commontradition, he said, that formerly a rookery in some high trees adjoined thechurch yard, which being cut down (probably in the spring, the buildingseason), the rooks removed to the church, and built their nests on theoutside of the spire on the tops of windows, which by their projection alittle from the spire made them convenient room, but that they built alsoon the inside. I saw two nests made with sticks on the outside, and in thespires, and Mr. Ridgehill said there were always a great many. "I spent the day with Mr. Wright, a clergyman, at Fulbeck, near Welbourn, and in the afternoon Dr. Ellis of Headenham, about two miles from Welbourn, drank tea at Mr. Wright's, who said he remembered, when Mr. Welby lived atWelbourn, that he received a letter from an acquaintance in the west ofEngland, desiring an answer, whether the report of rooks building inWelbourn church was true, as a wager was depending on that subject; towhich he returned an answer ascertaining the fact, and decided the wager. "Aug. 30, 1794. So the jackdaw (corvus monedula) generally builds in church-steeples, orunder the roofs of high houses; but at Selbourn, in Southamptonshire, wheretowers and steeples are not sufficiently numerous, these birds build inforsaken rabbit burrows. See a curious account of these subterranean nestsin White's History of Selbourn, p. 59. Can the skilful change ofarchitecture in these birds and the sparrows above mentioned be governed byinstinct? Then they must have two instincts, one for common, and the otherfor extraordinary occasions. I have seen green worsted in a nest, which no where exists in nature: andthe down of thistles in those nests, that were by some accident constructedlater in the summer, which material could not be procured for the earliernests: in many different climates they cannot procure the same materials, that they use in ours. And it is well known, that the canary birds, thatare propagated in this country, and the finches, that are kept tame, willbuild their nests of any flexile materials, that are given them. Plutarch, in his Book on Rivers, speaking of the Nile, says, "that the swallowscollect a material, when the waters recede, with which they form nests, that are impervious to water. " And in India there is a swallow thatcollects a glutinous substance for this purpose, whose nest is esculent, and esteemed a principal rarity amongst epicures, (Lin. Syst. Nat. ) Boththese must be constructed of very different materials from those used bythe swallows of our country. In India the birds exert more artifice in building their nests on accountof the monkeys and snakes: some form their pensile nests in the shape of apurse, deep and open at top; others with a hole in the side; and others, still more cautious, with an entrance at the very bottom, forming theirlodge near the summit. But the taylor-bird will not ever trust its nest tothe extremity of a tender twig, but makes one more advance to safety byfixing it to the leaf itself. It picks up a dead leaf, and sews it to theside of a living one, its slender bill being its needle, and its threadsome fine fibres; the lining consists of feathers, gossamer, and down; itseggs are white, the colour of the bird light yellow, its length threeinches, its weight three sixteenths of an ounce; so that the materials ofthe nest, and the weight of the bird, are not likely to draw down anhabitation so slightly suspended. A nest of this bird is preserved in theBritish Museum, (Pennant's Indian Zoology). This calls to one's mind theMosaic account of the origin of mankind, the first dawning of art thereascribed to them, is that of sewing leaves together. For many other curiouskinds of nests see Natural History for Children, by Mr. Galton. Johnson. London. Part I. P. 47. Gen. Oriolus. 3. Those birds that are brought up by our care, and have had littlecommunication with others of their own species, are very defective in thisacquired knowledge; they are not only very awkward in the construction oftheir nests, but generally scatter their eggs in various parts of the roomor cage, where they are confined, and seldom produce young ones, till, byfailing in their first attempt, they have learnt something from their ownobservation. 4. During the time of incubation birds are said in general to turn theireggs every day; some cover them, when they leave the nest, as ducks andgeese; in some the male is said to bring food to the female, that she mayhave less occasion of absence, in others he is said to take her place, whenshe goes in quest of food; and all of them are said to leave their eggs ashorter time in cold weather than in warm. In Senegal the ostrich sits onher eggs only during the night, leaving them in the day to the heat of thesun; but at the Cape of Good Hope, where the heat is less, she sits on themday and night. If it should be asked, what induces a bird to sit weeks on its first eggsunconscious that a brood of young ones will be the product? The answer mustbe, that it is the same passion that induces the human mother to hold heroffspring whole nights and days in her fond arms, and press it to herbosom, unconscious of its future growth to sense and manhood, tillobservation or tradition have informed her. 5. And as many ladies are too refined to nurse their own children, anddeliver them to the care and provision of others; so is there one instanceof this vice in the feathered world. The cuckoo in some parts of England, as I am well informed by a very distinct and ingenious gentleman, hatchesand educates her own young; whilst in other parts she builds no nest, butuses that of some lesser bird, generally either of the wagtail, or hedgesparrow, and depositing one egg in it, takes no further care of herprogeny. As the Rev. Mr. Stafford was walking in Glosop Dale, in the Peak ofDerbyshire, he saw a cuckoo rise from its nest. The nest was on the stumpof a tree, that had been some time felled, among some chips that were inpart turned grey, so as much to resemble the colour of the bird, in thisnest were two young cuckoos: tying a string about the leg of one of them, he pegged the other end of it to the ground, and very frequently for manydays beheld the old cuckoo feed these her young, as he stood very nearthem. The following extract of a Letter from the Rev. Mr. Wilmot, of Morley, nearDerby, strengthens the truth of the fact above mentioned, of the cuckoosometimes making a nest, and hatching her own young. "In the beginning of July 1792, I was attending some labourers on my farm, when one of them said to me, "There is a bird's nest upon one of theCoal-slack Hills; the bird is now sitting, and is exactly like a cuckoo. They say that cuckoo's never hatch their own eggs, otherwise I should havesworn it was one. " He took me to the spot, it was in an open fallow ground;the bird was upon the nest, I stood and observed her some time, and wasperfectly satisfied it was a cuckoo; I then put my hand towards her, andshe almost let me touch her before she rose from the nest, which sheappeared to quit with great uneasiness, skimming over the ground in themanner that a hen partridge does when disturbed from a new hatched brood, and went only to a thicket about forty or fifty yards from the nest; andcontinued there as long as I staid to observe her, which was not manyminutes. In the nest, which was barely a hole scratched out of thecoal-slack in the manner of a plover's nest, I observed three eggs, but didnot touch them. As I had labourers constantly at work in that field, I wentthither every day, and always looked to see if the bird was there, but didnot disturb her for seven or eight days, when I was tempted to drive herfrom the nest, and found _two_ young ones, that appeared to have beenhatched some days, but there was no appearance of the third egg. I thenmentioned this extraordinary circumstance (for such I thought it) to Mr. And Mrs. Holyoak of Bidford Grange, Warwickshire, and to Miss M. Willes, who were on a visit at my house, and who all went to see it. Very lately Ireminded Mr. Holyoak of it, who told me he had a perfect recollection ofthe whole, and that, considering it a curiosity, he walked to look at itseveral times, was perfectly satisfied as to its being a cuckoo, andthought her more attentive to her young, than any other bird he everobserved, having always found her brooding her young. In about a week afterI first saw the young ones, one of them was missing, and I rather suspectedmy plough-boys having taken it; though it might possibly have been taken bya hawk, some time when the old one was seeking food. I never found her offher nest but once, and that was the last time I saw the remaining youngone, when it was almost full feathered. I then went from home for two orthree days, and, when I returned, the young one was gone, which I take forgranted had flown. Though during this time I frequently saw cuckoos in thethicket I mention, I never observed any one, that I supposed to be thecock-bird, paired with this hen. " Nor is this a new observation, though it is entirely overlooked by themodern naturalists, for Aristotle speaking of the cuckoo, asserts that shesometimes builds her nest among broken rocks, and on high mountains, (L. 6. H. C. 1. ) but adds in another place that she generally possesses the nestof another bird, (L. 6. H. C. 7. ) And Niphus says that cuckoos rarely buildfor themselves, most frequently laying their eggs in the nests of otherbirds, (Gesner, L. 3. De Cuculo. ) The Philosopher who is acquainted with these facts concerning the cuckoo, would seem to have very little _reason_ himself, if he could imagine thisneglect of her young to be a necessary _instinct_! XIV. The deep recesses of the ocean are inaccessible to mankind, whichprevents us from having much knowledge of the arts and government of itsinhabitants. 1. One of the baits used by the fisherman is an animal called an OldSoldier, his size and form are somewhat like the craw-fish, with thisdifference, that his tail is covered with a tough membrane instead of ashell; and to obviate this defect, he seeks out the uninhabited shell ofsome dead fish, that is large enough to receive his tail, and carries itabout with him as part of his clothing or armour. 2. On the coasts about Scarborough, where the haddocks, cods, and dog-fish, are in great abundance, the fishermen universally believe that the dog-fishmake a line, or semicircle, to encompass a shoal of haddocks and cod, confining them within certain limits near the shore, and eating them asoccasion requires. For the haddocks and cod are always found near the shorewithout any dog-fish among them, and the dog-fish further off without anyhaddocks or cod; and yet the former are known to prey upon the latter, andin some years devour such immense quantities as to render this fishery moreexpensive than profitable. 3. The remora, when he wishes to remove his situation, as he is a very slowswimmer, is content to take an outside place on whatever conveyance isgoing his way; nor can the cunning animal be tempted to quit his hold of aship when she is sailing, not even for the lucre of a piece of pork, lestit should endanger the loss of his passage: at other times he is easilycaught with the hook. 4. The crab-fish, like many other testaceous animals, annually changes itsshell; it is then in a soft state, covered only with a mucous membrane, andconceals itself in holes in the sand or under weeds; at this place a hardshelled crab always stands centinel, to prevent the sea insects frominjuring the other in its defenceless state; and the fishermen from hisappearance know where to find the soft ones, which they use for baits incatching other fish. And though the hard shelled crab, when he is on this duty, advances boldlyto meet the foe, and will with difficulty quit the field; yet at othertimes he shews great timidity, and has a wonderful speed in attempting hisescape; and, if often interrupted, will pretend death like the spider, andwatch an opportunity to sink himself into the sand, keeping only his eyesabove. My ingenious friend Mr. Burdett, who favoured me with these accountsat the time he was surveying the coasts, thinks the commerce between thesexes takes place at this time, and inspires the courage of the creature. 5. The shoals of herrings, cods, haddocks, and other fish, which approachour shores at certain seasons, and quit them at other seasons withoutleaving one behind; and the salmon, that periodically frequent our rivers, evince, that there are vagrant tribes of fish, that perform as regularmigrations as the birds of passage already mentioned. 6. There is a cataract on the river Liffey in Ireland about nineteen feethigh: here in the salmon season many of the inhabitants amuse themselves inobserving these fish leap up the torrent. They dart themselves quite out ofthe water as they ascend, and frequently fall back many times before theysurmount it, and baskets made of twigs are placed near the edge of thestream to catch them in their fall. I have observed, as I have sat by a spout of water, which descends from astone trough about two feet into a stream below, at particular seasons ofthe year, a great number of little fish called minums, or pinks, throwthemselves about twenty times their own length out of the water, expectingto get into the trough above. This evinces that the storgee, or attention of the dam to provide for theoffspring, is strongly exerted amongst the nations of fish, where it wouldseem to be the most neglected; as these salmon cannot be supposed toattempt so difficult and dangerous a task without being conscious of thepurpose or end of their endeavours. It is further remarkable, that most of the old salmon return to the seabefore it is proper for the young shoals to attend them, yet that a few oldones continue in the rivers so late, that they become perfectly emaciatedby the inconvenience of their situation, and this apparently to guide or toprotect the unexperienced brood. Of the smaller water animals we have still less knowledge, who neverthelessprobably possess many superior arts; some of these are mentioned in BotanicGarden, P. I. Add. Note XXVII. And XXVIII. The nympha of the water-moths ofour rivers, which cover themselves with cases of straw, gravel, and shell, contrive to make their habitations, nearly in equilibrium with the water;when too heavy, they add a bit of wood or straw; when too light, a bit ofgravel. Edinb. Trans. All these circumstances bear a near resemblance to the deliberate actionsof human reason. XV. We have a very imperfect acquaintance with the various tribes ofinsects: their occupations, manner of life, and even the number of theirsenses, differ from our own, and from each other; but there is reason toimagine, that those which possess the sense of touch in the most exquisitedegree, and whole occupations require the most constant exertion of theirpowers, are induced with a greater proportion or knowledge and ingenuity. The spiders of this country manufacture nets of various forms, adapted tovarious situations, to arrest the flies that are their food; and some ofthem have a house or lodging-place in the middle of the net, well contrivedfor warmth, security, or concealment. There is a large spider in SouthAmerica, who constructs nets of so strong a texture as to entangle smallbirds, particularly the humming bird. And in Jamaica there is anotherspider, who digs a hole in the earth obliquely downwards, about threeinches in length, and one inch in diameter, this cavity she lines with atough thick web, which when taken out resembles a leathern purse: but whatis most curious, this house has a door with hinges, like the operculum ofsome sea shells; and herself and family, who tenant this nest, open andshut the door, whenever they pass or repass. This history was told me, andthe nest with its operculum shewn me by the late Dr. Butt of Bath, who wassome years physician in Jamaica. The production of these nets is indeed a part of the nature or conformationof the animal, and their natural use is to supply the place of wings, whenshe wishes to remove to another situation. But when she employs them toentangle her prey, there are marks of evident design, for she adapts theform of each net to its situation, and strengthens those lines, thatrequire it, by joining others to the middle of them, and attaching thoseothers to distant objects, with the same individual art, that is used bymankind in supporting the masts and extending the sails of ships. This workis executed with more mathematical exactness and ingenuity by the fieldspiders, than by those in our houses, as their constructions are moresubjected to the injuries of dews and tempests. Besides the ingenuity shewn by these little creatures in taking their prey, the circumstance of their counterfeiting death, when they are put intoterror, is truly wonderful; and as soon as the object of terror is removed, they recover and run away. Some beetles are also said to possess this pieceof hypocrisy. The curious webs, or chords, constructed by some young caterpillars todefend themselves from cold, or from insects of prey; and by silk-worms andsome other caterpillars, when they transmigrate into aureliæ or larvæ, havedeservedly excited the admiration of the inquisitive. But our ignorance oftheir manner of life, and even of the number of their senses, totallyprecludes us from understanding the means by which they acquire thisknowledge. The care of the salmon in choosing a proper situation for her spawn, thestructure of the nests of birds, their patient incubation, and the art ofthe cuckoo in depositing her egg in her neighbour's nursery, are instancesof great sagacity in those creatures: and yet they are much inferior to thearts exerted by many of the insect tribes on similar occasions. The hairyexcrescences on briars, the oak apples, the blasted leaves of trees, andthe lumps on the backs of cows, are situations that are rather producedthan chosen by the mother insect for the convenience of her offspring. Thecells of bees, wasps, spiders, and of the various coralline insects, equally astonish us, whether we attend to the materials or to thearchitecture. But the conduct of the ant, and of some species of the ichneumon fly in theincubation of their eggs, is equal to any exertion of human science. Theants many times in a day move their eggs nearer the surface of theirhabitation, or deeper below it, as the heat of the weather varies; and incolder days lie upon them in heaps for the purpose of incubation: if theirmansion is too dry, they carry them to places where there is moisture, andyou may distinctly see the little worms move and suck up the water. Whentoo much moisture approaches their nest, they convey their eggs deeper inthe earth, or to some other place of safety. (Swammerd. Epil. Ad Hist. Insects, p. 153. Phil. Trans. No. 23. Lowthrop. V. 2. P. 7. ) There is one species of ichneumon-fly, that digs a hole in the earth, andcarrying into it two or three living caterpillars, deposits her eggs, andnicely closing up the nest leaves them there; partly doubtless to assistthe incubation, and partly to supply food to her future young, (Derham. B. 4, c. 13. Aristotle Hist. Animal, L. 5. C. 20. ) A friend of mine put about fifty large caterpillars collected from cabbageson some bran and a few leaves into a box, and covered it with gauze toprevent their escape. After a few days we saw, from more than three fourthsof them, about eight or ten little caterpillars of the ichneumon-fly comeout of their backs, and spin each a small cocoon of silk, and in a few daysthe large caterpillars died. This small fly it seems lays its egg in theback of the cabbage caterpillar, which when hatched preys upon thematerial, which is produced there for the purpose of making silk for thefuture nest of the cabbage caterpillar; of which being deprived, thecreature wanders about till it dies, and thus our gardens are preserved bythe ingenuity of this cruel fly. This curious property of producing a silkthread, which is common to some sea animals, see Botanic Garden, Part I. Note XXVII. And is designed for the purpose of their transformation as inthe silk-worm, is used for conveying themselves from higher branches tolower ones of trees by some caterpillars, and to make themselves temporarynests or tents, and by the spider for entangling his prey. Nor is itstrange that so much knowledge should be acquired by such small animals;since there is reason to imagine, that these insects have the sense oftouch, either in their proboscis, or their antennæ, to a great degree ofperfection; and thence may possess, as far as their sphere extends, asaccurate knowledge, and as subtle invention, as the discoverers of humanarts. XVI. 1. If we were better acquainted with the histories of those insectsthat are formed into societies, as the bees, wasps, and ants, I make nodoubt but we should find, that their arts and improvements are not sosimilar and uniform as they now appear to us, but that they arose in thesame manner from experience and tradition, as the arts of our own species;though their reasoning is from fewer ideas, is busied about fewer objects, and is exerted with less energy. There are some kinds of insects that migrate like the birds beforementioned. The locust of warmer climates has sometimes come over toEngland; it is shaped like a grasshopper, with very large wings, and a bodyabove an inch in length. It is mentioned as coming into Egypt with an eastwind, "The lord brought an east wind upon the land all that day and night, and in the morning the east wind brought the locusts, and covered the faceof the earth, so that the land was dark, " Exod. X. 13. The migrations ofthese insects are mentioned in another part of the scripture, "The locustshave no king, yet go they forth all of them in bands, " Prov. Xxx. 27. The accurate Mr. Adanson, near the river Gambia in Africa, was witness tothe migration of these insects. "About eight in the morning, in the monthof February, there suddenly arose over our heads a thick cloud, whichdarkened the air, and deprived us of the rays of the sun. We found it was acloud of locusts raised about twenty or thirty fathoms from the ground, andcovering an extent of several leagues; at length a shower of these insectsdescended, and after devouring every green herb, while they rested, againresumed their flight. This cloud was brought by a strong east-wind, and wasall the morning in passing over the adjacent country. " (Voyage to Senegal, 158. ) In this country the gnats are sometimes seen to migrate in clouds, like themusketoes of warmer climates, and our swarms of bees frequently travel manymiles, and are said in North America always to fly towards the south. Theprophet Isaiah has a beautiful allusion to these migrations, "The Lordshall call the fly from the rivers of Egypt, and shall hiss for the beethat is in the land of Assyria, " Isa. Vii. 18. Which has been latelyexplained by Mr. Bruce, in his travels to discover the source of the Nile. 2. I am well informed that the bees that were carried into Barbadoes, andother western islands, ceased to lay up any honey after the first year, asthey found it not useful to them: and are now become very troublesome tothe inhabitants of those islands by infesting their sugar houses; but thosein Jamaica continue to make honey, as the cold north winds, or rainyseasons of that island, confine them at home for several weeks together. And the bees of Senegal, which differ from those of Europe only in size, make their honey not only superior to ours in delicacy of flavour, but ithas this singularity, that it never concretes, but remains liquid as syrup, (Adanson). From some observations of Mr. Wildman, and of other people ofveracity, it appears, that during the severe part of the winter season forweeks together the bees are quite benumbed and torpid from the cold, and donot consume any of their provision. This state of sleep, like that ofswallows and bats, seems to be the natural resource of those creatures incold climates, and the making of honey to be an artificial improvement. As the death of our hives of bees appears to be owning to their being keptso warm, as to require food when their stock is exhausted; a very observinggentleman at my request put two hives for many weeks into a dry cellar, andobserved, during all that time, they did not consume any of theirprovision, for their weight did not decrease as it had done when they werekept in the open air. The same observation is made in the Annual Registerfor 1768, p. 113. And the Rev. Mr. White, in his Method of preserving Bees, adds, that those on the north side of his house consumed less honey in thewinter than those on the south side. There is another observation on bees well ascertained, that they at varioustimes, when the season begins to be cold, by a general motion of their legsas they hang in clusters produce a degree of warmth, which is easilyperceptible by the hand. Hence by this ingenious exertion, they for a longtime prevent the torpid state they would naturally fall into. According to the late observations of Mr. Hunter, it appears that thebee's-wax is not made from the dust of the anthers of flowers, which theybring home on their thighs, but that this makes what is termed bee-bread, and is used for the purpose of feeding the bee-maggots; in the same mannerbutterflies live on honey, but the previous caterpillar lives on vegetableleaves, while the maggots of large flies require flesh for their food, andthose of the ichneumon fly require insects for their food. What induces thebee who lives on honey to lay up vegetable powder for its young? Whatinduces the butterfly to lay its eggs on leaves, when itself feeds onhoney? What induces the other flies to seek a food for their progenydifferent from what they consume themselves? If these are not deductionsfrom their own previous experience or observation, all the actions ofmankind must be resolved into instinct. 3. The dormouse consumes but little of its food during the rigour of theseason, for they roll themselves up, or sleep, or lie torpid the greatestpart of the time; but on warm sunny days experience a short revival, andtake a little food, and then relapse into their former state. " (PennantZoolog. P. 67. ) Other animals, that sleep in winter without laying up anyprovender, are observed to go into their winter beds fat and strong, butreturn to day-light in the spring season very lean and feeble. The commonflies sleep during the winter without any provision for their nourishment, and are daily revived by the warmth of the sun, or of our fires. Thesewhenever they see light endeavour to approach it, having observed, that byits greater vicinity they get free from the degree of torpor, that the coldproduces; and are hence induced perpetually to burn themselves in ourcandles: deceived, like mankind, by the misapplication of their knowledge. Whilst many of the subterraneous insects, as the common worms, seem toretreat so deep into the earth as not to be enlivened or awakened by thedifference of our winter days; and stop up their holes with leaves orstraws, to prevent the frosts from injuring them, or the centipes fromdevouring them. The habits of peace, or the stratagems of war, of thesesubterranean nations are covered from our view; but a friend of mineprevailed on a distressed worm to enter the hole of another worm on abowling-green, and he presently returned much wounded about his head. And Ionce saw a worm rise hastily out of the earth into the sunshine, andobserved a centipes hanging at its tail: the centipes nimbly quitted thetail, and seizing the worm about its middle cut it in half with itsforceps, and preyed upon one part, while the other escaped. Which evincesthey have design in stopping the mouths of their habitations. 4. The wasp of this country fixes his habitation under ground, that he maynot be affected with the various changes of our climate; but in Jamaica hehangs it on the bough of a tree, where the seasons are less severe. Heweaves a very curious paper of vegetable fibres to cover his nest, which isconstructed on the same principle with that of the bee, but with adifferent material; but as his prey consists of flesh, fruits, and insects, which are perishable commodities, he can lay up no provender for thewinter. M. De la Loubiere, in his relation of Siam, says, "That in a part of thatkingdom, which lies open to great inundations, all the ants make theirsettlements upon trees; no ants' nests are to be seen any where else. "Whereas in our country the ground is their only situation. From thescriptual account of these insects, one might be led to suspect, that insome climates they lay up a provision for the winter. Origen affirms thesame, (Cont. Cels. L. 4. ) But it is generally believed that in this countrythey do not, (Prov. Vi. 6. Xxx. 25. ) The white ants of the coast of Africamake themselves pyramids eight or ten feet high, on a base of about thesame width, with a smooth surface of rich clay, excessively hard and wellbuilt, which appear at a distance like an assemblage of the huts of thenegroes, (Adanson). The history of these has been lately well described inthe Philosoph. Transactions, under the name of termes, or termites. Thesediffer very much from the nest of our large ant; but the real history ofthis creature, as well as of the wasp, is yet very imperfectly known. Wasps are said to catch large spiders, and to cut off their legs, and carrytheir mutilated bodies to their young, Dict. Raison. Tom. I. P. 152. One circumstance I shall relate which fell under my own eye, and shewed thepower or reason in a wasp, as it is exercised among men. A wasp, on agravel walk, had caught a fly nearly as large as himself; kneeling on theground I observed him separate the tail and the head from the body part, towhich the wings were attached. He then took the body part in his paws, androse about two feet from the ground with it; but a gentle breeze waftingthe wings of the fly turned him round in the air, and he settled again withhis prey upon the gravel. I then distinctly observed him cut off with hismouth, first one of the wings, and then the other, after which he flew awaywith it unmolested by the wind. Go, thou sluggard, learn arts and industry from the bee, and from the ant! Go, proud reasoner, and call the worm thy sister! XVII. _Conclusion. _ It was before observed how much the superior accuracy of our sense of touchcontributes to increase our knowledge; but it is the greater energy andactivity of the power of volition (as explained in the former Sections ofthis work) that marks mankind, and has given him the empire of the world. There is a criterion by which we may distinguish our voluntary acts orthoughts from those that are excited by our sensations: "The former arealways employed about the _means_ to acquire pleasureable objects, or toavoid painful ones: while the latter are employed about the _possession_ ofthose that are already in our power. " If we turn our eyes upon the fabric of our fellow animals, we find they aresupported with bones, covered with skins, moved by muscles; that theypossess the same senses, acknowledge the same appetites, and are nourishedby the same aliment with ourselves; and we should hence conclude from thestrongest analogy, that their internal faculties were also in some measuresimilar to our own. Mr. Locke indeed published an opinion, that other animals possessed noabstract or general ideas, and thought this circumstance was the barrierbetween the brute and the human world. But these abstracted ideas have beensince demonstrated by Bishop Berkley, and allowed by Mr. Hume, to have noexistence in nature, not even in the mind of their inventor, and we arehence necessitated to look for some other mark of distinction. The ideas and actions of brutes, like those of children, are almostperpetually produced by their present pleasures, or their present pains;and, except in the few instances that have been mentioned in this Section, they seldom busy themselves about the _means_ of procuring future bliss, orof avoiding future misery. Whilst the acquiring of languages, the making of tools, and the labouringfor money; which are all only the _means_ of procuring pleasure; and thepraying to the Deity, as another _means_ to procure happiness, arecharacteristic of human nature. * * * * * SECT. XVII. THE CATENATION OF MOTIONS. I. 1. _Catenations of animal motion. _ 2. _Are produced by irritations, by sensations, by volitions. _ 3. _They continue some time after they have been excited. Cause of catenation. _ 4. _We can then exert our attention on other objects. _ 5. _Many catenations of motions go on together. _ 6. _Some links of the catenations of motions may be left out without disuniting the chain. _ 7. _Interrupted circles of motion continue confusedly till they come to the part of the circle, where they were disturbed. _ 8. _Weaker catenations are dissevered by stronger. _ 9. _Then new catenations take place. _ 10. _Much effort prevents their reuniting. Impediment of speech. _ 11. _Trains more easily dissevered than circles. _ 12. _Sleep destroys volition and external stimulus. _ II. _Instances of various catenations in a young lady playing on the harpsichord. _ III. 1. _What catenations are the strongest. _ 2. _Irritations joined with associations from strongest connexions. Vital motions. _ 3. _New links with increased force, cold fits of fever produced. _ 4. _New links with decreased force. Cold bath. _ 5. _Irritation joined with sensation. Inflammatory fever. Why children cannot tickle themselves. 6. Volition joined with sensation. Irritative ideas of sound become sensible. _ 7. _Ideas of imagination, dissevered by irritations, by volition, production of surprise. _ I. 1. To investigate with precision the catenations of animal motions, itwould be well to attend to the manner of their production; but we cannotbegin this disquisition early enough for this purpose, as the catenationsof motion seem to begin with life, and are only extinguishable with it; Wehave spoken of the power of irritation, of sensation, of volition, and ofassociation, as preceding the fibrous motions; we now step forwards, andconsider, that conversely they are in their turn preceded by those motions;and that all the successive trains or circles of our actions are composedof this twofold concatenation. Those we shall call trains of action, whichcontinue to proceed without any stated repetitions; and those circles ofaction, when the parts of them return at certain periods, though thetrains, of which they consist, are not exactly similar. The reading an epicpoem is a train of actions; the reading a song with a chorus at equaldistances in the measure constitutes so many circles of action. 2. Some catenations of animal motion are produced by reiterated successiveirritations, as when we learn to repeat the alphabet in its order byfrequently reading the letters of it. Thus the vermicular motions of thebowels were originally produced by the successive irritations of thepassing aliment; and the succession of actions of the auricles andventricles of the heart was originally formed by successive stimulus of theblood, these afterwards become part of the diurnal circles of animalactions, as appears by the periodical returns of hunger, and the quickenedpulse of weak people in the evening. Other catenations of animal motion are gradually acquired by successiveagreeable sensations, as in learning a favourite song or dance; others bydisagreeable sensations, as in coughing or nictitation; these becomeassociated by frequent repetition, and afterwards compose parts of greatercircles of action like those above mentioned. Other catenations of motions are gradually acquired by frequent voluntaryrepetitions; as when we deliberately learn to march, read, fence, or anymechanic art, the motions of many of our muscles become gradually linkedtogether in trains, tribes, or circles of action. Thus when any one atfirst begins to use the tools in turning wood or metals in a lathe, hewills the motions of his hand or fingers, till at length these actionsbecome so connected with the effect, that he seems only to will the pointof the chisel. These are caused by volition, connected by association likethose above described, and afterwards become parts of our diurnal trains orcircles of action. 3. All these catenations of animal motions, are liable to proceed some timeafter they are excited, unless they are disturbed or impeded by otherirritations, sensations, or volitions; and in many instances in spite ofour endeavours to stop them; and this property of animal motions isprobably the cause of their catenation. Thus when a child revolves someminute on one foot, the spectra of the ambient objects appear to circulateround him some time after he falls upon the ground. Thus the palpitation ofthe heart continues some time after the object of fear, which occasionedit, is removed. The blush of shame, which is an excess of sensation, andthe glow of anger, which is an excess of volition, continue some time, though the affected person finds, that those emotions were caused bymistaken facts, and endeavours to extinguish their appearance. See Sect. XII. 1. 5. 4. When a circle of motions becomes connected, by frequent repetitions asabove, we can exert our attention strongly on other objects, and theconcatenated circle of motions will nevertheless proceed in due order; aswhilst you are thinking on this subject, you use variety of muscles inwalking about your parlour, or in sitting at your writing-table. 5. Innumerable catenations of motions may proceed at the same time, withoutincommoding each other. Of these are the motions of the heart and arteries;those of digestion and glandular secretion; of the ideas, or sensualmotions; those of progression, and of speaking; the great annual circle ofactions so apparent in birds in their times of breeding and moulting; themonthly circles of many female animals; and the diurnal circles of sleepingand waking, of fulness and inanition. 6. Some links of successive trains or of synchronous tribes of action maybe left out without disjoining the whole. Such are our usual trains ofrecollection; after having travelled through an entertaining country, andviewed many delightful lawns, rolling rivers, and echoing rocks; in therecollection of our journey we leave out the many districts, that wecrossed, which were marked with no peculiar pleasure. Such also are ourcomplex ideas, they are catenated tribes of ideas, which do not perfectlyresemble their correspondent perceptions, because some of the parts areomitted. 7. If an interrupted circle of actions is not entirely dissevered, it willcontinue to proceed confusedly, till it comes to the part of the circle, where it was interrupted. The vital motions in a fever from drunkenness, and in other periodicaldiseases, are instances of this circumstance. The accidental inebriate doesnot recover himself perfectly till about the same hour on the succeedingday. The accustomed drunkard is disordered, if he has not his usualpotation of fermented liquor. So if a considerable part of a connectedtribe of action be disturbed, that whole tribe goes on with confusion, tillthe part of the tribe affected regains its accustomed catenations. Sovertigo produces vomiting, and a great secretion of bile, as insea-sickness, all these being parts of the tribe of irritative catenations. 8. Weaker catenated trains may be dissevered by the sudden exertion of thestronger. When a child first attempts to walk across a room, call to him, and he instantly falls upon the ground. So while I am thinking over thevirtues of my friends, if the tea-kettle spurt out some hot water on mystocking; the sudden pain breaks the weaker chain of ideas, and introducesa new group of figures of its own. This circumstance is extended to someunnatural trains of action, which have not been confirmed by long habit; asthe hiccough, or an ague-fit, which are frequently curable by surprise. Ayoung lady about eleven years old had for five days had a contraction ofone muscle in her fore arm, and another in her arm, which occurred four orfive times every minute; the muscles were seen to leap, but without bendingthe arm. To counteract this new morbid habit, an issue was placed over theconvulsed muscle of her arm, and an adhesive plaster wrapped tight like abandage over the whole fore arm, by which the new motions were immediatelydestroyed, but the means were continued some weeks to prevent a return. 9. If any circle of actions is dissevered, either by omission of some ofthe links, as in sleep, or by insertion of other links, as in surprise, newcatenations take place in a greater or less degree. The last link of thebroken chain of actions becomes connected with the new motion which hasbroken it, or with that which was nearest the link omitted; and these newcatenations proceed instead of the old ones. Hence the periodic returns ofague-fits, and the chimeras of our dreams. 10. If a train of actions is dissevered, much effort of volition orsensation will prevent its being restored. Thus in the common impediment ofspeech, when the association of the motions of the muscles of enunciationwith the idea of the word to be spoken is disordered, the great voluntaryefforts, which distort the countenance, prevent the rejoining of the brokenassociations. See No. II. 10. Of this Section. It is thus likewiseobservable in some inflammations of the bowels, the too strong efforts madeby the muscles to carry forwards the offending material fixes it morefirmly in its place, and prevents the cure. So in endeavouring to recal toour memory some particular word of a sentence, if we exert ourselves toostrongly about it, we are less likely to regain it. 11. Catenated trains or tribes of action are easier dissevered thancatenated circles of action. Hence in epileptic fits the synchronousconnected tribes of action, which keep the body erect, are dissevered, butthe circle of vital motions continues undisturbed. 12. Sleep destroys the power of volition, and precludes the stimuli ofexternal objects, and thence dissevers the trains, of which these are apart; which confirms the other catenations, as those of the vital motions, secretions, and absorptions; and produces the new trains of ideas, whichconstitute our dreams. II. 1. All the preceding circumstances of the catenations of animal motionswill be more clearly understood by the following example of a personlearning music; and when we recollect the variety of mechanic arts, whichare performed by associated trains of muscular actions catenated with theeffects they produce, as in knitting, netting, weaving; and the greatervariety of associated trains of ideas caused or catenated by volitions orsensations, as in our hourly modes of reasoning, or imagining, orrecollecting, we shall gain some idea of the innumerable catenated trainsand circles of action, which form the tenor of our lives, and which began, and will only cease entirely with them. 2. When a young lady begins to learn music, she voluntarily applies herselfto the characters of her music-book, and by many repetitions endeavours tocatenate them with the proportions of sound, of which they are symbols. Theideas excited by the musical characters are slowly connected with the keysof the harpsichord, and much effort is necessary to produce every note withthe proper finger, and in its due place and time; till at length a train ofvoluntary exertions becomes catenated with certain irritations. As thevarious notes by frequent repetitions become connected in the order, inwhich they are produced, a new catenation of sensitive exertions becomesmixed with the voluntary ones above described; and not only the musicalsymbols of crotchets and quavers, but the auditory notes and tones at thesame time, become so many successive or synchronous links in this circle ofcatenated actions. At length the motions of her fingers become catenated with the musicalcharacters; and these no sooner strike the eye, than the finger pressesdown the key without any voluntary attention between them; the activity ofthe hand being connected with the irritation of the figure or place of themusical symbol on the retina; till at length by frequent repetitions of thesame tune the movements of her fingers in playing, and the muscles of thelarynx in singing, become associated with each other, and form part ofthose intricate trains and circles of catenated motions, according with thesecond article of the preceding propositions in No. 1. Of this Section. 3. Besides the facility, which by habit attends the execution of thismusical performance, a curious circumstance occurs, which is, that when ouryoung musician has began a tune, she finds herself inclined to continue it;and that even when she is carelessly singing alone without attending to herown song; according with the third preceding article. 4. At the same time that our young performer continues to play with greatexactness this accustomed tune, she can bend her mind, and that intensely, on some other object, according with the fourth article of the precedingproportions. The manuscript copy of this work was lent to many of my friends atdifferent times for the purpose of gaining their opinions and criticisms onmany parts of it, and I found the following anecdote written with a pencilopposite to this page, but am not certain by whom. "I remember seeing thepretty young actress, who succeeded Mrs. Arne in the performance of thecelebrated Padlock, rehearse the musical parts at her harpsichord under theeye of her master with great taste and accuracy; though I observed hercountenance full of emotion, which I could not account for; at last shesuddenly burst into tears; for she had all this time been eyeing a belovedcanary bird, suffering great agonies, which at that instant fell dead fromits perch. " 5. At the same time many other catenated circles of action are going on inthe person of our fair musician, as well as the motions of her fingers, such as the vital motions, respiration, the movements of her eyes andeyelids, and of the intricate muscles of vocality, according with the fifthpreceding article. 6. If by any strong impression on the mind of our fair musician she shouldbe interrupted for a very inconsiderable time, she can still continue herperformance, according to the sixth article. 7. If however this interruption be greater, though the chain of actions benot dissevered, it proceeds confusedly, and our young performer continuesindeed to play, but in a hurry without accuracy and elegance, till shebegins the tune again, according to the seventh of the preceding articles. 8. But if this interruption be still greater, the circle of actions becomesentirely dissevered, and she finds herself immediately under the necessityto begin over again to recover the lost catenation, according to the eighthpreceding article. 9. Or in trying to recover it she will sing some dissonant notes, or strikesome improper keys, according to the ninth preceding article. 10. A very remarkable thing attends this breach of catenation, if theperformer has forgotten some word of her song, the more energy of mind sheuses about it, the more distant is she from regaining it; and artfullyemploys her mind in part on some other object, or endeavours to dull itsperceptions, continuing to repeat, as it were inconsciously, the formerpart of the song, that she remembers, in hopes to regain the lostconnexion. For if the activity of the mind itself be more energetic, or takes itsattention more, than the connecting word, which is wanted; it will notperceive the slighter link of this lost word; as who listens to a feeblesound, must be very silent and motionless; so that in this case the veryvigour of the mind itself seems to prevent it from regaining the lostcatenation, as well as the too great exertion in endeavouring to regain it, according to the tenth preceding article. We frequently experience, when we are doubtful about the spelling of aword, that the greater voluntary exertion we use, that is the moreintensely we think about it, the further are we from regaining the lostassociation between the letters of it, but which readily recurs when wehave become careless about it. In the same manner, after having for an hourlaboured to recollect the name of some absent person, it shall seem, particularly after sleep, to come into the mind as it were spontaneously;that is the word we are in search of, was joined to the preceding one byassociation; this association being dissevered, we endeavour to recover itby volition; this very action of the mind strikes our attention more, thanthe faint link of association, and we find it impossible by this means toretrieve the lost word. After sleep, when volition is entirely suspended, the mind becomes capable of perceiving the fainter link of association, andthe word is regained. On this circumstance depends the impediment of speech before mentioned; thefirst syllable of a word is causable by volition, but the remainder of itis in common conversation introduced by its associations with this firstsyllable acquired by long habit. Hence when the mind of the stammerer isvehemently employed on some idea of ambition of shining, or fear of notsucceeding, the associations of the motions of the muscles of articulationwith each other become dissevered by this greater exertion, and heendeavours in vain by voluntary efforts to rejoin the broken association. For this purpose he continues to repeat the first syllable, which iscausable by volition, and strives in vain, by various distortions ofcountenance, to produce the next links, which are subject to association. See Class IV. 3. 1. 1. 11. After our accomplished musician has acquired great variety of tunes andsongs, so that some of them begin to cease to be easily recollected, shefinds progressive trains of musical notes more frequently forgotten, thanthose which are composed of reiterated circles, according with the eleventhpreceding article. 12. To finish our example with the preceding articles we must at lengthsuppose, that our fair performer falls asleep over her harpsichord; andthus by the suspension of volition, and the exclusion of external stimuli, she dissevers the trains and circles of her musical exertions. III. 1. Many of these circumstances of catenations of motions receive aneasy explanation from the four following consequences to the seventh law ofanimal causation in Sect. IV. These are, first, that those successions orcombinations of animal motions, whether they were united by causation, association, or catenation, which have been most frequently repeated, acquire the strongest connection. Secondly, that of these, those, whichhave been less frequently mixed with other trains or tribes of motion, havethe strongest connection. Thirdly, that of these, those, which were firstformed, have the strongest connection. Fourthly, that if an animal motionbe excited by more than one causation, association, or catenation, at thesame time, it will be performed with greater energy. 2. Hence also we understand, why the catenations of irritative motions aremore strongly connected than those of the other classes, where the quantityof unmixed repetition has been equal; because they were first formed. Suchare those of the secerning and absorbent systems of vessels, where theaction of the gland produces a fluid, which stimulates the mouths of itscorrespondent absorbents. The associated motions seem to be the next moststrongly united, from their frequent repetition; and where both thesecircumstances unite, as in the vital motions, their catenations areindissoluble but by the destruction of the animal. 3. Where a new link has been introduced into a circle of actions by someaccidental defect of stimulus; if that defect of stimulus be repeated atthe same part of the circle a second or a third time, the defective motionsthus produced, both by the repeated defect of stimulus and by theircatenation with the parts of the circle of actions, will be performed withless and less energy. Thus if any person is exposed to cold at a certainhour to-day, so long as to render some part of the system for a timetorpid; and is again exposed to it at the same hour to-morrow, and the nextday; he will be more and more affected by it, till at length a cold fit offever is completely formed, as happens at the beginning of many of thosefevers, which are called nervous or low fevers. Where the patient hasslight periodical shiverings and paleness for many days before the febrileparoxysm is completely formed. 4. On the contrary, if the exposure to cold be for so short a time, as notto induce any considerable degree of torpor or quiescence, and is repeateddaily as above mentioned, it loses its effect more and more at everyrepetition, till the constitution can bear it without inconvenience, orindeed without being conscious of it. As in walking into the cold air infrosty weather. The same rule is applicable to increased stimulus, as ofheat, or of vinous spirit, within certain limits, as is applied in the twolast paragraphs to Deficient Stimulus; as is further explained in Sect. XXXVI. On the Periods of Diseases. 5. Where irritation coincides with sensation to produce the samecatenations of motion, as in inflammatory fevers, they are excited withstill greater energy than by the irritation alone. So when children expectto be tickled in play, by a feather lightly passed over the lips, or bygently vellicating the soles of their feet, laughter is most vehementlyexcited; though they can stimulate these parts with their own fingersunmoved. Here the pleasureable idea of playfulness coincides with thevellication; and there is no voluntary exertion used to diminish thesensation, as there would be, if a child should endeavour to ticklehimself. See Sect. XXXIV. 1. 4. 6. And lastly, the motions excited by the junction of voluntary exertionwith irritation are performed with more energy, than those by irritationsingly; as when we listen to small noises, as to the ticking of a watch inthe night, we perceive the most weak sounds, that are at other timesunheeded. So when we attend to the irritative ideas of sound in our ears, which are generally not attended to, we can hear them; and can see thespectra of objects, which remain in the eye, whenever we please to exertour voluntary power in aid of those weak actions of the retina, or of theauditory nerve. 7. The temporary catenations of ideas, which are caused by the sensationsof pleasure or pain, are easily dissevered either by irritations, as when asudden noise disturbs a day-dream; or by the power of volition, as when weawake from sleep. Hence in our waking hours, whenever an idea occurs, whichis incongruous to our former experience, we instantly dissever the train ofimagination by the power of volition, and compare the incongruous idea withour previous knowledge of nature, and reject it. This operation of the mindhas not yet acquired a specific name, though it is exerted every minute ofour waking hours; unless it may be termed INTUITIVE ANALOGY. It is an actof reasoning of which we are unconscious except from its effects inpreserving the congruity of our ideas, and bears the same relation to thesensorial power of volition, that irritative ideas, of which we areinconscious except by their effects, do to the sensorial power ofirritation; as the former is produced by volition without our attention toit, and the latter by irritation without our attention to them. If on the other hand a train of imagination or of voluntary ideas areexcited with great energy, and passing on with great vivacity, and becomedissevered by some violent stimulus, as the discharge of a pistol nearone's ear, another circumstance takes place, which is termed SURPRISE;which by exciting violent irritation, and violent sensation, employs for atime the whole sensorial energy, and thus dissevers the passing trains ofideas, before the power of volition has time to compare them with the usualphenomena of nature. In this case fear is generally the companion ofsurprise, and adds to our embarrassment, as every one experiences in somedegree when he hears a noise in the dark, which he cannot instantly accountfor. This catenation of fear with surprise is owing to our perpetualexperience of injuries from external bodies in motion, unless we are uponour guard against them. See Sect. XVIII. 17. XIX. 2. Many other examples of the catenations of animal motions are explained inSect. XXXVI. On the Periods of Diseases. * * * * * SECT. XVIII. OF SLEEP. 1. _Volition is suspended in sleep. _ 2. _Sensation continues. Dreams prevent delirium and inflammation. _ 3. _Nightmare. _ 4. _Ceaseless flow of ideas in dreams. _ 5. _We seem to receive them by the senses. Optic nerve perfectly sensible in sleep. Eyes less dazzled after dreaming of visible objects. _ 6. _Reverie, belief. _ 7. _How we distinguish ideas from perceptions. _ 8. _Variety of scenery in dreams, excellence of the sense of vision. _ 9. _Novelty of combination in dreams. _ 10. _Distinctness of imagery in dreams. _ 11. _Rapidity of transaction in dreams. _ 12. _Of measuring time. Of dramatic time and place. Why a dull play induces sleep, and an interesting one reverie. _ 13. _Consciousness of our existence and identity in dreams. _ 14. _How we awake sometimes suddenly, sometimes frequently. _ 15. _Irritative motions continue in sleep, internal irritations are succeeded by sensation. Sensibility increases during sleep, and irritability. Morning dreams. Why epilepsies occur in sleep. Ecstacy of children. Case of convulsions in sleep. Cramp, why painful. Asthma. Morning sweats. Increase of heat. Increase of urine in sleep. Why more liable to take cold in sleep. Catarrh from thin night-caps. Why we feel chilly at the approach of sleep, and at waking in the open air. _ 16. _Why the gout commences in sleep. Secretions are more copious in sleep, young animals and plants grow more in sleep. _ 17. _Inconsistency of dreams. Absence of surprise in dreams. _ 18. _Why we forget some dreams and not others. _ 19. _Sleep-talkers awake with surprise. _ 20. _Remote causes of sleep. Atmosphere with less oxygene. Compression of the brain in spina bifida. By whirling on an horizontal wheel. By cold. _ 21. _Definition of sleep. _ 1. There are four situations of our system, which in their moderate degreesare not usually termed diseases, and yet abound with many very curious andinstructive phenomena; these are sleep, reverie, vertigo, drunkenness. These we shall previously consider, before we step forwards to develop thecauses and cures of diseases with the modes of the operation of medicines. As all those trains and tribes of animal motion, which are subjected tovolition, were the last that were caused, their connection is weaker thanthat of the other classes; and there is a peculiar circumstance attendingthis causation, which is, that it is entirely suspended during sleep;whilst the other classes of motion, which are more immediately necessary tolife, as those caused by internal stimuli, for instance the pulsations ofthe heart and arteries, or those catenated with pleasurable sensation, asthe powers of digestion, continue to strengthen their habits withoutinterruption. Thus though man in his sleeping state is a much less perfectanimal, than in his waking hours; and though he consumes more than onethird of his life in this his irrational situation; yet is the wisdom ofthe Author of nature manifest even in this seeming imperfection of hiswork! The truth of this assertion with respect to the large muscles of the body, which are concerned in locomotion, is evident; as no one in perfect sanitywalks about in his sleep, or performs any domestic offices: and in respectto the mind, we never exercise our reason or recollection in dreams; we maysometimes seem distracted between contending passions, but we never comparetheir objects, or deliberate about the acquisition of those objects, if oursleep is perfect. And though many synchronous tribes or successive trainsof ideas may represent the houses or walks, which have real existence, yetare they here introduced by their connection with our sensations, and arein truth ideas of imagination, not of recollection. 2. For our sensations of pleasure and pain are experienced with greatvivacity in our dreams; and hence all that motley group of ideas, which arecaused by them, called the ideas of imagination, with their variousassociated trains, are in a very vivid manner acted over in the sensorium;and these sometimes call into action the larger muscles, which have beenmuch associated with them; as appears from the muttering sentences, whichsome people utter in their dreams, and from the obscure barking of sleepingdogs, and the motions of their feet and nostrils. This perpetual flow of the trains of ideas, which constitute our dreams, and which are caused by painful or pleasurable sensation, might at firstview be conceived to be an useless expenditure of sensorial power. But ithas been shewn, that those motions, which are perpetually excited, as thoseof the arterial system by the stimulus of the blood, are attended by agreat accumulation of sensorial power, after they have been for a timesuspended; as the hot-fit of fever is the consequence of the cold one. Nowas these trains of ideas caused by sensation are perpetually excited duringour waking hours, if they were to be suspended in sleep like the voluntarymotions, (which are exerted only by intervals during our waking hours, ) anaccumulation of sensorial power would follow; and on our awaking a deliriumwould supervene, since these ideas caused by sensation would be producedwith such energy, that we should mistake the trains of imagination forideas excited by irritation; as perpetually happens to people debilitatedby fevers on their first awaking; for in these fevers with debility thegeneral quantity of irritation being diminished, that of sensation isincreased. In like manner if the actions of the stomach, intestines, andvarious glands, which are perhaps in part at least caused by or catenatedwith agreeable sensation, and which perpetually exist during our wakinghours, were like the voluntary motions suspended in our sleep; the greataccumulation of sensorial power, which would necessarily follow, would beliable to excite inflammation in them. 3. When by our continued posture in sleep, some uneasy sensations areproduced, we either gradually awake by the exertion of volition, or themuscles connected by habit with such sensations alter the position of thebody; but where the sleep is uncommonly profound, and those uneasysensations great, the disease called the incubus, or nightmare, isproduced. Here the desire of moving the body is painfully exerted, by thepower of moving it, or volition, is incapable of action, till we awake. Many less disagreeable struggles in our dreams, as when we wish in vain tofly from terrifying objects, constitute a slighter degree of this disease. In awaking from the nightmare I have more than once observed, that therewas no disorder in my pulse; nor do I believe the respiration is laborious, as some have affirmed. It occurs to people whose sleep is too profound, andsome disagreeable sensation exists, which at other times would haveawakened them, and have thence prevented the disease of nightmare; as aftergreat fatigue or hunger with too large a supper and wine, which occasionour sleep to be uncommonly profound. See No. 14, of this Section. 4. As the larger muscles of the body are much more frequently excited byvolition than by sensation, they are but seldom brought into action in oursleep: but the ideas of the mind are by habit much more frequentlyconnected with sensation than with volition; and hence the ceaseless flowof our ideas in dreams. Every one's experience will teach him this truth, for we all daily exert much voluntary muscular motion: but few of mankindcan bear the fatigue of much voluntary thinking. 5. A very curious circumstance attending these our sleeping imaginationsis, that we seem to receive them by the senses. The muscles, which aresubservient to the external organs of sense, are connected with volition, and cease to act in sleep; hence the eyelids are closed, and the tympanumof the ear relaxed; and it is probable a similarity of voluntary exertionmay be necessary for the perceptions of the other nerves of sense; for itis observed that the papillæ of the tongue can be seen to become erected, when we attempt to taste any thing extremely grateful. Hewson Exper. Enquir. V. 2. 186. Albini Annot. Acad. L. I. C. 15. Add to this, that theimmediate organs of sense have no objects to excite them in the darknessand silence of the night, but their nerves of sense nevertheless continueto possess their perfect activity subservient to all their numeroussensitive connections. This vivacity of our nerves of sense during the timeof sleep is evinced by a circumstance, which almost every one must at sometime or other have experienced; that is, if we sleep in the daylight, andendeavour to see some object in our dream, the light is exceedingly painfulto our eyes; and after repeated struggles we lament in our sleep, that wecannot see it. In this case I apprehend the eyelid is in some degree openedby the vehemence of our sensations; and, the iris being dilated, the opticnerve shews as great or greater sensibility than in our waking hours. SeeNo. 15. Of this Section. When we are forcibly waked at midnight from profound sleep, our eyes aremuch dazzled with the light of the candle for a minute or two, after therehas been sufficient time allowed for the contraction of the iris; which isowing to the accumulation of sensorial power in the organ of vision duringits state of less activity. But when we have dreamt much of visibleobjects, this accumulation of sensorial power in the organ of vision islessened or prevented, and we awake in the morning without being dazzledwith the light, after the iris has had time to contract itself. This is amatter of great curiosity, and may be thus tried by any one in theday-light. Close your eyes, and cover them with your hat; think for aminute on a tune, which you are accustomed to, and endeavour to sing itwith as little activity of mind as possible. Suddenly uncover and open youreyes, and in one second of time the iris will contract itself, but you willperceive the day more luminous for several seconds, owing to theaccumulation of sensorial power in the optic nerve. Then again close and cover your eyes, and think intensely on a cube ofivory two inches diameter, attending first to the north and south sides ofit, and then to the other four sides of it; then get a clear image in yourmind's eye of all the sides of the same cube coloured red; and then of itcoloured green; and then of it coloured blue; lastly, open your eyes as inthe former experiment, and after the first second of time allowed for thecontraction of the iris, you will not perceive any increase of the light ofthe day, or dazzling; because now there is no accumulation of sensorialpower in the optic nerve; that having been expended by its action inthinking over visible objects. This experiment is not easy to be made at first, but by a few patienttrials the fact appears very certain; and shews clearly, that our ideas ofimagination are repetitions of the motions of the nerve, which wereoriginally occasioned by the stimulus of external bodies; because theyequally expend the sensorial power in the organ of sense. See Sect. III. 4. Which is analogous to our being as much fatigued by thinking as by labour. 6. Nor is it in our dreams alone, but even in our waking reveries, and ingreat efforts of invention, so great is the vivacity of our ideas, that wedo not for a time distinguish them from the real presence of substantialobjects; though the external organs of sense are open, and surrounded withtheir usual stimuli. Thus whilst I am thinking over the beautiful valley, through which I yesterday travelled, I do not perceive the furniture of myroom: and there are some, whose waking imaginations are so apt to run intoperfect reverie, that in their common attention to a favourite idea they donot hear the voice of the companion, who accosts them, unless it isrepeated with unusual energy. This perpetual mistake in dreams and reveries, where our ideas ofimagination are attended with a belief of the presence of external objects, evinces beyond a doubt, that all our ideas are repetitions of the motionsof the nerves of sense, by which they were acquired; and that this beliefis not, as some late philosophers contend, an instinct necessarilyconnected only with our perceptions. 7. A curious question demands our attention in this place; as we do notdistinguish in our dreams and reveries between our perceptions of externalobjects, and our ideas of them in their absence, how do we distinguish themat any time? In a dream, if the sweetness of sugar occurs to myimagination, the whiteness and hardness of it, which were ideas usuallyconnected with the sweetness, immediately follow in the train; and Ibelieve a material lump of sugar present before my senses: but in my wakinghours, if the sweetness occurs to my imagination, the stimulus of the tableto my hand, or of the window to my eye, prevents the other ideas of thehardness and whiteness of the sugar from succeeding; and hence I perceivethe fallacy, and disbelieve the existence of objects correspondent to thoseideas, whose tribes or trains are broken by the stimulus of other objects. And further in our waking hours, we frequently exert our volition incomparing present appearances with such, as we have usually observed; andthus correct the errors of one sense by our general knowledge of nature byintuitive analogy. See Sect. XVII. 3. 7. Whereas in dreams the power ofvolition is suspended, we can recollect and compare our present ideas withnone of our acquired knowledge, and are hence incapable of observing anyabsurdities in them. By this criterion we distinguish our waking from our sleeping hours, we canvoluntarily recollect our sleeping ideas, when we are awake, and comparethem with our waking ones; but we cannot in our sleep _voluntarily_recollect our waking ideas at all. 8. The vast variety of scenery, novelty of combination, and distinctness ofimagery, are other curious circumstances of our sleeping imaginations. Thevariety of scenery seems to arise from the superior activity and excellenceof our sense of vision; which in an instant unfolds to the mind extensivefields of pleasurable ideas; while the other senses collect their objectsslowly, and with little combination; add to this, that the ideas, whichthis organ presents us with, are more frequently connected with oursensation than those of any other. 9. The great novelty of combination is owing to another circumstance; thetrains of ideas, which are carried on in our waking thoughts, are in ourdreams dissevered in a thousand places by the suspension of volition, andthe absence of irritative ideas, and are hence perpetually falling into newcatenations. As explained in Sect. XVII. 1. 9. For the power of volition isperpetually exerted during our waking hours in comparing our passing trainsof ideas with our acquired knowledge of nature, and thus forms manyintermediate links in their catenation. And the irritative ideas excited bythe stimulus of the objects, with which we are surrounded, are every momentintruded upon us, and form other links of our unceasing catenations ofideas. 10. The absence of the stimuli of external bodies, and of volition, in ourdreams renders the organs of sense liable to be more strongly affected bythe powers of sensation, and of association. For our desires or aversions, or the obtrusions of surrounding bodies, dissever the sensitive andassociate tribes of ideas in our waking hours by introducing those ofirritation and volition amongst them. Hence proceeds the superiordistinctness of pleasurable or painful imagery in our sleep; for we recalthe figure and the features of a long lost friend, whom we loved, in ourdreams with much more accuracy and vivacity than in our waking thoughts. This circumstance contributes to prove, that our ideas of imagination arereiterations of those motions of our organs of sense, which were excited byexternal objects; because while we are exposed to the stimuli of presentobjects, our ideas of absent objects cannot be so distinctly formed. 11. The rapidity of the succession of transactions in our dreams is almostinconceivable; insomuch that, when we are accidentally awakened by thejarring of a door, which is opened into our bed-chamber, we sometimes dreama whole history of thieves or fire in the very instant of awaking. During the suspension of volition we cannot compare our other ideas withthose of the parts of time in which they exist; that is, we cannot comparethe imaginary scene, which is before us, with those changes of it, whichprecede or follow it: because this act of comparing requires recollectionor voluntary exertion. Whereas in our waking hours, we are perpetuallymaking this comparison, and by that means our waking ideas are keptconfident with each other by intuitive analogy; but this companion retardsthe succession of them, by occasioning their repetition. Add to this, thatthe transactions of our dreams consist chiefly of visible ideas, and that awhole history of thieves and fire may be _beheld_ in an instant of timelike the figures in a picture. 12. From this incapacity of attending to the parts of time in our dreams, arises our ignorance of the length of the night; which, but from ourconstant experience to the contrary, we should conclude was but a fewminutes, when our sleep is perfect. The same happens in our reveries; thuswhen we are possessed with vehement joy, grief, or anger, time appearsshort, for we exert no volition to compare the present scenery with thepast or future; but when we are compelled to perform those exercises ofmind or body, which, are unmixed with passion, as in travelling over adreary country, time appears long; for our desire to finish our journeyoccasions us more frequently to compare our present situation with theparts of time or place, which are before and behind us. So when we are enveloped in deep contemplation of any kind, or in reverie, as in reading a very interesting play or romance, we measure time veryinaccurately; and hence, if a play greatly affects our passions, theabsurdities of passing over many days or years, and or perpetual changes ofplace, are not perceived by the audience; as is experienced by every one, who reads or sees some plays of the immortal Shakespear; but it isnecessary for inferior authors to observe those rules of the [Greek:pithanon] and [Greek: prepon] inculcated by Aristotle, because their worksdo not interest the passions sufficiently to produce complete reverie. Those works, however, whether a romance or a sermon, which do not interestus so much as to induce reverie, may nevertheless incline us to sleep. Forthose pleasurable ideas, which are presented to us, and are too gentle toexcite laughter, (which is attended with interrupted voluntary exertions, as explained Sect. XXXIV. 1. 4. ) and which are not accompanied with anyother emotion, which usually excites some voluntary exertion, as anger, orfear, are liable to produce sleep; which consists in a suspension of allvoluntary power. But if the ideas thus presented to us, and interest ourattention, are accompanied with so much pleasurable or painful sensation asto excite our voluntary exertion at the same time, reverie is theconsequence. Hence an interesting play produces reverie, a tedious oneproduces sleep: in the latter we become exhausted by attention, and are notexcited to any voluntary exertion, and therefore sleep; in the former weare excited by some emotion, which prevents by its pain the suspension ofvolition, and in as much as it interests us, induces reverie, as explainedin the next Section. But when our sleep is imperfect, as when we have determined to rise in halfan hour, time appears longer to us than in most other situations. Here oursolicitude not to oversleep the determined time induces us in thisimperfect sleep to compare the quick changes of imagined scenery with theparts of time or place, they would have taken up, had they real exigence;and that more frequently than in our waking hours; and hence the timeappears longer to us: and I make no doubt, but the permitted time appearslong to a man going to the gallows, as the fear of its quick lapse willmake him think frequently about it. 13. As we gain our knowledge of time by comparing the present scenery withthe past and future, and of place by comparing the situations of objectswith each other; so we gain our idea of consciousness by comparingourselves with the scenery around us; and of identity by comparing ourpresent consciousness with our past consciousness: as we never think oftime or place, but when we make the companions above mentioned, so we neverthink of consciousness, but when we compare our own existence with that ofother objects; nor of identity, but when we compare our present and ourpast consciousness. Hence the consciousness of our own existence, and ofour identity, is owing to a voluntary exertion of our minds: and on thataccount in our complete dreams we neither measure time, are surprised atthe sudden changes of place, nor attend to our own existence, or identity;because our power of volition is suspended. But all these circumstances aremore or less observable in our incomplete ones; for then we attend a littleto the lapse of time, and the changes of place, and to our own existence;and even to our identity of person; for a lady seldom dreams, that she is asoldier; nor a man, that he is brought to bed. 14. As long as our sensations only excite their sensual motions, or ideas, our sleep continues sound; but as soon as they excite desires or aversions, our sleep becomes imperfect; and when that desire or aversion is so strong, as to produce voluntary motions, we begin to awake; the larger muscles ofthe body are brought into action to remove that irritation or sensation, which a continued posture has caused; we stretch our limbs, and yawn, andour sleep is thus broken by the accumulation of voluntary power. Sometimes it happens, that the act of waking is suddenly produced, and thissoon after the commencement of sleep; which is occasioned by some sensationso disagreeable, as instantaneously to excite the power of volition; and atemporary action of all the voluntary motions suddenly succeeds, and westart awake. This is sometimes accompanied with loud noise in the ears, andwith some degree of fear; and when it is in great excess, so as to producecontinued convulsive motions of those muscles, which are generallysubservient to volition, it becomes epilepsy: the fits of which in somepatients generally commence during sleep. This differs from the night-maredescribed in No. 3. Of this Section, because in that the disagreeablesensation is not so great as to excite the power of volition into action;for as soon as that happens, the disease ceases. Another circumstance, which sometimes awakes people soon after thecommencement of their sleep, is where the voluntary power is already sogreat in quantity as almost to prevent them from falling asleep, and then alittle accumulation of it soon again awakens them; this happens in cases ofinsanity, or where the mind has been lately much agitated by fear or anger. There is another circumstance in which sleep is likewise of short duration, which arises from great debility, as after great over-fatigue, and in somefevers, where the strength of the patient is greatly diminished, as inthese cases the pulse intermits or flutters, and the respiration ispreviously affected, it seems to originate from the want of some voluntaryefforts to facilitate respiration, as when we are awake. And is furthertreated of in Vol. II. Class I. 2. 1. 2. On the Diseases of the VoluntaryPower. Art. Somnus interruptus. 15. We come now to those motions which depend on irritation. The motions ofthe arterial and glandular systems continue in our sleep, proceeding slowerindeed, but stronger and more uniformly, than in our waking hours, whenthey are incommoded by external stimuli, or by the movements of volition;the motions of the muscles subservient to respiration continue to bestimulated into action, and the other internal senses of hunger, thirst, and lust, are not only occasionally excited in our sleep, but theirirritative motions are succeeded by their usual sensations, and make a partof the farrago of our dreams. These sensations of the want of air, ofhunger, thirst, and lust, in our dreams, contribute to prove, that thenerves of the external senses are also alive and excitable in our sleep;but as the stimuli of external objects are either excluded from them by thedarkness and silence of the night, or their access to them is prevented bythe suspension of volition, these nerves of sense fall more readily intotheir connexions with sensation and with association; because muchsensorial power, which during the day was expended in moving the externalorgans of sense in consequence of irritation from external stimuli, or inconsequence of volition, becomes now in some degree accumulated, andrenders the internal or immediate organs of sense more easily excitable bythe other sensorial powers. Thus in respect to the eye, the irritation fromexternal stimuli, and the power of volition during our waking hours, elevate the eye-lids, adapt the aperture of the iris to the quantity oflight, the focus of the crystalline humour, and the angle of the opticaxises to the distance of the object, all which perpetual activity duringthe day expends much sensorial power, which is saved during our sleep. Hence it appears, that not only those parts of the system, which are alwaysexcited by internal stimuli, as the stomach, intestinal canal, bile-ducts, and the various glands, but the organs of sense also may be more violentlyexcited into action by the irritation from internal stimuli, or bysensation, during our sleep than in our waking hours; because during thesuspension of volition, there is a greater quantity of the spirit ofanimation to be expended by the other sensorial powers. On this account ourirritability to internal stimuli, and our sensibility to pain or pleasure, is not only greater in sleep, but increases as our sleep is prolonged. Whence digestion and secretion are performed better in sleep, than in ourwaking hours, and our dreams in the morning have greater variety andvivacity, as our sensibility increases, than at night when we first liedown. And hence epileptic fits, which are always occasioned by somedisagreeable sensation, so frequently attack those, who are subject tothem, in their sleep; because at this time the system is more excitable bypainful sensation in consequence of internal stimuli; and the power ofvolition is then suddenly exerted to relieve this pain, as explained Sect. XXXIV. 1. 4. There is a disease, which frequently affects children in the cradle, whichis termed ecstasy, and seems to consist in certain exertions to relievepainful sensation, in which the voluntary power is not so far excited astotally to awaken them, and yet is sufficient to remove the disagreeablesensation, which excites it; in this case changing the posture of the childfrequently relieves it. I have at this time under my care an elegant young man about twenty-twoyears of age, who seldom sleeps more than an hour without experiencing aconvulsion fit; which ceases in about half a minute without any subsequentstupor. Large doses of opium only prevented the paroxysms, so long as theyprevented him from sleeping by the intoxication, which they induced. Othermedicines had no effect on him. He was gently awakened every half hour forone night, but without good effect, as he soon slept again, and the fitreturned at about the same periods of time, for the accumulated sensorialpower, which occasioned the increased sensibility to pain, was not thusexhausted. This case evinces, that the sensibility of the system tointernal excitation increases, as our sleep is prolonged; till the painthus occasioned produces voluntary exertion; which, when it is in its usualdegree, only awakens us; but when it is more violent, it occasionsconvulsions. The cramp in the calf of the leg is another kind of convulsion, whichgenerally commences in sleep, occasioned by the continual increase ofirritability from internal stimuli, or of sensibility, during that state ofour existence. The cramp is a violent exertion to relieve pain, generallyeither of the skin from cold, or of the bowels, as in some diarrhoeas, orfrom the muscles having been previously overstretched, as in walking up ordown steep hills. But in these convulsions of the muscles, which form thecalf of the leg, the contraction is so violent as to occasion another painin consequence of their own too violent contraction; as soon as theoriginal pain, which caused the contraction, is removed. And hence thecramp, or spasm, of these muscles is continued without intermission by thisnew pain, unlike the alternate convulsions and remissions in epilepticfits. The reason, that the contraction of these muscles of the calf of theleg is more violent during their convulsion than that of others, depends onthe weakness of their antagonist muscles; for after these have beencontracted in their usual action, as at every step in walking, they areagain extended, not, as most other muscles are, by their antagonists, butby the weight of the whole body on the balls of the toes; and that weightapplied to great mechanical advantage on the heel, that is, on the otherend of the bone of the foot, which thus acts as a lever. Another disease, the periods of which generally commence during our sleep, is the asthma. Whatever may be the remote cause of paroxysms of asthma, theimmediate cause of the convulsive respiration, whether in the commonasthma, or in what is termed the convulsive asthma, which are perhaps onlydifferent degrees of the same disease, must be owing to violent voluntaryexertions to relieve pain, as in other convulsions; and the increase ofirritability to internal stimuli, or of sensibility, during sleep mustoccasion them to commence at this time. Debilitated people, who have been unfortunately accustomed to greatingurgitation of spirituous potation, frequently part with a great quantityof water during the night, but with not more than usual in the day-time. This is owing to a beginning torpor of the absorbent system, and precedesanasarca, which commences in the day, but is cured in the night by theincrease of the irritability of the absorbent system during sleep, whichthus imbibes from the cellular membrane the fluids, which had beenaccumulated there during the day; though it is possible the horizontalposition of the body may contribute something to this purpose, and also thegreater irritability of some branches of the absorbent vessels, which opentheir mouths in the cells of the cellular membrane, than that of otherbranches. As soon as a person begins to sleep, the irritability and sensibility ofthe system begins to increase, owing to the suspension of volition and theexclusion of external stimuli. Hence the actions of the vessels inobedience to internal stimulation become stronger and more energetic, though less frequent in respect to number. And as many of the secretionsare increased, so the heat of the system is gradually increased, and theextremities of feeble people, which had been cold during the day, becomewarm. Till towards morning many people become so warm, as to find itnecessary to throw off some of their bed-clothes, as soon as they awake;and in others sweats are so liable to occur towards morning during theirsleep. Thus those, who are not accustomed to sleep in the open air, are veryliable to take cold, if they happen to fall asleep on a garden bench, or ina carriage with the window open. For as the system is warmer during sleep, as above explained, if a current of cold air affects any part of the body, a torpor of that part is more effectually produced, as when a cold blast ofair through a key-hole or casement falls upon a person in a warm room. Inthose cases the affected part possesses less irritability in respect toheat, from its having previously been exposed to a greater stimulus ofheat, as in the warm room, or during sleep; and hence, when the stimulus ofheat is diminished, a torpor is liable to ensue; that is, we take cold. Hence people who sleep in the open air, generally feel chilly both at theapproach of sleep, and on their awaking; and hence many people areperpetually subject to catarrhs if they sleep in a less warm head-dress, than that which they wear in the day. 16. Not only the sensorial powers of irritation and of sensation, but thatof association also appear to act with greater vigour during the suspensionof volition in sleep. It will be shewn in another place, that the goutgenerally first attacks the liver, and that afterwards an inflammation ofthe ball of the great toe commences by association, and that of the liverceases. Now as this change or metastasis of the activity of the systemgenerally commences in sleep, it follows, that these associations of motionexist with greater energy at that time; that is, that the sensorial facultyof association, like those of irritation and of sensation, becomes in somemeasure accumulated during the suspension of volition. Other associate tribes and trains of motions, as well as the irritative andsensitive ones, appear to be increased in their activity during thesuspension of volition in sleep. As those which contribute to circulate theblood, and to perform the various secretions; as well as the associatetribes and trains of ideas, which contribute to furnish the perpetualdreams of our dreaming imaginations. In sleep the secretions have generally been supposed to be diminished, asthe expectorated mucus in coughs, the fluids discharged in diarrhoeas, andin salivation, except indeed the secretion of sweat, which is often visiblyincreased. This error seems to have arisen from attention to the excretionsrather than to the secretions. For the secretions, except that of sweat, are generally received into reservoirs, as the urine into the bladder, andthe mucus of the intestines and lungs into their respective cavities; butthese reservoirs do not exclude these fluids immediately by their stimulus, but require at the same time some voluntary efforts, and therefore permitthem to remain during sleep. And as they thus continue longer in thosereceptacles in our sleeping hours, a greater part is absorbed from them, and the remainder becomes thicker, and sometimes in less quantity, thoughat the time it was secreted the fluid was in greater quantity than in ourwaking hours. Thus the urine is higher coloured after long sleep; whichshews that a greater quantity has been secreted, and that more of theaqueous and saline part has been reabsorbed, and the earthy part left inthe bladder; hence thick urine in fevers shews only a greater action of thevessels which secrete it in the kidneys, and of those which absorb it fromthe bladder. The same happens to the mucus expectorated in coughs, which is thusthickened by absorption of its aqueous and saline parts; and the same ofthe feces of the intestines. From hence it appears, and from what has beensaid in No. 15. Of this Section concerning the increase of irritability andof sensibility during sleep, that the secretions are in general ratherincreased than diminished during these hours of our existence; and it isprobable that nutrition is almost entirely performed in sleep; and thatyoung animals grow more at this time than in their waking hours, as youngplants have long since been observed to grow more in the night, which istheir time of sleep. 17. Two other remarkable circumstances of our dreaming ideas are theirinconsistency, and the total absence of surprise. Thus we seem to bepresent at more extraordinary metamorphoses of animals or trees, than areto be met with in the fables of antiquity; and appear to be transportedfrom place to place, which seas divide, as quickly as the changes ofscenery are performed in a play-house; and yet are not sensible of theirinconsistency, nor in the least degree affected with surprise. We must consider this circumstance more minutely. In our waking trains ofideas, those that are inconsistent with the usual order of nature, sorarely have occurred to us, that their connexion is the slightest of allothers: hence, when a consistent train of ideas is exhausted, we attend tothe external stimuli, that usually surround us, rather than to anyinconsistent idea, which might otherwise present itself; and if aninconsistent idea should intrude itself, we immediately compare it with thepreceding one, and voluntarily reject the train it would introduce; thisappears further in the Section on Reverie, in which state of the mindexternal stimuli are not attended to, and yet the streams of ideas are keptconsistent by the efforts of volition. But as our faculty of volition issuspended, and all external stimuli are excluded in sleep, this slighterconnexion of ideas takes place; and the train is said to be inconsistent;that is, dissimilar to the usual order of nature. But, when any consistent train of sensitive or voluntary ideas is flowingalong, if any external stimulus affects us so violently, as to intrudeirritative ideas forcibly into the mind, it disunites the former train ofideas, and we are affected with surprise. These stimuli of unusual energyor novelty not only disunite our common trains of ideas, but the trains ofmuscular motions also, which have not been long established by habit, anddisturb those that have. Some people become motionless by great surprise, the fits of hiccup and or ague have been often removed by it, and it evenaffects the movements of the heart, and arteries; but in our sleep, allexternal stimuli are excluded, and in consequence no surprise can exist. See Section XVII. 3. 7. 18. We frequently awake with pleasure from a dream, which has delighted us, without being able to recollect the transactions of it; unless perhaps at adistance of time, some analogous idea may introduce afresh this forgottentrain: and in our waking reveries we sometimes in a moment lose the trainof thought, but continue to feel the glow of pleasure, or the depression ofspirits, it occasioned: whilst at other times we can retrace with easethese histories of our reveries and dreams. The above explanation of surprise throws light upon this subject. When weare suddenly awaked by any violent stimulus, the surprise totally disunitesthe trains of our sleeping ideas from these of our waking ones; but if wegradually awake, this does not happen; and we readily unravel the precedingtrains of imagination. 19. There are various degrees of surprise; the more intent we are upon thetrain of ideas, which we are employed about, the more violent must be thestimulus that interrupts them, and the greater is the degree of surprise. Ihave observed dogs, who have slept by the fire, and by their obscurebarking and struggling have appeared very intent on their prey, that shewedgreat surprise for a few seconds after their awaking by looking eagerlyaround them; which they did not do at other times of waking. And anintelligent friend of mine has remarked, that his lady, who frequentlyspeaks much and articulately in her sleep, could never recollect her dreamsin the morning, when this happened to her: but that when she did not speakin her sleep, she could always recollect them. Hence, when our sensations act so strongly in sleep as to influence thelarger muscles, as in those, who talk or struggle in their dreams; or inthose, who are affected with complete reverie (as described in the nextSection), great surprise is produced, when they awake; and these as well asthose, who are completely drunk or delirious, totally forget afterwardstheir imaginations at those times. 20. As the immediate cause of sleep consists in the suspension of volition, it follows, that whatever diminishes the general quantity of sensorialpower, or derives it from the faculty of volition, will constitute a remotecause of sleep; such as fatigue from muscular or mental exertion, whichdiminishes the general quantity of sensorial power; or an increase of thesensitive motions, as by attending to soft music, which diverts thesensorial power from the faculty of volition; or lastly, by increase of theirritative motions, as by wine, or food; or warmth; which not only by theirexpenditure of sensorial power diminish the quantity of volition; but alsoby their producing pleasureable sensations (which occasion other muscularor sensual motions in consequence), doubly decrease the voluntary power, and thus more forcibly produce sleep. See Sect. XXXIV. 1. 4. Another method of inducing sleep is delivered in a very ingenious worklately published by Dr. Beddoes. Who, after lamenting that opium frequentlyoccasions restlessness, thinks, "that in most cases it would be better toinduce sleep by the abstraction of stimuli, than by exhausting theexcitability;" and adds, "upon this principle we could not have a bettersoporific than an atmosphere with a diminished proportion of oxygene air, and that common air might be admitted after the patient was asleep. "(Observ. On Calculus, &c. By Dr. Beddoes, Murray. ) If it should be found tobe true, that the excitability of the system depends on the quantity ofoxygene absorbed by the lungs in respiration according to the theory of Dr. Beddoes, and of M. Girtanner, this idea of sleeping in an atmosphere withless oxygene in its composition might be of great service in epilepticcases, and in cramp, and even in fits of the asthma, where their periodscommence from the increase of irritability during sleep. Sleep is likewise said to be induced by mechanic pressure on the brain inthe cases of spina bifida. Where there has been a defect of one of thevertebræ of the back, a tumour is protruded in consequence; and, wheneverthis tumour has been compressed by the hand, sleep is said to be induced, because the whole of the brain both within the head and spine becomescompressed by the retrocession of the fluid within the tumour. But by whatmeans a compression of the brain induces sleep has not been explained, butprobably by diminishing the secretion of sensorial power, and then thevoluntary motions become suspended previously to the irritative ones, asoccurs in most dying persons. Another way of procuring sleep mechanically was related to me by Mr. Brindley, the famous canal engineer, who was brought up to the business ofa mill-wright; he told me, that he had more than once seen the experimentof a man extending himself across the large stone of a corn-mill, and thatby gradually letting the stone whirl, the man fell asleep, before the stonehad gained its full velocity, and he supposed would have died without painby the continuance or increase of the motion. In this case the centrifugalmotion of the head and feet must accumulate the blood in both thoseextremities of the body, and thus compress the brain. Lastly, we should mention the application of cold; which, when in a lessdegree, produces watchfulness by the pain it occasions, and the tremulousconvulsions of the subcutaneous muscles; but when it is applied in greatdegree, is said to produce sleep. To explain this effect it has been said, that as the vessels of the skin and extremities become first torpid by thewant of the stimulus of heat, and as thence less blood is circulatedthrough them, as appears from their paleness, a greater quantity of bloodpoured upon the brain produces sleep by its compression of that organ. ButI should rather imagine, that the sensorial power becomes exhausted by theconvulsive actions in consequence of the pain of cold, and of the voluntaryexercise previously used to prevent it, and that the sleep is only thebeginning to die, as the suspension of voluntary power in lingering deathsprecedes for many hours the extinction of the irritative motions. 21. The following are the characteristic circumstances attending perfectsleep. 1. The power of volition is totally suspended. 2. The trains of ideas caused by sensation proceed with greater facilityand vivacity; but become inconsistent with the usual order of nature. Themuscular motions caused by sensation continue; as those concerned in ourevacuations during infancy, and afterwards in digestion, and in priapismus. 3. The irritative muscular motions continue, as those concerned in thecirculation, in secretion, in respiration. But the irritative sensualmotions, or ideas, are not excited; as the immediate organs of sense arenot stimulated into action by external objects, which are excluded by theexternal organs of sense; which are not in sleep adapted to their receptionby the power of volition, as in our waking hours. 4. The associate motions continue; but their first link is not excited intoaction by volition, or by external stimuli. In all respects, except thoseabove mentioned, the three last sensorial powers are somewhat increased inenergy during the suspension of volition, owing to the consequentaccumulation of the spirit of animation. * * * * * SECT. XIX. OF REVERIE. 1. _Various degrees of reverie. _ 2. _Sleep-walkers. Case of a young lady. Great surprise at awaking. And total forgetfulness of what passed in reverie. _ 3. _No suspension of volition in reverie. _ 4. _Sensitive motions continue, and are consistent. _ 5. _Irritative motions continue, but are not succeeded by sensation. _ 6. _Volition necessary for the perception of feeble impressions. _ 7. _Associated motions continue. _ 8. _Nerves of sense are irritable in sleep, but not in reverie. _ 9. _Somnambuli are not asleep. Contagion received but once. _ 10. _Definition of reverie. _ 1. When we are employed with great sensation of pleasure, or with greatefforts of volition, in the pursuit of some interesting train of ideas, wecease to be conscious of our existence, are inattentive to time and place, and do not distinguish this train of sensitive and voluntary ideas from theirritative ones excited by the presence of external objects, though ourorgans of sense are furnished with their accustomed stimuli, till at lengththis interesting train of ideas becomes exhausted, or the appulses ofexternal objects are applied with unusual violence, and we return withsurprise, or with regret, into the common track of life. This is termedreverie or studium. In some constitutions these reveries continue a considerable time, and arenot to be removed without greater difficulty, but are experienced in a lessdegree by us all; when we attend earnestly to the ideas excited by volitionor sensation, with their associated connexions, but are at the same timeconscious at intervals of the stimuli of surrounding bodies. Thus in beingpresent at a play, or in reading a romance, some persons are so totallyabsorbed as to forget their usual time of sleep, and to neglect theirmeals; while others are said to have been so involved in voluntary study asnot to have heard the discharge of artillery; and there is a story of anItalian politician, who could think so intensely on other subjects, as tobe insensible to the torture of the rack. From hence it appears, that these catenations of ideas and muscularmotions, which form the trains of reverie, are composed both of voluntaryand sensitive associations of them; and that these ideas differ from thoseof delirium or of sleep, as they are kept consistent by the power ofvolition; and they differ also from the trains of ideas belonging toinsanity, as they are as frequently excited by sensation as by volition. But lastly, that the whole sensorial power is so employed on these trainsof complete reverie, that like the violent efforts of volition, as inconvulsions or insanity; or like the great activity of the irritativemotions in drunkenness; or of the sensitive motions in delirium; theypreclude all sensation consequent to external stimulus. 2. Those persons, who are said to walk in their sleep, are affected withreverie to so great a degree, that it becomes a formidable disease; theessence of which consists in the inaptitude of the mind to attend toexternal stimuli. Many histories of this disease have been published bymedical writers; of which there is a very curious one in the LausanneTransactions. I shall here subjoin an account of such a case, with itscure, for the better illustration of this subject. A very ingenious and elegant young lady, with light eyes and hair, aboutthe age of seventeen, in other respects well, was suddenly seized soonafter her usual menstruation with this very wonderful malady. The diseasebegan with vehement convulsions of almost every muscle of her body, withgreat but vain efforts to vomit, and the most violent hiccoughs, that canbe conceived: these were succeeded in about an hour with a fixed spasm; inwhich one hand was applied to her head, and the other to support it: inabout half an hour these ceased, and the reverie began suddenly, and was atfirst manifest by the look of her eyes and countenance, which seemed toexpress attention. Then she conversed aloud with imaginary persons with hereyes open, and could not for about an hour be brought to attend to thestimulus of external objects by any kind of violence, which it was properto use; these symptoms returned in this order every day for five or sixweeks. These conversations were quite consistent, and we could understand, whatshe supposed her imaginary companions to answer, by the continuation of herpart of the discourse. Sometimes she was angry, at other times shewed muchwit and vivacity, but was most frequently inclined to melancholy. In thesereveries she sometimes sung over some music with accuracy, and repeatedwhole pages from the English poets. In repeating some lines from Mr. Pope'sworks she had forgot one word, and began again, endeavouring to recollectit; when she came to the forgotten word, it was shouted aloud in her ear, and this repeatedly, to no purpose; but by many trials she at lengthregained it herself. These paroxysms were terminated with the appearance of inexpressiblesurprise, and great fear, from which she was some minutes in recoveringherself, calling on her sister with great agitation, and very frequentlyunderwent a repetition of convulsions, apparently from the pain of fear. See Sect. XVII. 3. 7. After having thus returned for about an hour every day for two or threeweeks, the reveries seemed to become less complete, and some of theircircumstances varied; so that she could walk about the room in them withoutrunning against any of the furniture; though these motions were at firstvery unsteady and tottering. And afterwards she once drank a dish of tea, when the whole apparatus of the tea-table was set before her; and expressedsome suspicion, that a medicine was put into it, and once seemed to smellof a tuberose, which was in flower in her chamber, and deliberated aloudabout breaking it from the stem, saying, "it would make her sister socharmingly angry. " At another time in her melancholy moments she heard thesound of a passing bell, "I wish I was dead, " she cried, listening to thebell, and then taking off one of her shoes, as she sat upon the bed, "Ilove the colour black, " says she, "a little wider, and a little longer, even this might make me a coffin!"--Yet it is evident, she was not sensibleat this time, any more than formerly, of seeing or hearing any person abouther; indeed when great light was thrown upon her by opening the shutters ofthe window, her trains of ideas seemed less melancholy; and when I haveforcibly held her hands, or covered her eyes, she appeared to growimpatient, and would say, she could not tell what to do, for she couldneither see nor move. In all these circumstances her pulse continuedunaffected as in health. And when the paroxysm was over, she could neverrecollect a single idea of what had passed in it. This astonishing disease, after the use of many other medicines andapplications in vain, was cured by very large doses of opium given about anhour before the expected returns of the paroxysms; and after a fewrelapses, at the intervals of three or four months, entirely disappeared. But she continued at times to have other symptoms of epilepsy. 3. We shall only here consider, what happened during the time of herreveries, as that is our present subject; the fits of convulsion belong toanother part of this treatise. Sect. XXXIV. 1. 4. There seems to have been no suspension of volition during the fits ofreverie, because she endeavoured to regain the lost idea in repeating thelines of poetry, and deliberated about breaking the tuberose, and suspectedthe tea to have been medicated. 4. The ideas and muscular movements depending on sensation were exertedwith their usual vivacity, and were kept from being inconsistent by thepower of volition, as appeared from her whole conversation, and wasexplained in Sect. XVII. 3. 7. And XVIII. 16. 5. The ideas and motions dependant on irritation during the first weeks ofher disease, whilst the reverie was complete, were never succeeded by thesensation of pleasure or pain; as she neither saw, heard, nor felt any ofthe surrounding objects. Nor was it certain that any irritative motionssucceeded the stimulus of external objects, till the reverie became lesscomplete, and then she could walk about the room without running againstthe furniture of it. Afterwards, when the reverie became still lesscomplete from the use of opium, some few irritations were at timessucceeded by her attention to them. As when she smelt at a tuberose, anddrank a dish of tea, but this only when she seemed voluntarily to attend tothem. 6. In common life when we listen to distant sounds, or wish to distinguishobjects in the night, we are obliged strongly to exert our volition todispose the organs of sense to perceive them, and to suppress the othertrains of ideas, which might interrupt these feeble sensations. Hence inthe present history the strongest stimuli were not perceived, except whenthe faculty of volition was exerted on the organ of sense; and then evencommon stimuli were sometimes perceived: for her mind was so strenuouslyemployed in pursuing its own trains of voluntary or sensitive ideas, thatno common stimuli could so far excite her attention as to disunite them;that is, the quantity of volition or of sensation already existing wasgreater than any, which could be produced in consequence of common degreesof stimulation. But the few stimuli of the tuberose, and of the tea, whichshe did perceive, were such, as accidentally coincided with the trains ofthought, which were passing in her mind; and hence did not disunite thosetrains, and create surprise. And their being perceived at all was owing tothe power of volition preceding or coinciding with that of irritation. This explication is countenanced by a fact mentioned concerning asomnambulist in the Lausanne Transactions, who sometimes opened his eyesfor a short time to examine, where he was, or where his ink-pot stood, andthen shut them again, dipping his pen into the pot every now and then, andwriting on, but never opening his eyes afterwards, although he wrote onfrom line to line regularly, and corrected some errors of the pen, or inspelling: so much easier was it to him to refer to his ideas of thepositions of things, than to his perceptions of them. 7. The associated motions persisted in their usual channel, as appeared bythe combinations of her ideas, and the use of her muscles, and the equalityof her pulse; for the natural motions of the arterial system, thoughoriginally excited like other motions by stimulus, seem in part to continueby their association with each other. As the heart of a viper pulsates longafter it is cut out of the body, and removed from the stimulus of theblood. 8. In the section on sleep, it was observed that the nerves of sense areequally alive and susceptible to irritation in that state, as when we areawake; but that they are secluded from stimulating objects, or renderedunfit to receive them: but in complete reverie the reverse happens, theimmediate organs of sense are exposed to their usual stimuli; but areeither not excited into action at all, or not into so great action, as toproduce attention or sensation. The total forgetfulness of what passes in reveries; and the surprise onrecovering from them, are explained in Section XVIII. 19. And in SectionXVII. 3. 7. 9. It appears from hence, that reverie is a disease of the epileptic orcataleptic kind, since the paroxysms of this young lady always began andfrequently terminated with convulsions; and though in its greatest degreeit has been called somnambulation, or sleep-walking, it is totallydifferent from sleep; because the essential character of sleep consists inthe total suspension of volition, which in reverie is not affected; and theessential character of reverie consists not in the absence of thoseirritative motions of our senses, which are occasioned by the stimulus ofexternal objects, but in their never being productive of sensation. So thatduring a fit of reverie that strange event happens to the whole system ofnerves, which occurs only to some particular branches of them in those, whoare a second time exposed to the action of contagious matter. If the matterof the small-pox be inserted into the arm of one, who has previously hadthat disease, it will stimulate the wound, but the general sensation orinflammation of the system does not follow, which constitutes the disease. See Sect. XII. 3. 6. XXXIII. 2. 8. 10. The following is the definition or character of complete reverie. 1. The irritative motions occasioned by internal stimuli continue, those fromthe stimuli of external objects are either not produced at all, or arenever succeeded by sensation or attention, unless they are at the same timeexcited by volition. 2. The sensitive motions continue, and are keptconsistent by the power of volition. 3. The voluntary motions continueundisturbed. 4. The associate motions continue undisturbed. Two other cases of reverie are related in Section XXXIV. 3. Which furtherevince, that reverie is an effort of the mind to relieve some painfulsensation, and is hence allied to convulsion, and to insanity. Another caseis related in Class III. 1. 2. 2. * * * * * SECT. XX. OF VERTIGO. 1. _We determine our perpendicularity by the apparent motions of objects. A person hood-winked cannot walk in a straight line. Dizziness in looking from a tower, in a room stained with uniform lozenges, on riding over snow. _ 2. _Dizziness from moving objects. A whirling-wheel. Fluctuations of a river. Experiment with a child. _ 3. _Dizziness from our own motions and those of other objects. _ 4. _Riding over a broad stream. Sea-sickness. _ 5. _Of turning round on one foot. Dervises in Turkey. Attention of the mind prevents slight sea-sickness. After a voyage ideas of vibratory motions are still perceived on shore. _ 6. _Ideas continue some time after they are excited. Circumstances of turning on one foot, standing on a tower, and walking in the dark, explained. _ 7. _Irritative ideas of apparent motions. Irritative ideas of sounds. Battèment of the sound of bells and organ-pipes. Vertiginous noise in the head. Irritative motions of the stomach, intestines, and glands. _ 8. _Symptoms that accompany vertigo. Why vomiting comes on in strokes of the palsy. By the motion of a ship. By injuries on the head. Why motion makes sick people vomit. _ 9. _Why drunken people are vertiginous. Why a stone in the ureter, or bile-duct, produces vomiting. _ 10. _Why after a voyage ideas of vibratory motions are perceived on shore. _ 11. _Kinds of vertigo and their cure. _ 12. _Definition of vertigo. _ 1. In learning to walk we judge of the distances of the objects, which weapproach, by the eye; and by observing their perpendicularity determine ourown. This circumstance not having been attended to by the writers onvision, the disease called vertigo or dizziness has been little understood. When any person loses the power of muscular action, whether he is erect orin a sitting posture, he sinks down upon the ground; as is seen in faintingfits, and other instances of great debility. Hence it follows, that someexertion of muscular power is necessary to preserve our perpendicularattitude. This is performed by proportionally exerting the antagonistmuscles of the trunk, neck, and limbs; and if at any time in ourlocomotions we find ourselves inclining to one side, we either restore ourequilibrium by the efforts of the muscles on the other side, or by movingone of our feet extend the base, which we rest upon, to the new center ofgravity. But the most easy and habitual manner of determining our want ofperpendicularity, is by attending to the apparent motion of the objectswithin the sphere of distinct vision; for this apparent motion of objects, when we incline from our perpendicularity, or begin to fall, is as muchgreater than the real motion of the eye, as the diameter of the sphere ofdistinct vision is to our perpendicular height. Hence no one, who is hood-winked, can walk in a straight line for a hundredsteps together; for he inclines so greatly, before he is warned of his wantof perpendicularity by the sense of touch, not having the apparent motionsof ambient objects to measure this inclination by, that he is necessitatedto move one of his feet outwards, to the right or to the left, to supportthe new centre of gravity, and thus errs from the line he endeavours toproceed in. For the same reason many people become dizzy, when they look from thesummit of a tower, which is raised much above all other objects, as theseobjects are out of the sphere of distinct vision, and they are obliged tobalance their bodies by the less accurate feelings of their muscles. There is another curious phenomenon belonging to this place, if thecircumjacent visible objects are so small, that we do not distinguish theirminute parts; or so similar, that we do not know them from each other; wecannot determine our perpendicularity by them. Thus in a room hung with apaper, which is coloured over with similar small black lozenges orrhomboids, many people become dizzy; for when they begin to fall, the nextand the next lozenge succeeds upon the eye; which they mistake for thefirst, and are not aware, that they have any apparent motion. But if youfix a sheet of paper, or draw any other figure, in the midst of theselozenges, the charm ceases, and no dizziness is perceptible. --The sameoccurs, when we ride over a plain covered with snow without trees or othereminent objects. 2. But after having compared visible objects at rest with the sense oftouch, and learnt to distinguish their shapes and shades, and to measureour want of perpendicularity by their apparent motions, we come to considerthem in real motion. Here a new difficulty occurs, and we require someexperience to learn the peculiar mode of motion of any moving objects, before we can make use of them for the purposes of determining ourperpendicularity. Thus some people become dizzy at the sight of a whirlingwheel, or by gazing on the fluctuations of a river, if no steady objectsare at the same time within the sphere of their distinct vision; and when achild first can stand erect upon his legs, if you gain his attention to awhite handkerchief steadily extended like a sail, and afterwards make itundulate, he instantly loses his perpendicularity, and tumbles on theground. 3. A second difficulty we have to encounter is to distinguish our own realmovements from the apparent motions of objects. Our daily practice ofwalking and riding on horseback soon instructs us with accuracy to discernthese modes of motion, and to ascribe the apparent motions of the ambientobjects to ourselves; but those, which we have not acquired by repeatedhabit, continue to confound us. So as we ride on horseback the trees andcottages, which occur to us, appear at rest; we can measure their distanceswith our eye, and regulate our attitude by them; yet if we carelesslyattend to distant hills or woods through a thin hedge, which is near us, weobserve the jumping and progressive motions of them; as this is increasedby the paralax of these objects; which we have not habituated ourselves toattend to. When first an European mounts an elephant sixteen feet high, andwhose mode of motion he is not accustomed to, the objects seem to undulate, as he passes, and he frequently becomes sick and vertiginous, as I am wellinformed. Any other unusual movement of our bodies has the same effect, asriding backwards in a coach, swinging on a rope, turning round swiftly onone leg, scating on the ice, and a thousand others. So after a patient hasbeen long confined to his bed, when he first attempts to walk, he findshimself vertiginous, and is obliged by practice to learn again theparticular modes of the apparent motions of objects, as he walks by them. 4. A third difficulty, which occurs to us in learning to balance ourselvesby the eye, is, when both ourselves and the circumjacent objects are inreal motion. Here it is necessary, that we should be habituated to boththese modes of motion in order to preserve our perpendicularity. Thus onhorseback we accurately observe another person, whom we meet, trottingtowards us, without confounding his jumping and progressive motion with ourown, because we have been accustomed to them both; that is, to undergo theone, and to see the other at the same time. But in riding over a broad andfluctuating stream, though we are well experienced in the motions of ourhorse, we are liable to become dizzy from our inexperience in that of thewater. And when first we go on ship-board, where the movements ofourselves, and the movements of the large waves are both new to us, thevertigo is almost unavoidable with the terrible sickness, which attends it. And this I have been assured has happened to several from being removedfrom a large ship into a small one; and again from a small one into a manof war. 5. From the foregoing examples it is evident, that, when we are surroundedwith unusual motions, we lose our perpendicularity: but there are somepeculiar circumstances attending this effect of moving objects, which wecome now to mention, and shall hope from the recital of them to gain someinsight into the manner of their production. When a child moves round quick upon one foot, the circumjacent objectsbecome quite indistinct, as their distance increases their apparentmotions; and this great velocity confounds both their forms, and theircolours, as is seen in whirling round a many coloured wheel; he then loseshis usual method of balancing himself by vision, and begins to stagger, andattempts to recover himself by his muscular feelings. This staggering addsto the instability of the visible objects by giving a vibratory motionbesides their rotatory one. The child then drops upon the ground, and theneighbouring objects seem to continue for some seconds of time to circulatearound him, and the earth under him appears to librate like a balance. Insome seconds of time these sensations of a continuation of the motion ofobjects vanish; but if he continues turning round somewhat longer, beforehe falls, sickness and vomiting are very liable to succeed. But none ofthese circumstances affect those who have habituated themselves to thiskind of motion, as the dervises in Turkey, amongst whom these swiftgyrations are a ceremony of religion. In an open boat passing from Leith to Kinghorn in Scotland, a sudden changeof the wind shook the undistended sail, and stopt our boat; from thisunusual movement the passengers all vomited except myself. I observed, thatthe undulation of the ship, and the instability of all visible objects, inclined me strongly to be sick; and this continued or increased, when Iclosed my eyes, but as often as I bent my attention with energy on themanagement and mechanism of the ropes and sails, the sickness ceased; andrecurred again, as often as I relaxed this attention; and I am assured by agentleman of observation and veracity, that he has more than once observed, when the vessel has been in immediate danger, that the sea-sickness of thepassengers has instantaneously ceased, and recurred again, when the dangerwas over. Those, who have been upon the water in a boat or ship so long, that theyhave acquired the necessary habits of motion upon that unstable element, attheir return on land frequently think in their reveries, or betweensleeping and waking, that they observe the room, they sit in, or some ofits furniture, to librate like the motion of the vessel. This I haveexperienced myself, and have been told, that after long voyages, it is sometime before these ideas entirely vanish. The same is observable in a lessdegree after having travelled some days in a stage coach, and particularlywhen we lie down in bed, and compose ourselves to sleep; in this case it isobservable, that the rattling noise of the coach, as well as the undulatorymotion, haunts us. The drunken vertigo, and the vulgar custom of rockingchildren, will be considered in the next Section. 6. The motions, which are produced by the power of volition, may beimmediately stopped by the exertion of the same power on the antagonistmuscles; otherwise these with all the other classes of motion continue togo on, some time after they are excited, as the palpitation of the heartcontinues after the object of fear, which occasioned it, is removed. Butthis circumstance is in no class of motions more remarkable than in thosedependent on irritation; thus if any one looks at the sun, and then covershis eyes with his hand, he will for many seconds of time, perceive theimage of the sun marked on his retina: a similar image of all other visibleobjects would remain some time formed on the retina, but is extinguished bythe perpetual change of the motions of this nerve in our attention to otherobjects. To this must be added, that the longer time any movements havecontinued to be excited without fatigue to the organ, the longer will theycontinue spontaneously, after the excitement is withdrawn: as the taste oftobacco in the mouth after a person has been smoaking it. This taste remains so strong, that if a person continues to draw airthrough a tobacco pipe in the dark, after having been smoking some time, hecannot distinguish whether his pipe be lighted or not. From these two considerations it appears, that the dizziness felt in thehead, after seeing objects in unusual motion, is no other than acontinuation of the motions of the optic nerve excited by those objects andwhich engage our attention. Thus on turning round on one foot, the vertigocontinues for some seconds of time after the person is fallen on theground; and the longer he has continued to revolve, the longer willcontinue these successive motions of the parts of the optic nerve. _Additional Observations on _VERTIGO. After revolving with your eyes open till you become vertiginous, as soon as you cease to revolve, not only the circum-ambient objects appear to circulate round you in a direction contrary to that, in which you have been turning, but you are liable to roll your eyes forwards and backwards; as is well observed, and ingeniously demonstrated by Dr. Wells in a late publication on vision. The same occurs, if you revolve with your eyes closed, and open them immediately at the time of your ceasing to turn; and even during the whole time of revolving, as may be felt by your hand pressed lightly on your closed eyelids. To these movements of the eyes, of which he supposes the observer to be inconscious, Dr. Wells ascribes the apparent circumgyration of objects on ceasing to revolve. The cause of thus turning our eyes forwards, and then back again, after our body is at rest, depends, I imagine, on the same circumstance, which induces us to follow the indistinct spectra, which are formed on one side of the center of the retina, when we observe them apparently on clouds, as described in Sect. XL. 2. 2. ; and then not being able to gain a more distinct vision of them, we turn our eyes back, and again and again pursue the flying shade. But this rolling of the eyes, after revolving till we become vertiginous, cannot cause the apparent circumgyration of objects, in a direction contrary to that in which we have been revolving, for the following reasons. 1. Because in pursuing a spectrum in the sky, or on the ground, as above mentioned, we perceive no retrograde motions of objects. 2. Because the apparent retrograde motions of objects, when we have revolved till we are vertiginous, continues much longer than the rolling of the eyes above described. 3. When we have revolved from right to left, the apparent motion of objects, when we stop, is from left to right; and when we have revolved from left to right, the apparent circulation of objects is from right to left; yet in both these cases the eyes of the revolver are seen equally to roll forwards and backwards. 4. Because this rolling of the eyes backwards and forwards takes place during our revolving, as may be perceived by the hand lightly pressed on the closed eyelids, and therefore exists before the effect ascribed to it. And fifthly, I now come to relate an experiment, in which the rolling of the eyes does not take place at all after revolving, and yet the vertigo is more distressing than in the situations above mentioned. If any one looks steadily at a spot in the ceiling over his head, or indeed at his own finger held up high over his head, and in that situation turns round till he becomes giddy; and then stops, and looks horizontally; he now finds, that the apparent rotation of objects is from above downwards, or from below upwards; that is, that the apparent circulation of objects is now vertical instead of horizontal, making part of a circle round the axis of his _eye_; and this without any rolling of his eyeballs. The reason of there being no rolling of the eyeballs, perceived after this experiment, is, because the images of objects are formed in rotation round the axis of the eye, and not from one side to the other of the axis of it; so that, as the eyeball has not power to turn in its socket round its own axis, it cannot follow the apparent motions of these evanescent spectra, either before or after the body is at rest. From all which arguments it is manifest, that these apparent retrograde gyrations of objects are not caused by the rolling of the eyeballs; first, because no apparent retrogression of objects is observed in other rollings of the eyes: secondly, because the apparent retrogression of objects continues many seconds after the rolling of the eyeballs ceases. Thirdly, because the apparent retrogression of objects is sometimes one way, and sometimes another, yet the rolling of the eyeballs is the same. Fourthly, because the rolling of the eyeballs exists before the apparent retrograde motions of objects is observed; that is, before the revolving person stops. And fifthly, because the apparent retrograde gyration of objects is produced, when there is no rolling of the eyeballs at all. Doctor Wells imagines, that no spectra can be gained in the eye, if a person revolves with his eyelids closed, and thinks this a sufficient argument against the opinion, that the apparent progression of the spectra of light or colours in the eye can cause the apparent retrogression of objects in the vertigo above described; but it is certain, when any person revolves in a light room with his eyes closed, that he nevertheless perceives differences of light both in quantity and colour through his eyelids, as he turns round; and readily gains spectra of those differences. And these spectra are not very different except in vivacity from those, which he acquires, when he revolves with unclosed eyes, since if he then revolves very rapidly the colours and forms of surrounding objects are as it were mixed together in his eye;. As when, the prismatic colours are painted on a wheel, they appear white as they revolve. The truth of this is evinced by the staggering or vertigo of men perfectly blind, when they turn round; which is not attended with apparent circulation of objects, but is a vertiginous disorder of the sense of touch. Blind men balance themselves by their sense of touch; which, being less adapted for perceiving small deviations from their perpendicular, occasions them to carry themselves more erect in walking. This method of balancing themselves by the direction of their pressure against the floor, becomes disordered by the unusual mode of action in turning round, and they begin to lose their perpendicularity, that is, they become vertiginous; but without any apparent circular motions of visible objects. It will appear from the following experiments, that the apparent progression of the ocular spectra of light or colours is the cause of the apparent retrogression of objects, after a person has revolved, till he is vertiginous. First, when a person turns round in a light room with his eyes open, but closes them before he stops, he will seem to be carried forwards in the direction he was turning for a short time after he stops. But if he opens his eyes again, the objects before him instantly appear to move in a retrograde direction, and he loses the sensation of being carried forwards. The same occurs if a person revolves in a light room with his eyes closed; when he stops, he seems to be for a time carried forwards, if his eyes are still closed; but the instant he opens them, the surrounding objects appear to move in retrograde gyration. From hence it may be concluded, that it is the sensation or imagination of our continuing to go forwards in the direction in which we were turning, that causes the apparent retrograde circulation of objects. Secondly, though there is an audible vertigo, as is known by the battement, or undulations of sound in the ears, which many vertiginous people experience; and though there is also a tangible vertigo, as when a blind person turns round, as mentioned above; yet as this circumgyration of objects is an hallucination or deception of the sense of sight, we are to look for the cause of our appearing to move forward, when we stop with our eyes closed after gyration, to some affection of this sense. Now, thirdly, if the spectra formed in the eye during our rotation, continue to change, when we stand still, like the spectra described in Sect. III. 3. 6. Such changes must suggest to us the idea or sensation of our still continuing to turn round; as is the case, when we revolve in a light room, and close our eyes before we stop. And lastly, on opening our eyes in the situation above described, the objects we chance to view amid these changing spectra in the eye, must seem to move in a contrary direction; as the moon sometimes appears to move retrograde, when swift-gliding clouds are passing forwards so much nearer the eye of the beholder. To make observations on faint ocular spectra requires some degree of habit, and composure of mind, and even patience; some of those described in Sect. XL. Were found difficult to see, by many, who tried them; now it happens, that the mind, during the confusion of vertigo, when all the other irritative tribes of motion, as well as those of vision, are in some degree disturbed, together with the fear of falling, is in a very unfit state for the contemplation of such weak sensations, as are occasioned by faint ocular spectra. Yet after frequently revolving, both with my eyes closed, and with them open, and attending to the spectra remaining in them, by shading the light from my eyelids more or less with my hand, I at length ceased to have the idea of going forward, after I stopped with my eyes closed; and saw changing spectra in my eyes, which seemed to move, as it were, over the field of vision; till at length, by repeated trials on sunny days, I persuaded myself, on opening my eyes, after revolving some time, on a shelf of gilded books in my library, that I could perceive the spectra in my eyes move forwards over one or two of the books, like the vapours in the air of a summer's day; and could so far undeceive myself, as to perceive the books to stand still. After more trials I sometimes brought myself to believe, that I saw changing spectra of lights and shades moving in my eyes, after turning round for some time, but did not imagine either the spectra or the objects to be in a state of gyration. I speak, however, with diffidence of these facts, as I could not always make the experiments succeed, when there was not a strong light in my room, or when my eyes were not in the most proper state for such observations. The ingenious and learned M. Sauvage has mentioned other theories to account for the apparent circumgyration of objects in vertiginous people. As the retrograde motions of the particles of blood in the optic arteries, by spasm, or by fear, as is seen in the tails of tadpoles, and membranes between the fingers of frogs. Another cause he thinks may be from the librations to one side, and to the other, of the crystalline lens in the eye, by means of involuntary actions of the muscles, which constitute the ciliary process. Both these theories lie under the same objection as that of Dr. Wells before mentioned; namely, that the apparent motions of objects, after the observer has revolved for some time, should appear to vibrate this way and that; and not to circulate uniformly in a direction contrary to that, in which the observer had revolved. M. Sauvage has, lastly, mentioned the theory of colours left in the eye, which he has termed impressions on the retina. He says, "Experience teaches us, that impressions made on the retina by a visible object remain some seconds after the object is removed; as appears from the circle of fire which we see, when a fire-stick is whirled round in the dark; therefore when we are carried round our own axis in a circle, we undergo a temporary vertigo, when we stop; because the impressions of the circumjacent objects remain for a time afterwards on the retina. " Nosolog. Method. Clas. VIII. I. 1. We have before observed, that the changes of these colours remaining in the eye, evinces them to be motions of the fine terminations of the retina, and not impressions on it; as impressions on a passive substance must either remain, or cease intirely. See an additional note at the end of the second volume. Any one, who stands alone on the top of a high tower, if he has not beenaccustomed to balance himself by objects placed at such distances and withsuch inclinations, begins to stagger, and endeavours to recover himself byhis muscular feelings. During this time the apparent motion of objects at adistance below him is very great, and the spectra of these apparent motionscontinue a little time after he has experienced them; and he is persuadedto incline the contrary way to counteract their effects; and eitherimmediately falls, or applying his hands to the building, uses his muscularfeelings to preserve his perpendicular attitude, contrary to the erroneouspersuasions of his eyes. Whilst the person, who walks in the dark, staggers, but without dizziness; for he neither has the sensation of movingobjects to take off his attention from his muscular feelings, nor has hethe spectra of those motions continued on his retina to add to hisconfusion. It happens indeed sometimes to one landing on a tower, that theidea of his not having room to extend his base by moving one of his feetoutwards, when he begins to incline, superadds fears to his otherinconveniences; which like surprise, joy, or any great degree of sensation, enervates him in a moment, by employing the whole sensorial power, and bythus breaking all the associated trains and tribes of motion. 7. The irritative ideas of objects, whilst we are awake, are perpetuallypresent to our sense of sight; as we view the furniture of our rooms, orthe ground, we tread upon, throughout the whole day without attending toit. And as our bodies are never at perfect rest during our waking hours, these irritative ideas of objects are attended perpetually with irritativeideas of their apparent motions. The ideas of apparent motions are alwaysirritative ideas, because we never attend to them, whether we attend to theobjects themselves, or to their real motions, or to neither. Hence theideas of the apparent motions of objects are a complete circle ofirritative ideas, which continue throughout the day. Also during all our waking hours, there is a perpetual confused sound ofvarious bodies, as of the wind in our rooms, the fire, distantconversations, mechanic business; this continued buzz, as we are seldomquite motionless, changes its loudness perpetually, like the sound of abell; which rises and falls as long as it continues, and seems to pulsateon the ear. This any one may experience by turning himself round near awaterfall; or by striking a glass bell, and then moving the direction ofits mouth towards the ears, or from them, as long as its vibrationscontinue. Hence this undulation of indistinct sound makes anotherconcomitant circle of irritative ideas, which continues throughout the day. We hear this undulating sound, when we are perfectly at rest ourselves, from other sonorous bodies besides bells; as from two organ-pipes, whichare nearly but not quite in unison, when they are sounded together. When abell is struck, the circular form is changed into an eliptic one; thelongest axis of which, as the vibrations continue, moves round theperiphery of the bell; and when either axis of this elipse is pointedtowards our ears, the sound is louder; and less when the intermediate partsof the elipse are opposite to us. The vibrations of the two organ-pipes maybe compared to Nonius's rule; the sound is louder, when they coincide, andless at the intermediate times. But, as the sound of bells is the mostfamiliar of those sounds, which have a considerable battement, thevertiginous patients, who attend to the irritative circles of sounds abovedescribed, generally compare it to the noise of bells. The peristaltic motions of our stomach and intestines, and the secretionsof the various glands, are other circles of irritative motions, some ofthem more or less complete, according to our abstinence or satiety. So that the irritative ideas of the apparent motions of objects, theirritative battements of sounds, and the movements of our bowels and glandscompose a great circle of irritative tribes of motion: and when oneconsiderable part of this circle of motions becomes interrupted, the wholeproceeds in confusion, as described in Section XVII. 1. 7. On Catenation ofMotions. 8. Hence a violent vertigo, from whatever cause it happens, is generallyattended with undulating noise in the head, perversions of the motions ofthe stomach and duodenum, unusual excretion of bile and gastric juice, withmuch pale urine, sometimes with yellowness of the skin, and a disorderedsecretion of almost every gland of the body, till at length the arterialsystem is affected, and fever succeeds. Thus bilious vomitings accompany the vertigo occasioned by the motion of aship; and when the brain is rendered vertiginous by a paralytic affectionof any part of the body, a vomiting generally ensues, and a great dischargeof bile: and hence great injuries of the head from external violence aresucceeded with bilious vomitings, and sometimes with abscesses of theliver. And hence, when a patient is inclined to vomit from other causes, asin some fevers, any motions of the attendants in his room, or of himselfwhen he is raised or turned in his bed, presently induces the vomiting bysuperadding a degree of vertigo. 9. And conversely it is very usual with those, whose stomachs are affectedfrom internal causes, to be afflicted with vertigo, and noise in the head;such is the vertigo of drunken people, which continues, when their eyes areclosed, and themselves in a recumbent posture, as well as when they are inan erect posture, and have their eyes open. And thus the irritation of astone in the bile-duct, or in the ureter, or an inflammation of any of theintestines, are accompanied with vomitings and vertigo. In these cases the irritative motions of the stomach, which are in generalnot attended to, become so changed by some unnatural stimulus, as to becomeuneasy, and excite our sensation or attention. And thus the otherirritative trains of motions, which are associated with it, becomedisordered by their sympathy. The same happens, when a piece of gravelsticks in the ureter, or when some part of the intestinal canal becomesinflamed. In these cases the irritative muscular motions are firstdisturbed by unusual stimulus, and a disordered action of the sensualmotions, or dizziness ensues. While in sea-sickness the irritative sensualmotions, as vertigo, precedes; and the disordered irritative muscularmotions, as those of the stomach in vomiting, follow. 10. When these irritative motions are disturbed, if the degree be not verygreat, the exertion of voluntary attention to any other object, or anysudden sensation, will disjoin these new habits of motion. Thus somedrunken people have become sober immediately, when any accident hasstrongly excited their attention; and sea-sickness has vanished, when theship has been in danger. Hence when our attention to other objects is mostrelaxed, as just before we fall asleep, or between our reveries when awake, these irritative ideas of motion and sound are most liable to be perceived;as those, who have been at sea, or have travelled long in a coach, seem toperceive the vibrations of the ship, or the rattling of the wheels, atthese intervals; which cease again, as soon as they exert their attention. That is, at those intervals they attend to the apparent motions, and to thebattement of sounds of the bodies around them, and for a moment mistakethem for those real motions of the ship, and noise of wheels, which theyhad lately been accustomed to: or at these intervals of reverie, or on theapproach of sleep, these supposed motions or sounds may be producedentirely by imagination. We may conclude from this account of vertigo, that sea-sickness is not aneffort of nature to relieve herself, but a necessary consequence of theassociations or catenations of animal motions. And may thence infer, thatthe vomiting, which attends the gravel in the ureter, inflammations of thebowels, and the commencement of some fevers, has a similar origin, and isnot always an effort of the vis medicatrix naturæ. But where the action ofthe organ is the immediate consequence of the stimulating cause, it isfrequently exerted to dislodge that stimulus, as in vomiting up an emeticdrug; at other times, the action of an organ is a general effort to relievepain, as in convulsions of the locomotive muscles; other actions drink upand carry on the fluids, as in absorption and secretion; all which may betermed efforts of nature to relieve, or to preserve herself. 11. The cure of vertigo will frequently depend on our previouslyinvestigating the cause of it, which from what has been delivered above mayoriginate from the disorder of any part of the great tribes of irritativemotions, and of the associate motions catenated with them. Many people, when they arrive at fifty or sixty years of age, are affectedwith slight vertigo; which is generally but wrongly ascribed toindigestion, but in reality arises from a beginning defect of their sight;as about this time they also find it necessary to begin to use spectacles, when they read small prints, especially in winter, or by candle light, butare yet able to read without them during the summer days, when the light isstronger. These people do not see objects so distinctly as formerly, and byexerting their eyes more than usual, they perceive the apparent motions ofobjects, and confound them with the real motions of them; and thereforecannot accurately balance themselves so as easily to preserve theirperpendicularity by them. That is, the apparent motions of objects, which are at rest, as we move bythem, should only excite irritative ideas: but as these are now become lessdistinct, owing to the beginning imperfection of our sight, we are induced_voluntarily_ to attend to them; and then these apparent motions becomesucceeded by sensation; and thus the other parts of the trains ofirritative ideas, or irritative muscular motions, become disordered, asexplained above. In these cases of slight vertigo I have always promised mypatients, that they would get free from it in two or three months, as theyshould acquire the habit of balancing their bodies by less distinctobjects, and have seldom been mistaken in my prognostic. There is an auditory vertigo, which is called a noise in the head, explained in No. 7. Of this section, which also is very liable to affectpeople in the advance of life, and is owing to their hearing less perfectlythan before. This is sometimes called a ringing, and sometimes a singing, or buzzing, in the ears, and is occasioned by our first experiencing adisagreeable sensation from our not being able distinctly to hear thesounds, we used formerly to hear distinctly. And this disagreeablesensation excites desire and consequent volition; and when we voluntarilyattend to small indistinct sounds, even the whispering of the air in aroom, and the pulsations of the arteries of the ear are succeeded bysensation; which minute sounds ought only to have produced irritativesensual motions, or unperceived ideas. See Section XVII. 3. 6. Thesepatients after a while lose this auditory vertigo, by acquiring a new habitof not attending voluntarily to these indistinct sounds, but contentingthemselves with the less accuracy of their sense of hearing. Another kind of vertigo begins with the disordered action of someirritative muscular motions, as those of the stomach from intoxication, orfrom emetics; or those of the ureter, from the stimulus of a stone lodgedin it; and it is probable, that the disordered motions of some of the greatcongeries of glands, as of those which form the liver, or of the intestinalcanal, may occasion vertigo in consequence of their motions beingassociated or catenated with the great circles of irritative motions; andfrom hence it appears, that the means of cure must be adapted to the cause. To prevent sea-sickness it is probable, that the habit of swinging for aweek or two before going on shipboard might be of service. For the vertigofrom failure of sight, spectacles may be used. For the auditory vertigo, æther may be dropt into the ear to stimulate the part, or to dissolveear-wax, if such be a part of the cause. For the vertigo arising fromindigestion, the peruvian bark and a blister are recommended. And for thatowing to a stone in the ureter, venesection, cathartics, opiates, sal sodaaerated. 12. Definition of vertigo. 1. Some of the irritative sensual, or muscularmotions, which were usually not succeeded by sensation, are in this diseasesucceeded by sensation; and the trains or circles of motions, which wereusually catenated with them, are interrupted, or inverted, or proceed inconfusion. 2. The sensitive and voluntary motions continue undisturbed. 3. The associate trains or circles of motions continue; but their catenationswith some of the irritative motions are disordered, or inverted, ordissevered. * * * * * SECT. XXI. OF DRUNKENNESS. 1. _Sleep from satiety of hunger. From rocking children. From uniform sounds. _ 2. _Intoxication from common food after fatigue and inanition. _ 3. _From wine or of opium. Chilness after meals. Vertigo. Why pleasure is produced by intoxication, and by swinging and rocking children. And why pain is relieved by it. _ 4. _Why drunkards stagger and stammer, and are liable to weep. _ 5. _And become delirious, sleepy, and stupid. _ 6. _Or make pale urine and vomit. _ 7. _Objects are seen double. _ 8. _Attention of the mind diminishes drunkenness. _ 9. _Disordered irritative motions of all the senses. _ 10. _Diseases from drunkenness. _ 11. _Definition of drunkenness. _ 1. In the state of nature when the sense of hunger is appeased by thestimulus of agreeable food, the business of the day is over, and the humansavage is at peace with the world, he then exerts little attention toexternal objects, pleasing reveries of imagination succeed, and at lengthsleep is the result: till the nourishment which he has procured, is carriedover every part of the system to repair the injuries of action, and heawakens with fresh vigour, and feels a renewal of his sense of hunger. The juices of some bitter vegetables, as of the poppy and the laurocerasus, and the ardent spirit produced in the fermentation of the sugar found invegetable juices, are so agreeable to the nerves of the stomach, that, taken in a small quantity, they instantly pacify the sense of hunger; andthe inattention to external stimuli with the reveries of imagination, andsleep, succeeds, in the same manner as when the stomach is filled withother less intoxicating food. This inattention to the irritative motions occasioned by external stimuliis a very important circumstance in the approach of sleep, and is producedin young children by rocking their cradles: during which all visibleobjects become indistinct to them. An uniform soft repeated sound, as themurmurs of a gentle current, or of bees, are said to produce the sameeffect, by presenting indistinct ideas of inconsequential sounds, and bythus stealing our attention from other objects, whilst by their continuedreiterations they become familiar themselves, and we cease gradually toattend to any thing, and sleep ensues. 2. After great fatigue or inanition, when the stomach is suddenly filledwith flesh and vegetable food, the inattention to external stimuli, and thereveries of imagination, become so conspicuous as to amount to a degree ofintoxication. The same is at any time produced by superadding a little wineor opium to our common meals; or by taking these separately in considerablequantity; and this more efficaciously after fatigue or inanition; because aless quantity of any stimulating material will excite an organ intoenergetic action, after it has lately been torpid from defect of stimulus;as objects appear more luminous, after we have been in the dark; andbecause the suspension of volition, which is the immediate cause of sleep, is sooner induced, after a continued voluntary exertion has in partexhausted the sensorial power of volition; in the same manner as we cannotcontract a single muscle long together without intervals of inaction. 3. In the beginning of intoxication we are inclined to sleep, as mentionedabove, but by the excitement of external circumstances, as of noise, light, business, or by the exertion of volition, we prevent the approaches of it, and continue to take into our stomach greater quantities of the inebriatingmaterials. By these means the irritative movements of the stomach areexcited into greater action than is natural; and in consequence all theirritative tribes and trains of motion, which are catenated with them, become susceptible of stronger action from their accustomed stimuli;because these motions are excited both by their usual irritation, and bytheir association with the increased actions of the stomach and lacteals. Hence the skin glows, and the heat of the body is increased, by the moreenergetic action of the whole glandular system; and pleasure is introducedin consequence of these increased motions from internal stimulus. Accordingto Law 5. Sect. IV. On Animal Causation. From this great increase of irritative motions from internal stimulus, andthe increased sensation introduced into the system in consequence; andsecondly, from the increased sensitive motions in consequence of thisadditional quantity of sensation, so much sensorial power is expended, thatthe voluntary power becomes feebly exerted, and the irritation from thestimulus of external objects is less forcible; the external parts of theeye are not therefore voluntarily adapted to the distances of objects, whence the apparent motions of those objects either are seen double, orbecome too indistinct for the purpose of balancing the body, and vertigo isinduced. Hence we become acquainted with that very curious circumstance, why thedrunken vertigo is attended with an increase of pleasure; for theirritative ideas and motions occasioned by internal stimulus, that were notattended to in our sober hours, are now just so much increased as to besucceeded by pleasurable sensation, in the same manner as the more violentmotions of our organs are succeeded by painful sensation. And hence agreater quantity of pleasurable sensation is introduced into theconstitution; which is attended in some people with an increase ofbenevolence and good humour. If the apparent motions of objects is much increased, as when we revolve onone foot, or are swung on a rope, the ideas of these apparent motions arealso attended to, and are succeeded with pleasureable sensation, till theybecome familiar to us by frequent use. Hence children are at firstdelighted with these kinds of exercise, and with riding, and failing, andhence rocking young children inclines them to sleep. For though in thevertigo from intoxication the irritative ideas of the apparent motions ofobjects are indistinct from their decrease of energy: yet in the vertigooccasioned by rocking or swinging the irritative ideas of the apparentmotions of objects are increased in energy, and hence they induce pleasureinto the system, but are equally indistinct, and in consequence equallyunfit to balance ourselves by. This addition of pleasure precludes desireor aversion, and in consequence the voluntary power is feebly exerted, andon this account rocking young children inclines them to sleep. In what manner opium and wine act in relieving pain is another article, that well deserves our attention. There are many pains that originate fromdefect as well as from excess of stimulus; of these are those of the sixappetites of hunger, thirst, lust, the want of heat, of distention, and offresh air. Thus if our cutaneous capillaries cease to act from thediminished stimulus of heat, when we are exposed to cold weather, or ourstomach is uneasy for want of food; these are both pains from defect ofstimulus, and in consequence opium, which stimulates all the moving systeminto increased action, must relieve them. But this is not the case in thosepains, which arise from excess of stimulus, as in violent inflammations: inthese the exhibition of opium is frequently injurious by increasing theaction of the system already too great, as in inflammation of the bowelsmortification is often produced by the stimulus of opium. Where, however, no such bad consequences follow; the stimulus of opium, by increasing allthe motions of the system, expends so much of the sensorial power, that theactions of the whole system soon become feebler, and in consequence thosewhich produced the pain and inflammation. 4. When intoxication proceeds a little further, the quantity of pleasurablesensation is so far increased, that all desire ceases, for there is no painin the system to excite it. Hence the voluntary exertions are diminished, staggering and stammering succeed; and the trains of ideas become more andmore inconsistent from this defect of voluntary exertion, as explained inthe sections on sleep and reverie, whilst those passions which are unmixedwith volition are more vividly felt, and shewn with less reserve; hencepining love, or superstitious fear, and the maudling tear dropped on theremembrance of the most trifling distress. 5. At length all these circumstances are increased; the quantity ofpleasure introduced into the system by the increased irritative muscularmotions of the whole sanguiferous, and glandular, and absorbent systems, becomes so great, that the organs of sense are more forcibly excited intoaction by this internal pleasurable sensation, than by the irritation fromthe stimulus of external objects. Hence the drunkard ceases to attend toexternal stimuli, and as volition is now also suspended, the trains of hisideas become totally inconsistent as in dreams, or delirium: and at lengtha stupor succeeds from the great exhaustion of sensorial power, whichprobably does not even admit of dreams, and in which, as in apoplexy, nomotions continue but those from internal stimuli, from sensation, and fromassociation. 6. In other people a paroxysm of drunkenness has another termination; theinebriate, as soon as he begins to be vertiginous, makes pale urine ingreat quantities and very frequently, and at length becomes sick, vomitsrepeatedly, or purges, or has profuse sweats, and a temporary fever ensueswith a quick strong pulse. This in some hours is succeeded by sleep; butthe unfortunate bacchanalian does not perfectly recover himself till aboutthe same time of the succeeding day, when his course of inebriation began. As shewn in Sect. XVII. 1. 7. On Catenation. The temporary fever withstrong pulse is owing to the same cause as the glow on the skin mentionedin the third paragraph of this Section: the flow of urine and sicknessarises from the whole system of irritative motions being thrown intoconfusion by their associations with each other; as in sea-sickness, mentioned in Sect. XX. 4. On Vertigo; and which is more fully explained inSection XXIX. On Diabetes. 7. In this vertigo from internal causes we see objects double, as twocandles instead of one, which is thus explained. Two lines drawn throughthe axes of our two eyes meet at the object we attend to: this angle of theoptic axes increases or diminishes with the less or greater distances ofobjects. All objects before or behind the place where this angle is formed, appear double; as any one may observe by holding up a pen between his eyesand the candle; when he looks attentively at a spot on the pen, andcarelessly at the candle, it will appear double; and the reverse when helooks attentively at the candle and carelessly at the pen; so that in thiscase the muscles of the eye, like those of the limbs, stagger and aredisobedient to the expiring efforts of volition. Numerous objects areindeed sometimes seen by the inebriate, occasioned by the refractions madeby the tears, which stand upon his eye-lids. 8. This vertigo also continues, when the inebriate lies in his bed, in thedark, or with his eyes closed; and this more powerfully than when he iserect, and in the light. For the irritative ideas of the apparent motionsof objects are now excited by irritation from internal stimulus, or byassociation with other irritative motions; and the inebriate, like one in adream, believes the objects of these irritative motions to be present, andfeels himself vertiginous. I have observed in this situation, so long as myeyes and mind were intent upon a book, the sickness and vertigo ceased, andwere renewed again the moment I discontinued this attention; as wasexplained in the preceding account of sea-sickness. Some drunken peoplehave been known to become sober instantly from some accident, that hasstrongly excited their attention, as the pain of a broken bone, or the newsof their house being on fire. 9. Sometimes the vertigo from internal causes, as from intoxication, or atthe beginning of some fevers, becomes so universal, that the irritativemotions which belong to other organs of sense are succeeded by sensation orattention, as well as those of the eye. The vertiginous noise in the earshas been explained in Section XX. On Vertigo. The taste of the saliva, which in general is not attended to, becomes perceptible, and the patientscomplain of a bad taste in their mouth. The common smells of the surrounding air sometimes excite the attention ofthese patients, and bad smells are complained of, which to other people areimperceptible. The irritative motions that belong to the sense of pressure, or of touch, are attended to, and the patient conceives the bed to librate, and is fearful of falling out of it. The irritative motions belonging tothe senses of distention, and of heat, like those above mentioned, becomeattended to at this time: hence we feel the pulsation of our arteries allover us, and complain of heat, or of cold, in parts of the body where thereis no accumulation or diminution of actual heat. All which are to beexplained, as in the last paragraph, by the irritative ideas belonging tothe various senses being now excited by internal stimuli, or by theirassociations with other irritative motions. And that the inebriate, likeone in a dream, believes the external objects, which usually caused theseirritative ideas, to be now present. 10. The diseases in consequence of frequent inebriety, or of daily takingmuch vinous spirit without inebriety, consist in the paralysis, which isliable to succeed violent stimulation. Organs, whose actions are associatedwith others, are frequently more affected than the organ, which isstimulated into too violent action. See Sect. XXIV. 2. 8. Hence in drunkenpeople it generally happens, that the secretory vessels of the liver becomefirst paralytic, and a torpor with consequent gall-stones or schirrus ofthis viscus is induced with concomitant jaundice; otherwise it becomesinflamed in consequence of previous torpor, and this inflammation isfrequently transferred to a more sensible part, which is associated withit, and produces the gout, or the rosy eruption of the face, or some otherleprous eruption on the head, or arms, or legs. Sometimes the stomach isfirst affected, and paralysis of the lacteal system is induced: whence atotal abhorrence from flesh-food, and general emaciation. In others thelymphatic system is affected with paralysis, and dropsy is the consequence. In some inebriates the torpor of the liver produces pain without apparentschirrus, or gall stones, or inflammation, or consequent gout, and in theseepilepsy or insanity are often the consequence. All which will be morefully treated of in the course of the work. I am well aware, that it is a common opinion, that the gout is asfrequently owing to gluttony in eating, as to intemperance in drinkingfermented or spirituous liquors. To this I answer, that I have seen noperson afflicted with the gout, who has not drank freely of fermentedliquor, as wine and water, or small beer; though as the disposition to allthe diseases, which have originated from intoxication, is in some degreehereditary, a less quantity of spirituous potation will induce the gout inthose, who inherit the disposition from their parents. To which I must add, that in young people the rheumatism is frequently mistaken for the gout. Spice is seldom taken in such quantity as to do any material injury to thesystem, flesh-meats as well as vegetables are the natural diet of mankind;with these a glutton may be crammed up to the throat, and fed fat like astalled ox; but he will not be diseased, unless he adds spirituous orfermented liquor to his food. This is well known in the distilleries, wherethe swine, which are fattened by the spirituous sediments of barrels, acquire diseased livers. But mark what happens to a man, who drinks a quartof wine or of ale, if he has not been habituated to it. He loses the useboth of his limbs and of his understanding! He becomes a temporary idiot, and has a temporary stroke of the palsy! And though he slowly recoversafter some hours, is it not reasonable to conclude, that a perpetualrepetition of so powerful a poison must at length permanently affecthim?--If a person accidentally becomes intoxicated by eating a fewmushrooms of a peculiar kind, a general alarm is excited, and he is said tobe poisoned, and emetics are exhibited; but so familiarised are we to theintoxication from vinous spirit, that it occasions laughter rather thanalarm. There is however considerable danger in too hastily discontinuing the useof so strong a stimulus, lest the torpor of the system, or paralysis, should sooner be induced by the omission than by the continuance of thishabit, when unfortunately acquired. A golden rule for determining thequantity, which may with safety be discontinued, is delivered in Sect. XII. 7. 8. 11. Definition of drunkenness. Many of the irritative motions are muchincreased in energy by internal stimulation. 2. A great additional quantity of pleasurable sensation is occasioned bythis increased exertion of the irritative motions. And many sensitivemotions are produced in consequence of this increased sensation. 3. The associated trains and tribes of motions, catenated with theincreased irritative and sensitive motions, are disturbed, and proceed inconfusion. 4. The faculty of volition is gradually impaired, whence proceeds theinstability of locomotion, inaccuracy of perception, and inconsistency ofideas; and is at length totally suspended, and a temporary apoplexysucceeds. * * * * * SECT. XXII. OF PROPENSITY TO MOTION, REPETITION AND IMITATION. I. _Accumulation of sensorial power in hemiplagia, in sleep, in cold fit of fever, in the locomotive muscles, in the organs of sense. Produces propensity to action. _ II. _Repetition by three sensorial powers. In rhimes and alliterations, in music, dancing, architecture, landscape-painting, beauty. _ III. 1. _Perception consists in imitation. Four kinds of imitation. _ 2. _Voluntary. Dogs taught to dance. _ 3. _Sensitive. Hence sympathy, and all our virtues. Contagious matter of venereal ulcers, of hydrophobia, of jail-fever, of small-pox, produced by imitation, and the sex of the embryon. _ 4. _Irritative imitation. _ 5. _Imitations resolvable into associations. _ I. 1. In the hemiplagia, when the limbs on one side have lost their powerof voluntary motion, the patient is for many days perpetually employed inmoving those of the other. 2. When the voluntary power is suspended duringsleep, there commences a ceaseless flow of sensitive motions, or ideas ofimagination, which compose our dreams. 3. When in the cold fit of anintermittent fever some parts of the system have for a time continuedtorpid, and have thus expended less than their usual expenditure ofsensorial power; a hot fit succeeds, with violent action of those vessels, which had previously been quiescent. All these are explained from anaccumulation of sensorial power during the inactivity of some part of thesystem. Besides the very great quantity of sensorial power perpetually produced andexpended in moving the arterial, venous, and glandular systems, with thevarious organs or digestion, as described in Section XXXII. 3. 2. There isalso a constant expenditure of it by the action of our locomotive musclesand organs of sense. Thus the thickness of the optic nerves, where theyenter the eye, and the great expansion of the nerves of touch beneath thewhole of the cuticle, evince the great consumption of sensorial power bythese senses. And our perpetual muscular actions in the common offices oflife, and in constantly preserving the perpendicularity of our bodiesduring the day, evince a considerable expenditure of the spirit ofanimation by our locomotive muscles. It follows, that if the exertion ofthese organs of sense and muscles be for a while intermitted, that somequantity of sensorial power must be accumulated, and a propensity toactivity of some kind ensue from the increased excitability of the system. Whence proceeds the irksomeness of a continued attitude, and of an indolentlife. However small this hourly accumulation of the spirit of animation may be, it produces a propensity to some kind of action; but it neverthelessrequires either desire or aversion, either pleasure or pain, or someexternal stimulus, or a previous link of association, to excite the systeminto activity; thus it frequently happens, when the mind and body are sounemployed as not to possess any of the three first kinds of stimuli, thatthe last takes place, and consumes the small but perpetual accumulation ofsensorial power. Whence some indolent people repeat the same verse forhours together, or hum the same tune. Thus the poet: Onward he trudged, not knowing what he sought, And whistled, as he went, for want of thought. II. The repetitions of motions may be at first produced either by volition, or by sensation, or by irritation, but they soon become easier to performthan any other kinds of action, because they soon become associatedtogether, according to Law the seventh, Section IV. On Animal Causation. And because their frequency of repetition, if as much sensorial power beproduced during every reiteration as is expended, adds to the facility oftheir production. If a stimulus be repeated at uniform intervals of time, as described inSect. XII. 3. 3. The action, whether of our muscles or organs of sense, isproduced with still greater facility or energy; because the sensorial powerof association, mentioned above, is combined with the sensorial power ofirritation; that is, in common language, the acquired habit assists thepower of the stimulus. This not only obtains in the annual, lunar, and diurnal catenations ofanimal motions, as explained in Sect. XXXVI. Which are thus performed withgreat facility and energy; but in every less circle of actions or ideas, asin the burthen of a song, or the reiterations of a dance. To the facilityand distinctness, with which we hear sounds at repeated intervals, we owethe pleasure, which we receive from musical time, and from poetic time; asdescribed in Botanic Garden, P. 2. Interlude 3. And to this the pleasure wereceive from the rhimes and alliterations of modern verification; thesource of which without this key would be difficult to discover. And tothis likewise should be ascribed the beauty of the duplicature in theperfect tense of the Greek verbs, and of some Latin ones, as tango tetegi, mordeo momordi. There is no variety of notes referable to the gamut in the beating of thedrum, yet if it be performed in musical time, it is agreeable to our ears;and therefore this pleasurable sensation must be owing to the repetition ofthe divisions of the sounds at certain intervals of time, or musical bars. Whether these times or bars are distinguished by a pause, or by anemphasis, or accent, certain it is, that this distinction is perpetuallyrepeated; otherwise the ear could not determine instantly, whether thesuccessions of sound were in common or in triple time. In common time thereis a division between every two crotchets, or other notes of equivalenttime; though the bar in written music is put after every fourth crotchet, or notes equivalent in time; in triple time the division or bar is afterevery three crotchets, or notes equivalent; so that in common time therepetition recurs more frequently than in triple time. The grave or heroicverses of the Greek and Latin poets are written in common time; the Frenchheroic verses, and Mr. Anstie's humorous verses in his Bath Guide, arewritten in the same time as the Greek and Latin verses, but are one barshorter. The English grave or heroic verses are measured by triple time, asMr. Pope's translation of Homer. But besides these little circles of musical time, there are the greaterreturning periods, and the still more distant choruses, which, like therhimes at the ends of verses, owe their beauty to repetition; that is, tothe facility and distinctness with which we perceive sounds, which weexpect to perceive, or have perceived before; or in the language of thiswork, to the greater ease and energy with which our organ is excited by thecombined sensorial powers of association and irritation, than by the lattersingly. A certain uniformity or repetition of parts enters the very composition ofharmony. Thus two octaves nearest to each other in the scale commence theirvibrations together after every second vibration of the higher one. Andwhere the first, third, and fifth compose a chord the vibrations concur orcoincide frequently, though less to than in the two octaves. It is probablethat these chords bear some analogy to a mixture of three alternate coloursin the sun's spectrum separated by a prism. The pleasure we receive from a melodious succession of notes referable tothe gamut is derived from another source, viz. To the pandiculation orcounteraction of antagonist fibres. See Botanic Garden, P. 2. Interlude 3. If to these be added our early associations of agreeable ideas with certainproportions of sound, I suppose, from these three sources springs all thedelight of music, so celebrated by ancient authors, and so enthusiasticallycultivated at present. See Sect. XVI. No. 10. On Instinct. This kind of pleasure arising from repetition, that is from the facilityand distinctness, with which we perceive and understand repeatedsensations, enters into all the agreeable arts; and when it is carried toexcess is termed formality. The art of dancing like that of music dependsfor a great part of the pleasure, it affords, on repetition; architecture, especially the Grecian, consists of one part being a repetition of another;and hence the beauty of the pyramidal outline in landscape-painting; whereone side of the picture may be said in some measure to balance the other. So universally does repetition contribute to our pleasure in the fine arts, that beauty itself has been defined by some writers to consist in a duecombination of uniformity and variety. See Sect. XVI. 6. III. 1. Man is termed by Aristotle an imitative animal; this propensity toimitation not only appears in the actions of children, but in all thecustoms and fashions of the world: many thousands tread in the beaten pathsof others, for one who traverses regions of his own discovery. The originof this propensity of imitation has not, that I recollect, been deducedfrom any known principle; when any action presents itself to the view of achild, as of whetting a knife, or threading a needle, the parts of thisaction in respect of time, motion, figure, is imitated by a part of theretina of his eye; to perform this action therefore with his hands iseasier to him than to invent any new action, because it consists inrepeating with another set of fibres, viz. With the moving muscles, what hehad just performed by some parts of the retina; just as in dancing wetransfer the times of motion from the actions of the auditory nerves to themuscles of the limbs. Imitation therefore consists of repetition, which wehave shewn above to be the easiest kind of animal action, and which weperpetually fall into, when we possess an accumulation of sensorial power, which is not otherwise called into exertion. It has been shewn, that our ideas are configurations of the organs ofsense, produced originally in consequence of the stimulus of externalbodies. And that these ideas, or configurations of the organs of sense, referable in some property a correspondent property of external matter; asthe parts of the senses of light and of touch, which are excited intoaction, resemble in figure the figure of the stimulating body; and probablyalso the colour, and the quantity of density, which they perceive. Asexplained in Sect. XIV. 2. 2. Hence it appears, that our perceptionsthemselves are copies, that is, imitations of some properties of externalmatter; and the propensity to imitation is thus interwoven with ourexistence, as it is produced by the stimuli of external bodies, and isafterwards repeated by our volitions and sensations, and thus constitutesall the operations of our minds. 2. Imitations resolve themselves into four kinds, voluntary, sensitive, irritative, and associate. The voluntary imitations are, when we imitatedeliberately the actions of others, either by mimicry, as in acting a play, or in delineating a flower; or in the common actions of our lives, as inour dress, cookery, language, manners, and even in our habits of thinking. Not only the greatest part of mankind learn all the common arts of life byimitating others, but brute animals seem capable of acquiring knowledgewith greater facility by imitating each other, than by any methods by whichwe can teach them; as dogs and cats, when they are sick, learn of eachother to eat grass; and I suppose, that by making an artificial dog performcertain tricks, as in dancing on his hinder legs, a living dog might beeasily induced to imitate them; and that the readiest way of instructingdumb animals is by practising them with others of the same species, whichhave already learned the arts we wish to teach them. The important use ofimitation in acquiring natural language is mentioned in Section XVI. 7. And8. On Instinct. 3. The sensitive imitations are the immediate consequences of pleasure orpain, and these are often produced even contrary to the efforts of thewill. Thus many young men on seeing cruel surgical operations become sick, and some even feel pain in the parts of their own bodies, which they seetortured or wounded in others; that is, they in some measure imitate by theexertions of their own fibres the violent actions, which they witnessed inthose of others. In this case a double imitation takes place, first theobserver imitates with the extremities of the optic nerve the mangledlimbs, which are present before his eyes; then by a second imitation heexcites to violent action of the fibres of his own limbs as to produce painin those parts of his own body, which he saw wounded in another. In thesepains produced by imitation the effect has some similarity to the cause, which distinguishes them from those produced by association; as the painsof the teeth, called tooth-edge, which are produced by association withdisagreeable sounds, as explained in Sect. XVI. 10. The effect of this powerful agent, imitation, in the moral world, ismentioned in Sect. XVI. 7. As it is the foundation of all our intellectualsympathies with the pains and pleasures of others, and is in consequencethe source of all our virtues. For in what consists our sympathy with themiseries, or with the joys, of our fellow creatures, but in an involuntaryexcitation of ideas in some measure similar or imitative of those, which webelieve to exist in the minds of the persons, whom we commiserate orcongratulate? There are certain concurrent or successive actions of some of the glands, or other parts of the body, which are possessed of sensation, which becomeintelligible from this propensity to imitation. Of these are the productionof matter by the membranes of the fauces, or by the skin, in consequence ofthe venereal disease previously affecting the parts of generation. Since asno fever is excited, and as neither the blood of such patients, nor eventhe matter from ulcers of the throat, or from cutaneous ulcers, will byinoculation produce the venereal disease in others, as observed by Mr. Hunter, there is reason to conclude, that no contagious matter is conveyedthither by the blood-vessels, but that a milder matter is formed by theactions of the fine vessels in those membranes imitating each other. SeeSection XXXIII. 2. 9. In this disease the actions of these vesselsproducing ulcers on the throat and skin are imperfect imitations of thoseproducing chanker, or gonorrhoea; since the matter produced by them is notinfectious, while the imitative actions in the hydrophobia appear to beperfect resemblances, as they produce a material equally infectious withthe original one, which induced them. The contagion from the bite of a mad dog differs from other contagiousmaterials, from its being communicable from other animals to mankind, andfrom many animals to each other; the phenomena attending the hydrophobiaare in some degree explicable on the foregoing theory. The infectiousmatter does not appear to enter the circulation, as it cannot be tracedalong the course of the lymphatics from the wound, nor is there anyswelling of the lymphatic glands, nor does any fever attend, as occurs inthe small-pox, and in many other contagious diseases; yet by some unknownprocess the disease is communicated from the wound to the throat, and thatmany months after the injury, so as to produce pain and hydrophobia, with asecretion of infectious saliva of the same kind, as that of the mad dog, which inflicted the wound. This subject is very intricate. --It would appear, that by certain morbidactions of the salivary glands of the mad dog, a peculiar kind of saliva isproduced; which being instilled into a wound of another animal stimulatesthe cutaneous or mucous glands into morbid actions, but which areineffectual in respect to the production of a similar contagious material;but the salivary glands by irritative sympathy are thrown into similaraction, and produce an infectious saliva similar to that instilled into thewound. Though in many contagious fevers a material similar to that which producedthe disease, is thus generated by imitation; yet there are other infectiousmaterials, which do not thus propagate themselves, but which seem to actlike slow poisons. Of this kind was the contagious matter, which producedthe jail-fever at the assizes at Oxford about a century ago. Which, thoughfatal to so many, was not communicated to their nurses or attendants. Inthese cases, the imitations of the fine vessels, as above described, appearto be imperfect, and do not therefore produce a matter similar to that, which stimulates them; in this circumstance resembling the venereal matterin ulcers of the throat or skin, according to the curious discovery of Mr. Hunter above related, who found, by repeated inoculations, that it wouldnot infect. Hunter on Venereal Disease, Part vi. Ch. 1. Another example of morbid imitation is in the production of a greatquantity of contagious matter, as in the inoculated small-pox, from a smallquantity of it inserted into the arm, and probably diffused in the blood. These particles of contagious matter stimulate the extremities of the finearteries of the skin, and cause them to imitate some properties of thoseparticles of contagious matter, so as to produce a thousandfold of asimilar material. See Sect. XXXIII. 2. 6. Other instances are mentioned inthe Section on Generation, which shew the probability that the extremitiesof the seminal glands may imitate certain ideas of the mind, or actions ofthe organs of sense, and thus occasion the male or female sex of theembryon. See Sect. XXXIX. 6. 4. We come now to those imitations, which are not attended with sensation. Of these are all the irritative ideas already explained, as when the retinaof the eye imitates by its action or configuration the tree or the bench, which I shun in walking past without attending to them. Other examples ofthese irritative imitations are daily observable in common life; thus oneyawning person shall set a whole company a yawning; and some have acquiredwinking of the eyes or impediments of speech by imitating their companionswithout being conscious of it. 5. Besides the three species of imitations above described there may besome associate motions, which may imitate each other in the kind as well asin the quantity of their action; but it is difficult to distinguish themfrom the associations of motions treated of in Section XXXV. Where theactions of other persons are imitated there can be no doubt, or where weimitate a preconceived idea by exertion of our locomotive muscles, as inpainting a dragon; all these imitations may aptly be referred to thesources above described of the propensity to activity, and the facility ofrepetition; at the same time I do not affirm, that all those other apparentsensitive and irritative imitations may not be resolvable into associationsof a peculiar kind, in which certain distant parts of similar irritabilityor sensibility, and which have habitually acted together, may affect eachother exactly with the same kinds of motion; as many parts are known tosympathise in the quantity of their motions. And that therefore they may beultimately resolvable into associations of action, as described in Sect. XXXV. * * * * * SECT. XXIII. OF THE CIRCULATORY SYSTEM. I. _The heart and arteries have no antagonist muscles. Veins absorb the blood, propel it forwards, and distend the heart; contraction of the heart distends the arteries. Vena portarum. _ II. _Glands which take their fluids from the blood. With long necks, with short necks. _ III. _Absorbent system. _ IV. _Heat given out from glandular secretions. Blood changes colour in the lungs and in the glands and capillaries. _ V. _Blood is absorbed by veins, as chyle by lacteal vessels, otherwise they could not join their streams. _ VI. _Two kinds of stimulus, agreeable and disagreeable. Glandular appetency. Glands originally possessed sensation. _ I. We now step forwards to illustrate some of the phenomena of diseases, and to trace out their most efficacious methods of cure; and shall commencethis subject with a short description of the circulatory system. As the nerves, whose extremities form our various organs of sense andmuscles, are all joined, or communicate, by means of the brain, for theconvenience perhaps of the distribution of a subtile ethereal fluid for thepurpose of motion; so all those vessels of the body, which carry thegrosser fluids for the purposes of nutrition, communicate with each otherby the heart. The heart and arteries are hollow muscles, and are therefore indued withpower of contraction in consequence of stimulus, like all other muscularfibres; but, as they have no antagonist muscles, the cavities of thevessels, which they form, would remain for ever closed, after they havecontracted themselves, unless some extraneous power be applied to againdistend them. This extraneous power in respect to the heart is the currentof blood, which is perpetually absorbed by the veins from the variousglands and capillaries, and pushed into the heart by a power probably verysimilar to that, which raises the sap in vegetables in the spring, which, according to Dr. Hale's experiment on the stump of a vine, exerted a forceequal to a column of water above twenty feet high. This force of thecurrent of blood in the veins is partly produced by their absorbent power, exerted at the beginning of every fine ramification; which may be conceivedto be a mouth absorbing blood, as the mouths of the lacteals and lymphaticsabsorb chyle and lymph. And partly by their intermitted compression by thepulsations of their generally concomitant arteries; by which the blood isperpetually propelled towards the heart, as the valves in many veins, andthe absorbent mouths in them all, will not suffer it to return. The blood, thus forcibly injected into the chambers of the heart, distendsthis combination of hollow muscles; till by the stimulus of distention theycontract themselves; and, pushing forwards the blood into the arteries, exert sufficient force to overcome in less than a second of time the visinertiæ, and perhaps some elasticity, of the very extensive ramificationsof the two great systems of the aortal and pulmonary arteries. The powernecessary to do this in so short a time must be considerable, and has beenvariously estimated by different physiologists. The muscular coats of the arterial system are then brought into action bythe stimulus of distention, and propel the blood to the mouths, or throughthe convolutions, which precede the secretory apertures of the variousglands and capillaries. In the vessels of the liver there is no intervention of the heart; but thevena portarum, which does the office of an artery, is distended by theblood poured into it from the mesenteric veins, and is by this distentionstimulated to contract itself, and propel the blood to the mouths of thenumerous glands, which compose that viscus. II. The glandular system of vessels may be divided into those, which takesome fluid from the circulation; and those, which give something to it. Those, which take their fluid from the circulation are the various glands, by which the tears, bile, urine, perspiration, and many other secretionsare produced; these glands probably consist of a mouth to select, a bellyto digest, and an excretory aperture to emit their appropriated fluids; theblood is conveyed by the power of the heart and arteries to the mouths ofthese glands, it is there taken up by the living power of the gland, andcarried forwards to its belly, and excretory aperture, where a part isseparated, and the remainder absorbed by the veins for further purposes. Some of these glands are furnished with long convoluted necks or tubes, asthe seminal ones, which are curiously seen when injected with quicksilver. Others seem to consist of shorter tubes, as that great congeries of glands, which constitute the liver, and those of the kidneys. Some have theirexcretory apertures opening into reservoirs, as the urinary andgall-bladders. And others on the external body, as those which secrete thetears, and perspirable matter. Another great system of glands, which have very short necks, are thecapillary vessels; by which the insensible perspiration is secreted on theskin; and the mucus of various consistences, which lubricates theinterstices of the cellular membrane, of the muscular fibres, and of allthe larger cavities of the body. From the want of a long convolution ofvessels some have doubted, whether these capillaries should be consideredas glands, and have been led to conclude, that the perspirable matterrather exuded than was secreted. But the fluid of perspiration is notsimple water, though that part of it, which exhales into the air may besuch; for there is another part of it, which in a state of health isabsorbed again; but which, when the absorbents are diseased, remains on thesurface of the skin, in the form of scurf, or indurated mucus. Anotherthing, which shews their similitude to other glands, is their sensibilityto certain affections of the mind; as is seen in the deeper colour of theskin in the blush of shame, or the greater paleness of it from fear. III. Another series of glandular vessels is called the absorbent system;these open their mouths into all the cavities, and upon all those surfacesof the body, where the excretory apertures of the other glands pour outtheir fluids. The mouths of the absorbent system drink up a part or thewhole of these fluids, and carry them forwards by their living power totheir respective glands, which are called conglobate glands. There thesefluids undergo some change, before they pass on into the circulation; butif they are very acrid, the conglobate gland swells, and sometimessuppurates, as in inoculation of the small-pox, in the plague, and invenereal absorptions; at other times the fluid may perhaps continue there, till it undergoes some chemical change, that renders it less noxious; or, what is more likely, till it is regurgitated by the retrograde motion ofthe gland in spontaneous sweats or diarrhoeas, as disagreeing food isvomited from the stomach. IV. As all the fluids, that pass through these glands, and capillaryvessels, undergo a chemical change, acquiring new combinations, the matterof heat is at the same time given out; this is apparent, since whateverincreases insensible perspiration, increases the heat of the skin; and whenthe action of these vessels is much increased but for a moment, as inblushing, a vivid heat on the skin is the immediate consequence. So whengreat bilious secretions, or those of any other gland, are produced, heatis generated in the part in proportion to the quantity of the secretion. The heat produced on the skin by blushing may be thought by some too suddento be pronounced a chemical effect, as the fermentations or newcombinations taking place in a fluid is in general a slower process. Yetare there many chemical mixtures in which heat is given out asinstantaneously; as in solutions of metals in acids, or in mixtures ofessential oils and acids, as of oil of cloves and acid of nitre. So thebruised parts of an unripe apple become almost instantaneously sweet; andif the chemico-animal process of digestion be stopped for but a moment, asby fear, or even by voluntary eructation, a great quantity of air isgenerated, by the fermentation, which instantly succeeds the stop ofdigestion. By the experiments of Dr. Hales it appears, that an apple duringfermentation gave up above six hundred times its bulk of air; and thematerials in the stomach are such, and in such a situation, as immediatelyto run into fermentation, when digestion is impeded. As the blood passes through the small vessels of the lungs, which connectthe pulmonary artery and vein, it undergoes a change of colour from a darkto a light red; which may be termed a chemical change, as it is known to beeffected by an admixture of oxygene, or vital air; which, according to adiscovery of Dr. Priestley, passes through the moist membranes, whichconstitute the sides of these vessels. As the blood passes through thecapillary vessels, and glands, which connect the aorta and its variousbranches with their correspondent veins in the extremities of the body, itagain loses the bright red colour, and undergoes some new combinations inthe glands or capillaries, in which the matter of heat is given out fromthe secreted fluids. This process therefore, as well as the process ofrespiration, has some analogy to combustion, as the vital air or oxygeneseems to become united to some inflammable base, and the matter of heatescapes from the new acid, which is thus produced. V. After the blood has passed these glands and capillaries, and parted withwhatever they chose to take from it, the remainder is received by theveins, which are a set of blood-absorbing vessels in general correspondingwith the ramifications of the arterial system. At the extremity of the fineconvolutions of the glands the arterial force ceases; this in respect tothe capillary vessels, which unite the extremities of the arteries with thecommencement of the veins, is evident to the eye, on viewing the tail of atadpole by means of a solar, or even by a common microscope, for globulesof blood are seen to endeavour to pass, and to return again and again, before they become absorbed by the mouths of the veins; which returning ofthese globules evinces, that the arterial force behind them has ceased. Theveins are furnished with valves like the lymphatic absorbents; and thegreat trunks of the veins, and of the lacteals and lymphatics, jointogether before the ingress of their fluids into the left chamber of theheart; both which evince, that the blood in the veins, and the lymph andchyle in the lacteals and lymphatics, are carried on by a similar force;otherwise the stream, which was propelled with a less power, could notenter the vessels, which contained the stream propelled with a greaterpower. From whence it appears, that the veins are a system of vesselsabsorbing blood, as the lacteals and lymphatics are a system of vesselsabsorbing chyle and lymph. See Sect. XXVII. 1. VI. The movements of their adapted fluids in the various vessels of thebody are carried forwards by the actions of those vessels in consequence oftwo kinds of stimulus, one of which may be compared to a pleasurablesensation or desire inducing the vessel to seize, and, as it were, toswallow the particles thus selected from the blood; as is done by themouths of the various glands, veins, and other absorbents, which may becalled glandular appetency. The other kind of stimulus may be compared todisagreeable sensation, or aversion, as when the heart has received theblood, and is stimulated by it to push it forwards into the arteries; thesame again stimulates the arteries to contract, and carry forwards theblood to their extremities, the glands and capillaries. Thus the mesentericveins absorb the blood from the intestines by glandular appetency, andcarry it forward to the vena portarum; which acting as an artery contractsitself by disagreeable stimulus, and pushes it to its ramified extremities, the various glands, which constitute the liver. It seems probable, that at the beginning of the formation of these vesselsin the embryon, an agreeable sensation was in reality felt by the glandsduring secretion, as is now felt in the act of swallowing palatable food;and that a disagreeable sensation was originally felt by the heart from thedistention occasioned by the blood, or by its chemical stimulus; but thatby habit these are all become irritative motions; that is, such motions asdo not affect the whole system, except when the vessels are diseased byinflammation. * * * * * SECT. XXIV. OF THE SECRETIONS OF SALIVA, AND OF TEARS, AND OF THE LACRYMAL SACK. I. _Secretion of saliva increased by mercury in the blood. _ 1. _By the food in the mouth. Dryness of the mouth not from a deficiency of saliva. _ 2. _By Sensitive ideas. _ 3. _By volition. _ 4. _By distasteful substances. It is secreted in a dilute and saline state. It then becomes more viscid. _ 5. _By ideas of distasteful substances. _ 6. _By nausea. _ 7. _By aversion. _ 8. _By catenation with stimulating substances in the ear. _ II. 1. _Secretion of tears less in sleep. From stimulation of their excretory duct. _ 2. _Lacrymal sack is a gland. _ 3. _Its uses. _ 4. _Tears are secreted, when the nasal duct is stimulated. _ 5. _Or when it is excited by sensation. _ 6. _Or by volition. _ 7. _The lacrymal sack can regurgitate its contents into the eye. _ 8. _More tears are secreted by association with the irritation of the nasal duct of the lacrymal sack, than the puncta lacrymalia can imbibe. Of the gout in the liver and stomach. _ I. The salival glands drink up a certain fluid from the circumfluent blood, and pour it into the mouth. They are sometimes stimulated into action bythe blood, that surrounds their origin, or by some part of thatheterogeneous fluid: for when mercurial salts, or oxydes, are mixed withthe blood, they stimulate these glands into unnatural exertions; and thenan unusual quantity of saliva is separated. 1. As the saliva secreted by these glands is most wanted during themastication of our food, it happens, when the terminations of their ductsin the mouth are stimulated into action, the salival glands themselves arebrought into increased action at the same time by association, and separatea greater quantity of their juices from the blood; in the same manner astears are produced in greater abundance during the stimulus of the vapourof onions, or of any other acrid material in the eye. The saliva is thus naturally poured into the mouth only during the stimulusof our food in mastication; for when there is too great an exhalation ofthe mucilaginous secretion from the membranes, which line the mouth, or toogreat an absorption of it, the mouth becomes dry, though there is nodeficiency in the quantity of saliva; as in those who sleep with theirmouths open, and in some fevers. 2. Though during the mastication of our natural food the salival glands areexcited into action by the stimulus on their excretory ducts, and a duequantity of saliva is separated from the blood, and poured into the mouth;yet as this mastication of our food is always attended with a degree ofpleasure; and that pleasurable sensation is also connected with our ideasof certain kinds of aliment; it follows, that when these ideas arereproduced, the pleasurable sensation arises along with them, and thesalival glands are excited into action, and fill the mouth with saliva fromthis sensitive association, as is frequently seen in dogs, who slaver atthe sight of food. 3. We have also a voluntary power over the action of these salival glands, for we can at any time produce a flow of saliva into our mouth, and spitout, or swallow it at will. 4. If any very acrid material be held in the mouth, as the root ofpyrethrum, or the leaves of tobacco, the salival glands are stimulated intostronger action than is natural, and thence secrete a much larger quantityof saliva; which is at the same time more viscid than in its natural state;because the lymphatics, that open their mouths into the ducts of thesalival glands, and on the membranes, which line the mouth, are likewisestimulated into stronger action, and absorb the more liquid parts of thesaliva with greater avidity; and the remainder is left both in greaterquantity and more viscid. The increased absorption in the mouth by some stimulating substances, whichare called astringents, as crab juice, is evident from the instant drynessproduced in the mouth by a small quantity of them. As the extremities of the glands are of exquisite tenuity, as appears bytheir difficulty of injection, it was necessary for them to secrete theirfluids in a very dilute state; and, probably for the purpose of stimulatingthem into action, a quantity of neutral salt is likewise secreted or formedby the gland. This aqueous and saline part of all secreted fluids is againreabsorbed into the habit. More than half of some secreted fluids is thusimbibed from the reservoirs, into which they are poured; as in the urinarybladder much more than half of what is secreted by the kidneys becomesreabsorbed by the lymphatics, which are thickly dispersed around the neckof the bladder. This seems to be the purpose of the urinary bladders offish, as otherwise such a receptacle for the urine could have been of nouse to an animal immersed in water. 5. The idea of substances disagreeably acrid will also produce a quantityof saliva in the mouth; as when we smell very putrid vapours, we areinduced to spit out our saliva, as if something disagreeable was actuallyupon our palates. 6. When disagreeable food in the stomach produces nausea, a flow of salivais excited in the mouth by association; as efforts to vomit are frequentlyproduced by disagreeable drugs in the mouth by the same kind ofassociation. 7. A preternatural flow of saliva is likewise sometimes occasioned by adisease of the voluntary power; for if we think about our saliva, anddetermine not to swallow it, or not to spit it out, an exertion is producedby the will, and more saliva is secreted against our wish; that is, by ouraversion, which bears the same analogy to desire, as pain does to pleasure;as they are only modifications of the same disposition of the sensorium. See Class IV. 3. 2. 1. 8. The quantity of saliva may also be increased beyond what is natural, bythe catenation of the motions of these glands with other motions, orsensations, as by an extraneous body in the ear; of which I have known aninstance; or by the application of stizolobium, siliqua hirsuta, cowhage, to the seat of the parotis, as some writers have affirmed. II. 1. The lacrymal gland drinks up a certain fluid from the circumfluentblood, and pours it on the ball of the eye, on the upper part of theexternal corner of the eyelids. Though it may perhaps be stimulated intothe performance of its natural action by the blood, which surrounds itsorigin, or by some part of that heterogeneous fluid; yet as the tearssecreted by this gland are more wanted at some times than at others, itssecretion is variable, like that of the saliva above mentioned, and ischiefly produced when its excretory duct is stimulated; for in our commonsleep there seems to be little or no secretion of tears; though they areoccasionally produced by our sensations in dreams. Thus when any extraneous material on the eye-ball, or the dryness of theexternal covering of it, or the coldness of the air, or the acrimony ofsome vapours, as of onions, stimulates the excretory duct of the lacrymalgland, it discharges its contents upon the ball; a quicker secretion takesplace in the gland, and abundant tears succeed, to moisten, clean, andlubricate the eye. These by frequent nictitation are diffused over thewhole ball, and as the external angle of the eye in winking is closedsooner than the internal angle, the tears are gradually driven forwards, and downwards from the lacrymal gland to the puncta lacrymalia. 2. The lacrymal sack, with its puncta lacrymalia, and its nasal duct, is acomplete gland; and is singular in this respect, that it neither derivesits fluid from, nor disgorges it into the circulation. The simplicity ofthe structure of this gland, and both the extremities of it being on thesurface of the body, makes it well worthy our minuter observation; as theactions of more intricate and concealed glands may be better understoodfrom their analogy to this. 3. This simple gland consists of two absorbing mouths, a belly, and anexcretory duct. As the tears are brought to the internal angle of the eye, these two mouths drink them up, being stimulated into action by this fluid, which they absorb. The belly of the gland, or lacrymal sack, is thusfilled, in which the saline part of the tears is absorbed, and when theother end of the gland, or nasal duct, is stimulated by the dryness, orpained by the coldness of the air, or affected by any acrimonious dust orvapour in the nostrils, it is excited into action together with the sack, and the tears are disgorged upon the membrane, which lines the nostrils;where they serve a second purpose to moisten, clean, and lubricate, theorgan of smell. 4. When the nasal duct of this gland is stimulated by any very acridmaterial, as the powder of tobacco, or volatile spirits, it not onlydisgorges the contents of its belly or receptacle (the lacrymal sack), andabsorbs hastily all the fluid, that is ready for it in the corner of theeye; but by the association of its motions with those of the lacrymalgland, it excites that also into increased action, and a large flow oftears is poured into the eye. 5. This nasal duct is likewise excited into strong action by sensitiveideas, as in grief, or joy, and then also by its associations with thelacrymal gland it produces a great flow of tears without any externalstimulus; as is more fully explained in Sect. XVI. 8. On Instinct. 6. There are some, famous in the arts of exciting compassion, who are saidto have acquired a voluntary power of producing a flow of tears in the eye;which, from what has been said in the section on Instinct above mentioned, I should suspect, is performed by acquiring a voluntary power over theaction of this nasal duct. 7. There is another circumstance well worthy our attention, that when byany accident this nasal duct is obstructed, the lacrymal sack, which is thebelly or receptacle of this gland, by slight pressure of the finger isenabled to disgorge its contents again into the eye; perhaps the bile inthe same manner, when the biliary ducts are obstructed, is returned intothe blood by the vessels which secrete it? 8. A very important though minute occurrence must here be observed, thatthough the lacrymal gland is only excited into action, when we weep at adistressful tale, by its association with this nasal duct, as is more fullyexplained in Sect. XVI. 8; yet the quantity of tears secreted at once ismore than the puncta lacrymalia can readily absorb; which shews _that themotions occasioned by associations are frequently more energetic than theoriginal motions, by which they were occasioned_. Which we shall haveoccasion to mention hereafter, to illustrate, why pains frequently exist ina part distant from the cause of them, as in the other end of the urethra, when a stone stimulates the neck of the bladder. And why inflammationsfrequently arise in parts distant from their cause, as the gutta rosea ofdrinking people, from an inflamed liver. The inflammation of a part is generally preceded by a torpor or quiescenceof it; if this exists in any large congeries of glands, as in the liver, orany membranous part, as the stomach, pain is produced and chilliness inconsequence of the torpor of the vessels. In this situation sometimes aninflammation of the parts succeeds the torpor; at other times a distantmore sensible part becomes inflamed; whose actions have previously beenassociated with it; and the torpor of the first part ceases. This Iapprehend happens, when the gout of the foot succeeds a pain of the biliaryduct, or of the stomach. Lastly, it sometimes happens, that the pain oftorpor exists without any consequent inflammation of the affected part, orof any distant part associated with it, as in the membranes about thetemple and eye-brows in hemicrania, and in those pains, which occasionconvulsions; if this happens to gouty people, when it affects the liver, Isuppose epileptic fits are produced; and, when it affects the stomach, death is the consequence. In these cases the pulse is weak, and theextremities cold, and such medicines as stimulate the quiescent parts intoaction, or which induce inflammation in them, or in any distant part, whichis associated with them, cures the present pain of torpor, and saves thepatient. I have twice seen a gouty inflammation of the liver, attended withjaundice; the patients after a few days were both of them affected withcold fits, like ague-fits, and their feet became affected with gout, andthe inflammation of their livers ceased. It is probable, that the uneasysensations about the stomach, and indigestion, which precedes goutyparoxysms, are generally owing to torpor or slight inflammation of theliver, and biliary ducts; but where great pain with continued sickness, with feeble pulse, and sensation of cold, affect the stomach in patientsdebilitated by the gout, that it is a torpor of the stomach itself, anddestroys the patient from the great connexion of that viscus with the vitalorgans. See Sect. XXV. 17. * * * * * SECT. XXV. OF THE STOMACH AND INTESTINES. 1. _Of swallowing our food. Ruminating animals. _ 2. _Action of the stomach. _ 3. _Action of the intestines. Irritative motions connected with these. _ 4. _Effects of repletion. _ 5. _Stronger action of the stomach and intestines from more stimulating food. _ 6. _Their action inverted by still greater stimuli. Or by disgustful ideas. Or by volition. _ 7. _Other glands strengthen or invert their motions by sympathy. _ 8. _Vomiting performed by intervals. _ 9. _Inversion of the cutaneous absorbents. _ 10. _Increased secretion of bile and pancreatic juice. _ 11. _Inversion of the lacteals. _ 12. _And of the bile-ducts. _ 13. _Case of a cholera. _ 14. _Further account of the inversion of lacteals. _ 15. _Iliac passions. Valve of the colon. _ 16. _Cure of the iliac passion. _ 17. _Pain of gall-stone distinguished from pain of the stomach. Gout of the stomach from torpor, from inflammation. Intermitting pulse owing to indigestion. To overdose of foxglove. Weak pulse from emetics. Death from a blow on the stomach. From gout of the stomach. _ 1. The throat, stomach, and intestines, may be considered as one greatgland; which like the lacrymal sack above mentioned, neither begins norends in the circulation. Though the act of masticating our aliment belongsto the sensitive class of motions, for the pleasure of its taste inducesthe muscles of the jaw into action; yet the deglutition of it whenmasticated is generally, if not always, an irritative motion, occasioned bythe application of the food already masticated to the origin of thepharinx; in the same manner as we often swallow our spittle withoutattending to it. The ruminating class of animals have the power to invert the motion oftheir gullet, and of their first stomach, from the stimulus of thisaliment, when it is a little further prepared; as is their daily practicein chewing the cud; and appears to the eye of any one, who attends to them, whilst they are employed in this second mastication of their food. 2. When our natural aliment arrives into the stomach, this organ issimulated into its proper vermicular action; which beginning at the upperorifice of it, and terminating at the lower one, gradually mixes togetherand pushes forwards the digesting materials into the intestine beneath it. At the same time the glands, that supply the gastric juices, which arenecessary to promote the chemical part of the process of digestion, arestimulated to discharge their contained fluids, and to separate a furthersupply from the blood-vessels: and the lacteals or lymphatics, which opentheir mouths into the stomach, are stimulated into action, and take up somepart of the digesting materials. 3. The remainder of these digesting materials is carried forwards into theupper intestines, and stimulates them into their peristaltic motion similarto that of the stomach; which continues gradually to mix the changingmaterials, and pass them along through the valve of the colon to theexcretory end of this great gland, the sphincter ani. The digesting materials produce a flow of bile, and of pancreatic juice, asthey pass along the duodenum, by stimulating the excretory ducts of theliver and pancreas, which terminate in that intestine: and other branchesof the absorbent or lymphatic system, called lacteals, are excited to drinkup, as it passes, those parts of the digesting materials, that are properfor their purpose, by its stimulus on their mouths. 4. When the stomach and intestines are thus filled with their proper food, not only the motions of the gastric glands, the pancreas, liver, andlacteal vessels, are excited into action; but at the same time the wholetribe of irritative motions are exerted with greater energy, a greaterdegree of warmth, colour, plumpness, and moisture, is given to the skinfrom the increased action of those glands called capillary vessels;pleasurable sensation is excited, the voluntary motions are less easilyexerted, and at length suspended; and sleep succeeds, unless it beprevented by the stimulus of surrounding objects, or by voluntary exertion, or by an acquired habit, which was originally produced by one or other ofthese circumstances, as is explained in Sect. XXI. On Drunkenness. At this time also, as the blood-vessels become replete with chyle, moreurine is separated into the bladder, and less of it is reabsorbed; moremucus poured into the cellular membranes, and less of it reabsorbed; thepulse becomes fuller, and softer, and in general quicker. The reason whyless urine and cellular mucus is absorbed after a full meal with sufficientdrink is owing to the blood-vessels being fuller: hence one means topromote absorption is to decrease the resistance by emptying the vessels byvenesection. From this decreased absorption the urine becomes pale as wellas copious, and the skin appears plump as well as florid. By daily repetition of these movements they all become connected together, and make a diurnal circle of irritative action, and if one of this chain bedisturbed, the whole is liable to be put into disorder. See Sect. XX. OnVertigo. 5. When the stomach and intestines receive a quantity of food, whosestimulus is greater than usual, all their motions, and those of the glandsand lymphatics, are stimulated into stronger action than usual, and performtheir offices with greater vigour and in less time: such are the effects ofcertain quantities of spice or of vinous spirit. 6. But if the quantity or duration of these stimuli are still furtherincreased, the stomach and throat are stimulated into a motion, whosedirection is contrary to the natural one above described; and theyregurgitate the materials, which they contain, instead of carrying themforwards. This retrograde motion of the stomach may be compared to thestretchings of wearied limbs the contrary way, and is well elucidated bythe following experiment. Look earnestly for a minute or two on an area aninch square of pink silk, placed in a strong light, the eye becomesfatigued, the colour becomes faint, and at length vanishes, for thefatigued eye can no longer be stimulated into direct motions; then onclosing the eye a green spectrum will appear in it, which is a colourdirectly contrary to pink, and which will appear and disappear repeatedly, like the efforts in vomiting. See Section XXIX. 11. Hence all those drugs, which by their bitter or astringent stimulusincrease the action of the stomach, as camomile and white vitriol, if theirquantity is increased above a certain dose become emetics. These inverted motions of the stomach and throat are generally producedfrom the stimulus of unnatural food, and are attended with the sensation ofnausea or sickness: but as this sensation is again connected with an ideaof the distasteful food, which induced it; so an idea of nauseous food willalso sometimes excite the action of nausea; and that give rise byassociation to the inversion of the motions of the stomach and throat. Assome, who have had horse-flesh or dogs-flesh given them for beef or mutton, are said to have vomited many hours afterwards, when they have been told ofthe imposition. I have been told of a person, who had gained a voluntary command over theseinverted motions of the stomach and throat, and supported himself byexhibiting this curiosity to the public. At these exhibitions he swalloweda pint of red rough gooseberries, and a pint of white smooth ones, broughtthem up in small parcels into his mouth, and restored them separately tothe spectators, who called for red or white as they pleased, till the wholewere redelivered. 7. At the same time that these motions of the stomach and throat arestimulated into inversion, some of the other irritative motions, that hadacquired more immediate connexions with the stomach, as those of thegastric glands, are excited into stronger action by this association; andsome other of these motions, which are more easily excited, as those of thegastric lymphatics, are inverted by their association with the retrogrademotions of the stomach, and regurgitate their contents, and thus a greaterquantity of mucus, and of lymph, or chyle, is poured into the stomach, andthrown up along with its contents. 8. These inversions of the motion of the stomach in vomiting are performedby intervals, for the same reason that many other motions are reciprocallyexerted and relaxed; for during the time of exertion the stimulus, orsensation, which caused this exertion, is not perceived; but begins to beperceived again, as soon as the exertion ceases, and is some time in againproducing its effect. As explained in Sect. XXXIV. On Volition, where it isshewn, that the contractions of the fibres, and the sensation of pain, which occasioned that exertion, cannot exist at the same time. The exertionceases from another cause also, which is the exhaustion of the sensorialpower of the part, and these two causes frequently operate together. 9. At the times of these inverted efforts of the stomach not only thelymphatics, which open their mouths into the stomach, but those of the skinalso, are for a time inverted; for sweats are sometimes pushed out duringthe efforts of vomiting without an increase of heat. 10. But if by a greater stimulus the motions of the stomach are invertedstill more violently or more permanently, the duodenum has its peristalticmotions inverted at the same time by their association with those of thestomach; and the bile and pancreatic juice, which it contains, are by theinverted motions brought up into the stomach, and discharged along with itscontents; while a greater quantity of bile and pancreatic juice is pouredinto this intestine; as the glands, that secrete them, are by theirassociation with the motions of the intestine excited into stronger actionthan usual. 11. The other intestines are by association excited into more powerfulaction, while the lymphatics, that open their mouths into them, suffer aninversion of their motions corresponding with the lymphatics of thestomach, and duodenum; which with a part of the abundant secretion of bileis carried downwards, and contributes both to stimulate the bowels, and toincrease the quantity of the evacuations. This inversion of the motion ofthe lymphatics appears from the quantity of chyle, which comes away bystools; which is otherwise absorbed as soon as produced, and by the immensequantity of thin fluid, which is evacuated along with it. 12. But if the stimulus, which inverts the stomach, be still more powerful, or more permanent, it sometimes happens, that the motions of the biliaryglands, and of their excretory ducts, are at the same time inverted, andregurgitate their contained bile into the blood-vessels, as appears by theyellow colour of the skin, and of the urine; and it is probable thepancreatic secretion may suffer an inversion at the same time, though wehave yet no mark by which this can be ascertained. 13. Mr. ---- eat two putrid pigeons out of a cold pigeon-pye, and drankabout a pint of beer and ale along with them, and immediately rode aboutfive miles. He was then seized with vomiting, which was after a few periodssucceeded by purging; these continued alternately for two hours; and thepurging continued by intervals for six or eight hours longer. During thistime he could not force himself to drink more than one pint in the whole;this great inability to drink was owing to the nausea, or inverted motionsof the stomach, which the voluntary exertion of swallowing could seldom andwith difficulty overcome; yet he discharged in the whole at least sixquarts; whence came this quantity of liquid? First, the contents of thestomach were emitted, then of the duodenum, gall-bladder, and pancreas, byvomiting. After this the contents of the lower bowels, then the chyle, thatwas in the lacteal vessels, and in the receptacle of chyle, wasregurgitated into the intestines by a retrograde motion of these vessels. And afterwards the mucus deposited in the cellular membrane, and on thesurface of all the other membranes, seems to have been absorbed; and withthe fluid absorbed from the air to have been carried up their respectivelymphatic branches by the increased energy of their natural motions, anddown the visceral lymphatics, or lacteals, by the inversion of theirmotions. 14. It may be difficult to invent experiments to demonstrate the truth ofthis inversion of some branches of the absorbent system, and increasedabsorption of others, but the analogy of these vessels to the intestinalcanal, and the symptoms of many diseases, render this opinion more probablethan many other received opinions of the animal oeconomy. In the above instance, after the yellow excrement was voided, the fluidceased to have any smell, and appeared like curdled milk, and then athinner fluid, and some mucus, were evacuated; did not these seem topartake of the chyle, of the mucous fluid from all the cells of the body, and lastly, of the atmospheric moisture? All these facts may be easilyobserved by any one, who takes a brisk purge. 15. Where the stimulus on the stomach, or on some other part of theintestinal canal, is still more permanent, not only the lacteal vessels, but the whole canal itself, becomes inverted from its associations: this isthe iliac passion, in which all the fluids mentioned above are thrown up bythe mouth. At this time the valve in the colon, from the inverted motionsof that bowel, and the inverted action of this living valve, does notprevent the regurgitation of its contents. The structure of this valve may be represented by a flexile leathern pipestanding up from the bottom of a vessel of water: its sides collapse by thepressure of the ambient fluid, as a small part of that fluid passes throughit; but if it has a living power, and by its inverted action keeps itselfopen, it becomes like a rigid pipe, and will admit the whole liquid topass. See Sect. XXIX. 2. 5. In this case the patient is averse to drink, from the constant inversion ofthe motions of the stomach, and yet many quarts are daily ejected from thestomach, which at length smell of excrement, and at last seem to be only athin mucilaginous or aqueous liquor. From whence is it possible, that this great quantity of fluid for manysuccessive days can be supplied, after the cells of the body have given uptheir fluids, but from the atmosphere? When the cutaneous branch ofabsorbents acts with unnatural strength, it is probable the intestinalbranch has its motions inverted, and thus a fluid is supplied withoutentering the arterial system. Could oiling or painting the skin give acheck to this disease? So when the stomach has its motions inverted, the lymphatics of thestomach, which are most strictly associated with it, invert their motionsat the same time. But the more distant branches of lymphatics, which areless strictly associated with it, act with increased energy; as thecutaneous lymphatics in the cholera, or iliac passion, above described. Andother irritative motions become decreased, as the pulsations of thearteries, from the extra-derivation or exhaustion of the sensorial power. Sometimes when stronger vomiting takes place the more distant branches ofthe lymphatic system invert their motions with those of the stomach, andloose stools are produced, and cold sweats. So when the lacteals have their motions inverted, as during the operationof strong purges, the urinary and cutaneous absorbents have their motionsincreased to supply the want of fluid in the blood, as in great thirst; butafter a meal with sufficient potation the urine is pale, that is, theurinary absorbents act weakly, no supply of water being wanted for theblood. And when the intestinal absorbents act too violently, as when toogreat quantities of fluid have been drank, the urinary absorbents inverttheir motions to carry off the superfluity, which is a new circumstance ofassociation, and a temporary diabetes supervenes. 16. I have had the opportunity of seeing four patients in the iliacpassion, where the ejected material smelled and looked like excrement. Twoof these were so exhausted at the time I saw them, that more blood couldnot be taken from them, and as their pain had ceased, and they continued tovomit up every thing which they drank, I suspected that a mortification ofthe bowel had already taken place, and as they were both women advanced inlife, and a mortification is produced with less preceding pain in old andweak people, these both died. The other two, who were both young men, hadstill pain and strength sufficient for further venesection, and theyneither of them had any appearance of hernia, both recovered by repeatedbleeding, and a scruple of calomel given to one, and half a dram to theother, in very small pills: the usual means of clysters, and purges joinedwith opiates, had been in vain attempted. I have thought an ounce or two ofcrude mercury in less violent diseases of this kind has been of use, bycontributing to restore its natural motion to some part of the intestinalcanal, either by its weight or stimulus; and that hence the whole tuberecovered its usual associations of progressive peristaltic motion. I havein three cases seen crude mercury given in small doses, as one or twoounces twice a day, have great effect in stopping pertinacious vomitings. 17. Besides the affections above described, the stomach is liable, likemany other membranes of the body, to torpor without consequentinflammation: as happens to the membranes about the head in some cases ofhemicrania, or in general head-ach. This torpor of the stomach is attendedwith indigestion, and consequent flatulency, and with pain, which isusually called the cramp of the stomach, and is relievable by aromatics, essential oils, alcohol, or opium. The intrusion of a gall-stone into the common bile-duct from thegall-bladder is sometimes mistaken for a pain of the stomach, as neither ofthem are attended with fever; but in the passage of a gall-stone, the painis confined to a less space, which is exactly where the common bile-ductenters the duodenum, as explained in Section XXX. 1. 3. Whereas in thisgastrodynia the pain is diffused over the whole stomach; and, like otherdiseases from torpor, the pulse is weaker, and the extremities colder, andthe general debility greater, than in the passage of a gall-stone; for inthe former the debility is the consequence of the pain, in the latter it isthe cause of it. Though the first fits of the gout, I believe, commence with a torpor of theliver; and the ball of the toe becomes inflamed instead of the membranes ofthe liver in consequence of this torpor, as a coryza or catarrh frequentlysucceeds a long exposure of the feet to cold, as in snow, or on a moistbrick-floor; yet in old or exhausted constitutions, which have been longhabituated to its attacks, it sometimes commences with a torpor of thestomach, and is transferable to every membrane of the body. When the goutbegins with torpor of the stomach, a painful sensation of cold occurs, which the patient compares to ice, with weak pulse, cold extremities, andsickness; this in its slighter degree is relievable by spice, wine, oropium; in its greater degree it is succeeded by sudden death, which isowing to the sympathy of the stomach with the heart, as explained below. If the stomach becomes inflamed in consequence of this gouty torpor of it, or in consequence of its sympathy with some other part, the danger is less. A sickness and vomiting continues many days, or even weeks, the stomachrejecting every thing stimulant, even opium or alcohol, together with muchviscid mucus; till the inflammation at length ceases, as happens when othermembranes, as those of the joints, are the seat of gouty inflammation; asobserved in Sect. XXIV. 2. 8. The sympathy, or association of motions, between those of the stomach andthose of the heart, are evinced in many diseases. First, many people areoccasionally affected with an intermission of their pulse for a few days, which then ceases again. In this case there is a stop of the motion of theheart, and at the same time a tendency to eructation from the stomach. Assoon as the patient feels a tendency to the intermission of the motion ofhis heart, if he voluntarily brings up wind from his stomach, the stop ofthe heart does not occur. From hence I conclude that the stop of digestionis the primary disease; and that air is instantly generated from thealiment, which begins to ferment, if the digestive process is impeded for amoment, (see Sect. XXIII. 4. ); and that the stop of the heart is inconsequence of the association of the motions of these viscera, asexplained in Sect. XXXV. 1. 4. ; but if the little air, which is instantlygenerated during the temporary torpor of the stomach, be evacuated, thedigestion recommences, and the temporary torpor of the heart does notfollow. One patient, whom I lately saw, and who had been five or six daysmuch troubled with this intermission of a pulsation of his heart, and whohad hemicrania with some fever, was immediately relieved from them all bylosing ten ounces of blood, which had what is termed an inflammatory cruston it. Another instance of this association between the motions of the stomach andheart is evinced by the exhibition of an over dose of foxglove, whichinduces an incessant vomiting, which is attended with very slow, andsometimes intermitting pulse. --Which continues in spite of the exhibitionof wine and opium for two or three days. To the same association must beascribed the weak pulse, which constantly attends the exhibition of emeticsduring their operation. And also the sudden deaths, which have beenoccasioned in boxing by a blow on the stomach; and lastly, the sudden deathof those, who have been long debilitated by the gout, from the torpor ofthe stomach. See Sect. XXXV. 1. 4. * * * * * SECT. XXVI. OF THE CAPILLARY GLANDS AND MEMBRANES. I. 1. _The capillary vessels are glands. _ 2. _Their excretory ducts. Experiments on the mucus of the intestines, abdomen, cellular membrane, and on the humours of the eye. _ 3. _Scurf on the head, cough, catarrh, diarrhoea, gonorrhoea. _ 4. _Rheumatism. Gout. Leprosy. _ II. 1. _The most minute membranes are unorganized. _ 2. _Larger membranes are composed of the ducts of the capillaries, and the mouths of the absorbents. _ 3. _Mucilaginous fluid is secreted on their surfaces. _ III. _Three kinds of rheumatism. _ I. 1. The capillary-vessels are like all the other glands except theabsorbent system, inasmuch as they receive blood from the arteries, separate a fluid from it, and return the remainder by the veins. 2. This series of glands is of the most extensive use, as their excretoryducts open on the whole external skin forming its perspirative pores, andon the internal surfaces of every cavity of the body. Their secretion onthe skin is termed insensible perspiration, which in health is in partreabsorbed by the mouths of the lymphatics, and in part evaporated in theair; the secretion on the membranes, which line the larger cavities of thebody, which have external openings, as the mouth and intestinal canal, istermed mucus, but is not however coagulable by heat; and the secretion onthe membranes of those cavities of the body, which have no externalopenings, is called lymph or water, as in the cavities of the cellularmembrane, and of the abdomen; this lymph however is coagulable by the heatof boiling water. Some mucus nearly as viscid as the white of egg, whichwas discharged by stool, did not coagulate, though I evaporated it to onefourth of the quantity, nor did the aqueous and vitreous humours of asheep's eye coagulate by the like experiment: but the serosity from ananasarcous leg, and that from the abdomen of a dropsical person, and thecrystalline humour of a sheep's eye, coagulated in the same heat. 3. When any of these capillary glands are stimulated into greaterirritative actions, than is natural, they secrete a more copious material;and as the mouths of the absorbent system, which open in their vicinity, are at the same time stimulated into greater action, the thinner and moresaline part of the secreted fluid is taken up again; and the remainder isnot only more copious but also more viscid than natural. This is more orless troublesome or noxious according to the importance of the functions ofthe part affected: on the skin and bronchiæ, where this secretion oughtnaturally to evaporate, it becomes so viscid as to adhere to the membrane;on the tongue it forms a pellicle, which can with difficulty be scrapedoff; produces the scurf on the heads of many people; and the mucus, whichis spit up by others in coughing. On the nostrils and fauces, when thesecretion of these capillary glands is increased, it is termed simplecatarrh; when in the intestines, a mucous diarrhoea; and in the urethra, orvagina, it has the name of gonorrhoea, or fluor albus. 4. When these capillary glands become inflamed, a still more viscid or evencretaceous humour is produced upon the surfaces of the membranes, which isthe cause or the effect of rheumatism, gout, leprosy, and of hard tumoursof the legs, which are generally termed scorbutic; all which will betreated of hereafter. II. 1. The whole surface of the body, with all its cavities and contents, are covered with membrane. It lines every vessel, forms every cell, andbinds together all the muscular and perhaps the osseous fibres of the body;and is itself therefore probably a simpler substance than those fibres. Andas the containing vessels of the body from the largest to the least arethus lined and connected with membranes, it follows that these membranesthemselves consisted of unorganized materials. For however small we may conceive the diameters of the minutest vessels ofthe body, which escape our eyes and glasses, yet these vessels must consistof coats or sides, which are made up of an unorganized material, and whichare probably produced from a gluten, which hardens after its production, like the silk or web of caterpillars and spiders. Of this material consistthe membranes, which line the shells of eggs, and the shell itself, bothwhich are unorganized, and are formed from mucus, which hardens after it isformed, either by the absorption of its more fluid part, or by its unitingwith some part of the atmosphere. Such is also the production of the shellsof snails, and of shell-fish, and I suppose of the enamel of the teeth. 2. But though the membranes, that compose the sides of the most minutevessels, are in truth unorganized materials, yet the larger membranes, which are perceptible to the eye, seem to be composed of an intertexture ofthe mouths of the absorbent system, and of the excretory ducts of thecapillaries, with their concomitant arteries, veins, and nerves: and fromthis construction it is evident, that these membranes must possess greatirritability to peculiar stimuli, though they are incapable of any motions, that are visible to the naked eye: and daily experience shews us, that intheir inflamed state they have the greatest sensibility to pain, as in thepleurisy and paronychia. 3. On all these membranes a mucilaginous or aqueous fluid is secreted, which moistens and lubricates their surfaces, as was explained in SectionXXIII. 2. Some have doubted, whether this mucus is separated from the bloodby an appropriated set of glands, or exudes through the membranes, or is anabrasion or destruction of the surface of the membrane itself, which iscontinually repaired on the other side of it, but the great analogy betweenthe capillary vessels, and the other glands, countenances the formeropinion; and evinces, that these capillaries are the glands, that secreteit; to which we must add, that the blood in passing these capillary vesselsundergoes a change in its colour from florid to purple, and gives out aquantity of heat; from whence, as in other glands, we must conclude thatsomething is secreted from it. III. The seat of rheumatism is in the membranes, or upon them; but thereare three very distinct diseases, which commonly are confounded under thisname. First, when a membrane becomes affected with torpor, or inactivity ofthe vessels which compose it, pain and coldness succeed, as in thehemicrania, and other head-achs, which are generally termed nervousrheumatism; they exist whether the part be at rest or in motion, and aregenerally attended with other marks of debility. Another rheumatism is said to exist, when inflammation and swelling, aswell as pain, affect some of the membranes of the joints, as of the ancles, wrists, knees, elbows, and sometimes of the ribs. This is accompanied withfever, is analogous to pleurisy and other inflammations, and is termed theacute rheumatism. A third disease is called chronic rheumatism, which is distinguished fromthat first mentioned, as in this the pain only affects the patient duringthe motion of the part, and from the second kind of rheumatism abovedescribed, as it is not attended with quick pulse or inflammation. It isgenerally believed to succeed the acute rheumatism of the same part, andthat some coagulable lymph, or cretaceous, or calculous material, has beenleft on the membrane; which gives pain, when the muscles move over it, assome extraneous body would do, which was too insoluble to be absorbed. Hence there is an analogy between this chronic rheumatism and the diseaseswhich produce gravel or gout-stones; and it may perhaps receive relief fromthe same remedies, such as aerated sal soda. * * * * * SECT. XXVII. OF HÆMORRHAGES. I. _The veins are absorbent vessels. _ 1. _Hæmorrhages from inflammation. Case of hæmorrhage from the kidney cured by cold bathing. Case of hæmorrhage from the nose cured by cold immersion. _ II. _Hæmorrhage from venous paralysis. Of Piles. Black stools. Petechiæ. Consumption. Scurvy of the lungs. Blackness of the face and eyes in epileptic fits. Cure of hæmorrhages from venous inability. _ I. As the imbibing mouths of the absorbent system already described open onthe surface, and into the larger cavities of the body, so there is anothersystem of absorbent vessels, which are not commonly esteemed such, I meanthe veins, which take up the blood from the various glands and capillaries, after their proper fluids or secretions have been separated from it. The veins resemble the other absorbent vessels; as the progression of theircontents is carried on in the same manner in both, they alike absorb theirappropriated fluids, and have valves to prevent its regurgitation by theaccidents of mechanical violence. This appears first, because there is nopulsation in the very beginnings of the veins, as is seen by microscopes;which must happen, if the blood was carried into them by the actions of thearteries. For though the concurrence of various venous streams of bloodfrom different distances must prevent any pulsation in the larger branches, yet in the very beginnings of all these branches a pulsation mustunavoidably exist, if the circulation in them was owing to the intermittedforce of the arteries. Secondly, the venous absorption of blood from thepenis, and from the teats of female animals after their erection, is stillmore similar to the lymphatic absorption, as it is previously poured intocells, where all arterial impulse must cease. There is an experiment, which seems to evince this venous absorption, whichconsists in the external application of a stimulus to the lips, as ofvinegar, by which they become instantly pale; that is, the bibulous mouthsof the veins by this stimulus are excited to absorb the blood faster, thanit can be supplied by the usual arterial exertion. See Sect. XXIII. 5. There are two kinds of hæmorrhages frequent in diseases, one is where theglandular or capillary action is too powerfully exerted, and propels theblood forwards more hastily, than the veins can absorb it; and the otheris, where the absorbent power of the veins is diminished, or a branch ofthem is become totally paralytic. 1. The former of these cases is known by the heat of the part, and thegeneral fever or inflammation that accompanies the hæmorrhage. Anhæmorrhage from the nose or from the lungs is sometimes a crisis ofinflammatory diseases, as of the hepatitis and gout, and generally ceasesspontaneously, when the vessels are considerably emptied. Sometimes thehæmorrhage recurs by daily periods accompanying the hot fits of fever, andceasing in the cold fits, or in the intermissions; this is to be cured byremoving the febrile paroxysms, which will be treated of in their place. Otherwise it is cured by venesection, by the internal or externalpreparations of lead, or by the application of cold, with an abstemiousdiet, and diluting liquids, like other inflammations. Which by inducing aquiescence on those glandular parts, that are affected, prevents a greaterquantity of blood from being protruded forwards, than the veins are capableof absorbing. Mr. B---- had an hæmorrhage from his kidney, and parted with not less thana pint of blood a day (by conjecture) along with his urine for above afortnight: venesections, mucilages, balsams, preparations of lead, thebark, alum, and dragon's blood, opiates, with a large blister on his loins, were separately tried, in large doses, to no purpose. He was then directedto bathe in a cold spring up to the middle of his body only, the upper partbeing covered, and the hæmorrhage diminished at the first, and ceased atthe second immersion. In this case the external capillaries were rendered quiescent by thecoldness of the water, and thence a less quantity of blood was circulatedthrough them; and the internal capillaries, or other glands, becamequiescent from their irritative associations with the external ones; andthe hæmorrhage was stopped a sufficient time for the ruptured vessels tocontract their apertures, or for the blood in those apertures to coagulate. Mrs. K---- had a continued haemorrhage from her nose for some days; theruptured vessel was not to be reached by plugs up the nostrils, and thesensibility of her fauces was such that nothing could be born behind theuvula. After repeated venesection, and other common applications, she wasdirected to immerse her whole head into a pail of water, which was madecolder by the addition of several handfuls of salt, and the hæmorrhageimmediately ceased, and returned no more; but her pulse continued hard, andshe was necessitated to lose blood from the arm on the succeeding day. Query, might not the cold bath instantly stop hæmorrhages from the lungs ininflammatory cases?--for the shortness of breath of those, who go suddenlyinto cold water, is not owing to the accumulation of blood in the lungs, but to the quiescence of the pulmonary capillaries from association, asexplained in Section XXXII. 3. 2. II. The other kind of hæmorrhage is known from its being attended with aweak pulse, and other symptoms of general debility, and very frequentlyoccurs in those, who have diseased livers, owing to intemperance in the useof fermented liquors. These constitutions are shewn to be liable toparalysis of the lymphatic absorbents, producing the various kinds ofdropsies in Section XXIX. 5. Now if any branch of the venous system losesits power of absorption, the part swells, and at length bursts anddischarges the blood, which the capillaries or other glands circulatethrough them. It sometimes happens that the large external veins of the legs burst, andeffuse their blood; but this occurs most frequently in the veins of theintestines, as the vena portarum is liable to suffer from a schirrus of theliver opposing the progression of the blood, which is absorbed from theintestines. Hence the piles are a symptom of hepatic obstruction, and hencethe copious discharges downwards or upwards of a black material, which hasbeen called melancholia, or black bile; but is no other than the blood, which is probably discharged from the veins of the intestines. J. F. Meckel, in his Experimenta de Finibus Vasorum, published at Berlin, 1772, mentions his discovery of a communication of a lymphatic vessel withthe gastric branch of the vena portarum. It is possible, that when themotion of the lymphatic becomes retrograde in some diseases, that blood mayobtain a passage into it, where it anastomoses with the vein, and thus bepoured into the intestines. A discharge of blood with the urine sometimesattends diabetes, and may have its source in the same manner. Mr. A----, who had been a hard drinker, and had the gutta rosacea on hisface and breast, after a stroke of the palsy voided near a quart of a blackviscid material by stool: on diluting it with water it did not becomeyellow, as it must have done if it had been inspissated bile, but continuedblack like the grounds of coffee. But any other part of the venous system may become quiescent or totallyparalytic as well as the veins of the intestines: all which occur morefrequently in those who have diseased livers, than in any others. Hencetroublesome bleedings of the nose, or from the lungs with a weak pulse;hence hæmorrhages from the kidneys, too great menstruation; and hence theoozing of blood from every part of the body, and the petechiæ in thosefevers, which are termed putrid, and which is erroneously ascribed to thethinness of the blood: for the blood in inflammatory diseases is equallyfluid before it coagulates in the cold air. Is not that hereditary consumption, which occurs chiefly in dark-eyedpeople about the age of twenty, and commences with slight pulmonaryhæmorrhages without fever, a disease of this kind?--These hæmorrhagesfrequently begin during sleep, when the irritability of the lungs is notsufficient in these patients to carry on the circulation without theassistance of volition; for in our waking hours, the motions of the lungsare in part voluntary, especially if any difficulty of breathing rendersthe efforts of volition necessary. See Class I. 2. 1. 3. And Class III. 2. 1. 12. Another species of pulmonary consumption which seems more certainlyof scrophulous origin is described in the next Section, No. 2. I have seen two cases of women, of about forty years of age, both of whomwere seized with quick weak pulse, with difficult respiration, and who spitup by coughing much viscid mucus mixed with dark coloured blood. They hadboth large vibices on their limbs, and petechiæ; in one the feet were indanger of mortification, in the other the legs were oedematous. To relievethe difficult respiration, about six ounces of blood were taken from one ofthem, which to my surprise was sizy, like inflamed blood: they had bothpalpitations or unequal pulsations of the heart. They continued four orfive weeks with pale and bloated countenances, and did not cease spittingphlegm mixed with black blood, and the pulse seldom slower than 130 or 135in a minute. This blood, from its dark colour, and from the many vibicesand petechiæ, seems to have been venous blood; the quickness of the pulse, and the irregularity of the motion of the heart, are to be ascribed todebility of that part of the system; as the extravasation of bloodoriginated from the defect of venous absorption. The approximation of thesetwo cases to sea-scurvy is peculiar, and may allow them to be calledscorbutus pulmonalis. Had these been younger subjects, and the paralysis ofthe veins had only affected the lungs, it is probable the disease wouldhave been a pulmonary consumption. Last week I saw a gentleman of Birmingham, who had for ten days labouredunder great palpitation of his heart, which was so distinctly felt by thehand, as to discountenance the idea of there being a fluid in thepericardium. He frequently spit up mucus stained with dark coloured blood, his pulse very unequal and very weak, with cold hands and nose. He couldnot lie down at all, and for about ten days past could not sleep a minutetogether, but waked perpetually with great uneasiness. Could those symptomsbe owing to very extensive adhesions of the lungs? or is this a scorbutuspulmonalis? After a few days he suddenly got so much better as to be ableto sleep many hours at a time by the use of one grain of powder of foxglovetwice a day, and a grain of opium at night. After a few days longer, thebark was exhibited, and the opium continued with some wine; and thepalpitations of his heart became much relieved, and he recovered his usualdegree of health, but died suddenly some months afterwards. In epileptic fits the patients frequently become black in the face, fromthe temporary paralysis of the venous system of this part. I have known twoinstances where the blackness has continued many days. M. P----, who haddrank intemperately, was seized with the epilepsy when he was in hisfortieth year; in one of these fits the white part of his eyes was lefttotally black with effused blood; which was attended with no pain or heat, and was in a few weeks gradually absorbed, changing colour as is usual withvibices from bruises. The hæmorrhages produced from the inability of the veins to absorb therefluent blood, is cured by opium, the preparations of steel, lead, thebark, vitriolic acid, and blisters; but these have the effect with muchmore certainty, if a venesection to a few ounces, and a moderate catharticwith four or six grains of calomel be premised, where the patient is notalready too much debilitated; as one great means of promoting theabsorption of any fluid consists in previously emptying the vessels, whichare to receive it. * * * * * SECT. XXVIII. OF THE PARALYSIS OF THE ABSORBENT SYSTEM. I. _Paralysis of the lacteals, atrophy. Distaste to animal food. _ II. _Cause of dropsy. Cause of herpes. Scrophula. Mesenteric consumption. Pulmonary consumption. Why ulcers in the lungs are so difficult to heal. _ The term paralysis has generally been used to express the loss of voluntarymotion, as in the hemiplagia, but may with equal propriety be applied toexpress the disobediency of the muscular fibres to the other kinds ofstimulus; as to those of irritation or sensation. I. There is a species of atrophy, which has not been well understood; whenthe absorbent vessels of the stomach and intestines have been long inuredto the stimulus of too much spirituous liquor, they at length, either bythe too sudden omission of fermented or spirituous potation, or from thegradual decay of nature, become in a certain degree paralytic; now it isobserved in the larger muscles of the body, when one side is paralytic, theother is more frequently in motion, owing to the less expenditure ofsensorial power in the paralytic limbs; so in this case the other part ofthe absorbent system acts with greater force, or with greater perseverance, in consequence of the paralysis of the lacteals; and the body becomesgreatly emaciated in a small time. I have seen several patients in this disease, of which the following arethe circumstances. 1. They were men about fifty years of age, and had livedfreely in respect to fermented liquors. 2. They lost their appetite toanimal food. 3. They became suddenly emaciated to a great degree. 4. Theirskins were dry and rough. 5. They coughed and expectorated with difficultya viscid phlegm. 6. The membrane of the tongue was dry and red, and liableto become ulcerous. The inability to digest animal food, and the consequent distaste to it, generally precedes the dropsy, and other diseases, which originate fromspirituous potation. I suppose when the stomach becomes inirritable, thatthere is at the same time a deficiency of gastric acid; hence milk seldomagrees with these patients, unless it be previously curdled, as they havenot sufficient gastric acid to curdle it; and hence vegetable food, whichis itself acescent, will agree with their stomachs longer than animal food, which requires more of the gastric acid for its digestion. In this disease the skin is dry from the increased absorption of thecutaneous lymphatics, the fat is absorbed from the increased absorption ofthe cellular lymphatics, the mucus of the lungs is too viscid to be easilyspit up by the increased absorption of the thinner parts of it, themembrana sneideriana becomes dry, covered with hardened mucus, and atlength becomes inflamed and full of aphthæ, and either these sloughs, orpulmonary ulcers, terminate the scene. II. The immediate cause of dropsy is the paralysis of some other branchesof the absorbent system, which are called lymphatics, and which open intothe larger cavities of the body, or into the cells of the cellularmembrane; whence those cavities or cells become distended with the fluid, which is hourly secreted into them for the purpose of lubricating theirsurfaces. As is more fully explained in No. 5. Of the next Section. As those lymphatic vessels consist generally of a long neck or mouth, whichdrinks up its appropriated fluid, and of a conglobate gland, in which thisfluid undergoes some change, it happens, that sometimes the mouth of thelymphatic, and sometimes the belly or glandular part of it, becomes totallyor partially paralytic. In the former case, where the mouths of thecutaneous lymphatics become torpid or quiescent, the fluid secreted on theskin ceases to be absorbed, and erodes the skin by its saline acrimony, andproduces eruptions termed herpes, the discharge from which is as salt, asthe tears, which are secreted too fast to be reabsorbed, as in grief, orwhen the puncta lacrymalia are obstructed, and which running down the cheekredden and inflame the skin. When the mouths of the lymphatics, which open on the mucous membrane of thenostrils, become torpid, as on walking into the air in a frosty morning;the mucus, which continues to be secreted, has not its aqueous and salinepart reabsorbed, which running over the upper lip inflames it, and has asalt taste, if it falls on the tongue. When the belly, or glandular part of these lymphatics, becomes torpid, thefluid absorbed by its mouth stagnates, and forms a tumour in the gland. This disease is called the scrophula. If these glands suppurate externally, they gradually heal, as those of the neck; if they suppurate without anopening on the external habit, as the mesenteric glands, a hectic feverensues, which destroys the patient; if they suppurate in the lungs, apulmonary consumption ensues, which is believed thus to differ from thatdescribed in the preceding Section, in respect to its seat or proximatecause. It is remarkable, that matter produced by suppuration will lie concealed inthe body many weeks, or even months, without producing hectic fever; but assoon as the wound is opened, so as to admit air to the surface of theulcer, a hectic fever supervenes, even in very few hours, which is probablyowing to the azotic part of the atmosphere rather than to the oxygene;because those medicines, which contain much oxygene, as the calces oroxydes of metals, externally applied, greatly contribute to heal ulcers, ofthese are the solutions of lead and mercury, and copper in acids, or theirprecipitates. Hence when wounds are to be healed by the first intention, as it is called, it is necessary carefully to exclude the air from them. Hence we have onecause, which prevents pulmonary ulcers from healing, which is their beingperpetually exposed to the air. Both the dark-eyed patients, which are affected with pulmonary ulcers fromdeficient venous absorption, as described in Section. XXVII. 2. And thelight-eyed patients from deficient lymphatic absorption, which we are nowtreating of, have generally large apertures of the iris; these large pupilsof the eyes are a common mark of want of irritability; and it generallyhappens, that an increase of sensibility, that is, of motions inconsequence of sensation, attends these constitutions. See Sect. XXXI. 2. Whence inflammations may occur in these from stagnated fluids morefrequently than in those constitutions, which possess more irritability andless sensibility. Great expectations in respect to the cure of consumptions, as well as ofmany other diseases, are produced by the very ingenious exertions of DR. BEDDOES; who has established an apparatus for breathing various mixtures ofairs or gasses, at the hot-wells near Bristol, which well deserves theattention of the public. DR. BEDDOES very ingeniously concludes, from the florid colour of the bloodof consumptive patients, that it abounds in oxygene; and that the rednessof their tongues, and lips, and the fine blush of their cheeks shew thepresence of the same principle, like flesh reddened by nitre. And adds, that the circumstance of the consumptions of pregnant women being stoppedin their progress during pregnancy, at which time their blood may besupposed to be in part deprived of its oxygene, by oxygenating the blood ofthe foetus, is a forceable argument in favour of this theory; which mustsoon be confirmed or confuted by his experiments. See Essay on Scurvy, Consumption, &c. By Dr. Beddoes. Murray. London. Also Letter to Dr. Darwin, by the same. Murray. London. * * * * * SECT. XXIX. ON THE RETROGRADE MOTIONS OF THE ABSORBENT SYSTEM. I. _Account of the absorbent system. _ II. _The valves of the absorbent vessels may suffer their fluids to regurgitate in some diseases. _ III. _Communication from the alimentary canal to the bladder by means of the absorbent vessels. _ IV. _The phenomena of diabetes explained. _ V. 1. _The phenomena of dropsies explained. _ 2. _Cases of the use of foxglove. _ VI. _Of cold sweats. _ VII. _Translations of matter, of chyle, of milk, of urine, operation of purging drugs applied externally. _ VIII. _Circumstances by which the fluids, that are effused by the retrograde motions of the absorbent vessels, are distinguished. _ IX. _Retrograde motions of vegetable juices. _ X. _Objections answered. _ XI. _The causes, which induce the retrograde motions of animal vessels, and the medicines by which the natural motions are restored. _ _N. B. The following Section is a translation of a part of a Latin thesis written by the late Mr. Charles Darwin, which was printed with his prize-dissertation on a criterion between matter and mucus in 1780. Sold by Cadell, London. _ I. _Account of the Absorbent System. _ 1. The absorbent system of vessels in animal bodies consists of severalbranches, differing in respect to their situations, and to the fluids, which they absorb. The intestinal absorbents open their mouths on the internal surfaces of theintestines; their office is to drink up the chyle and the other fluids fromthe alimentary canal; and they are termed lacteals, to distinguish themfrom the other absorbent vessels, which have been termed lymphatics. Those, whose mouths are dispersed on the external skin, imbibe a greatquantity of water from the atmosphere, and a part of the perspirablematter, which does not evaporate, and are termed cutaneous absorbents. Those, which arise from the internal surface of the bronchia, and whichimbibe moisture from the atmosphere, and a part of the bronchial mucus, arecalled pulmonary absorbents. Those, which open their innumerable mouths into the cells of the wholecellular membrane; and whose use is to take up the fluid, which is pouredinto those cells, after it has done its office there; may be calledcellular absorbents. Those, which arise from the internal surfaces of the membranes, which linethe larger cavities of the body, as the thorax, abdomen, scrotum, pericardium, take up the mucus poured into those cavities; and aredistinguished by the names of their respective cavities. Whilst those, which arise from the internal surfaces of the urinarybladder, gall-bladder, salivary ducts, or other receptacles of secretedfluids, may take their names from those fluids; the thinner parts of whichit is their office to absorb: as urinary, bilious, or salivary absorbents. 2. Many of these absorbent vessels, both lacteals and lymphatics, like someof the veins, are replete with valves: which seem designed to assist theprogress of their fluids, or at least to prevent their regurgitation; wherethey are subjected to the intermitted pressure of the muscular, or arterialactions in their neighbourhood. These valves do not however appear to be necessary to all the absorbents, any more than to all the veins; since they are not found to exist in theabsorbent system of fish; according to the discoveries of the ingenious, and much lamented Mr. Hewson. Philos. Trans. V. 59, Enquiries into theLymph. Syst. P. 94. 3. These absorbent vessels are also furnished with glands, which are calledconglobate glands; whose use is not at present sufficiently investigated;but it is probable that they resemble the conglomerate glands both instructure and in use, except that their absorbent mouths are for theconveniency of situation placed at a greater distance from the body of thegland. The conglomerate glands open their mouths immediately into thesanguiferous vessels, which bring the blood, from whence they absorb theirrespective fluids, quite up to the gland: but these conglobate glandscollect their adapted fluids from very distant membranes, or cysts, bymeans of mouths furnished with long necks for this purpose; and which arecalled lacteals, or lymphatics. 4. The fluids, thus collected from various parts of the body, pass by meansof the thoracic duct into the left subclavian near the jugular vein; exceptindeed that those collected from the right side of the head and neck, andfrom the right arm, are carried into the right subclavian vein: andsometimes even the lymphatics from the right side of the lungs are insertedinto the right subclavian vein; whilst those of the left side of the headopen but just into the summit of the thoracic duct. 5. In the absorbent system there are many anastomoses of the vessels, whichseem of great consequence to the preservation of health. These anastomosesare discovered by dissection to be very frequent between the intestinal andurinary lymphatics, as mentioned by Mr. Hewson, (Phil. Trans. V. 58. ) 6. Nor do all the intestinal absorbents seem to terminate in the thoracicduct, as appears from some curious experiments of D. Munro, who gave madderto some animals, having previously put a ligature on the thoracic duct, andfound their bones, and the serum of their blood, coloured red. II. _The Valves of the Absorbent System may suffer their Fluids toregurgitate in some Diseases. _ 1. The many valves, which occur in the progress of the lymphatic andlacteal vessels, would seem insuperable obstacles to the regurgitation oftheir contents. But as these valves are placed in vessels, which are induedwith life, and are themselves indued with life also; and are very irritableinto those natural motions, which absorb, or propel the fluids theycontain; it is possible, in some diseases, where these valves or vesselsare stimulated into unnatural exertions, or are become paralytic, thatduring the diastole of the part of the vessel to which the valve isattached, the valve may not so completely close, as to prevent the relapseof the lymph or chyle. This is rendered more probable, by the experimentsof injecting mercury, or water, or suet, or by blowing air down thesevessels: all which pass the valves very easily, contrary to the naturalcourse of their fluids, when the vessels are thus a little forciblydilated, as mentioned by Dr. Haller, Elem. Physiol. T. Iii. S. 4. "The valves of the thoracic duct are few, some assert they are not morethan twelve, and that they do not very accurately perform their office, asthey do not close the whole area of the duct, and thence may permit chyleto repass them downwards. In living animals, however, though not always, yet more frequently than in the dead, they prevent the chyle fromreturning. The principal of these valves is that, which presides over theinsertion of the thoracic duct, into the subclavian vein; many havebelieved this also to perform the office of a valve, both to admit thechyle into the vein, and to preclude the blood from entering the duct; butin my opinion it is scarcely sufficient for this purpose. " Haller, Elem. Phys. T. Vii. P. 226. 2. The mouths of the lymphatics seem to admit water to pass through themafter death, the inverted way, easier than the natural one; since aninverted bladder readily lets out the water with which it is filled; whenceit may be inferred, that there is no obstacle at the mouths of thesevessels to prevent the regurgitation of their contained fluids. I was induced to repeat this experiment, and having accurately tied theureters and neck of a fresh ox's bladder, I made an opening at the fundusof it; and then, having turned it inside outwards, filled it half full withwater, and was surprised to see it empty itself so hastily. I thought theexperiment more apposite to my purpose by suspending the bladder with itsneck downwards, as the lymphatics are chiefly spread upon this part of it, as shewn by Dr. Watson, Philos. Trans. V. 59. P. 392. 3. In some diseases, as in the diabetes and scrophula, it is probable thevalves themselves are diseased, and are thence incapable of preventing thereturn of the fluids they should support. Thus the valves of the aortaitself have frequently been found schirrous, according to the dissectionsof Mons. Lieutaud, and have given rise to an interrupted pulse, andlaborious palpitations, by suffering a return of part of the blood into theheart. Nor are any parts of the body so liable to schirrosity as thelymphatic glands and vessels, insomuch that their schirrosities haveacquired a distinct name, and been termed scrophula. 4. There are valves in other parts of the body, analogous to those of theabsorbent system, and which are liable, when diseased, to regurgitate theircontents: thus the upper and lower orifices of the stomach are closed byvalves, which, when too great quantities of warm water have been drank witha design to promote vomiting, have sometimes resisted the utmost efforts ofthe abdominal muscles, and diaphragm: yet, at other times, the upper valve, or cardia, easily permits the evacuation of the contents of the stomach;whilst the inferior valve, or pylorus, permits the bile, and other contentsof the duodenum, to regurgitate into the stomach. 5. The valve of the colon is well adapted to prevent the retrograde motionof the excrements; yet, as this valve is possessed of a living power, inthe iliac passion, either from spasm, or other unnatural exertions, itkeeps itself open, and either suffers or promotes the retrograde movementsof the contents of the intestines below; as in ruminating animals the mouthof the first stomach seems to be so constructed, as to facilitate or assistthe regurgitation of the food; the rings of the oesophagus afterwardscontracting themselves in inverted order. De Haeu, by means of a syringe, forced so much water into the rectum intestinum of a dog, that he vomitedit in a full stream from his mouth; and in the iliac passion abovementioned, excrements and clyster are often evacuated by the mouth. SeeSection XXV. 15. 6. The puncta lacrymalia, with the lacrymal sack and nasal duct, compose acomplete gland, and much resemble the intestinal canal: the punctalacrymalia are absorbent mouths, that take up the tears from the eye, whenthey have done their office there, and convey them into the nostrils; butwhen the nasal duct is obstructed, and the lacrymal sack distended with itsfluid, on pressure with the finger the mouths of this gland (punctalacrymalia) will readily disgorge the fluid, they had previously absorbed, back into the eye. 7. As the capillary vessels receive blood from the arteries, and separatingthe mucus, or perspirable matter from it, convey the remainder back by theveins; these capillary vessels are a set of glands, in every respectsimilar to the secretory vessels of the liver, or other large congeries ofglands. The beginnings of these capillary vessels have frequent anastomosesinto each other, in which circumstance they are resembled by the lacteals;and like the mouths or beginnings of other glands, they are a set ofabsorbent vessels, which drink up the blood which is brought to them by thearteries, as the chyle is drank up by the lacteals: for the circulation ofthe blood through the capillaries is proved to be independent of arterialimpulse; since in the blush of shame, and in partial inflammations, theiraction is increased, without any increase of the motion of the heart. 8. Yet not only the mouths, or beginnings of these anastomosing capillariesare frequently seen by microscopes, to regurgitate some particles of blood, during the struggles of the animal; but retrograde motion of the blood, inthe veins of those animals, from the very heart of the extremity of thelimbs, is observable, by intervals, during the distresses of the dyingcreature. Haller, Elem. Physiol. T. I. P. 216. Now, as the veins haveperhaps all of them a valve somewhere between their extremities and theheart, here is ocular demonstration of the fluids in this diseasedcondition of the animal, repassing through venous valves: and it is hencehighly probable, from the strictest analogy, that if the course of thefluids, in the lymphatic vessels, could be subjected to microscopicobservation, they would also, in the diseased state of the animal, be seento repass the valves, and the mouths of those vessels, which had previouslyabsorbed them, or promoted their progression. III. _Communication from the Alimentary Canal to the Bladder, by means ofthe Absorbent Vessels. _ Many medical philosophers, both ancient and modern, have suspected thatthere was a nearer communication between the stomach and the urinarybladder, than that of the circulation: they were led into this opinion fromthe great expedition with which cold water, when drank to excess, passesoff by the bladder; and from the similarity of the urine, when produced inthis hasty manner, with the material that was drank. The former of these circumstances happens perpetually to those who drinkabundance of cold water, when they are much heated by exercise, and to manyat the beginning of intoxication. Of the latter, many instances are recorded by Etmuller, t. Xi. P. 716. Where simple water, wine, and wine with sugar, and emulsions, were returnedby urine unchanged. There are other experiments, that seem to demonstrate the existence ofanother passage to the bladder, besides that through the kidneys. Thus Dr. Kratzenstein put ligatures on the ureters of a dog, and then emptied thebladder by a catheter; yet in a little time the dog drank greedily, andmade a quantity of water, (Disputat. Morbor. Halleri. T. Iv. P. 63. ) Asimilar experiment is related in the Philosophical Transactions, with thesame event, (No. 65, 67, for the year 1670. ) Add to this, that in some morbid cases the urine has continued to pass, after the suppuration or total destruction of the kidneys; of which manyinstances are referred to in the Elem. Physiol. T. Vii. P. 379. Of Dr. Haller. From all which it must be concluded, that some fluids have passed from thestomach or abdomen, without having gone through the sanguiferouscirculation: and as the bladder is supplied with many lymphatics, asdescribed by Dr. Watson, in the Philos. Trans. V. 59. P. 392. And as noother vessels open into it besides these and the ureters, it seems evident, that the unnatural urine, produced as above described, when the ureterswere tied, or the kidneys obliterated, was carried into the bladder by theretrograde motions of the urinary branch of the lymphatic system. The more certainly to ascertain the existence of another communicationbetween the stomach and bladder, besides that of the circulation, thefollowing experiment was made, to which I must beg your patientattention:--A friend of mine (June 14, 1772) on drinking repeatedly of coldsmall punch, till he began to be intoxicated, made a quantity of colourlessurine. He then drank about two drams of nitre dissolved in some of thepunch, and eat about twenty stalks of boiled asparagus: on continuing todrink more of the punch, the next urine that he made was quite clear, andwithout smell; but in a little time another quantity was made, which wasnot quite so colourless, and had a strong smell of the asparagus: he thenlost about four ounces of blood from the arm. The smell of asparagus was not at all perceptible in the blood, neitherwhen fresh taken, nor the next morning, as myself and two others accuratelyattended to; yet this smell was strongly perceived in the urine, which wasmade just before the blood was taken from his arm. Some bibulous paper, moistened in the serum of this blood, and suffered todry, shewed no signs of nitre by its manner of burning. But some of thesame paper, moistened in the urine, and dried, on being ignited, evidentlyshewed the presence of nitre. This blood and the urine stood some daysexposed to the sun in the open air, till they were evaporated to about afourth of their original quantity, and began to stink: the paper, which wasthen moistened with the concentrated urine, shewed the presence of muchnitre by its manner of burning; whilst that moistened with the blood shewedno such appearance at all. Hence it appears, that certain fluids at the beginning of intoxication, find another passage to the bladder besides the long course of the arterialcirculation; and as the intestinal absorbents are joined with the urinarylymphatics by frequent anastomoses, as Hewson has demonstrated; and asthere is no other road, we may justly conclude, that these fluids pass intothe bladder by the urinary branch of the lymphatics, which has its motionsinverted during the diseased state of the animal. A gentleman, who had been some weeks affected with jaundice, and whoseurine was in consequence of a very deep yellow, took some cold small punch, in which was dissolved about a dram of nitre; he then took repeateddraughts of the punch, and kept himself in a cool room, till on theapproach of slight intoxication he made a large quantity of water; thiswater had a slight yellow tinge, as might be expected from a smalladmixture of bile secreted from the kidneys; but if the whole of it hadpassed through the sanguiferous vessels, which were now replete with bile(his whole skin being as yellow as gold) would not this urine also, as wellas that he had made for weeks before, have been of a deep yellow? Paperdipped in this water, and dryed, and ignited, shewed evident marks of thepresence of nitre, when the flame was blown out. IV. _The Phænomena of the Diabetes explained, and of some Diarrhoeas. _ The phenomena of many diseases are only explicable from the retrogrademotions of some of the branches of the lymphatic system; as the great andimmediate flow of pale urine in the beginning of drunkenness; in hystericparoxysms; from being exposed to cold air; or to the influence of fear oranxiety. Before we endeavour to illustrate this doctrine, by describing thephænomena of these diseases, we must premise one circumstance; that all thebranches of the lymphatic system have a certain sympathy with each other, insomuch that when one branch is stimulated into unusual kinds orquantities of motion, some other branch has its motions either increased, or decreased, or inverted at the same time. This kind of sympathy can onlybe proved by the concurrent testimony of numerous facts, which will berelated in the course of the work. I shall only add here, that it isprobable, that this sympathy does not depend on any communication ofnervous filaments, but on habit; owing to the various branches of thissystem having frequently been stimulated into action at the same time. There are a thousand instances of involuntary motions associated in thismanner; as in the act of vomiting, while the motions of the stomach andoesophagus are inverted, the pulsations of the arterial system by a certainsympathy become weaker; and when the bowels or kidneys are stimulated bypoison, a stone, or inflammation, into more violent action; the stomach andoesophagus by sympathy invert their motions. 1. When any one drinks a moderate quantity of vinous spirit, the wholesystem acts with more energy by consent with the stomach and intestines, asis seen from the glow on the skin, and the increase of strength andactivity; but when a greater quantity of this inebriating material isdrank, at the same time that the lacteals are excited into greater actionto absorb it; it frequently happens, that the urinary branch of absorbents, which is connected with the lacteals by many anastomoses, inverts itsmotions, and a great quantity of pale unanimalized urine is discharged. Bythis wise contrivance too much of an unnecessary fluid is prevented fromentering the circulation--This may be called the drunken diabetes, todistinguish it from the other temporary diabetes, which occur in hystericdiseases, and from continued fear or anxiety. 2. If this idle ingurgitation of too much vinous spirit be daily practised, the urinary branch of absorbents at length gains an habit of inverting itsmotions, whenever the lacteals are much stimulated; and the whole or agreat part of the chyle is thus daily carried to the bladder withoutentering the circulation, and the body becomes emaciated. This is one kindof chronic diabetes, and may be distinguished from the others by the tasteand appearance of the urine; which is sweet, and the colour of whey, andmay be termed the chyliferous diabetes. 3. Many children have a similar deposition of chyle in their urine, fromthe irritation of worms in their intestines, which stimulating the mouthsof the lacteals into unnatural action, the urinary branch of the absorbentsbecomes inverted, and carries part of the chyle to the bladder: part of thechyle also has been carried to the iliac and lumbar glands, of whichinstances are recorded by Haller, t. Vii. 225. And which can be explainedon no other theory: but the dissections of the lymphatic system of thehuman body, which have yet been published, are not sufficiently extensivefor our purpose; yet if we may reason from comparative anatomy, thistranslation of chyle to the bladder is much illustrated by the accountgiven of this system of vessels in a turtle, by Mr. Hewson, who observed, "That the lacteals near the root of the mesentery anastomose, so as to forma net-work, from which several large branches go into some considerablelymphatics lying near the spine; and which can be traced almost to theanus, and particularly to the kidneys. " Philos. Trans. V. 59. P. 199--Enquiries, p. 74. 4. At the same time that the urinary branch of absorbents, in the beginningof diabetes, is excited into inverted action, the cellular branch isexcited by the sympathy above mentioned, into more energetic action; andthe fat, that was before deposited, is reabsorbed and thrown into the bloodvessels; where it floats, and was mistaken for chyle, till the lateexperiments of the ingenious Mr. Hewson demonstrated it to be fat. This appearance of what was mistaken for chyle in the blood, which wasdrawn from these patients, and the obstructed liver, which very frequentlyaccompanies this disease, seems to have led Dr. Mead to suspect thediabetes was owing to a defect of sanguification; and that the schirrosityof the liver was the original cause of it: but as the schirrhus of theliver is most frequently owing to the same causes, that produce thediabetes and dropsies; namely, the great use of fermented liquors; there isno wonder they should exist together, without being the consequence of eachother. 5. If the cutaneous branch of absorbents gains a habit of being excitedinto stronger action, and imbibes greater quantities of moisture from theatmosphere, at the same time that the urinary branch has its motionsinverted, another kind of diabetes is formed, which may be termed theaqueous diabetes. In this diabetes the cutaneous absorbents frequentlyimbibe an amazing quantity of atmospheric moisture; insomuch that there areauthentic histories, where many gallons a day, for many weeks together, above the quantity that has been drank, have been discharged by urine. Dr. Keil, in his Medicina Statica, found that he gained eighteen ouncesfrom the moist air of one night; and Dr. Percival affirms, that one of hishands imbibed, after being well chafed, near an ounce and half of water, ina quarter of an hour. (Transact. Of the College, London, vol. Ii. P. 102. )Home's Medic. Facts, p. 2. Sect. 3. The pale urine in hysterical women, or which is produced by fear oranxiety, is a temporary complaint of this kind; and it would in reality bethe same disease, if it was confirmed by habit. 6. The purging stools, and pale urine, occasioned by exposing the nakedbody to cold air, or sprinkling it with cold water, originate from asimilar cause; for the mouths of the cutaneous lymphatics being suddenlyexposed to cold become torpid, and cease, or nearly cease, to act; whilst, by the sympathy above described, not only the lymphatics of the bladder andintestines cease also to absorb the more aqueous and saline part of thefluids secreted into them; but it is probable that these lymphatics inverttheir motions, and return the fluids, which were previously absorbed, intothe intestines and bladder. At the very instant that the body is exposednaked to the cold air, an unusual movement is felt in the bowels; as isexperienced by boys going into the cold bath: this could not occur from anobstruction of the perspirable matter, since there is not time, for that tobe returned to the bowels by the course of the circulation. There is also a chronic aqueous diarrhoea, in which the atmosphericmoisture, drank up by the cutaneous and pulmonary lymphatics, is pouredinto the intestines, by the retrograde motions of the lacteals. Thisdisease is most similar to the aqueous diabetes, and is frequentlyexchanged for it: a distinct instance of this is recorded by Benningerus, Cent. V. Obs. 98. In which an aqueous diarrhoea succeeded an aqueousdiabetes, and destroyed the patient. There is a curious example of this, described by Sympson (De Re Medica)--"A young man (says he) was seized witha fever, upon which a diarrhoea came on, with great stupor; and he refusedto drink any thing, though he was parched up with excessive heat: thebetter to supply him with moisture, I directed his feet to be immersed incold water; immediately I observed a wonderful decrease of water in thevessel, and then an impetuous stream of a fluid, scarcely coloured, wasdischarged by stool, like a cataract. " 7. There is another kind of diarrhoea, which has been called cæliaca; inthis disease the chyle, drank up by the lacteals of the small intestines, is probably poured into the large intestines, by the retrograde motions oftheir lacteals: as in the chyliferous diabetes, the chyle is poured intothe bladder, by the retrograde motions of the urinary branch of absorbents. The chyliferous diabetes, like this chyliferous diarrhoea, produces suddenatrophy; since the nourishment, which ought to supply the hourly waste ofthe body, is expelled by the bladder, or rectum: whilst the aqueousdiabetes, and the aqueous diarrhoea produce excessive thirst; because themoisture, which is obtained from the atmosphere, is not conveyed to thethoracic receptacle, as it ought to be, but to the bladder, or lowerintestines; whence the chyle, blood, and whole system of glands, are robbedof their proportion of humidity. 8. There is a third species of diabetes, in which the urine ismucilaginous, and appears ropy in pouring it from one vessel into another;and will sometimes coagulate over the fire. This disease appears byintervals, and ceases again, and seems to be occasioned by a previousdropsy in some part of the body. When such a collection is reabsorbed, itis not always returned into the circulation; but the same irritation thatstimulates one lymphatic branch to reabsorb the deposited fluid, invertsthe urinary branch, and pours it into the bladder. Hence this mucilaginousdiabetes is a cure, or the consequence of a cure, of a worse disease, rather than a disease itself. Dr. Cotunnius gave half an ounce of cream of tartar, every morning, to apatient, who had the anasarca; and he voided a great quantity of urine; apart of which, put over the fire, coagulated, on the evaporation of half ofit, so as to look like the white of an egg. De Ischiade Nervos. This kind of diabetes frequently precedes a dropsy; and has this remarkablecircumstance attending it, that it generally happens in the night; asduring the recumbent state of the body, the fluid, that was accumulated inthe cellular membrane, or in the lungs, is more readily absorbed, as it isless impeded by its gravity. I have seen more than one instance of thisdisease. Mr. D. A man in the decline of life, who had long accustomedhimself to spirituous liquor, had swelled legs, and other symptoms ofapproaching anasarca; about once in a week, or ten days, for severalmonths, he was seized, on going to bed, with great general uneasiness, which his attendants resembled to an hysteric fit; and which terminated ina great discharge of viscid urine; his legs became less swelled, and hecontinued in better health for some days afterwards. I had not theopportunity to try if this urine would coagulate over the fire, when partof it was evaporated, which I imagine would be the criterion of this kindof diabetes; as the mucilaginous fluid deposited in the cells and cysts ofthe body, which have no communication with the external air, seems toacquire, by stagnation, this property of coagulation by heat, which thesecreted mucus of the intestines and bladder do not appear to possess; as Ihave found by experiment: and if any one should suppose this coagulableurine was separated from the blood by the kidneys, he may recollect, thatin the most inflammatory diseases, in which the blood is most replete ormost ready to part with the coagulable lymph, none of this appears in theurine. 9. Different kinds of diabetes require different methods of cure. For thefirst kind, or chyliferous diabetes, after clearing the stomach andintestines, by ipecacuanha and rhubarb, to evacuate any acid material, which may too powerfully stimulate the mouths of the lacteals, repeated andlarge doses of tincture of cantharides have been much recommended. Thespecific stimulus of this medicine, on the neck of the bladder, is likelyto excite the numerous absorbent vessels, which are spread on that part, into stronger natural actions, and by that means prevent their retrogradeones; till, by persisting in the use of the medicine, their natural habitsof motions might again be established. Another indication of cure, requiressuch medicines, as by lining the intestines with mucilaginous substances, or with such as consist of smooth particles, or which chemically destroythe acrimony of their contents, may prevent the too great action of theintestinal absorbents. For this purpose, I have found the earthprecipitated from a solution of alum, by means of fixed alcali, given inthe dose of half a dram every six hours, of great advantage, with a fewgrains of rhubarb, so as to produce a daily evacuation. The food should consist of materials that have the least stimulus, withcalcareous water, as of Bristol and Matlock; that the mouths of thelacteals may be as little stimulated as is necessary for their properabsorption; lest with their greater exertions, should be connected bysympathy, the inverted motions of the urinary lymphatics. The same method may be employed with equal advantage in the aqueousdiabetes, so great is the sympathy between the skin and the stomach. Towhich, however, some application to the skin might be usefully added; asrubbing the patient all over with oil, to prevent the too great action ofthe cutaneous absorbents. I knew an experiment of this kind made upon onepatient with apparent advantage. The mucilaginous diabetes will require the same treatment, which is mostefficacious in the dropsy, and will be described below. I must add, thatthe diet and medicines above mentioned, are strongly recommended by variousauthors, as by Morgan, Willis, Harris, and Etmuller; but more histories ofthe successful treatment of these diseases are wanting to fully ascertainthe most efficacious methods of cure. In a letter from Mr. Charles Darwin, dated April 24, 1778, Edinburgh, isthe subsequent passage:--"A man who had long laboured under a diabetes diedyesterday in the clinical ward. He had for some time drank four, and passedtwelve pounds of fluid daily; each pound of urine contained an ounce ofsugar. He took, without considerable relief, gum kino, sanguis diaconismelted with alum, tincture of cantharides, isinglass, gum arabic, crabseyes, spirit of hartshorn, and eat ten or fifteen oysters thrice a day. Dr. Home, having read my thesis, bled him, and found that neither the freshblood nor the serum tasted sweet. His body was opened this morning--everyviscus appeared in a sound and natural state, except that the left kidneyhad a very small pelvis, and that there was a considerable enlargement ofmost of the mesenteric lymphatic glands. I intend to insert this in mythesis, as it coincides with the experiment, where some asparagus was eatenat the beginning of intoxication, and its smell perceived in the urine, though not in the blood. " The following case of chyliferous diabetes is extracted from some lettersof Mr. Hughes, to whose unremitted care the infirmary at Stafford for manyyears was much indebted. Dated October 10, 1778. Richard Davis, aged 33, a whitesmith by trade, had drank hard by intervals;was much troubled with sweating of his hands, which incommoded him in hisoccupation, but which ceased on his frequently dipping them in lime. Aboutseven months ago he began to make large quantities of water; his legs areoedematous, his belly tense, and he complains of a rising in his throat, like the globus hystericus: he eats twice as much as other people, drinksabout fourteen pints of small beer a day, besides a pint of ale, somemilk-porridge, and a bason of broth, and he makes about eighteen pints ofwater a day. He tried alum, dragon's blood, steel, blue vitriol, and cantharides inlarge quantities, and duly repeated, under the care of Dr. Underhill, butwithout any effect; except that on the day after he omitted thecantharides, he made but twelve pints of water, but on the next day thisgood effect ceased again. November 21. --He made eighteen pints of water, and he now, at Dr. Darwin'srequest, took a grain of opium every four hours, and five grains of aloesat night; and had a flannel shirt given him. 22. --Made sixteen pints. 23. --Thirteen pints: drinks less. 24. --Increased the opium to a grain and quarter every four hours: he madetwelve pints. 25. --Increased the opium to a grain and half: he now makes ten pints; anddrinks eight pints in a day. The opium was gradually increased during the next fortnight, till he tookthree grains every four hours, but without any further diminution of hiswater. During the use of the opium he sweat much in the nights, so as tohave large drops stand on his face and all over him. The quantity of opiumwas then gradually decreased, but not totally omitted, as he continued totake about a grain morning and evening. January 17. --He makes fourteen pints of water a day. Dr. Underhill nowdirected him two scruples of common rosin triturated with as much sugar, every six hours; and three grains of opium every night. 19. --Makes fifteen pints of water: sweats at night. 21. --Makes seventeen pints of water; has twitchings of his limbs in amorning, and pains of his legs: he now takes a dram of rosin for a dose, and continues the opium. 23. --Water more coloured, and reduced to sixteen pints, and he thinks has abrackish taste. 26. --Water reduced to fourteen pints. 28. --Water thirteen pints: he continues the opium, and takes four scruplesof the rosin for a dose. February 1. --Water twelve pints. 4. --Water eleven pints: twitchings less; takes five scruples for a dose. 8. --Water ten pints: has had many stools. 12. --Appetite less: purges very much. After this the rosin either purged him, or would not stay on his stomach;and he gradually relapsed nearly to his former condition, and in a fewmonths sunk under the disease. October 3, Mr. Hughes evaporated two quarts of the water, and obtained fromit four ounces and half of a hard and brittle saccharine mass, like treaclewhich had been some time boiled. Four ounces of blood, which he took fromhis arm with design to examine it, had the common appearances, except thatthe serum resembled cheese-whey; and that on the evidence of four persons, two of whom did not know what it was they tasted, _the serum had a saltishtaste_. From hence it appears, that the saccharine matter, with which the urine ofthese patients so much abounds, does not enter the blood-vessels like thenitre and asparagus mentioned above; but that the process of digestionresembles the process of the germination of vegetables, or of making barleyinto malt; as the vast quantity of sugar found in the urine must be madefrom the food which he took (which was double that taken by others), andfrom the fourteen pints of small beer which he drank. And, secondly, as theserum of the blood was not sweet, the chyle appears to have been conveyedto the bladder without entering the circulation of the blood, since solarge a quantity of sugar, as was found in the urine, namely, twenty ouncesa day, could not have previously existed in the blood without beingperceptible to the taste. November 1. Mr. Hughes dissolved two drams of nitre in a pint of adecoction of the roots of asparagus, and added to it two ounces of tinctureof rhubarb: the patient took a fourth part of this mixture every fiveminutes, till he had taken the whole. --In about half an hour he madeeighteen ounces of water, which was very manifestly tinged with therhubarb; the smell of asparagus was doubtful. He then lost four ounces of blood, the serum of which was not so opake asthat drawn before, but of a yellowish cast, as the serum of the bloodusually appears. Paper, dipped three or four times in the tinged urine and dried again, didnot scintillate when it was set on fire; but when the flame was blown out, the fire ran along the paper for half an inch; which, when the same paperwas unimpregnated, it would not do; nor when the same paper was dipped inurine made before he took the nitre, and dried in the same manner. Paper, dipped in the serum of the blood and dried in the same manner as inthe urine, did not scintillate when the flame was blown out, but burntexactly in the same manner as the same paper dipped in the serum of blooddrawn from another person. This experiment, which is copied from a letter of Mr. Hughes, as well asthe former, seems to evince the existence of another passage from theintestines to the bladder, in this disease, besides that of thesanguiferous system; and coincides with the curious experiment related insection the third, except that the smell of the asparagus was not hereperceived, owing perhaps to the roots having been made use of instead ofthe heads. The rising in the throat of this patient, and the twitchings of his limbs, seem to indicate some similarity between the diabetes and the hystericdisease, besides the great flow of pale urine, which is common to themboth. Perhaps if the mesenteric glands were nicely inspected in the dissectionsof these patients; and if the thoracic duct, and the larger branches of thelacteals, and if the lymphatics, which arise from the bladder, were wellexamined by injection, or by the knife, the cause of diabetes might be morecertainly understood. The opium alone, and the opium with the rosin, seem much to have servedthis patient, and might probably have effected a cure, if the disease hadbeen slighter, or the medicine had been exhibited, before it had beenconfirmed by habit during the seven months it had continued. The increaseof the quantity of water on beginning the large doses of rosin was probablyowing to his omitting the morning doses of opium. V. _The Phænomena of Dropsies explained. _ I. Some inebriates have their paroxysms of inebriety terminated by muchpale urine, or profuse sweats, or vomiting, or stools; others have theirparoxysms terminated by stupor, or sleep, without the above evacuations. The former kind of these inebriates have been observed to be more liable todiabetes and dropsy; and the latter to gout, gravel, and leprosy. Evoe!attend ye bacchanalians! start at this dark train of evils, and, amid yourimmodest jests, and idiot laughter, recollect, Quem Deus vult perdere, prius dementat. In those who are subject to diabetes and dropsy, the absorbent vessels arenaturally more irritable than in the latter; and by being frequentlydisturbed or inverted by violent stimulus, and by their too great sympathywith each other, they become at length either entirely paralytic, or areonly susceptible of motion from the stimulus of very acrid materials; asevery part of the body, after having been used to great irritations, becomes less affected by smaller ones. Thus we cannot distinguish objectsin the night, for some time after we come out of a strong light, though theiris is presently dilated; and the air of a summer evening appears cold, after we have been exposed to the heat of the day. There are no cells in the body, where dropsy may not be produced, if thelymphatics cease to absorb that mucilaginous fluid, which is perpetuallydeposited in them, for the purpose of lubricating their surfaces. If the lymphatic branch, which opens into the cellular membrane, eitherdoes its office imperfectly, or not at all; these cells become replete witha mucilaginous fluid, which, after it has stagnated some time in the cells, will coagulate over the fire; and is erroneously called water. Wherever theseat of this disease is, (unless in the lungs or other pendent viscera) themucilaginous liquid above mentioned will subside to the most dependingparts of the body, as the feet and legs, when those are lower than the headand trunk; for all these cells have communications with each other. When the cellular absorbents are become insensible to their usualirritations, it most frequently happens, but not always, that the cutaneousbranch of absorbents, which is strictly associated with them, suffers thelike inability. And then, as no water is absorbed from the atmosphere, theurine is not only less diluted at the time of its secretion, andconsequently in less quantity and higher coloured: but great thirst is atthe same time induced, for as no water is absorbed from the atmosphere todilute the chyle and blood, the lacteals and other absorbent vessels, whichhave not lost their powers, are excited into more constant or more violentaction, to supply this deficiency; whence the urine becomes still less inquantity, and of a deeper colour, and turbid like the yolk of an egg, owingto a greater absorption of its thinner parts. From this stronger action ofthose absorbents, which still retain their irritability, the fat is alsoabsorbed, and the whole body becomes emaciated. This increased exertion ofsome branches of the lymphatics, while others are totally or partiallyparalytic, is resembled by what constantly occurs in the hemiplagia; whenthe patient has lost the use of the limbs on one side, he is incessantlymoving those of the other; for the moving power, not having access to theparalytic limbs, becomes redundant in those which are not diseased. The paucity of urine and thirst cannot be explained from a greater quantityof mucilaginous fluid being deposited in the cellular membrane: for thoughthese symptoms have continued many weeks, or even months, this collectionfrequently does not amount to more than very few pints. Hence also thedifficulty of promoting copious sweats in anasarca is accounted for, aswell as the great thirst, paucity of urine, and loss of fat; since, whenthe cutaneous branch of absorbents is paralytic, or nearly so, there isalready too small a quantity of aqueous fluid in the blood: nor can thesetorpid cutaneous lymphatics be readily excited into retrograde motions. Hence likewise we understand, why in the ascites, and some other dropsies, there is often no thirst, and no paucity of urine; in these cases thecutaneous absorbents continue to do their office. Some have believed, that dropsies were occasioned by the inability of thekidneys, from having only observed the paucity of urine; and have thencelaboured much to obtain diuretic medicines; but it is daily observable, that those who die of a total inability to make water, do not becomedropsical in consequence of it: Fernelius mentions one, who laboured undera perfect suppression of urine during twenty days before his death, and yethad no symptoms of dropsy. Pathol. 1. Vi. C. 8. From the same idea manyphysicians have restrained their patients from drinking, though theirthirst has been very urgent; and some cases have been published, where thiscruel regimen has been thought advantageous: but others of nicerobservation are of opinion, that it has always aggravated the distresses ofthe patient; and though it has abated his swellings, yet by inducing afever it has hastened his dissolution. See Transactions of the College, London, vol. Ii. P. 235. Cases of Dropsy by Dr. G. Baker. The cure of anasarca, so far as respects the evacuation of the accumulatedfluid, coincides with the idea of the retrograde action of the lymphaticsystem. It is well known that vomits, and other drugs, which inducesickness or nausea; at the same time that they evacuate the stomach, produce a great absorption of the lymph accumulated in the cellularmembrane. In the operation of a vomit, not only the motions of the stomachand duodenum become inverted, but also those of the lymphatics andlacteals, which belong to them; whence a great quantity of chyle and lymphis perpetually poured into the stomach and intestines, during theoperation, and evacuated by the mouth. Now at the same time, other branchesof the lymphatic system, viz. Those which open on the cellular membrane, are brought into more energetic action, by the sympathy above mentioned, and an increase of their absorption is produced. Hence repeated vomits, and cupreous salts, and small doses of squill orfoxglove, are so efficacious in this disease. And as drastic purges actalso by inverting the motions of the lacteals; and thence the otherbranches of lymphatics are induced into more powerful natural action, bysympathy, and drink up the fluids from all the cells of the body; and bytheir anastomoses, pour them into the lacteal branches; which, by theirinverted actions, return them into the intestines; and they are thusevacuated from the body:--these purges also are used with success indischarging the accumulated fluid in anasarca. II. The following cases are related with design to ascertain the particularkinds of dropsy in which the digitalis purpurea, or common foxglove, ispreferable to squill, or other evacuants, and were first published in 1780, in a pamphlet entitled Experiments on mucilaginous and purulent Matter, &c. Cadell. London. Other cases of dropsy, treated with digitalis, wereafterwards published by Dr. Darwin in the Medical Transactions, vol. Iii. In which there is a mistake in respect to the dose of the powder offoxglove, which should have been from five grains to one, instead of fromfive grains to ten. _Anasarca of the Lungs. _ 1. A lady, between forty and fifty years of age, had been indisposed sometime, was then seized with cough and fever, and afterwards expectoratedmuch digested mucus. This expectoration suddenly ceased, and a considerabledifficulty of breathing supervened, with a pulse very irregular both invelocity and strength; she was much distressed at first lying down, and atfirst rising; but after a minute or two bore either of those attitudes withease. She had no pain or numbness in her arms; she had no hectic fever, norany cold shiverings, and the urine was in due quantity, and of the naturalcolour. The difficulty of breathing was twice considerably relieved by small dosesof ipecacuanha, which operated upwards and downwards, but recurred in a fewdays: she was then directed a decoction of foxglove, (digitalis purpurea)prepared by boiling four ounces of the fresh leaves from two pints of waterto one pint; to which was added two ounces of vinous spirit: she took threelarge spoonfuls of this mixture every two hours, till she had taken it fourtimes; a continued sickness supervened, with frequent vomiting, and acopious flow of urine: these evacuations continued at intervals for two orthree days, and relieved the difficulty of breathing--She had some relapsesafterwards, which were again relieved by the repetition of the decoction offoxglove. 2. A gentleman, about sixty years of age, who had been addicted to animmoderate use of fermented liquors, and had been very corpulent, graduallylost his strength and flesh, had great difficulty of breathing, with legssomewhat swelled, and a very irregular pulse. He was very much distressedat first lying down, and at first rising from his bed, yet in a minute ortwo was easy in both those attitudes. He made straw-coloured urine in duequantity, and had no pain or numbness of his arms. He took a large spoonful of the decoction of foxglove, as above, everyhour, for ten or twelve successive hours, had incessant sickness for abouttwo days, and passed a large quantity of urine; upon which his breathbecame quite easy, and the swelling of his legs subsided; but as his wholeconstitution was already sinking from the previous intemperance of hislife, he did not survive more than three or four months. _Hydrops Pericardii. _ 3. A gentleman of temperate life and sedulous application to business, between thirty and forty years of age, had long been subject, at intervals, to an irregular pulse: a few months ago he became weak, with difficulty ofbreathing, and dry cough. In this situation a physician of eminencedirected him to abstain from all animal food and fermented liquor, duringwhich regimen all his complaints increased; he now became emaciated, andtotally lost his appetite; his pulse very irregular both in velocity andstrength; with great difficulty of breathing, and some swelling of hislegs; yet he could lie down horizontally in his bed, though he got littlesleep, and passed a due quantity of urine, and of the natural colour: nofullness or hardness could be perceived about the region of the liver; andhe had no pain or numbness in his arms. One night he had a most profuse sweat all over his body and limbs, whichquite deluged his bed, and for a day or two somewhat relieved hisdifficulty of breathing, and his pulse became less irregular: this copioussweat recurred three or four times at the intervals of five or six days, and repeatedly alleviated his symptoms. He was directed one large spoonful of the above decoction of foxglove everyhour, till it procured some considerable evacuation: after he had taken iteleven successive hours he had a few liquid stools, attended with a greatflow of urine, which last had a dark tinge, as if mixed with a few drops ofblood: he continued sick at intervals for two days, but his breath becamequite easy, and his pulse quite regular, the swelling of his legsdisappeared, and his appetite and sleep returned. He then took three grains of white vitriol twice a day, with some bittermedicines, and a grain of opium with five grains of rhubarb every night;was advised to eat flesh meat, and spice, as his stomach would bear it, with small beer, and a few glasses of wine; and had issues made in histhighs; and has suffered no relapse. 4. A lady, about fifty years of age, had for some weeks great difficulty ofbreathing, with very irregular pulse, and considerable general debility:she could lie down in bed, and the urine was in due quantity and of thenatural colour, and she had no pain or numbness of her arms. She took one large spoonful of the above decoction of foxglove every hour, for ten or twelve successive hours; was sick, and made a quantity of paleurine for about two days, and was quite relieved both of the difficulty ofbreathing, and the irregularity of her pulse. She then took a grain ofopium, and five grains of rhubarb, every night, night, for many weeks; withsome slight chalybeate and bitter medicines, and has suffered no relapse. _Hydrops Thoracis. _ 5. A tradesman, about fifty years of age, became weak and short of breath, especially on increase of motion, with pain in one arm, about the insertionof the biceps muscle. He observed he sometimes in the night made an unusualquantity of pale water. He took calomel, alum, and peruvian bark, and allhis symptoms increased: his legs began to swell considerably; his breathbecame more difficult, and he could not lie down in bed; but all this timehe made a due quantity of straw-coloured water. The decoction of foxglove was given as in the preceding cases, whichoperated chiefly by purging, and seemed to relieve his breath for a day ortwo; but also seemed to contribute to weaken him. --He became after someweeks universally dropsical, and died comatous. 6. A young lady of delicate constitution, with light eyes and hair, and whohad perhaps lived too abstemiously both in respect to the quantity andquality of what she eat and drank, was seized with great difficulty ofbreathing, so as to threaten immediate death. Her extremities were quitecold, and her breath felt cold to the back of one's hand. She had no sweat, nor could be down for a single moment; and had previously, and at present, complained of great weakness and pain and numbness of both her arms; had noswelling of her legs, no thirst, water in due quantity and colour. Hersister, about a year before, was afflicted with similar symptoms, wasrepeatedly blooded, and died universally dropsical. A grain of opium was given immediately, and repeated every six hours withevident and amazing advantage; afterwards a blister, with chalybeates, bitters, and essential oils, were exhibited, but nothing had such eminenteffect in relieving the difficulty of breathing and coldness of herextremities as opium, by the use of which in a few weeks she perfectlyregained her health, and has suffered no relapse. _Ascites. _ 7. A young lady of delicate constitution having been exposed to great fear, cold, and fatigue, by the overturn of a chaise in the night, began withpain and tumour in the right hypochondrium: in a few months a fluctuationwas felt throughout the whole abdomen, more distinctly perceptible indeedabout the region of the stomach; since the integuments of the lower part ofthe abdomen generally become thickened in this disease by a degree ofanasarca. Her legs were not swelled, no thirst, water in due quantity andcolour. --She took the foxglove so as to induce sickness and stools, butwithout abating the swelling, and was obliged at length to submit to theoperation of tapping. 8. A man about sixty-seven, who had long been accustomed to spirituouspotation, had some time laboured under ascites; his legs somewhat swelled;his breath easy in all attitudes; no appetite; great thirst; urine inexceedingly small quantity, very deep coloured, and turbid; pulse equal. Hetook the foxglove in such quantity as vomited him, and induced sickness fortwo days; but procured no flow of urine, or diminution of his swelling; butwas thought to leave him considerably weaker. 9. A corpulent man, accustomed to large potation of fermented liquors, hadvehement cough, difficult breathing, anasarca of his legs, thighs, andhands, and considerable tumour, with evident fluctuation of his abdomen;his pulse was equal; his urine in small quantity, of deep colour, andturbid. These swellings had been twice considerably abated by drasticcathartics. He took three ounces of a decoction of foxglove (made byboiling one ounce of the fresh leaves in a pint of water) every threehours, for two whole days; it then began to vomit and purge him violently, and promoted a great flow of urine; he was by these evacuations completelyemptied in twelve hours. After two or three months all these symptomsreturned, and were again relieved by the use of the foxglove; and thus inthe space of about three years he was about ten times evacuated, andcontinued all that time his usual potations: excepting at first, themedicine operated only by urine, and did not appear considerably to weakenhim--The last time he took it, it had no effect; and a few weeks afterwardshe vomited a great quantity of blood, and expired. QUERIES. 1. As the first six of these patients had a due discharge of urine, and ofthe natural colour, was not the feat of the disease confined to some partof the thorax, and the swelling of the legs rather a symptom of theobstructed circulation of the blood, than of a paralysis of the cellularlymphatics of those parts? 2. When the original disease is a general anasarca, do not the cutaneouslymphatics always become paralytic at the same time with the cellular ones, by their greater sympathy with each other? and hence the paucity of urine, and the great thirst, distinguish this kind of dropsy? 3. In the anasarca of the lungs, when the disease is not very great, thoughthe patients have considerable difficulty of breathing at their first lyingdown, yet after a minute or two their breath becomes easy again; and thesame occurs at their first rising. Is not this owing to the time necessaryfor the fluid in the cells of the lungs to change its place, so as theleast to incommode respiration in the new attitude? 4. In the dropsy of the pericardium does not the patient bear thehorizontal or perpendicular attitude with equal ease? Does thiscircumstance distinguish the dropsy of the pericardium from that of thelungs and of the thorax? 5. Do the universal sweats distinguish the dropsy of the pericardium, or ofthe thorax? and those, which cover the upper parts of the body only, theanasarca of the lungs? 6. When in the dropsy of the thorax, the patient endeavours to lie down, does not the extravasated fluid compress the upper parts of the bronchia, and totally preclude the access of air to every part of the lungs; whilstin the perpendicular attitude the inferior parts of the lungs only arecompressed? Does not something similar to this occur in the anasarca of thelungs, when the disease is very great, and thus prevent those patients alsofrom lying down? 7. As a principal branch of the fourth cervical nerve of the left side, after having joined a branch of the third and of the second cervicalnerves, descending between the subclavian vein and artery, is received in agroove formed for it in the pericardium, and is obliged to make aconsiderable turn outwards to go over the prominent part of it, where thepoint of the heart is lodged, in its course to the diaphragm; and as theother phrenic nerve of the right side has a straight course to thediaphragm; and as many other considerable branches of this fourth pair ofcervical nerves are spread on the arms; does not a pain in the left armdistinguish a disease of the pericardium, as in the angina pectoris, or inthe dropsy of the pericardium? and does not a pain or weakness in both armsdistinguish the dropsy of the thorax? 8. Do not the dropsies of the thorax and pericardium frequently existtogether, and thus add to the uncertainty and fatality of the disease? 9. Might not the foxglove be serviceable in hydrocephalus internus, inhydrocele, and in white swellings of the joints? VI. _Of cold Sweats. _ There have been histories given of chronical immoderate sweatings, whichbear some analogy to the diabetes. Dr. Willis mentions a lady then living, whose sweats where for many years so profuse, that all her bed-clothes werenot only moistened, but deluged with them every night; and that manyounces, and sometimes pints, of this sweat, were received in vesselsproperly placed, as it trickled down her body. He adds, that she had greatthirst, had taken many medicines, and submitted to various rules of life, and changes of climate, but still continued to have these immoderatesweats. Pharmac. Ration. De sudore anglico. Dr. Willis has also observed, that the sudor anglicanus which appeared inEngland, in 1483, and continued till 1551, was in some respects similar tothe diabetes; and as Dr. Caius, who saw this disease, mentions theviscidity, as well as the quantity of these sweats, and adds, that theextremities were often cold, when the internal parts were burnt up withheat and thirst, with great and speedy emaciation and debility: there isgreat reason to believe, that the fluids were absorbed from the cells ofthe body by the cellular and cystic branches of the lymphatics, and pouredon the skin by the retrograde motions of the cutaneous ones. Sydenham has recorded, in the stationary fever of the year 1685, the viscidsweats flowing from the head, which were probably from the same source asthose in the sweating plague above mentioned. It is very common in dropsies of the chest or lungs to have the difficultyof breathing relieved by copious sweats, flowing from the head and neck. Mr. P. About 50 years of age, had for many weeks been afflicted withanasarca of his legs and thighs, attended with difficulty of breathing; andhad repeatedly been relieved by squill, other bitters, andchalybeates. --One night the difficulty of breathing became so great, thatit was thought he must have expired; but so copious a sweat came out of hishead and neck, that in a few hours some pints, by estimation, were wipedoff from those parts, and his breath was for a time relieved. This dyspnoeaand these sweats recurred at intervals, and after some weeks he ceased toexist. The skin of his head and neck felt cold to the hand, and appearedpale at the time these sweats flowed so abundantly; which is a proof, thatthey were produced by an inverted motion of the absorbents of those parts:for sweats, which are the consequence of an increased action of thesanguiferous system, are always attended with a warmth of the skin, greaterthan is natural, and a more florid colour; as the sweats from exercise, orthose that succeed the cold fits of agues. Can any one explain how thesepartial sweats should relieve the difficulty of breathing in anasarca, butby supposing that the pulmonary branch of absorbents drank up the fluid inthe cavity of the thorax, or in the cells of the lungs, and threw it on theskin, by the retrograde motions of the cutaneous branch? for, if we couldsuppose, that the increased action of the cutaneous glands or capillariespoured upon the skin this fluid, previously absorbed from the lungs; why isnot the whole surface of the body covered with sweat? why is not the skinwarm? Add to this, that the sweats above mentioned were clammy orglutinous, which the condensed perspirable matter is not; whence it wouldseem to have been a different fluid from that of common perspiration. Dr. Dobson, of Liverpool, has given a very ingenious explanation of theacid sweats, which he observed in a diabetic patient--he thinks part of thechyle is secreted by the skin, and afterwards undergoes an acetousfermentation. --Can the chyle get thither, but by an inverted motion of thecutaneous lymphatics? in the same manner as it is carried to the bladder, by the inverted motions of the urinary lymphatics. Medic. Observat. AndEnq. London, vol. V. Are not the cold sweats in some fainting fits, and in dying people, owingto an inverted motion of the cutaneous lymphatics? for in these there canbe no increased arterial or glandular action. Is the difficulty of breathing, arising from anasarca of the lungs, relieved by sweats from the head and neck; whilst that difficulty ofbreathing, which arises from a dropsy of the thorax, or pericardium, isnever attended with these sweats of the head? and thence can these diseasesbe distinguished from each other? Do the periodic returns of nocturnalasthma rise from a temporary dropsy of the lungs, collected during theirmore torpid state in sound deep, and then re-absorbed by the vehementefforts of the disordered organs of respiration, and carried off by thecopious sweats about the head and neck? More extensive and accurate dissections of the lymphatic system are wantingto enable us to unravel these knots of science. VII. _Translations of Matter, of Chyle, of Milk, of Urine. Operation ofpurging Drugs applied externally. _ 1. The translations of matter from one part of the body to another, canonly receive an explanation from the doctrine of the occasional retrogrademotions of some branches of the lymphatic system: for how can matter, absorbed and mixed with the whole mass of blood, be so hastily collectedagain in any one part? and is it not an immutable law, in animal bodies, that each gland can secrete no other, but its own proper fluid? which is, in part, fabricated in the very gland by an animal process, which it thereundergoes: of these purulent translations innumerable and very remarkableinstances are recorded. 2. The chyle, which is seen among the materials thrown up by violentvomiting, or in purging stools, can only come thither by its having beenpoured into the bowels by the inverted motions of the lacteals: for ouraliment is not converted into chyle in the stomach or intestines by achemical process, but is made in the very mouths of the lacteals; or in themesenteric glands; in the same manner as other secreted fluids are made byan animal process in their adapted glands. Here a curious phænomenon in the exhibition of mercury is worthexplaining:--If a moderate dose of calomel, as six or ten grains, beswallowed, and within one or two days a cathartic is given, a salivation isprevented: but after three or four days, a salivation having come on, repeated purges every day, for a week or two, are required to eliminate themercury from the constitution. For this acrid metallic preparation, beingabsorbed by the mouth of the lacteals, continues, for a time arrested bythe mesenteric glands, (as the variolous or venereal poisons swell thesubaxillar or inguinal glands): which, during the operation of a cathartic, is returned into the intestines by the inverted action of the lacteals, andthus carried out of the system. Hence we understand the use of vomits or purges, to those who haveswallowed either contagious or poisonous materials, even though exhibited aday or even two days after such accidents; namely, that by the retrogrademotions of the lacteals and lymphatics, the material still arrested in themesenteric, or other glands, may be eliminated from the body. 3. Many instances of milk and chyle found in ulcers are given by Haller, El. Physiol. T. Vii. P. 12, 23, which admit of no other explanation than bysupposing, that the chyle, imbibed by one branch of the absorbent system, was carried to the ulcer, by the inverted motions of another branch of thesame system. 4. Mrs. P. On the second day after delivery, was seized with a violentpurging, in which, though opiates, mucilages, the bark, and testacea wereprofusely used, continued many days, till at length she recovered. Duringthe time of this purging, no milk could be drawn from her breasts; but thestools appeared like the curd of milk broken into small pieces. In thiscase, was not the milk taken up from the follicles of the pectoral glands, and thrown on the intestines, by a retrogression of the intestinalabsorbents? for how can we for a moment suspect that the mucous glands ofthe intestines could separate pure milk from the blood? Doctor Smelly hasobserved, that loose stools, mixed with milk, which is curdled in theintestines, frequently relieves the turgescency of the breasts of those whostudiously repel their milk. Cases in Midwifery, 43, No. 2. 1. 5. J. F. Meckel observed in a patient, whose urine was in small quantity andhigh coloured, that a copious sweat under the arm-pits, of a perfectlyurinous smell, stained the linen; which ceased again when the usualquantity of urine was discharged by the urethra. Here we must believe fromanalogy, that the urine was first secreted in the kidneys, then re-absorbedby the increased action of the urinary lymphatics, and lastly carried tothe axillae by the retrograde motions of the lymphatic branches of thoseparts. As in the jaundice it is necessary, that the bile should first besecreted by the liver, and re-absorbed into the circulation, to produce theyellowness of the skin; as was formerly demonstrated by the late Dr. Munro, (Edin. Medical Essays) and if in this patient the urine had beenre-absorbed into the mass of blood, as the bile in the jaundice, why was itnot detected in other parts of the body, as well as in the arm-pits? 6. Cathartic and vermifuge medicines applied externally to the abdomen, seem to be taken up by the cutaneous branch of lymphatics, and poured onthe intestines by the retrograde motions of the lacteals, without havingpassed the circulation. For when the drastic purges are taken by the mouth, they excite thelacteals of the intestines into retrograde motions, as appears from thechyle, which is found coagulated among the fæces, as was shewn above, (sect. 2 and 4. ) And as the cutaneous lymphatics are joined with thelacteals of the intestines, by frequent anastomoses; it would be moreextraordinary, when a strong purging drug, absorbed by the skin, is carriedto the anastomosing branches of the lacteals unchanged, if it should notexcite them into retrograde action as efficaciously, as if it was taken bythe mouth, and mixed with the food of the stomach. VIII. _Circumstances by which the Fluids, that are effused by theretrograde Motions of the absorbent Vessels, are distinguished. _ 1. We frequently observe an unusual quantity of mucus or other fluids insome diseases, although the action of the glands, by which those fluids areseparated from the blood, is not unusually increased; but when the power ofabsorption alone is diminished. Thus the catarrhal humour from the nostrilsof some, who ride in frosty weather; and the tears, which run down thecheeks of those, who have an obstruction of the puncta lacrymalia; and theichor of those phagedenic ulcers, which are not attended with inflammation, are all instances of this circumstance. These fluids however are easily distinguished from others by theirabounding in ammoniacal or muriatic salts; whence they inflame thecircumjacent skin: thus in the catarrh the upper lip becomes red andswelled from the acrimony of the mucus, and patients complain of thesaltness of its taste. The eyes and cheeks are red with the corrosivetears, and the ichor of some herpetic eruptions erodes far and wide thecontiguous parts, and is pungently salt to the taste, as some patients haveinformed me. Whilst, on the contrary, those fluids, which are effused by the retrogradeaction of the lymphatics, are for the most part mild and innocent; aswater, chyle, and the natural mucus: or they take their properties from thematerials previously absorbed, as in the coloured or vinous urine, or thatscented with asparagus, described before. 2. Whenever the secretion of any fluid is increased, there is at the sametime an increased heat in the part; for the secreted fluid, as the bile, did not previously exist in the mass of blood, but a new combination isproduced in the gland. Now as solutions are attended with cold, socombinations are attended with heat; and it is probable the sum of the heatgiven out by all the secreted fluids of animal bodies may be the cause oftheir general heat above that of the atmosphere. Hence the fluids derived from increased secretions are readilydistinguished from those originating from the retrograde motions of thelymphatics: thus an increase of heat either in the diseased parts, ordiffused over the whole body, is perceptible, when copious bilious stoolsare consequent to an inflamed liver; or a copious mucous salivation fromthe inflammatory angina. 3. When any secreted fluid is produced in an unusual quantity, and at thesame time the power of absorption is increased in equal proportion, notonly the heat of the gland becomes more intense, but the secreted fluidbecomes thicker and milder, its thinner and saline parts being re-absorbed:and these are distinguishable both by their greater consistence, and bytheir heat, from the fluids, which are effused by the retrograde motions ofthe lymphatics; as is observable towards the termination of gonorrhoea, catarrh, chincough, and in those ulcers, which are said to abound withlaudable pus. 4. When chyle is observed in stools, or among the materials ejected byvomit, we may be confident it must have been brought thither by theretrograde motions of the lacteals; for chyle does not previously existamid the contents of the intestines, but is made in the very mouths of thelacteals, as was before explained. 5. When chyle, milk, or other extraneous fluids are found in the urinarybladder, or in any other excretory receptacle of a gland; no one can for amoment believe, that these have been collected from the mass of blood by amorbid secretion, as it contradicts all analogy. ---- Aurea duræ Mala ferant quercus? Narcisco floreat alnus? Pinguia corticibus sudent electra myricæ?--VIRGIL. IX. _Retrograde Motions of Vegetable juices. _ There are besides some motions of the sap in vegetables, which bear analogyto our present subject; and as the vegetable tribes are by manyphilosophers held to be inferior animals, it may be a matter of curiosityat least to observe, that their absorbent vessels seem evidently, at times, to be capable of a retrograde motion. Mr. Perault cut off a forked branchof a tree, with the leaves on; and inverting one of the forks into a vesselof water, observed, that the leaves on the other branch continued greenmuch longer than those of a similar branch, cut off from the same tree;which shews, that the water from the vessel was carried up one part of theforked branch, by the retrograde motion of its vessels, and suppliednutriment some time to the other part of the branch, which was out of thewater. And the celebrated Dr. Hales found, by numerous very accurateexperiments, that the sap of trees rose upwards during the warmer hours ofthe day, and in part descended again during the cooler ones. VegetableStatics. It is well known that the branches of willows, and of many other trees, will either take root in the earth or engraft on other trees, so as to havetheir natural direction inverted, and yet flourish with vigour. Dr. Hope has also made this pleasing experiment, after the manner ofHales--he has placed a forked branch, cut from one tree, erect between twoothers; then cutting off a part of the bark from one fork applied it to asimilar branch of one of the trees in its vicinity; and the same of theother fork; so that a tree is seen to grow suspended in the air, betweentwo other trees; which supply their softer friend with due nourishment. Miranturque novas frondes, et non sua poma. All these experiments clearly evince, that the juices of vegetables canoccasionally pass either upwards or downwards in their absorbent system ofvessels. X. _Objections answered. _ The following experiment, at first view, would seem to invalidate thisopinion of the retrograde motions of the lymphatic vessels, in somediseases. About a gallon of milk having been giving to an hungry swine, he wassuffered to live about an hour, and was then killed by a stroke or two onhis head with an axe. --On opening his belly the lacteals were well seenfilled with chyle; on irritating many of the branches of them with a knife, they did not appear to empty themselves hastily; but they did however carryforwards their contents in a little time. I then passed a ligature round several branches of lacteals, and irritatedthem much with a knife beneath the ligature, but could not make themregurgitate their contained fluid into the bowels. I am not indeed certain, that the nerve was not at the same time includedin the ligature, and thus the lymphatic rendered unirritable or lifeless;but this however is certain, that it is not any quantity of any stimulus, which induces the vessels of animal bodies to revert their motions; but acertain quantity of a certain stimulus, as appears from wounds in thestomach, which do not produce vomiting; and wounds of the intestines, whichdo not produce the cholera morbus. At Nottingham, a few years ago, two shoemakers quarrelled, and one of themwith a knife, which they use in their occupation, stabbed his companionabout the region of the stomach. On opening the abdomen of the wounded manafter his death the food and medicines he had taken were in part found inthe cavity of the belly, on the outside of the bowels; and there was awound about half an inch long at the bottom of the stomach; which I supposewas distended with liquor and food at the time of the accident; and thencewas more liable to be injured at its bottom: but during the whole time helived, which was about ten days, he had no efforts to vomit, nor ever evencomplained of being sick at the stomach! Other cases similar to this arementioned in the philosophical transactions. Thus, if you vellicate the throat with a feather, nausea is produced; ifyou wound it with a penknife, pain is induced, but not sickness. So if thesoles of the feet of children or their armpits are tickled, convulsivelaughter is excited, which ceases the moment the hand is applied, so as torub them more forcibly. The experiment therefore above related upon the lacteals of a dead pig, which were included in a strict ligature, proves nothing; as it is not thequantity, but the kind of stimulus, which excites the lymphatic vesselsinto retrograde motion. XI. _The Causes which induce the retrograde Motions of animal Vessels; andthe Medicines by which the natural Motions are restored. _ 1. Such is the construction of animal bodies, that all their parts, whichare subjected to less stimuli than nature designed, perform their functionswith less accuracy: thus, when too watery or too acescent food is takeninto the stomach, indigestion, and flatulency, and heartburn succeed. 2. Another law of irritation, connate with our existence, is, that allthose parts of the body, which have previously been exposed to too great aquantity of such stimuli, as strongly affect them, become for some timeafterwards disobedient to the natural quantity of their adaptedstimuli. --Thus the eye is incapable of seeing objects in an obscure room, though the iris is quite dilated, after having been exposed to the meridiansun. 3. There is a third law of irritation, that all the parts of our bodies, which have been lately subjected to less stimulus, than they have beenaccustomed to, when they are exposed to their usual quantity of stimulus, are excited into more energetic motions: thus when we come from a duskycavern into the glare of daylight, our eyes are dazzled; and after emergingfrom the cold bath, the skin becomes warm and red. 4. There is a fourth law of irritation, that all the parts of our bodies, which are subjected to still stronger stimuli for a length of time, becometorpid, and refuse to obey even these stronger stimuli; and thence do theiroffices very imperfectly. --Thus, if any one looks earnestly for someminutes on an area, an inch diameter, of red silk, placed on a sheet ofwhite paper, the image of the silk will gradually become pale, and atlength totally vanish. 5. Nor is it the nerves of sense alone, as the optic and auditory nerves, that thus become torpid, when the stimulus is withdrawn or theirirritability decreased; but the motive muscles, when they are deprived oftheir natural stimuli, or of their irritability, become torpid andparalytic; as is seen in the tremulous hand of the drunkard in a morning;and in the awkward step of age. The hollow muscles also, of which the various vessels of the body areconstructed, when they are deprived of their natural stimuli, or of theirdue degree of irritability, not only become tremulous, as the arterialpulsations of dying people; but also frequently invert their motions, as invomiting, in hysteric suffocations, and diabetes above described. I must beg your patient attention, for a few moments whilst I endeavour toexplain, how the retrograde actions of our hollow muscles are theconsequence of their debility; as the tremulous actions of the solidmuscles are the consequence of their debility. When, through fatigue, amuscle can act no longer; the antagonist muscles, either by their inanimateelasticity, or by their animal action, draw the limb into a contrarydirection: in the solid muscles, as those of locomotion, their actions areassociated in tribes, which have been accustomed to synchronous actiononly; hence when they are fatigued, only a single contrary effort takesplace; which is either tremulous, when the fatigued muscles are againimmediately brought into action; or it is a pandiculation, or stretching, where they are not immediately again brought into action. Now the motions of the hollow muscles, as they in general propel a fluidalong their cavities, are associated in trains, which have been accustomedto successive actions: hence when one ring of such a muscle is fatiguedfrom its too great debility, and is brought into retrograde action, thenext ring from its association falls successively into retrograde action;and so on throughout the whole canal. See Sect. XXV. 6. 6. But as the retrograde motions of the stomach, oesophagus, and fauces invomiting are, as it were, apparent to the eye; we shall consider thisoperation more minutely, that the similar operations in the more reconditeparts of our system may be easier understood. From certain nauseous ideas of the mind, from an ungrateful taste in themouth, or from foetid smells, vomiting is sometimes instantly excited; oreven from a stroke on the head, or from the vibratory motions of a ship;all which originate from association, or sympathy. See Sect. XX. OnVertigo. But when the stomach is subjected to a less stimulus than is natural, according to the first law of irritation mentioned above, its motionsbecome disturbed, as in hunger; first pain is produced, then sickness, andat length vain efforts to vomit, as many authors inform us. But when a great quantity of wine, or of opium, is swallowed, theretrograde motions of the stomach do not occur till after several minutes, or even hours; for when the power of so strong a stimulus ceases, accordingto the second law of irritation, mentioned above, the peristaltic motionsbecome tremulous, and at length retrograde; as is well known to thedrunkard, who on the next morning has sickness and vomitings. When a still greater quantity of wine, or of opium, or when nauseousvegetables, or strong bitters, or metallic salts, are taken into thestomach, they quickly induce vomiting; though all these in less dosesexcite the stomach into more energetic action, and strengthen thedigestion; as the flowers of chamomile, and the vitriol of zinc: for, according to the fourth law of irritation, the stomach will not long beobedient to a stimulus so much greater than is natural; but its actionbecomes first tremulous and then retrograde. 7. When the motions of any vessels become retrograde, less heat of the bodyis produced; for in paroxysms of vomiting, of hysteric affections, ofdiabetes, of asthma, the extremities of the body are cold: hence we mayconclude, that these symptoms arise from the debility of the parts inaction; for an increase of muscular action is always attended with increaseof heat. 8. But as animal debility is owing to defect of stimulus, or to defect ofirritability, as shewn above, the method of cure is easily deduced: whenthe vascular muscles are not excited into their due action by the naturalstimuli, we should exhibit those medicines, which possess a still greaterdegree of stimulus; amongst these are the foetids, the volatiles, aromatics, bitters, metallic salts, opiates, wine, which indeed should begiven in small doses, and frequently repeated. To these should be addedconstant, but moderate exercise, cheerfulness of mind, and change ofcountry to a warmer climate; and perhaps occasionally the external stimulusof blisters. It is also frequently useful to diminish the quantity of natural stimulusfor a short time, by which afterwards the irritability of the systembecomes increased; according to the third law of irritationabove-mentioned, hence the use of baths somewhat colder than animal heat, and of equitation in the open air. _The catalogue of diseases owing to the retrograde motions of lymphatics ishere omitted, as it will appear in the second volume of this work. Thefollowing is the conclusion to this thesis of_ Mr. CHARLES DARWIN. Thus have I endeavoured in a concise manner to explain the numerousdiseases, which deduce their origin from the inverted motions of the hollowmuscles of our bodies: and it is probable, that Saint Vitus's dance, andthe stammering of speech, originate from a similar, inverted order of theassociated motions of some of the solid muscles; which, as it is foreign tomy present purpose, I shall not here discuss. I beg, illustrious professors, and ingenious fellow-students, that you willrecollect how difficult a talk I have attempted, to evince the retrogrademotions of the lymphatic vessels, when the vessels themselves for so manyages escaped the eyes and glasses of philosophers: and if you are not yetconvinced of the truth of this theory, hold, I entreat you, your minds insuspense, till ANATOMY draws her sword with happier omens, cuts asunder theknots, which entangle PHYSIOLOGY; and, like an augur inspecting theimmolated victim, announces to mankind the wisdom of HEAVEN. * * * * * SECT. XXX. PARALYSIS OF THE LIVER AND KIDNEYS. I. 1. _Bile-ducts less irritable after having been stimulated much. _ 2. _Jaundice from paralysis of the bile-ducts cured by electric shocks. _ 3. _From bile-stones. Experiments on bile-stones. Oil vomit. _ 4. _Palsy of the liver, two cases. _ 5. _Schirrosity of the liver. _ 6. _Large livers of geese. _ II. _Paralysis of the kidneys. _ III. _Story of Prometheus. _ I. 1. From the ingurgitation of spirituous liquors into the stomach andduodenum, the termination of the common bile-duct in that bowel becomesstimulated into unnatural action, and a greater quantity of bile isproduced from all the secretory vessels of the liver, by the association oftheir motions with those of their excretory ducts; as has been explained inSection XXIV. And XXV. But as all parts of the body, that have beenaffected with stronger stimuli for any length of time, become lesssusceptible of motion, from their natural weaker stimuli, it follows, thatthe motions of the secretory vessels, and in consequence the secretion ofbile, is less than is natural during the intervals of sobriety. 2. If thisingurgitation of spirituous liquors has been daily continued inconsiderable quantity, and is then suddenly intermitted, a languor orparalysis of the common bile-duct is induced; the bile is prevented frombeing poured into the intestines; and as the bilious absorbents arestimulated into stronger action by its accumulation, and by the acrimony orviscidity, which it acquires by delay, it is absorbed, and carried to thereceptacle of the chyle; or otherwise the secretory vessels of the liver, by the above-mentioned stimulus, invert their motions, and regurgitatetheir contents into the blood, as sometimes happens to the tears in thelachrymal sack, see Sect. XXIV. 2. 7. And one kind of jaundice is broughton. There is reason to believe, that the bile is most frequently returned intothe circulation by the inverted motions of these hepatic glands, for thebile does not seem liable to be absorbed by the lymphatics, for it soaksthrough the gall-ducts, and is frequently found in the cellular membrane. This kind of jaundice is not generally attended with pain, neither at theextremity of the bile-duct, where it enters the duodenum, nor on the regionof the gall-bladder. Mr. S. A gentleman between 40 and 50 years of age, had had the jaundiceabout six weeks, without pain, sickness, or fever; and had taken emetics, cathartics, mercurials, bitters, chalybeates, essential oil, and ether, without apparent advantage. On a supposition that the obstruction of thebile might be owing to the paralysis, or torpid action of the commonbile-duct, and the stimulants taken into the stomach seeming to have noeffect, I directed half a score smart electric shocks from a coated bottle, which held about a quart, to be passed through the liver, and along thecourse of the common gall-duct, as near as could be guessed, and on thatvery day the stools became yellow; he continued the electric shocks a fewdays more, and his skin gradually became clear. 3. The bilious vomiting and purging, that affects some people by intervalsof a few weeks, is a less degree of this disease; the bile-duct is lessirritable than natural, and hence the bile becomes accumulated in thegall-bladder, and hepatic ducts, till by its quantity, acrimony orviscidity, a greater degree of irritation is produced, and it is suddenlyevacuated, or lastly from the absorption of the more liquid parts of thebile, the remainder becomes inspissated, and chrystallizes into masses toolarge to pass, and forms another kind of jaundice, where the bile-duct isnot quite paralytic, or has regained its irritability. This disease is attended with much pain, which at first is felt at the pitof the stomach, exactly in the centre of the body, where the bile-ductenters the duodenum; afterwards, when the size of the bile-stones increase, it is also felt on the right side, where the gall-bladder is situated. Theformer pain at the pit of the stomach recurs by intervals, as thebile-stone is pushed against the neck of the duct; like the paroxysms ofthe stone in the urinary bladder, the other is a more dull and constantpain. Where these bile-stones are too large to pass, and the bile-ducts possesstheir sensibility, this becomes a very painful and hopeless disease. I madethe following experiments with a view to their chemical solution. Some fragments of the same bile-stone were put into the weak spirit ofmarine salt, which is sold in the shops, and into solution of mild alcali;and into a solution of caustic alcali; and into oil of turpentine; withouttheir being dissolved. All these mixtures were after some time put into aheat of boiling water, and then the oil of turpentine dissolved itsfragments of bile-stone, but no alteration was produced upon those in theother liquids except some change of their colour. Some fragments of the same bile-stone were put into vitriolic æther, andwere quickly dissolved without additional heat. Might not æther mixed withyolk of egg or with honey be given advantageously in bilious concretions? I have in two instances seen from 30 to 50 bile-stones come away by stool, about the size of large peas, after having given six grains of calomel inthe evening, and four ounces of oil of almonds or olives on the succeedingmorning. I have also given half a pint of good olive or almond oil as anemetic during the painful fit, and repeated it in half an hour, if thefirst did not operate, with frequent good effect. 4. Another disease of the liver, which I have several times observed, consists in the inability or paralysis of the secretory vessels. Thisdisease has generally the same cause as the preceding one, the too frequentpotation of spirituous liquors, or the too sudden omission of them, afterthe habit is confined; and is greater or less in proportion, as the wholeor a part of the liver is affected, and as the inability or paralysis ismore or less complete. This palsy of the liver is known from these symptoms, the patients havegenerally passed the meridian of life, have drank fermented liquors daily, but perhaps not been opprobrious drunkards; they lose their appetite, thentheir flesh and strength diminish in consequence, there appears no bile intheir stools, nor in their urine, nor is any hardness or swellingperceptible on the region of the liver. But what is peculiar to thisdisease, and distinguishes it from all others at the first glance of theeye, is the bombycinous colour of the skin, which, like that of full-grownsilkworms, has a degree of transparency with a yellow tint not greater thanis natural to the serum of the blood. Mr. C. And Mr. B. Both very strong men, between 50 and 60 years of age, whohad drank ale at their meals instead of small beer, but were not reputedhard-drinkers, suddenly became weak, lost their appetite, flesh, andstrength, with all the symptoms above enumerated, and died in about twomonths from the beginning of their malady. Mr. C. Became anasarcous a fewdays before his death, and Mr. B. Had frequent and great hæmorrhages froman issue, and some parts of his mouth, a few days before his death. In boththese cases calomel, bitters and chalybeates were repeatedly used withouteffect. One of the patients described above, Mr. C, was by trade a plumber; both ofthem could digest no food, and died apparently for want of blood. Might notthe transfusion of blood be used in these cases with advantage? 5. When the paralysis of the hepatic glands is less complete, or lessuniversal, a schirrosity of some part of the liver is induced; for thesecretory vessels retaining some of their living power take up a fluid fromthe circulation, without being sufficiently irritable to carry it forwardsto their excretory ducts; hence the body, or receptacle of each gland, becomes inflated, and this distension increases, till by its very greatstimulus inflammation is produced, or till those parts of the viscus becometotally paralytic. This disease is distinguishable from the foregoing bythe palpable hardness or largeness of the liver; and as the hepatic glandsare not totally paralytic, or the whole liver not affected, some bilecontinues to be made. The inflammations of this viscus, consequent to theschirrosity of it, belong to the diseases of the sensitive motions, andwill be treated of hereafter. 6. The ancients are said to have possessed an art of increasing the liversof geese to a size greater than the remainder of the goose. Martial. L. 13. Epig. 58. --This is said to have been done by fat and figs. Horace, l. 2. Sat. 8. --Juvenal sets these large livers before an epicure as a greatrarity. Sat. 5. L. 114; and Persius, sat. 6. L. 71. Pliny says these largegoose-livers were soaked in mulled milk, that is, I suppose, milk mixedwith honey and wine; and adds, "that it is uncertain whether ScipioMetellus, of consular dignity, or M. Sestius, a Roman knight, was the greatdiscoverer of this excellent dish. " A modern traveller, I believe Mr. Brydone, asserts that the art of enlarging the livers of geese still existsin Sicily; and it is to be lamented that he did not import it into hisnative country, as some method of affecting the human liver might perhapshave been collected from it; besides the honour he might have acquired inimproving our giblet pies. Our wiser caupones, I am told, know how to fatten their fowls, as well astheir geese, for the London markets, by mixing gin instead of figs and fatwith their food; by which they are said to become sleepy, and to fattenapace, and probably acquire enlarged livers; as the swine are asserted todo, which are fed on the sediments of barrels in the distilleries; andwhich so frequently obtains in those, who ingurgitate much ale, or wine, ordrams. II. The irritative diseases of the kidneys, pancreas, spleen, and otherglands, are analogous to those of the liver above described, differing onlyin the consequences attending their inability to action. For instance, whenthe secretory vessels of the kidneys become disobedient to the stimulus ofthe passing current of blood, no urine is separated or produced by them;their excretory mouths become filled with concreted mucus, or calculusmatter, and in eight or ten days stupor and death supervenes in consequenceof the retention of the feculent part of the blood. This disease in a slighter degree, or when only a part of the kidney isaffected, is succeeded by partial inflammation of the kidney in consequenceof previous torpor. In that case greater actions of the secretory vesselsoccur, and the nucleus of gravel is formed by the inflamed mucous membranesof the tubuli uriniferi, as farther explained in its place. This torpor, or paralysis of the secretory vessels of the kidneys, likethat of the liver, owes its origin to their being previously habituated totoo great stimulus; which in this country is generally owing to the alcoholcontained in ale or wine; and hence must be registered amongst the diseasesowing to inebriety; though it may be caused by whatever occasionallyinflames the kidney; as too violent riding on horseback, or the cold from adamp bed, or by sleeping on the cold ground; or perhaps by drinking ingeneral too little aqueous fluids. III. I shall conclude this section on the diseases of the liver induced byspirituous liquors, with the well known story of Prometheus, which seemsindeed to have been invented by physicians in those ancient times, when allthings were clothed in hieroglyphic, or in fable. Prometheus was painted asstealing fire from heaven, which might well represent the inflammablespirit produced by fermentation; which may be said to animate or enliventhe man of clay: whence the conquests of Bacchus, as well as the temporarymirth and noise of his devotees. But the after punishment of those, whosteal this accursed fire, is a vulture gnawing the liver; and wellallegorises the poor inebriate lingering for years under painful hepaticdiseases. When the expediency of laying a further tax on the distillationof spirituous liquors from grain was canvassed before the House of Commonssome years ago, it was said of the distillers, with great truth, "_Theytake the bread from the people, and convert it into poison!_" Yet is thismanufactory of disease permitted to continue, as appears by its paying intothe treasury above 900, 000l. Near a million of money annually. And thus, under the names of rum, brandy, gin, whisky, usquebaugh, wine, cyder, beer, and porter, alcohol is become the bane of the Christian world, as opium ofthe Mahometan. Evoe! parce, liber? Parce, gravi metuende thirso!--Hor. * * * * * SECT. XXXI. OF TEMPERAMENTS. I. _The temperament of decreased irritability known by weak pulse, large pupils of the eyes, cold extremities. Are generally supposed to be too irritable. Bear pain better than labour. Natives of North-America contrasted with those upon the coast of Africa. Narrow and broad shouldered people. Irritable constitutions bear labour better than pain. _ II. _Temperament of increased sensibility. Liable to intoxication, to inflammation, hæmoptoe, gutta serena, enthusiasm, delirium, reverie. These constitutions are indolent to voluntary exertions, and dull to irritations. The natives of South-America, and brute animals of this temperament. _ III. _Of increased voluntarity; these are subject to locked jaw, convulsions, epilepsy, mania. Are very active, bear cold, hunger, fatigue. Are suited to great exertions. This temperament distinguishes mankind from other animals. _ IV. _Of increased association. These have great memories, are liable to quartan agues, and stronger sympathies of parts with each other. _ V. _Change of temperaments into one another. _ Antient writers have spoken much of temperaments, but without sufficientprecision. By temperament of the system should be meant a permanentpredisposition to certain classes of diseases: without this definition atemporary predisposition to every distinct malady might be termed atemperament. There are four kinds of constitution, which permanentlydeviate from good health, and are perhaps sufficiently marked to bedistinguished from each other, and constitute the temperaments orpredispositions to the irritative, sensitive, voluntary, and associateclasses of diseases. I. _The Temperament of decreased Irritability. _ The diseases, which are caused by irritation, most frequently originatefrom the defect of it; for those, which are immediately owing to the excessof it, as the hot fits of fever, are generally occasioned by anaccumulation of sensorial power in consequence of a previous defect ofirritation, as in the preceding cold fits of fever. Whereas the diseases, which are caused by sensation and volition, most frequently originate fromthe excess of those sensorial powers, as will be explained below. The temperament of decreased irritability appears from the followingcircumstances, which shew that the muscular fibres or organs of sense areliable to become torpid or quiescent from less defect of stimulation thanis productive of torpor or quiescence in other constitutions. 1. The first is the weak pulse, which in some constitutions is at the sametime quick. 2. The next most marked criterion of this temperament is thelargeness of the aperture of the iris, or pupil of the eye, which has beenreckoned by some a beautiful feature in the female countenance, as anindication of delicacy, but to an experienced observer it is an indicationof debility, and is therefore a defect, not an excellence. The third mostmarked circumstance in this constitution is, that the extremities, as thehands and feet, or nose and ears, are liable to become cold and pale insituations in respect to warmth, where those of greater strength are notaffected. Those of this temperament are subject to hysteric affections, nervous fevers, hydrocephalus, scrophula, and consumption, and to all otherdiseases of debility. Those, who possess this kind of constitution, are popularly supposed to bemore irritable than is natural, but are in reality less so. This mistake has arisen from their generally having a greater quickness ofpulse, as explained in Sect. XII. 1. 4. XII. 3. 3. ; but this frequency ofpulse is not necessary to the temperament, like the debility of it. Persons of this temperament are frequently found amongst the softer sex, and amongst narrow-shouldered men; who are said to bear labour worse, andpain better than others. This last circumstance is supposed to haveprevented the natives of North America from having been made slaves by theEuropeans. They are a narrow-shouldered race of people, and will ratherexpire under the lash, than be made to labour. Some nations of Asia havesmall hands, as may be seen by the handles of their scymetars; which withtheir narrow shoulders shew, that they have not been accustomed to so greatlabour with their hands and arms, as the European nations in agriculture, and those on the coasts of Africa in swimming and rowing. Dr. Maningham, apopular accoucheur in the beginning of this century, observes in hisaphorisms, that broad-shouldered men procreate broad-shouldered children. Now as labour strengthens the muscles employed, and increases their bulk, it would seem that a few generations of labour or of indolence may in thisrespect change the form and temperament of the body. On the contrary, those who are happily possessed of a great degree ofirritability, bear labour better than pain; and are strong, active, andingenious. But there is not properly a temperament of increasedirritability tending to disease, because an increased quantity ofirritative motions generally induces an increase of pleasure or pain, as inintoxication, or inflammation; and then the new motions are the immediateconsequences of increased sensation, not of increased irritation; whichhave hence been so perpetually confounded with each other. II. _Temperament of Sensibility. _ There is not properly a temperament, or predisposition to disease, fromdecreased sensibility, since irritability and not sensibility isimmediately necessary to bodily health. Hence it is the excess of sensationalone, as it is the defect of irritation, that most frequently producesdisease. This temperament of increased sensibility is known from theincreased activity of all those motions of the organs of sense and muscles, which are exerted in consequence of pleasure or pain, as in the beginningof drunkenness, and in inflammatory fever. Hence those of this constitutionare liable to inflammatory diseases, as hepatitis; and to that kind ofconsumption which is hereditary, and commences with slight repeatedhæmoptoe. They have high-coloured lips, frequently dark hair and dark eyeswith large pupils, and are in that case subject to gutta serena. They areliable to enthusiasm, delirium, and reverie. In this last circumstance theyare liable to start at the clapping of a door; because the more intent anyone is on the passing current of his ideas, the greater surprise heexperiences on their being dissevered by some external violence, asexplained in Sect. XIX. On reverie. As in these constitutions more than the natural quantities of sensitivemotions are produced by the increased quantity of sensation existing in thehabit, it follows, that the irritative motions will be performed in somedegree with less energy, owing to the great expenditure of sensorial poweron the sensitive ones. Hence those of this temperament do not attend toslight stimulations, as explained in Sect. XIX. But when a stimulus is sogreat as to excite sensation, it produces greater sensitive actions of thesystem than in others; such as delirium or inflammation. Hence they areliable to be absent in company; sit or lie long in one posture; and inwinter have the skin of their legs burnt into various colours by the fire. Hence also they are fearful of pain; covet music and sleep; and delight inpoetry and romance. As the motions in consequence of sensation are more than natural, it alsohappens from the greater expenditure of sensorial power on them, that thevoluntary motions are less easily exerted. Hence the subjects of thistemperament are indolent in respect to all voluntary exertions, whether ofmind or body. A race of people of this description seems to have been found by theSpaniards in the islands of America, where they first landed, ten of whomare said not to have consumed more food than one Spaniard, nor to have beencapable of more than one tenth of the exertion of a Spaniard. Robertson'sHistory. --In a state similar to this the greatest part of the animal worldpass their lives, between sleep or inactive reverie, except when they areexcited by the call of hunger. III. _The Temperament of increased Voluntarity. _ Those of this constitution differ from both the last mentioned in this, that the pain, which gradually subsides in the first, and is productive ofinflammation or delirium in the second, is in this succeeded by theexertion of the muscles or ideas, which are most frequently connected withvolition; and they are thence subject to locked jaw, convulsions, epilepsy, and mania, as explained in Sect. XXXIV. Those of this temperament attend tothe slightest irritations or sensations, and immediately exert themselvesto obtain or avoid the objects of them; they can at the same time bear coldand hunger better than others, of which Charles the Twelfth of Sweden wasan instance. They are suited and generally prompted to all great exertionsof genius or labour, as their desires are more extensive and more vehement, and their powers of attention and of labour greater. It is this facility ofvoluntary exertion, which distinguishes men from brutes, and which has madethem lords of the creation. IV. _The Temperament of increased Association. _ This constitution consists in the too great facility, with which thefibrous motions acquire habits of association, and by which theseassociations become proportionably stronger than in those of the othertemperaments. Those of this temperament are slow in voluntary exertions, orin those dependent on sensation, or on irritation. Hence great memorieshave been said to be attended with less sense and less imagination fromAristotle down to the present time; for by the word memory these writersonly understood the unmeaning repetition of words or numbers in the orderthey were received, without any voluntary efforts of the mind. In this temperament those associations of motions, which are commonlytermed sympathies, act with greater certainty and energy, as those betweendisturbed vision and the inversion of the motion of the stomach, as insea-sickness; and the pains in the shoulder from hepatic inflammation. Addto this, that the catenated circles of actions are of greater extent thanin the other constitutions. Thus if a strong vomit or cathartic beexhibited in this temperament, a smaller quantity will produce as great aneffect, if it be given some weeks afterwards; whereas in other temperamentsthis is only to be expected, if it be exhibited in a few days after thefirst dose. Hence quartan agues are formed in those of this temperament, asexplained in Section XXXII. On diseases from irritation, and otherintermittents are liable to recur from slight causes many weeks after theyhave been cured by the bark. V. The first of these temperaments differs from the standard of health fromdefect, and the others from excess of sensorial power; but it sometimeshappens that the same individual, from the changes introduced into hishabit by the different seasons of the year, modes or periods of life, or byaccidental diseases, passes from one of these temperaments to another. Thusa long use of too much fermented liquor produces the temperament ofincreased sensibility; great indolence and solitude that of decreasedirritability; and want of the necessaries of life that of increasedvoluntarity. * * * * * SECT. XXXII. DISEASES OF IRRITATION. I. _Irritative fevers with strong pulse. With weak pulse. Symptoms of fever, Their source. _ II. 1. _Quick pulse is owing to decreased irritability_. 2. _Not in sleep or in apoplexy. _ 3. _From inanition. Owing to deficiency of sensorial power. _ III. 1. _Causes of fever. From defect of heat. Heat from secretions. Pain of cold in the loins and forehead. _ 2. _Great expense of sensorial power in the vital motions. Immersion in cold water. Succeeding glow of heat. Difficult respiration in cold bathing explained. Why the cold bath invigorates. Bracing and relaxation are mechanical terms. _ 3. _Uses of cold bathing. Uses of cold air in fevers. _ 4. _Ague fits from cold air. Whence their periodical returns. _ IV. _Defect of distention a cause of fever. Deficiency of blood. Transfusion of blood. _ V. 1. _Defect of momentum of the blood from mechanic stimuli. 2. Air injected into the blood-vessels. _ 3. _Exercise increases the momentum of the blood. _ 4. _Sometimes bleeding increases the momentum of it. _ VI. _Influence of the sun and moon on diseases. The chemical stimulus of the blood. Menstruation obeys the lunations. Queries. _ VII. _Quiesence of large glands a cause of fever. Swelling of the præcordia. _ VIII. _Other causes of quiescence, as hunger, bad air, fear, anxiety. _ IX. 1. _Symptoms of the cold fit. _ 2. _Of the hot fit. _ 3. _Second cold fit why. _ 4. _Inflammation introduced, or delirium, or stupor. _ X. _Recapitulation. Fever not an effort of nature to relieve herself. Doctrine of spasm. _ I. When the contractile sides of the heart and arteries perform a greaternumber of pulsations in a given time, and move through a greater area ateach pulsation, whether these motions are occasioned by the stimulus of theacrimony or quantity of the blood, or by their association with otherirritative motions, or by the increased irritability of the arterialsystem, that is, by an increased quantity of sensorial power, one kind offever is produced; which may be called Synocha irritativa, or Febrisirritativa pulsu forti, or irritative fever with strong pulse. When the contractile sides of the heart and arteries perform a greaternumber of pulsations in a given time, but move through a much less area ateach pulsation, whether these motions are occasioned by defect of theirnatural stimuli, or by the defect of other irritative motions with whichthey are associated, or from the inirritability of the arterial system, that is, from a decreased quantity of sensorial power, another kind offever arises; which may be termed, Typhus irritativus, or Febris irritativapulsu debili, or irritative fever with weak pulse. The former of thesefevers is the synocha of nosologists, and the latter the typhus mitior, ornervous fever. In the former there appears to be an increase of sensorialpower, in the latter a deficiency of it; which is shewn to be the immediatecause of strength and weakness, as defined in Sect. XII. 1. 3. It should be added, that a temporary quantity of strength or debility maybe induced by the defect or excess of stimulus above what is natural; andthat in the same fever _debility always exists during the cold fit, thoughstrength does not always exist during the hot fit. _ These fevers are always connected with, and generally induced by, thedisordered irritative motions of the organs of sense, or of the intestinalcanal, or of the glandular system, or of the absorbent system; and henceare always complicated with some or many of these disordered motions, whichare termed the symptoms of the fever, and which compose the great varietyin these diseases. The irritative fevers both with strong and with weak pulse, as well as thesensitive fevers with strong and with weak pulse, which are to be describedin the next section, are liable to periodical remissions, and then theytake the name of intermittent fevers, and are distinguished by theperiodical times of their access. II. For the better illustration of the phenomena of irritative fevers wemust refer the reader to the circumstances of irritation explained in Sect. XII. And shall commence this intricate subject by speaking of the quickpulse, and proceed by considering many of the causes, which eitherseparately or in combination most frequently produce the cold fits offevers. 1. If the arteries are dilated but to half their usual diameters, thoughthey contract twice as frequently in a given time, they will circulate onlyhalf their usual quantity of blood: for as they are cylinders, the bloodwhich they contain must be as the squares of their diameters. Hence whenthe pulse becomes quicker and smaller in the same proportion, the heart andarteries act with less energy than in their natural state. See Sect. XII. 1. 4. That this quick small pulse is owing to want of irritability, appears, first, because it attends other symptoms of want of irritability; and, secondly, because on the application of a stimulus greater than usual, itbecomes slower and larger. Thus in cold fits of agues, in hystericpalpitations of the heart, and when the body is much exhausted byhæmorrhages, or by fatigue, as well as in nervous fevers, the pulse becomesquick and small; and secondly, in all those cases if an increase ofstimulus be added, by giving a little wine or opium; the quick small pulsebecomes slower and larger, as any one may easily experience on himself, bycounting his pulse after drinking one or two glasses of wine, when he isfaint from hunger or fatigue. Now nothing can so strongly evince that this quick small pulse is owing todefect of irritability, than that an additional stimulus, above what isnatural, makes it become slower and larger immediately: for what is meantby a defect of irritability, but that the arteries and heart are notexcited into their usual exertions by their usual quantity of stimulus? butif you increase the quantity of stimulus, and they immediately act withtheir usual energy, this proves their previous want of their natural degreeof irritability. Thus the trembling hands of drunkards in a morning becomesteady, and acquire strength to perform their usual offices, by theaccustomed stimulus of a glass or two of brandy. 2. In sleep and in apoplexy the pulse becomes slower, which is not owing todefect of irritability, for it is at the same time larger; and thence thequantity of the circulation is rather increased than diminished. In thesecases the organs of sense are closed, and the voluntary power is suspended, while the motions dependent on internal irritations, as those of digestionand secretion, are carried on with more than their usual vigour; which hasled superficial observers to confound these cases with those arising fromwant of irritability. Thus if you lift up the eyelid of an apoplecticpatient, who is not actually dying, the iris will, as usual, contractitself, as this motion is associated with the stimulus of light; but it isnot so in the last stages of nervous fevers, where the pupil of the eyecontinues expanded in the broad day-light: in the former case there is awant of voluntary power, in the latter a want of irritability. Hence also those constitutions which are deficient in quantity ofirritability, and which possess too great sensibility, as during the painof hunger, of hysteric spasms, or nervous headachs, are generally supposedto have too much irritability; and opium, which in its due dose is a mostpowerful stimulant, is erroneously called a sedative; because by increasingthe irritative motions it decreases the pains arising from defect of them. Why the pulse should become quicker both from an increase of irritation, asin the synocha irritativa, or irritative fever with strong pulse; and fromthe decrease of it, as in the typhus irritativus, or irritative fever withweak pulse; seems paradoxical. The former circumstance needs noillustration; since if the stimulus of the blood, or the irritability ofthe sanguiferous system be increased, and the strength of the patient notdiminished, it is plain that the motions must be performed quicker andstronger. In the latter circumstance the weakness of the muscular power of the heartis soon over-balanced by the elasticity of the coats of the arteries, whichthey possess besides a muscular power of contraction; and hence thearteries are distended to less than their usual diameters. The heart beingthus stopped, when it is but half emptied, begins sooner to dilate again;and the arteries being dilated to less than their usual diameters, begin somuch sooner to contract themselves; insomuch, that in the last stages offevers with weakness the frequency of pulsation of the heart and arteriesbecomes doubled; which, however, is never the case in fevers with strength, in which they seldom exceed 118 or 120 pulsations in a minute. It must beadded, that in these cases, while the pulse is very small and very quick, the heart often feels large, and labouring to one's hand; which coincideswith the above explanation, shewing that it does not completely emptyitself. 3. In cases however of debility from paucity of blood, as in animals whichare bleeding to death in the slaughter-house, the quick pulsations of theheart and arteries may be owing to their not being distended to more thanhalf their usual diastole; and in consequence they must contract sooner, ormore frequently, in a given time. As weak people are liable to a deficientquantity of blood, this cause may occasionally contribute to quicken thepulse in fevers with debility, which may be known by applying one's handupon the heart as above; but the principal cause I suppose to consist inthe diminution of sensorial power. When a muscle contains, or is suppliedwith but little sensorial power, its contraction soon ceases, and inconsequence may soon recur, as is seen in the trembling hands of peopleweakened by age or by drunkenness. See Sect. XII. 1. 4. XII. 3. 4. It may nevertheless frequently happen, that both the deficiency ofstimulus, as where the quantity of blood is lessened (as described in No. 4. Of this section), and the deficiency of sensorial power, as in those ofthe temperament of irritability, described in Sect. XXXI. Occur at the sametime; which will thus add to the quickness of the pulse and to the dangerof the disease. III. 1. A certain degree of heat is necessary to muscular motion, and is, in consequence, essential to life. This is observed in those animals andinsects which pass the cold season in a torpid state, and which revive onbeing warmed by the fire. This necessary stimulus of heat has two sources;one from the fluid atmosphere of heat, in which all things are immersed, and the other from the internal combinations of the particles, which formthe various fluids, which are produced in the extensive systems of theglands. When either the external heat, which surrounds us, or the internalproduction of it, becomes lessened to a certain degree, the pain of cold isperceived. This pain of cold is experienced most sensibly by our teeth, when ice isheld in the mouth; or by our whole system after having been previouslyaccustomed to much warmth. It is probable, that this pain does not arisefrom the mechanical or chemical effects of a deficiency of heat; but that, like the organs of sense by which we perceive hunger and thirst, this senseof heat suffers pain, when the stimulus of its object is wanting to excitethe irritative motions of the organ; that is, when the sensorial powerbecomes too much accumulated in the quiescent fibres. See Sect. XII. 5. 3. For as the peristaltic motions of the stomach are lessened, when the painof hunger is great, so the action of the cutaneous capillaries are lessenedduring the pain of cold; as appears by the paleness of the skin, asexplained in Sect. XIV. 6. On the production of ideas. The pain in the small of the back and forehead in the cold fits of theague, in nervous hemicrania, and in hysteric paroxysms, when all theirritative motions are much impaired, seems to arise from this cause; thevessels of these membranes or muscles become torpid by their irritativeassociations with other parts of the body, and thence produce less of theiraccustomed secretions, and in consequence less heat is evolved, and theyexperience the pain of cold; which coldness may often be felt by the handapplied upon the affected part. 2. The importance of a greater or less deduction of heat from the systemwill be more easy to comprehend, if we first consider the great expense ofsensorial power used in carrying on the vital motions; that is, whichcirculates, absorbs, secretes, aerates, and elaborates the whole mass offluids with unceasing assiduity. The sensorial power, or spirit ofanimation, used in giving perpetual and strong motion to the heart, whichovercomes the elasticity and vis inertiæ of the whole arterial system; nextthe expense of sensorial power in moving with great force and velocity theinnumerable trunks and ramifications of the arterial system; the expense ofsensorial power in circulating the whole mass of blood through the long andintricate intortions of the very fine vessels, which compose the glands andcapillaries; then the expense of sensorial power in the exertions of theabsorbent extremities of all the lacteals, and of all the lymphatics, whichopen their mouths on the external surface of the skin, and on the internalsurfaces of every cell or interstice of the body; then the expense ofsensorial power in the venous absorption, by which the blood is receivedfrom the capillary vessels, or glands, where the arterial power ceases, andis drank up, and returned to the heart; next the expense of sensorial powerused by the muscles of respiration in their office of perpetually expandingthe bronchia, or air-vessels, of the lungs; and lastly in the unceasingperistaltic motions of the stomach and whole system of intestines, and inall the secretions of bile, gastric juice, mucus, perspirable matter, andthe various excretions from the system. If we consider the ceaselessexpense of sensorial power thus perpetually employed, it will appear to bemuch greater in a day than all the voluntary exertions of our muscles andorgans of sense consume in a week; and all this without any sensiblefatigue! Now, if but a part of these vital motions are impeded, or totallystopped for but a short time, we gain an idea, that there must be a greataccumulation of sensorial power; as its production in these organs, whichare subject to perpetual activity, is continued during their quiescence, and is in consequence accumulated. While, on the contrary, where those vital organs act too forcibly byincrease of stimulus without a proportionally-increased production ofsensorial power in the brain, it is evident, that a great deficiency ofaction, that is torpor, must soon follow, as in fevers; whereas thelocomotive muscles, which act only by intervals, are neither liable to sogreat accumulation of sensorial power during their times of inactivity, norto so great an exhaustion of it during their times of action. Thus, on going into a very cold bath, suppose at 33 degrees of heat onFahrenheit's scale, the action of the subcutaneous capillaries, or glands, and of the mouths of the cutaneous absorbents is diminished, or ceases fora time. Hence less or no blood passes these capillaries, and palenesssucceeds. But soon after emerging from the bath, a more florid colour and agreater degree of heat is generated on the skin than was possessed beforeimmersion; for the capillary glands, after this quiescent state, occasionedby the want of stimulus, become more irritable than usual to their naturalstimuli, owing to the accumulation of sensorial power, and hence a greaterquantity of blood is transmitted through them, and a greater secretion ofperspirable matter; and, in consequence, a greater degree of heat succeeds. During the continuance in cold water the breath is cold, and the act ofrespiration quick and laborious; which have generally been ascribed to theobstruction of the circulating fluid by a spasm of the cutaneous vessels, and by a consequent accumulation of blood in the lungs, occasioned by thepressure as well as by the coldness of the water. This is not asatisfactory account of this curious phænomenon, since at this time thewhole circulation is less, as appears from the smallness of the pulse andcoldness of the breath; which shew that less blood passes through the lungsin a given time; the same laborious breathing immediately occurs when thepaleness of the skin is produced by fear, where no external cold orpressure are applied. The minute vessels of the bronchia, through which the blood passes from thearterial to the venal system, and which correspond with the cutaneouscapillaries, have frequently been exposed to cold air, and become quiescentalong with those of the skin; and hence their motions are so associatedtogether, that when one is affected either with quiescence or exertion, theother sympathizes with it, according to the laws of irritative association. See Sect. XXVII. 1. On hæmorrhages. Besides the quiescence of the minute vessels of the lungs, there are manyother systems of vessels which become torpid from their irritativeassociations with those of the skin, as the absorbents of the bladder andintestines; whence an evacuation of pale urine occurs, when the naked skinis exposed only to the coldness of the atmosphere; and sprinkling the nakedbody with cold water is known to remove even pertinacious constipation ofthe bowels. From the quiescence of such extensive systems of vessels as theglands and capillaries of the skin, and the minute vessels of the lungs, with their various absorbent series of vessels, a great accumulation ofsensorial powers is occasioned; part of which is again expended in theincreased exertion of all these vessels, with an universal glow of heat inconsequence of this exertion, and the remainder of it adds vigour to boththe vital and voluntary exertions of the whole day. If the activity of the subcutaneous vessels, and of those with which theiractions are associated, was too great before cold immersion, as in the hotdays of summer, and by that means the sensorial power was previouslydiminished, we see the cause why the cold bath gives such present strength;namely, by stopping the unnecessary activity of the subcutaneous vessels, and thus preventing the too great exhaustion of sensorial power; which, inmetaphorical language, has been called _bracing_ the system: which is, however, a mechanical term, only applicable to drums, or musical strings:as on the contrary the word _relaxation_, when applied to living animalbodies, can only mean too small a quantity of stimulus, or too small aquantity of sensorial power; as explained in Sect. XII. 1. 3. This experiment of cold bathing presents us with a simple fever-fit; forthe pulse is weak, small, and quick during the cold immersion; and becomesstrong, full, and quick during the subsequent glow of heat; till in a fewminutes these symptoms subside, and the temporary fever ceases. In those constitutions where the degree of inirritability, or of debility, is greater than natural, the coldness and paleness of the skin with thequick and weak pulse continue a long time after the patient leaves thebath; and the subsequent heat approaches by unequal flushings, and he feelshimself disordered for many hours. Hence the bathing in a cold spring ofwater, where the heat is but forty-eight degrees on Fahrenheit'sthermometer, much disagrees with those of weak or inirritable habits ofbody; who possess so little sensorial power, that they cannot withoutinjury bear to have it diminished even for a short time; but who cannevertheless bear the more temperate coldness of Buxton bath, which isabout eighty degrees of heat, and which strengthens them, and makes them byhabit less liable to great quiescence from small variations of cold, andthence less liable to be disordered by the unavoidable accidents of life. Hence it appears, why people of these inirritable constitutions, which isanother expression for sensorial deficiency, are often much injured bybathing in a cold spring of water; and why they should continue but a veryshort time in baths, which are colder than their bodies; and shouldgradually increase both the degree of coldness of the water, and the timeof their continuance in it, if they would obtain salutary effects from coldimmersions. See Sect. XII. 2. 1. On the other hand, in all cases where the heat of the external surface ofthe body, or of the internal surface of the lungs, is greater than natural, the use of exposure to cool air may be deduced. In fever-fits attended withstrength, that is with great quantity of sensorial power, it removes theadditional stimulus of heat from the surfaces above mentioned, and thusprevents their excess of useless motion; and in fever-fits attended withdebility, that is with a deficiency of the quantity of sensorial power, itprevents the great and dangerous waste of sensorial power expended in theunnecessary increase of the actions of the glands and capillaries of theskin and lungs. 4. In the same manner, when any one is long exposed to very cold air, aquiescence is produced of the cutaneous and pulmonary capillaries andabsorbents, owing to the deficiency of their usual stimulus of heat; andthis quiescence of so great a quantity of vessels affects, by irritativeassociation, the whole absorbent and glandular system, which becomes in agreater or less degree quiescent, and a cold fit of fever is produced. If the deficiency of the stimulus of heat is very great, the quiescencebecomes so general as to extinguish life, as in those who are frozen todeath. If the deficiency of heat be in less degree, but yet so great as in somemeasure to disorder the system, and should occur the succeeding day, itwill induce a greater degree of quiescence than before, from its acting inconcurrence with the period of the diurnal circle of actions, explained inSect. XXXVI. Hence from a small beginning a greater and greater degree ofquiescence may be induced, till a complete fever-fit is formed; and whichwill continue to recur at the periods by which it was produced. See Sect. XVII. 3. 6. If the degree of quiescence occasioned by defect of the stimulus of heat bevery great, it will recur a second time by a slighter cause, than thatwhich first induced it. If the cause, which induces the second fit ofquiescence, recurs the succeeding day, the quotidian fever is produced; ifnot till the alternate day, the tertian fever; and if not till afterseventy-two hours from the first fit of quiescence, the quartan fever isformed. This last kind of fever recurs less frequently than the other, asit is a disease only of those of the temperament of associability, asmentioned in Sect. XXXI. ; for in other constitutions the capability offorming a habit ceases, before the new cause of quiescence is againapplied, if that does not occur sooner than in seventy-two hours. And hence those fevers, whose cause is from cold air of the night ormorning, are more liable to observe the solar day in their periods; whilethose from other causes frequently observe the lunar day in their periods, their paroxysms returning near an hour later every day, as explained inSect. XXXVI. IV. Another frequent cause of the cold fits of fever is the defect of thestimulus of distention. The whole arterial system would appear, by theexperiments of Haller, to be irritable by no other stimulus, and themotions of the heart and alimentary canal are certainly in some measuredependant on the same cause. See Sect. XIV. 7. Hence there can be nowonder, that the diminution of distention should frequently induce thequiescence, which constitutes the beginning of fever-fits. Monsieur Leiutaud has judiciously mentioned the deficiency of the quantityof blood amongst the causes of diseases, which he says is frequentlyevident in dissections: fevers are hence brought on by great hæmorrhages, diarrhoeas, or other evacuations; or from the continued use of diet, whichcontains but little nourishment; or from the exhaustion occasioned byviolent fatigue, or by those chronic diseases in which the digestion ismuch impaired; as where the stomach has been long affected with the gout orschirrus; or in the paralysis of the liver, as described in Sect. XXX. Hence a paroxysm of gout is liable to recur on bleeding or purging; as thetorpor of some viscus, which precedes the inflammation of the foot, is thusinduced by the want of the stimulus of distention. And hence theextremities of the body, as the nose and fingers, are more liable to becomecold, when we have long abstained from food; and hence the pulse isincreased both in strength and velocity above the natural standard after afull meal by the stimulus of distention. However, this stimulus of distention, like the stimulus of heat abovedescribed, though it contributes much to the due action not only of theheart, arteries, and alimentary canal, but seems necessary to the propersecretion of all the various glands; yet perhaps it is not the sole causeof any of these numerous motions: for as the lacteals, cutaneousabsorbents, and the various glands appear to be stimulated into action bythe peculiar pungency of the fluids they absorb, so in the intestinal canalthe pungency of the digesting aliment, or the acrimony of the fæces, seemto contribute, as well as their bulk, to promote the peristaltic motions;and in the arterial system, the momentum of the particles of thecirculating blood, and their acrimony, stimulate the arteries, as well asthe distention occasioned by it. Where the pulse is small this defect ofdistention is present, and contributes much to produce the febrisirritativa pulsu debili, or irritative fever with weak pulse, called bymodern writers nervous fever, as a predisponent cause. See Sect. XII. 1. 4. Might not the transfusion of blood, suppose of four ounces daily from astrong man, or other healthful animal, as a sheep or an ass, be used in theearly state of nervous or putrid fevers with great prospect of success? V. 1. The defect of the momentum of the particles of the circulating bloodis another cause of the quiescence, with which the cold fits of fevercommence. This stimulus of the momentum of the progressive particles of theblood does not act over the whole body like those of heat and distentionabove described, but is confined to the arterial system; and differs fromthe stimulus of the distention of the blood, as much as the vibration ofthe air does from the currents of it. Thus are the different organs of ourbodies stimulated by four different mechanic properties of the externalworld: the sense of touch by the pressure of solid bodies so as todistinguish their figure; the muscular system by the distention, which theyoccasion; the internal surface of the arteries, by the momentum of theirmoving particles; and the auditory nerves, by the vibration of them: andthese four mechanic properties are as different from each other as thevarious chemical ones, which are adapted to the numerous glands, and to theother organs of sense. 2. The momentum of the progressive particles of blood is compounded oftheir velocity and their quantity of matter: hence whatever circumstancesdiminish either of these without proportionally increasing the other, andwithout superadding either of the general stimuli of heat or distention, will tend to produce a quiescence of the arterial system, and from thenceof all the other irritative motions, which are connected with it. Hence in all those constitutions or diseases where the blood contains agreater proportion of serum, which is the lightest part of its composition, the pulsations of the arteries are weaker, as in nervous fevers, chlorosis, and hysteric complaints; for in these cases the momentum of the progressiveparticles of blood is less: and hence, where the denser parts of itscomposition abound, as the red part of it, or the coagulable lymph, thearterial pulsations are stronger; as in those of robust health, and ininflammatory diseases. That this stimulus of the momentum of the particles of the circulatingfluid is of the greatest consequence to the arterial action, appears fromthe experiment of injecting air into the blood vessels, which seems todestroy animal life from the want of this stimulus of momentum; for thedistention of the arteries is not diminished by it, it possesses nocorrosive acrimony, and is less liable to repass the valves than the blooditself; since air-valves in all machinery require much less accuracy ofconstruction than those which are opposed to water. 3. One method of increasing the velocity of the blood, and in consequencethe momentum of its particles, is by the exercise of the body, or by thefriction of its surface: so, on the contrary, too great indolencecontributes to decrease this stimulus of the momentum of the particles ofthe circulating blood, and thus tends to induce quiescence; as is seen inhysteric cases, and chlorosis, and the other diseases of sedentary people. 4. The velocity of the particles of the blood in certain circumstances isincreased by venesection, which, by removing a part of it, diminishes theresistance to the motion of the other part, and hence the momentum of theparticles of it is increased. This may be easily understood by consideringit in the extreme, since, if the resistance was greatly increased, so as toovercome the propelling power, there could be no velocity, and inconsequence no momentum at all. From this circumstance arises that curiousphænomenon, the truth of which I have been more than once witness to, thatvenesection will often instantaneously relieve those nervous pains, whichattend the cold periods of hysteric, asthmatic, or epileptic diseases; andthat even where large doses of opium have been in vain exhibited. In thesecases the pulse becomes stronger after the bleeding, and the extremitiesregain their natural warmth; and an opiate then given acts with much morecertain effect. VI. There is another cause, which seems occasionally to induce quiescenceinto some part of our system, I mean the influence of the sun and moon; theattraction of these luminaries, by decreasing the gravity of the particlesof the blood, cannot affect their momentum, as their vis inertiæ remainsthe same; but it may nevertheless produce some chemical change in them, because whatever affects the general attractions of the particles of mattermay be supposed from analogy to affect their specific attractions oraffinities: and thus the stimulus of the particles of blood may bediminished, though not their momentum. As the tides of the sea obey thesouthing and northing of the moon (allowing for the time necessary fortheir motion, and the obstructions of the shores), it is probable, thatthere are also atmospheric tides on both sides of the earth, which to theinhabitants of another planet might so deflect the light as to resemble thering of Saturn. Now as these tides of water, or of air, are raised by thediminution of their gravity, it follows, that their pressure on the surfaceof the earth is no greater than the pressure of the other parts of theocean, or of the atmosphere, where no such tides exist; and therefore thatthey cannot affect the mercury in the barometer. In the same manner, thegravity of all other terrestrial bodies is diminished at the times of thesouthing and northing of the moon, and that in a greater degree when thiscoincides with the southing and northing of the sun, and this in a stillgreater degree about the times of the equinoxes. This decrease of thegravity of all bodies during the time the moon passes our zenith or nadirmight possibly be shewn by the slower vibrations of a pendulum, comparedwith a spring clock, or with astronomical observation. Since a pendulum ofa certain length moves slower at the line than near the poles, because thegravity being diminished and the vis inertiæ continuing the same, themotive power is less, but the resistance to be overcome continues the same. The combined powers of the lunar and solar attraction is estimated by SirIsaac Newton not to exceed one 7, 868, 850th part of the power ofgravitation, which seems indeed but a small circumstance to produce anyconsiderable effect on the weight of sublunary bodies, and yet this issufficient to raise the tides at the equator above ten feet high; and if itbe considered, what small impulses of other bodies produce their effects onthe organs of sense adapted to the perception of them, as of vibration onthe auditory nerves, we shall cease to to be surprised, that so minute adiminution in the gravity of the particles of blood should so far affecttheir chemical changes, or their stimulating quality, as, joined with othercauses, sometimes to produce the beginnings of diseases. Add to this, that if the lunar influence produces a very small degree ofquiescence at first, and if that recurs at certain periods even with lesspower to produce quiescence than at first, yet the quiescence will dailyincrease by the acquired habit acting at the same time, till at length sogreat a degree of quiescence is induced as to produce phrensy, caninemadness, epilepsy, hysteric pains or cold fits of fever, instances of manyof which are to be found in Dr. Mead's work on this subject. The solarinfluence also appears daily in several diseases; but as darkness, silence, sleep, and our periodical meals mark the parts of the solar circle ofactions, it is sometimes dubious to which of these the periodical returnsof these diseases are to be ascribed. As far as I have been able to observe, the periods of inflammatory diseasesobserve the solar day; as the gout and rheumatism have their greatestquiescence about noon and midnight, and their exacerbations some hoursafter; as they have more frequently their immediate cause from cold air, inanition, or fatigue, than from the effects of lunations: whilst the coldfits of hysteric patients, and those in nervous fevers, more frequentlyoccur twice a day, later by near half an hour each time, according to thelunar day; whilst some fits of intermittents, which are undisturbed bymedicines, return at regular solar periods, and others at lunar ones; whichmay, probably, be owing to the difference of the periods of those externalcircumstances of cold, inanition, or lunation, which immediately causedthem. We must, however, observe, that the periods of quiescence and exacerbationin diseases do not always commence at the times of the syzygies orquadratures of the moon and sun, or at the times of their passing thezenith or nadir; but as it is probable, that the stimulus of the particlesof the circumfluent blood is gradually diminished from the time of thequadratures to that of the syzygies, the quiescence may commence at anyhour, when co-operating with other causes of quiescence, it becomes greatenough to produce a disease: afterwards it will continue to recur at thesame period of the lunar or solar influence; the same cause operatingconjointly with the acquired habit, that is with the catenation of this newmotion with the dissevered links of the lunar or solar circles of animalaction. In this manner the periods of menstruation obey the lunar month with greatexactness in healthy patients (and perhaps the venereal orgasm in bruteanimals does the same), yet these periods do not commence either at thesyzygies or quadratures of the lunations, but at whatever time of the lunarperiods they begin, they observe the same in their returns till somegreater cause disturbs them. Hence, though the best way to calculate the time of the expected returns ofthe paroxysms of periodical diseases is to count the number of hoursbetween the commencement of the two preceding fits, yet the followingobservations may be worth attending to, when we endeavour to prevent thereturns of maniacal or epileptic diseases; whose periods (at the beginningof them especially) frequently observe the syzygies of the moon and sun, and particularly about the equinox. The greatest of the two tides happening in every revolution of the moon, isthat when the moon approaches nearest to the zenith or nadir; for thisreason, while the sun is in the northern signs, that is during the vernaland summer months, the greater of the two diurnal tides in our latitude isthat, when the moon is above the horizon; and when the sun is in thesouthern signs, or during the autumnal and winter months, the greater tideis that, which arises when the moon is below the horizon: and as the sunapproaches somewhat nearer the earth in winter than in summer, the greatestequinoctial tides are observed to be a little before the vernal equinox, and a little after the autumnal one. Do not the cold periods of lunar diseases commence a few hours before thesouthing of the moon during the vernal and summer months, and before thenorthing of the moon during the autumnal and winter months? Do not palsiesand apoplexies, which occur about the equinoxes, happen a few days beforethe vernal equinoctial lunation, and after the autumnal one? Are not theperiods of those diurnal diseases more obstinate, that commence many hoursbefore the southing or northing of the moon, than of those which commenceat those times? Are not those palsies and apoplexies more dangerous whichcommence many days before the syzygies of the moon, than those which happenat those times? See Sect. XXXVI. On the periods of diseases. VII. Another very frequent cause of the cold fit of fever is the quiescenceof some of those large congeries of glands, which compose the liver, spleen, or pancreas; one or more of which are frequently so enlarged in theautumnal intermittents as to be perceptible to the touch externally, andare called by the vulgar ague-cakes. As these glands are stimulated intoaction by the specific pungency of the fluids, which they absorb, thegeneral cause of their quiescence seems to be the too great insipidity ofthe fluids of the body, co-operating perhaps at the same time with othergeneral causes of quiescence. Hence, in marshy countries at cold seasons, which have succeeded hot ones, and amongst those, who have lived on innutritious and unstimulating diet, these agues are most frequent. The enlargement of these quiescent viscera, and the swelling of the præcordia in many other fevers, is, most probably, owing to the same cause; which may consist in a general deficiency of theproduction of sensorial power, as well as in the diminished stimulation ofthe fluids; and when the quiescence of so great a number of glands, asconstitute one of those large viscera, commences, all the other irritativemotions are affected by their connection with it, and the cold fit of feveris produced. VIII. There are many other causes, which produce quiescence of some part ofthe animal system, as fatigue, hunger, thirst, bad diet, disappointed love, unwholesome air, exhaustion from evacuations, and many others; but the lastcause, that we shall mention, as frequently productive of cold fits offever, is fear or anxiety of mind. The pains, which we are first and mostgenerally acquainted with, have been produced by defect of some stimulus;thus, soon after our nativity we become acquainted with the pain from thecoldness of the air, from the want of respiration, and from the want offood. Now all these pains occasioned by defect of stimulus are attendedwith quiescence of the organ, and at the same time with a greater or lessdegree of quiescence of other parts of the system: thus, if we even endurethe pain of hunger so as to miss one meal instead of our daily habit ofrepletion, not only the peristaltic motions of the stomach and bowels arediminished, but we are more liable to coldness of our extremities, as ofour noses, and ears, and feet, than at other times. Now, as fear is originally excited by our having experienced pain, and isitself a painful affection, the same quiescence of other fibrous motionsaccompany it, as have been most frequently connected with this kind ofpain, as explained in Sect. XVI. 8. 1. As the coldness and paleness of theskin, trembling, difficult respiration, indigestion, and other symptoms, which contribute to form the cold fit of fevers. Anxiety is fear continuedthrough a longer time, and, by producing chronical torpor of the system, extinguishes life slowly, by what is commonly termed a broken heart. IX. 1. We now step forwards to consider the other symptoms in consequenceof the quiescence which begins the fits of fever. If by any of thecircumstances before described, or by two or more of them acting at thesame time, a great degree of quiescence is induced on any considerable partof the circle of irritative motions, the whole class of them is more orless disturbed by their irritative associations. If this torpor beoccasioned by a deficient supply of sensorial power, and happens to any ofthose parts of the system, which are accustomed to perpetual activity, asthe vital motions, the torpor increases rapidly, because of the greatexpenditure of sensorial power by the incessant activity of those parts ofthe system, as shewn in No. 3. 2. Of this Section. Hence a deficiency ofall the secretions succeeds, and as animal heat is produced in proportionto the quantity of those secretions, the coldness of the skin is the firstcircumstance, which is attended to. Dr. Martin asserts, that some parts ofhis body were warmer than natural in the cold fit of fever; but it iscertain, that those, which are uncovered, as the fingers, and nose, andears, are much colder to the touch, and paler in appearance. It ispossible, that his experiments were made at the beginning of the subsequenthot fits; which commence with partial distributions of heat, owing to someparts of the body regaining their natural irritability sooner than others. From the quiescence of the anastomosing capillaries a paleness of the skinsucceeds, and a less secretion of the perspirable matter; from thequiescence of the pulmonary capillaries a difficulty of respiration arises;and from the quiescence of the other glands less bile, less gastric andpancreatic juice, are secreted into the stomach and intestines, and lessmucus and saliva are poured into the mouth; whence arises the dry tongue, costiveness, dry ulcers, and paucity of urine. From the quiescence of theabsorbent system arises the great thirst, as less moisture is absorbed fromthe atmosphere. The absorption from the atmosphere was observed by Dr. Lyster to amount to eighteen ounces in one night, above what he had at thesame time insensibly perspired. See Langrish. On the same account the urineis pale, though in small quantity, for the thinner part is not absorbedfrom it; and when repeated ague-fits continue long, the legs swell from thediminished absorption of the cellular absorbents. From the quiescence of the intestinal canal a loss of appetite andflatulencies proceed. From the partial quiescence of the glandular visceraa swelling and tension about the præcordia becomes sensible to the touch;which is occasioned by the delay of the fluids from the defect of venous orlymphatic absorption. The pain of the forehead, and of the limbs, and ofthe small of the back, arises from the quiescence of the membranous fascia, or muscles of those parts, in the same manner as the skin becomes painful, when the vessels, of which it is composed, become quiescent from cold. Thetrembling in consequence of the pain of coldness, the restlessness, and theyawning, and stretching of the limbs, together with the shuddering, orrigours, are convulsive motions; and will be explained amongst the diseasesof volition; Sect. XXXIV. Sickness and vomiting is a frequent symptom in the beginnings offever-fits, the muscular fibres of the stomach share the general torpor anddebility of the system; their motions become first lessened, and then stop, and then become retrograde; for the act of vomiting, like the globushystericus and the borborigmi of hypochondriasis, is always a symptom ofdebility, either from want of stimulus, as in hunger; or from want ofsensorial power, as after intoxication; or from sympathy with some othertorpid irritative motions, as in the cold fits of ague. See Sect. XII. 5. 5. XXIX. 11. And XXXV. 1. 3. Where this act of vomiting is furtherexplained. The small pulse, which is said by some writers to be slow at thecommencement of ague-fits, and which is frequently trembling andintermittent, is owing to the quiescence of the heart and arterial system, and to the resistance opposed to the circulating fluid from the inactivityof all the glands and capillaries. The great weakness and inability tovoluntary motions, with the insensibility of the extremities, are owing tothe general quiescence of the whole moving system; or, perhaps, simply tothe deficient production of sensorial power. If all these symptoms are further increased, the quiescence of all themuscles, including the heart and arteries, becomes complete, and deathensues. This is, most probably, the case of those who are starved to deathwith cold, and of those who are said to die in Holland from long skaitingon their frozen canals. 2. As soon as this general quiescence of the system ceases, either by thediminution of the cause, or by the accumulation of sensorial power, (as insyncope, Sect. XII. 7. 1. ) which is the natural consequence of previousquiescence, the hot fit commences. Every gland of the body is nowstimulated into stronger action than is natural, as its irritability isincreased by accumulation of sensorial power during its late quiescence, asuperabundance of all the secretions is produced, and an increase of heatin consequence of the increase of these secretions. The skin becomes red, and the perspiration great, owing to the increased action of thecapillaries during the hot part of the paroxysm. The secretion ofperspirable matter is perhaps greater during the hot fit than in thesweating fit which follows; but as the absorption of it also is greater, itdoes not stand on the skin in visible drops: add to this, that theevaporation of it also is greater, from the increased heat of the skin. Butat the decline of the hot fit, as the mouths of the absorbents of the skinare exposed to the cooler air, or bed-clothes, these vessels sooner losetheir increased activity, and cease to absorb more than their naturalquantity: but the secerning vessels for some time longer, being kept warmby the circulating blood, continue to pour out an increased quantity ofperspirable matter, which now stands on the skin in large visible drops;the exhalation of it also being lessened by the greater coolness of theskin, as well as its absorption by the diminished action of the lymphatics. See Class I. 1. 2. 3. The increased secretion of bile and of other fluids poured into theintestines frequently induce a purging at the decline of the hot fit; foras the external absorbent vessels have their mouths exposed to the coldair, as above mentioned, they cease to be excited into unnatural activitysooner than the secretory vessels, whose mouths are exposed to the warmthof the blood: now, as the internal absorbents sympathize with the externalones, these also, which during the hot fit drank up the thinner part of thebile, or of other secreted fluids, lose their increased activity before thegland loses its increased activity, at the decline of the hot fit; and theloose dejections are produced from the same cause, that the increasedperspiration stands on the surface of the skin, from the increasedabsorption ceasing sooner than the increased secretion. The urine during the cold fit is in small quantity and pale, both from adeficiency of the secretion and a deficiency of the absorption. During the hot fit it is in its usual quantity, but very high coloured andturbid, because a greater quantity had been secreted by the increasedaction of the kidnies, and also a greater quantity of its more aqueous parthad been absorbed from it in the bladder by the increased action of theabsorbents; and lastly, at the decline of the hot fit it is in largequantity and less coloured, or turbid, because the absorbent vessels of thebladder, as observed above, lose their increased action by sympathy withthe cutaneous ones sooner than the secretory vessels of the kidnies losetheir increased activity. Hence the quantity of the sediment, and thecolour of the urine, in fevers, depend much on the quantity secreted by thekidnies, and the quantity absorbed from it again in the bladder: the kindsof sediment, as the lateritious, purulent, mucous, or bloody sediments, depend on other causes. It should be observed, that if the sweating beincreased by the heat of the room, or of the bed-clothes, that a paucity ofturbid urine will continue to be produced, as the absorbents of the bladderwill have their activity increased by their sympathy with the vessels ofthe skin, for the purpose of supplying the fluid expended in perspiration. The pulse becomes strong and full owing to the increased irritability ofthe heart and arteries, from the accumulation of sensorial power duringtheir quiescence, and to the quickness of the return of the blood from thevarious glands and capillaries. This increased action of all the secretoryvessels does not occur very suddenly, nor universally at the same time. Theheat seems to begin about the center, and to be diffused from thenceirregularly to the other parts of the system. This may be owing to thesituation of the parts which first became quiescent and caused thefever-fit, especially when a hardness or tumour about the præcordia can befelt by the hand; and hence this part, in whatever viscus it is seated, might be the first to regain its natural or increased irritability. 3. It must be here noted, that, by the increased quantity of heat, and ofthe impulse of the blood at the commencement of the hot fit, a greatincrease of stimulus is induced, and is now added to the increasedirritability of the system, which was occasioned by its previousquiescence. This additional stimulus of heat and momentum of the bloodaugments the violence of the movements of the arterial and glandular systemin an increasing ratio. These violent exertions still producing more heatand greater momentum of the moving fluids, till at length the sensoralpower becomes wasted by this great stimulus beneath its natural quantity, and predisposes the system to a second cold fit. At length all these unnatural exertions spontaneously subside with theincreased irritability that produced them; and which was itself produced bythe preceding quiescence, in the same manner as the eye, on coming fromdarkness into day-light, in a little time ceases to be dazzled and pained, and gradually recovers its natural degree of irritability. 4. But if the increase of irritability, and the consequent increase of thestimulus of heat and momentum, produce more violent exertions than thoseabove described; great pain arises in some part of the moving system, as inthe membranes of the brain, pleura, or joints; and new motions of thevessels are produced in consequence of this pain, which are calledinflammation; or delirium or stupor arises; as explained in Sect. XXI. AndXXXIII. : for the immediate effect is the same, whether the great energy ofthe moving organs arises from an increase of stimulus or an increase ofirritability; though in the former case the waste of sensorial power leadsto debility, and in the latter to health. _Recapitulation. _ X. Those muscles, which are less frequently exerted, and whose actions areinterrupted by sleep, acquire less accumulation of sensorial power duringtheir quiescent state, as the muscles of locomotion. In these muscles aftergreat exertion, that is, after great exhaustion of sensorial power, thepain of fatigue ensues; and during rest there is a renovation of thenatural quantity of sensorial power; but where the rest, or quiescence ofthe muscle, is long continued, a quantity of sensorial power becomesaccumulated beyond what is necessary; as appears by the uneasinessoccasioned by want of exercise; and which in young animals is one causeexciting them into action, as is seen in the play of puppies and kittens. But when those muscles, which are habituated to perpetual actions, as thoseof the stomach by the stimulus of food, those of the vessels of the skin bythe stimulus of heat, and those which constitute the arteries and glands bythe stimulus of the blood, become for a time quiescent, from the want oftheir appropriated stimuli, or by their associations with other quiescentparts of the system; a greater accumulation of sensorial power is acquiredduring their quiescence, and a greater or quicker exhaustion of it isproduced during their increased action. This accumulation of sensorial power from deficient action, if it happensto the stomach from want of food, occasions the pain of hunger; if ithappens to the vessels of the skin from want of heat, it occasions the painof cold; and if to the arterial system from the want of its adaptedstimuli, many disagreeable sensations are occasioned, such as areexperienced in the cold fits of intermittent fevers, and are as various, asthere are glands or membranes in the system, and are generally termeduniversal uneasiness. When the quiescence of the arterial system is not owing to defect ofstimulus as above, but to the defective quantity of sensorial power, as inthe commencement of nervous fever, or irritative fever with weak pulse, agreat torpor of this system is quickly induced; because both the irritationfrom the stimulus of the blood, and the association of the vascular motionswith each other, continue to excite the arteries into action, and thencequickly exhaust the ill-supplied vascular muscles; for to rest is death;and therefore those vascular muscles continue to proceed, though withfeebler action, to the extreme of weariness or faintness: while nothingsimilar to this affects the locomotive muscles, whose actions are generallycaused by volition, and not much subject either to irritation or to otherkinds of associations besides the voluntary ones, except indeed when theyare excited by the lash of slavery. In these vascular muscles, which are subject to perpetual action, andthence liable to great accumulation of sensorial power during theirquiescence from want of stimulus, a great increase of activity occurs, either from the renewal of their accustomed stimulus, or even from muchless quantities of stimulus than usual. This increase of action constitutesthe hot fit of fever, which is attended with various increased secretions, with great concomitant heat, and general uneasiness. The uneasinessattending this hot paroxysm of fever, or fit of exertion, is very differentfrom that, which attends the previous cold fit, or fit of quiescence, andis frequently the cause of inflammation, as in pleurisy, which is treatedof in the next section. A similar effect occurs after the quiescence of our organs of sense; thosewhich are not subject to perpetual action, as the taste and smell, are lessliable to an exuberant accumulation of sensorial power after their havingfor a time been inactive; but the eye, which is in perpetual action duringthe day, becomes dazzled, and liable to inflammation after a temporaryquiescence. Where the previous quiescence has been owing to a defect of sensorialpower, and not to a defect of stimulus, as in the irritative fever withweak pulse, a similar increase of activity of the arterial system succeeds, either from the usual stimulus of the blood, or from a stimulus less thanusual; but as there is in general in these cases of fever with weak pulse adeficiency of the quantity of the blood, the pulse in the hot fit is weakerthan in health, though it is stronger than in the cold fit, as explained inNo. 2. Of this section. But at the same time in those fevers, where thedefect of irritation is owing to the defect of the quantity of sensorialpower, as well as to the defect of stimulus, another circumstance occurs;which consists in the partial distribution of it, as appears in partialflushings, as of the face or bosom, while the extremities are cold; and inthe increase of particular secretions, as of bile, saliva, insensibleperspiration, with great heat of the skin, or with partial sweats, ordiarrhoea. There are also many uneasy sensations attending these increased actions, which, like those belonging to the hot fit of fever with strong pulse, arefrequently followed by inflammation, as in scarlet fever; whichinflammation is nevertheless accompanied with a pulse weaker, thoughquicker, than the pulse during the remission or intermission of theparoxysms, though stronger than that of the previous cold fit. From hence I conclude, that both the cold and hot fits of fever arenecessary consequences of the perpetual and incessant action of thearterial and glandular system; since those muscular fibres and those organsof sense, which are most frequently exerted, become necessarily mostaffected both with defect and accumulation of sensorial power: and thathence _fever-fits are not an effort of nature to relieve herself_, and thattherefore they should always be prevented or diminished as much aspossible, by any means which decrease the general or partial vascularactions, when they are greater, or by increasing them when they are lessthan in health, as described in Sect. XII. 6. 1. Thus have I endeavoured to explain, and I hope to the satisfaction of thecandid and patient reader, the principal symptoms or circumstances of feverwithout the introduction of the supernatural power of spasm. To thearguments in favour of the doctrine of spasm it may be sufficient to reply, that in the evolution of medical as well as of dramatic catastrophe, Nec Deus intersit, nisi dignus vindice nodus inciderit. --HOR. * * * * * SECT. XXXIII. DISEASES OF SENSATION. I. 1. _Motions excited by sensation. Digestion. Generation. Pleasure of existence. Hypochondriacism. _ 2. _Pain introduced. Sensitive fevers of two kinds. _ 3. _Two sensorial powers exerted in sensitive fevers. Size of the blood. Nervous fevers distinguished from putrid ones. The septic and antiseptic theory. _ 4. _Two kinds of delirium. _ 5. _Other animals are less liable to delirium, cannot receive our contagious diseases, and are less liable to madness. _ II. 1. _Sensitive motions generated. _ 2. _Inflammation explained. _ 3. _Its remote causes from excess of irritation, or of irritability, not from those pains which are owing to defect of irritation. New vessels produced, and much heat. _ 4. _Purulent matter secreted. _ 5. _Contagion explained. _ 6. _Received but once. _ 7. _If common matter be contagious?_ 8. _Why some contagions are received but once. _ 9. _Why others may be received frequently. Contagions of small-pox and measles do not act at the same times. Two cases of such patients. _ 10. _The blood from patients in the small-pox will not infect others. Cases of children thus inoculated. The variolous contagion is not received into the blood. It acts by sensitive association between the stomach and skin. _ III. 1. _Absorption of solids and fluids. _ 2. _Art of healing ulcers. _ 3. _Mortification attended with less pain in weak people. _ I. 1. As many motions of the body are excited and continued by irritations, so others require, either conjunctly with these, or separately, thepleasurable or painful sensations, for the purpose of producing them withdue energy. Amongst these the business of digestion supplies us with aninstance: if the food, which we swallow, is not attended with agreeablesensation, it digests less perfectly; and if very disagreeable sensationaccompanies it, such as a nauseous idea, or very disgustful taste, thedigestion becomes impeded; or retrograde motions of the stomach andoesophagus succeed, and the food is ejected. The business of generation depends so much on agreeable sensation, that, where the object is disgustful, neither voluntary exertion nor irritationcan effect the purpose; which is also liable to be interrupted by the painof fear or bashfulness. Besides the pleasure, which attends the irritations produced by the objectsof lust and hunger, there seems to be a sum of pleasurable affectionaccompanying the various secretions of the numerous glands, whichconstitute the pleasure of life, in contradistinction to the tedium vitæ. This quantity or sum of pleasurable affection, seems to contribute to thedue or energetic performance of the whole moveable system, as well that ofthe heart and arteries, as of digestion and of absorption; since withoutthe due quantity of pleasurable sensation, flatulency and hypochondriacismaffect the intestines, and a languor seizes the arterial pulsations andsecretions; as occurs in great and continued anxiety of the mind. 2. Besides the febrile motions occasioned by irritation, described in Sect. XXXII. And termed irritative fever, it frequently happens that pain isexcited by the violence of the fibrous contractions; and other new motionsare then superadded, in consequence of sensation, which we shall termfebris sensitiva, or sensitive fever. It must be observed, that mostirritative fevers begin with a decreased exertion of irritation, owing todefect of stimulus; but that on the contrary the sensitive fevers, orinflammations, generally begin with the increased exertion of sensation, asmentioned in Sect. XXXI. On temperaments: for though the cold fit, whichintroduces inflammation, commences with decreased irritation, yet theinflammation itself commences in the hot fit during the increase ofsensation. Thus a common pustule, or phlegmon, in a part of littlesensibility does not excite an inflammatory fever; but if the stomach, intestines, or the tender substance beneath the nails, be injured, greatsensation is produced, and the whole system is thrown into that kind ofexertion, which constitutes inflammation. These sensitive fevers, like the irritative ones, resolve themselves intothose with arterial strength, and those with arterial debility, that iswith excess or defect of sensorial power; these may be termed the febrissensitiva pulsu forti, sensitive fever with strong pulse, which is thesynocha, or inflammatory fever; and the febris sensitiva pulsu debili, sensitive fever with weak pulse, which is the typhus gravior, or putridfever of some writers. 3. The inflammatory fevers, which are here termed sensitive fevers withstrong pulse, are generally attended with some topical inflammation, aspleurisy, peripneumony, or rheumatism, which distinguishes them fromirritative fevers with strong pulse. The pulse is strong, quick, and full;for in this fever there is great irritation, as well as great sensation, employed in moving the arterial system. The size, or coagulable lymph, which appears on the blood, is probably an increased secretion from theinflamed internal lining of the whole arterial system, the thinner partbeing taken away by the increased absorption of the inflamed lymphatics. The sensitive fevers with weak pulse, which are termed putrid or malignantfevers, are distinguished from irritative fevers with weak pulse, callednervous fevers, described in the last section, as the former consist ofinflammation joined with debility, and the latter of debility alone. Hencethere is greater heat and more florid colour of the skin in the former, with petechiæ, or purple spots, and aphthæ, or sloughs in the throat, andgenerally with previous contagion. When animal matter dies, as a slough in the throat, or the mortified partof a carbuncle, if it be kept moist and warm, as during its abhesion to aliving body, it will soon putrify. This, and the origin of contagion fromputrid animal substances, seem to have given rise to the septic andantiseptic theory of these fevers. The matter in pustules and ulcers is thus liable to become putrid, and toproduce microscopic animalcula; the urine, if too long retained, may alsogain a putrescent smell, as well as the alvine feces; but some writers havegone so far as to believe, that the blood itself in these fevers has smeltputrid, when drawn from the arm of the patient: but this seems not wellfounded; since a single particle of putrid matter taken into the blood canproduce fever, how can we conceive that the whole mass could continue aminute in a putrid state without destroying life? Add to this, that putridanimal substances give up air, as in gangrenes; and that hence if the bloodwas putrid, air should be given out, which in the blood-vessels is known tooccasion immediate death. In these sensitive fevers with strong pulse (or inflammations) there aretwo sensorial faculties concerned in producing the disease, viz. Irritationand sensation; and hence, as their combined action is more violent, thegeneral quantity of sensorial power becomes further exhausted during theexacerbation, and the system more rapidly weakened than in irritative feverwith strong pulse; where the spirit of animation is weakened by but onemode of its exertion: so that this febris sensitiva pulsu forti (orinflammatory fever, ) may be considered as the febris irritativa pulsuforti, with the addition of inflammation; and the febris sensitiva pulsudebili (or malignant fever) may be considered as the febris irritativapulsu debili (or nervous fever), with the addition of inflammation. 4. In these putrid or malignant fevers a deficiency of irritabilityaccompanies the increase of sensibility; and by this waste of sensorialpower by the excess of sensation, which was already too small, arises thedelirium and stupor which so perpetually attend these inflammatory feverswith arterial debility. In these cases the voluntary power first ceases toact from deficiency of sensorial spirit; and the stimuli from externalbodies have no effect on the exhausted sensorial power, and a delirium likea dream is the consequence. At length the internal stimuli cease to excitesufficient irritation, and the secretions are either not produced at all, or too parsimonious in quantity. Amongst these the secretion of the brain, or production of the sensorial power, becomes deficient, till at last allsensorial power ceases, except what is just necessary to perform the vitalmotions, and a stupor succeeds; which is thus owing to the same cause asthe preceding delirium exerted in a greater degree. This kind of delirium is owing to a suspension of volition, and to thedisobedience of the senses to external stimuli, and is always occasioned bygreat debility, or paucity of sensorial power; it is therefore a bad signat the end of inflammatory fevers, which had previous arterial strength, asrheumatism, or pleurisy, as it shews the presence of great exhaustion ofsensorial power in a system, which having lately been exposed to greatexcitement, is not so liable to be stimulated into its healthy action, either by additional stimulus of food and medicines, or by the accumulationof sensorial power during its present torpor. In inflammatory fevers withdebility, as those termed putrid fevers, delirium is sometimes, as well asstupor, rather a favourable sign; as less sensorial power is wasted duringits continuance (see Class II. 1. 6. 8. ), and the constitution not havingbeen previously exposed to excess of stimulation, is more liable to beexcited after previous quiescence. When the sum of general pleasurable sensation becomes too great, anotherkind of delirium supervenes, and the ideas thus excited are mistaken forthe irritations of external objects: such a delirium is produced for a timeby intoxicating drugs, as fermented liquors, or opium: a permanent deliriumof this kind is sometimes induced by the pleasures of inordinate vanity, orby the enthusiastic hopes of heaven. In these cases the power of volitionis incapable of exertion, and in a great degree the external senses becomeincapable of perceiving their adapted stimuli, because the whole sensorialpower is employed or expended on the ideas excited by pleasurablesensation. This kind of delirium is distinguished from that which attends the feversabove mentioned from its not being accompanied with general debility, butsimply with excess of pleasurable sensation; and is therefore in somemeasure allied to madness or to reverie; it differs from the delirium ofdreams, as in this the power of volition is not totally suspended, nor arethe senses precluded from external stimulation; there is therefore a degreeof consistency, in this kind of delirium, and a degree of attention toexternal objects, neither of which exist in the delirium of fevers or indreams. 5. It would appear, that the vascular system of other animals are lessliable to be put into action by their general sum of pleasurable or painfulsensation; and that the trains of their ideas, and the muscular motionsusually associated with them, are less powerfully connected than in thehuman system. For other animals neither weep, nor smile, nor laugh; and arehence seldom subject to delirium, as treated of in Sect. XVI. On Instinct. Now as our epidemic and contagious diseases are probably produced bydisagreeable sensation, and not simply by irritation; there appears areason, why brute animals are less liable to epidemic or contagiousdiseases; and secondly, why none of our contagions, as the small-pox ormeasles, can be communicated to them, though one of theirs, viz. Thehydrophobia, as well as many of their poisons, as those of snakes and of ininsects, communicate their deleterious or painful effects to mankind. Where the quantity of general painful sensation is too great in the system, inordinate voluntary exertions are produced either of our ideas, as inmelancholy and madness, or of our muscles, as in convulsion. From thesemaladies also brute animals are much more exempt than mankind, owing totheir greater inaptitude to voluntary exertion, as mentioned in Sect. XVI. On Instinct. II. 1. When any moving organ is excited into such violent motions, that aquantity of pleasurable or painful sensation is produced, it frequentlyhappens (but not always) that new motions of the affected organ aregenerated in consequence of the pain or pleasure, which are termedinflammation. These new motions are of a peculiar kind, tending to distend the old, andto produce new fibres, and thence to elongate the straight muscles, whichserve locomotion, and to form new vessels at the extremities or sides ofthe vascular muscles. 2. Thus the pleasurable sensations produce an enlargement of the nipples ofnurses, of the papillæ of the tongue, of the penis, and probably producethe growth of the body from its embryon state to its maturity; whilst thenew motions in consequence of painful sensation, with the growth of thefibres or vessels, which they occasion, are termed inflammation. Hence when the straight muscles are inflamed, part of their tendons at eachextremity gain new life and sensibility, and thus the muscle is for a timeelongated; and inflamed bones become soft, vascular, and sensible. Thus newvessels shoot over the cornea of inflamed eyes, and into scirrhous tumours, when they become inflamed; and hence all inflamed parts grow together byintermixture, and inosculation of the new and old vessels. The heat is occasioned from the increased secretions either of mucus, or ofthe fibres, which produce or elongate the vessels. The red colour is owingto the pellucidity of the newly formed vessels, and as the arterial partsof them are probably formed before their correspondent venous parts. 3. These new motions are excited either from the increased quantity ofsensation in consequence of greater fibrous contractions, or from increasedsensibility, that is, from the increased quantity of sensorial power in themoving organ. Hence they are induced by great external stimuli, as bywounds, broken bones; and by acrid or infectious materials; or by commonstimuli on those organs, which have been some time quiescent; as the usuallight of the day inflames the eyes of those, who have been confined indungeons; and the warmth of a common fire inflames those, who have beenpreviously exposed to much cold. But these new motions are never generated by that pain, which arises fromdefect of stimulus, as from hunger, thirst, cold, or inanition, with allthose pains, which are termed nervous. Where these pains exist, the motionsof the affected part are lessened; and if inflammation succeeds, it is insome distant parts; as coughs are caused by coldness and moisture beinglong applied to the feet; or it is in consequence of the renewal of thestimulus, as of heat or food, which excites our organs into stronger actionafter their temporary quiescence; as kibed heels after walking in snow. 4. But when these new motions of the vascular muscles are exerted withgreater violence, and these vessels are either elongated too much or toohastily, a new material is secreted from their extremities, which is ofvarious kinds according to the peculiar animal motions of this new kind ofgland, which secretes it; such is the pus laudabile or common matter, thevariolous matter, venereal matter, catarrhous matter, and many others. 5. These matters are the product of an animal process; they are secreted orproduced from the blood by certain diseased motions of the extremities ofthe blood-vessels, and are on that account all of them contagious; for if aportion of any of these matters is transmitted into the circulation, orperhaps only inserted into the skin, or beneath the cuticle of an healthyperson, its stimulus in a certain time produces the same kind of morbidmotions, by which itself was produced; and hence a similar kind isgenerated. See Sect. XXXIX. 6. 1. 6. It is remarkable, that many of these contagious matters are capable ofproducing a similar disease but once; as the small-pox and measles; and Isuppose this is true of all those contagious diseases, which arespontaneously cured by nature in a certain time; for if the body wascapable of receiving the disease a second time, the patient mustperpetually infect himself by the very matter, which he has himselfproduced, and is lodged about him; and hence he could never become freefrom the disease. Something similar to this is seen in the secondary feverof the confluent small-pox; there is a great absorption of variolousmatter, a very minute part of which would give the genuine small-pox toanother person; but here it only stimulates the system into common fever;like that which common puss, or any other acrid material might occasion. 7. In the pulmonary consumption, where common matter is daily absorbed, anirritative fever only, without new inflammation, is generally produced;which is terminated like other irritative fevers by sweats, or loosestools. Hence it does not appear, that this absorbed matter always acts asa contagious material producing fresh inflammation or new abscesses. Thoughthere is reason to believe, that the first time any common matter isabsorbed, it has this effect, but not the second time, like the variolousmatter above mentioned. This accounts for the opinion, that the pulmonary consumption is sometimesinfectious, which opinion was held by the ancients, and continues in Italyat present; and I have myself seen three or four instances, where a husbandand wife, who have slept together, and have thus much received each other'sbreath, who have infected each other, and both died in consequence of theoriginal taint of only one of them. This also accounts for the abscesses invarious parts of the body, that are sometimes produced after the inoculatedsmall-pox is terminated; for this second absorption of variolous matteracts like common matter, and produces only irritative fever in thosechildren, whose constitutions have already experienced the absorption ofcommon matter; and inflammation with a tendency to produce new abscesses inthose, whose constitutions have not experienced the absorptions of commonmatter. It is probable, that more certain proofs might have been found to shew, that common matter is infectious the first time it is absorbed, tending toproduce similar abscesses, but not the second time of its absorption, ifthis subject had been attended to. 8. These contagious diseases are very numerous, as the plague, small-pox, chicken-pox, measles, scarlet-fever, pemphigus, catarrh, chincough, venereal disease, itch, trichoma, tinea. The infectious material does notseem to be dissolved by the air, but only mixed with it perhaps in finepowder, which soon subsides; since many of these contagions can only bereceived by actual contact; and others of them only at small distances fromthe infected person; as is evident from many persons having been nearpatients of the small-pox without acquiring the disease. The reason, why many of these diseases are received but once, and othersrepeatedly, is not well understood; it appears to me, that the constitutionbecomes so accustomed to the stimuli of these infectious materials, byhaving once experienced them, that though irritative motions, as hecticfevers, may again be produced by them, yet no sensation, and in consequenceno general inflammation succeeds; as disagreeable smells or tastes by habitcease to be perceived; they continue indeed to excite irritative ideas onthe organs of sense, but these are not succeeded by sensation. There are many irritative motions, which were at first succeeded bysensation, but which by frequent repetition cease to excite sensation, asexplained in Sect. XX. On Vertigo. And, that this circumstance exists inrespect to infectious matter appears from a known fact; that nurses, whohave had the small-pox, are liable to experience small ulcers on their armsby the contact of variolous matter in lifting their patients; and that whenpatients, who have formerly had the small-pox have been inoculated in thearm, a phlegmon, or inflamed sore, has succeeded, but no subsequent fever. Which shews, that the contagious matter of the small-pox has not lost itspower of stimulating the part it is applied to, but that the general systemis not affected in consequence. See Section XII. 7. 6. XIX. 9. 9. From the accounts of the plague, virulent catarrh, and putrid dysentery, it seems uncertain, whether these diseases are experienced more than once;but the venereal disease and itch are doubtless repeatedly infectious; andas these diseases are never cured spontaneously, but require medicines, which act without apparent operation, some have suspected, that thecontagious material produces similar matter rather by a chemical change ofthe fluids, than by an animal process; and that the specific medicinesdestroy their virus by chemically combining with it. This opinion issuccessfully combated by Mr. Hunter, in his Treatise on Venereal Disease, Part I. C. I. But this opinion wants the support of analogy, as there is no known processin animal bodies, which is purely chemical, not even digestion; nor can anyof these matters be produced by chemical processes. Add to this, that it isprobable, that the insects, observed in the pustules of the itch, and inthe stools of dysenteric patients, are the consequences, and not the causesof these diseases. And that the specific medicines, which cure the itch andlues venerea, as brimstone and mercury, act only by increasing theabsorption of the matter in the ulcuscles of those diseases, and thencedisposing them to heal; which would otherwise continue to spread. Why the venereal disease, and itch, and tenia, or scald head, arerepeatedly contagious, while those contagions attended with fever can bereceived but once, seems to depend on their being rather local diseasesthan universal ones, and are hence not attended with fever, except thepurulent fever in their last stages, when the patient is destroyed by them. On this account the whole of the system does not become habituated to thesemorbid actions, so as to cease to be affected with sensation by arepetition of the contagion. Thus the contagious matter of the venerealdisease, and of the tenia, affects the lymphatic glands, as the inquinalglands, and those about the roots of the hair and neck, where it isarrested, but does not seem to affect the blood-vessels, since no feverensues. Hence it would appear, that these kinds of contagion are propagated not bymeans of the circulation, but by sympathy of distant parts with each other;since if a distant part, as the palate, should be excited by sensitiveassociation into the same kind of motions, as the parts originally affectedby the contact of infectious matter; that distant part will produce thesame kind of infectious matter; for every secretion from the blood isformed from it by the peculiar motions of the fine extremities of thegland, which secretes it; the various secreted fluids, as the bile, saliva, gastric juice, not previously existing, as such, in the blood-vessels. And this peculiar sympathy between the genitals and the throat, owing tosensitive association, appears not only in the production of venerealulcers in the throat, but in variety of other instances, as in the mumps, in the hydrophobia, some coughs, strangulation, the production of thebeard, change of voice at puberty. Which are further described in Class IV. 1. 2. 7. To evince that the production of such large quantities of contagiousmatter, as are seen in some variolous patients, so as to cover the wholeskin almost with pustules, does not arise from any chemical fermentation inthe blood, but that it is owing to morbid motions of the fine extremitiesof the capillaries, or glands, whether these be ruptured or not, appearsfrom the quantity of this matter always corresponding with the quantity ofthe fever; that is, with the violent exertions of those glands andcapillaries, which are the terminations of the arterial system. The truth of this theory is evinced further by a circumstance observed byMr. J. Hunter, in his Treatise on Venereal Disease; that in a patient, whowas inoculated for the small-pox, and who appeared afterwards to have beenpreviously infested with the measles, the progress of the small-pox wasdelayed till the measles had run their course, and that then the small-poxwent through its usual periods. Two similar cases fell under my care, which I shall here relate, as itconfirms that of Mr. Hunter, and contributes to illustrate this part of thetheory of contagious diseases. I have transcribed the particulars from aletter of Mr. Lightwood of Yoxal, the surgeon who daily attended them, andat my request, after I had seen them, kept a kind of journal of theircases. Miss H. And Miss L. Two sisters, the one about four and the other aboutthree years old, were inoculated Feb. 7, 1791. On the 10th there was aredness on both arms discernible by a glass. On the 11th their arms were somuch inflamed as to leave no doubt of the infection having taken place. Onthe 12th less appearance of inflammation on their arms. In the evening MissL. Had an eruption, which resembled the measles. On the 12th the eruptionon Miss L. Was very full on the face and breast, like the measles, withconsiderable fever. It was now known, that the measles were in a farm housein the neighbourhood. Miss H. 's arm less inflamed than yesterday. On the14th Miss L. 's fever great, and the eruption universal. The arm appears tobe healed. Miss H. 's arm somewhat redder. They were now put into separaterooms. On the 15th Miss L. 's arms as yesterday. Eruption continues. MissH. 's arms have varied but little. 16th, the eruptions on Miss L. Are dyingaway, her fever gone. Begins to have a little redness in one arm at theplace of inoculation. Miss H. 's arms get redder, but she has no appearanceof complaint. 20th, Miss L. 's arms have advanced slowly till this day, andnow a few pustules appear. Miss H. 's arm has made little progress from the16th to this day, and now she has some fever. 21st, Miss L. As yesterday. Miss H. Has much inflammation, and an increase of the red circle on one armto the size of half a crown, and had much fever at night, with fetidbreath. 22d, Miss L. 's pustules continue advancing. Miss H. 's inflammationof her arm and red circle increases. A few red spots appear in differentparts with some degree of fever this morning, 23d. Miss L. Has a largercrop of pustules. Miss H. Has small pustules and great inflammation of herarms, with but one pustule likely to suppurate. After this day theygradually got well, and the pustules disappeared. In one of these cases the measles went through their common course withmilder symptoms than usual, and in the other the measly contagion seemedjust sufficient to stop the progress of variolous contagion, but withoutitself throwing the constitution into any disorder. At the same time boththe measles and small-pox seem to have been rendered milder. Does not thisgive an idea, that if they were both inoculated at the same time, thatneither of them might affect the patient? From these cases I contend, that the contagious matter of these diseasesdoes not affect the constitution by a fermentation, or chemical change ofthe blood, because then they must have proceeded together, and haveproduced a third something, not exactly similar to either of them: but thatthey produce new motions of the cutaneous terminations of theblood-vessels, which for a time proceed daily with increasing activity, like some paroxysms of fever, till they at length secrete or form a similarpoison by these unnatural actions. Now as in the measles one kind of unnatural motion takes place, and in thesmall-pox another kind, it is easy to conceive, that these different kindsof morbid motions cannot exist together; and therefore, that that which hasfirst begun will continue till the system becomes habituated to thestimulus which occasions it, and has ceased to be thrown into action by it;and then the other kind of stimulus will in its turn produce fever, and newkinds of motions peculiar to itself. 10. On further considering the action of contagious matter, since theformer part of this work was sent to the press; where I have asserted, inSect. XXII. 3. 3. That it is probable, that the variolous matter isdiffused through the blood; I prevailed on my friend Mr. Power, surgeon atBosworth in Leicestershire to try, whether the small-pox could beinoculated by using the blood of a variolous patient instead of the matterfrom the pustules; as I thought such an experiment might throw some lightat least on this interesting subject. The following is an extract from hisletter:-- "March 11, 1793. I inoculated two children, who had not had the small-pox, with blood; which was taken from a patient on the second day after theeruption commenced, and before it was completed. And at the same time Iinoculated myself with blood from the same person, in order to compare theappearances, which might arise in a person liable to receive the infection, and in one not liable to receive it. On the same day I inoculated fourother children liable to receive the infection with blood taken fromanother person on the fourth day after the commencement of the eruption. The patients from whom the blood was taken had the disease mildly, but hadthe most pustules of any I could select from twenty inoculated patients;and as much of the blood was insinuated under the cuticle as I couldintroduce by elevating the skin without drawing blood; and three or foursuch punctures were made in each of their arms, and the blood was used inits fluid state. "As the appearances in all these patients, as well as in myself, weresimilar, I shall only mention them in general terms. March 13. A slightsubcuticular discoloration, with rather a livid appearance, withoutsoreness or pain, was visible in them all, as well as in my own hand. 15. The discoloration somewhat less, without pain or soreness. Some patientsinoculated on the same day with variolous matter have considerableinflammation. 17. The discoloration is quite gone in them all, and from myown hand, a dry mark only remaining. And they were all inoculated on the18th, with variolous matter, which produced the disease in them all. " Mr. Power afterwards observes, that, as the patients from whom the bloodwas taken had the disease mildly, it may be supposed, that though thecontagious matter might be mixed with the blood, it might still be in toodilute a state to convey the infection; but adds at the same time, that hehas diluted recent matter with at least five times its quantity of water, and which has still given the infection; though he has sometimes diluted itso far as to fail. The following experiments were instituted at my request by my friend Mr. Hadley, surgeon in Derby, to ascertain whether the blood of a person in thesmall-pox be capable of communicating the disease. "Experiment 1st. October18th, 1793. I took some blood from a vein in the arm of a person who hadthe small-pox, on the second day of the eruption, and introduced a smallquantity of it immediately with the point of a lancet between the scars andtrue skin of the right arm of a boy nine years old in two or threedifferent places; the other arm was inoculated with variolous matter at thesame time. "19th. The punctured parts of the right arm were surrounded with somedegree of subcuticular inflammation. 20th. The inflammation moreconsiderable, with a slight degree of itching, but no pain upon pressure. 21st. Upon examining the arm this day with a lens I found the inflammationless extensive, and the redness changing to a deep yellow or orange-colour, 22d. Inflammation nearly gone. 23d. Nothing remained, except a slightdiscoloration and a little scurfy appearance on the punctures. At the sametime the inflammation of the arm inoculated with variolous matter wasincreasing fast, and he had the disease mildly at the usual time. "Experiment 2d. I inoculated another child at the same time and in the samemanner, with blood taken on the first day of the eruption; but as theappearance and effects were similar to those in the preceding experiment, Ishall not relate them minutely. "Experiment 3d. October 20th. Blood was taken from a person who had thesmall-pox, on the third day of the eruption, and on the sixth from thecommencement of the eruptive fever. I introduced some of it in its fluidstate into both arms of a boy seven years old. 21st. There appeared to be some inflammation under the cuticle, where thepunctures were made. 22d. Inflammation more considerable. 23d. On this daythe inflammation was somewhat greater, and the cuticle rather elevated. "24th. Inflammation much less, and only a brown or orange-colour remained. 25th. Scarcely any discoloration left. On this day he was inoculated withvariolous matter, the progress of the infection went on in the usual way, and he had the small-pox very favourably. "At this time I was requested to inoculate a young person, who was thoughtto have had the small-pox, but his parents were not quite certain; in onearm I introduced variolous matter, and in the other blood, taken as inexperiment 3d. On the second day after the operation, the punctured partswere inflamed, though I think the arm in which I had inserted variolousmatter was rather more so than the other. On the third the inflammation wasincreased, and looked much the same as in the preceding experiment. 4th. The inflammation was much diminished, and on the 5th almost gone. He wasexposed at the same time to the natural infection, but has continuedperfectly well. "I have frequently observed (and believe most practitioners have done thesame), that if variolous matter be inserted in the arm of a person who haspreviously had the small-pox, that the inflammation on the second or thirddays is much greater, than if they had not had the disease, but on thefourth or fifth it disappears. "On the 23d I introduced blood into the arms of three more children, takenon the third and fourth days of the eruption. The appearances were much thesame as mentioned in experiments first and third. They were afterwardsinoculated with variolous matter, and had the disease in the regular way. "The above experiments were made with blood taken from a small vein in thehand or foot of three or four different patients, whom I had at that timeunder inoculation. They were selected from 160, as having the greatestnumber of pustules. The part was washed with warm water before the bloodwas taken, to prevent the possibility of any matter being mixed with itfrom the surface. " Shall we conclude from hence, that the variolous matter never enters theblood-vessels? but that the morbid motions of the vessels of the skinaround the insertion of it continue to increase in a larger and largercircle for six or seven days; that then their quantity of morbid actionbecomes great enough to produce a fever-fit, and to affect the stomach byassociation of motions? and finally, that a second association of motionsis produced between the stomach and the other parts of the skin, inducingthem into morbid actions similar to those of the circle round the insertionof the variolous matter? Many more experiments and observations arerequired before this important question can be satisfactorily answered. It may be adduced, that as the matter inserted into the skin of the armfrequently swells the lymphatic in the axilla, that in that circumstance itseems to be there arrested in its progress, and cannot be imagined to enterthe blood by that lymphatic gland till the swelling of it subsides. Someother phænomena of the disease are more easily reconcileable to this theoryof sympathetic motions than to that of absorption; as the time taken upbetween the insertion of the matter, and the operation of it on the system, as mentioned above. For the circle around the insertion is seen toincrease, and to inflame; and I believe, undergoes a kind of diurnalparoxysm of torpor and paleness with a succeeding increase of action andcolour, like a topical fever-fit. Whereas if the matter is conceived tocirculate for six or seven days with the blood, without producing disorder, it ought to be rendered milder, or the blood-vessels more familiarized toits acrimony. It is much easier to conceive from this doctrine of associated orsympathetic motions of distant parts of the system, how it happens, thatthe variolous infection can be received but once, as before explained; thanby supposing, that a change is effected in the mass of blood by any kind offermentative process. The curious circumstance of the two contagions of small-pox and measles notacting at the same time, but one of them resting or suspending its actiontill that of the other ceases, may be much easier explained fromsympathetic or associated actions of the infected part with other parts ofthe system, than it can from supposing the two contagions to enter thecirculation. The skin of the face is subject to more frequent vicissitudes of heat andcold, from its exposure to the open air, and is in consequence more liableto sensitive association with the stomach than any other part of thesurface of the body, because their actions have been more frequently thusassociated. Thus in a surfeit from drinking cold water, when a person isvery hot and fatigued, an eruption is liable to appear on the face inconsequence of this sympathy. In the same manner the rosy eruption on thefaces of drunkards more probably arises from the sympathy of the face withthe stomach, rather than between the face and the liver, as is generallysupposed. This sympathy between the stomach and the skin of the face is apparent inthe eruption of the small-pox; since, where the disease is in considerablequantity, the eruption on the face first succeeds the sickness of thestomach. In the natural disease the stomach seems to be frequentlyprimarily affected, either alone or along with the tonsils, as the matterseems to be only diffused in the air, and by being mixed with the saliva, or mucus of the tonsils, to be swallowed into the stomach. After some days the irritative circles of motions become disordered by thisnew stimulus, which acts upon the mucus lining of the stomach; andsickness, vertigo, and a diurnal fever succeed. These disordered irritativemotions become daily increased for two or three days, and then by theirincreased action certain sensitive motions, or inflammation, is produced, and at the next cold fit of fever, when the stomach recovers from itstorpor, an inflammation of the external skin is formed in points (whichafterwards suppurate), by sensitive association, in the same manner as acough is produced in consequence of exposing the feet to cold, as describedin Sect. XXV. 17. And Class IV. 2. I. 7. If the inoculated skin of the arm, as far as it appears inflamed, was to be cut out, or destroyed by caustic, before the fever commenced, as suppose on the fourth day after inoculation, would this prevent the disease? as it is supposed to prevent thehydrophobia. III. 1. Where the new vessels, and enlarged old ones, which constituteinflammation, are not so hastily distended as to burst, and form a new kindof gland for the secretion of matter, as above mentioned; if suchcircumstances happen as diminish the painful sensation, the tendency togrowth ceases, and by and by an absorption commences, not only of thesuperabundant quantity of fluids deposited in the inflamed part, but of thesolids likewise, and this even of the hardest kind. Thus during the growth of the second set of teeth in children, the roots ofthe first set are totally absorbed, till at length nothing of them remainsbut the crown; though a few weeks before, if they are drawn immaturely, their roots are found complete. Similar to this Mr. Hunter has observed, that where a dead piece of bone is to exfoliate, or to separate from aliving one, that the dead part does not putrify, but remains perfectlysound, while the surface of the living part of the bone, which is incontact with the dead part, becomes absorbed, and thus effects itsseparation. Med. Comment. Edinb. V. 1. 425. In the same manner thecalcareous matter of gouty concretions, the coagulable lymph deposited oninflamed membranes in rheumatism and extravasated blood become absorbed;which are all as solid and as indissoluble materials as the new vesselsproduced in inflammation. This absorption of the new vessels and deposited fluids of inflamed partsis called resolution: it is produced by first using such internal means asdecrease the pain of the part, and in consequence its new motions, asrepeated bleeding, cathartics, diluent potations, and warm bath. After the vessels are thus emptied, and the absorption of the new vesselsand deposited fluids is evidently begun, it is much promoted by stimulatingthe part externally by solutions of lead, or other metals, and internallyby the bark, and small doses of opium. Hence when an ophthalmy begins tobecome paler, any acrid eye-water, as a solution of six grains of whitevitriol in an ounce of water, hastens the absorption, and clears the eye ina very short time. But the same application used a few days sooner wouldhave increased the inflammation. Hence after evacuation opium in smalldoses may contribute to promote the absorption of fluids deposited on thebrain, as observed by Mr. Bromfield in his treatise of surgery. 2. Where an abscess is formed by the rupture of these new vessels, theviolence of inflammation ceases, and a new gland separates a materialcalled pus: at the same time a less degree of inflammation produces newvessels called vulgarly proud flesh; which, if no bandage confines itsgrowth, nor any other circumstance promotes absorption in the wound, wouldrise to a great height above the usual size of the part. Hence the art of healing ulcers consists in producing a tendency toabsorption in the wound greater than the deposition. Thus when anill-conditioned ulcer separates a copious and thin discharge, by the use ofany stimulus, as of salts of lead, or mercury, or copper externallyapplied, the discharge becomes diminished in quantity, and becomes thicker, as the thinner parts are first absorbed. But nothing so much contributes to increase the absorption in a wound ascovering the whole limb above the sore with a bandage, which should bespread with some plaster, as with emplastrum de minio, to prevent it fromslipping. By this artificial tightness of the skin, the arterial pulsationsact with double their usual power in promoting the ascending current of thefluid in the valvular lymphatics. Internally the absorption from ulcers should be promoted first byevacuation, then by opium, bark, mercury, steel. 3. Where the inflammation proceeds with greater violence or rapidity, thatis, when by the painful sensation a more inordinate activity of the organis produced, and by this great activity an additional quantity of painfulsensation follows in an increasing ratio, till the whole of the sensorialpower, or spirit of animation, in the part becomes exhausted, amortification ensues, as in a carbuncle, in inflammations of the bowels, inthe extremities of old people, or in the limbs of those who are broughtnear a fire after having been much benumbed with cold. And from hence itappears, why weak people are more subject to mortification than strongones, and why in weak persons less pain will produce mortification, namely, because the sensorial power is sooner exhausted by any excess of activity. I remember seeing a gentleman who had the preceding day travelled twostages in a chaise with what he termed a bearable pain in his bowels; whichwhen I saw him had ceased rather suddenly, and without a passage throughhim; his pulse was then weak, though not very quick; but as nothing whichhe swallowed would continue in his stomach many minutes, I concluded thatthe bowel was mortified; he died on the next day. It is usual for patientssinking under the small-pox with mortified pustules, and with purple spotsintermixed, to complain of no pain, but to say they are pretty well to thelast moment. _Recapitulation. _ IV. When the motions of any part of the system, in consequence of previoustorpor, are performed with more energy than in the irritative fevers, adisagreeable sensation is produced, and new actions of some part of thesystem commence in consequence of this sensation conjointly with theirritation: which motions constitute inflammation. If the fever be attendedwith a strong pulse, as in pleurisy, or rheumatism, it is termed synochasensitiva, or sensitive fever with strong pulse; which is usually termedinflammatory fever. If it be attended with weak pulse, it is termed typhussensitivus, or sensitive fever with weak pulse, or typhus gravior, orputrid malignant fever. The synocha sensitiva, or sensitive fever with strong pulse, is generallyattended with some topical inflammation, as in peripneumony, hepatitis, andis accompanied with much coagulable lymph, or size; which rises to thesurface of the blood, when taken into a bason, as it cools; and which isbelieved to be the increased mucous secretion from the coats of thearteries, inspissated by a greater absorption of its aqueous and salinepart, and perhaps changed by its delay in the circulation. The typhus sensitivus, or sensitive fever with weak pulse, is frequentlyattended with delirium, which is caused by the deficiency of the quantityof sensorial power, and with variety of cutaneous eruptions. Inflammation is caused by the pains occasioned by excess of action, and notby those pains which are occasioned by defect of action. These morbidactions, which are thus produced by two sensorial powers, viz. Byirritation and sensation, secrete new living fibres, which elongate the oldvessels, or form new ones, and at the same time much heat is evolved fromthese combinations. By the rupture of these vessels, or by a newconstruction of their apertures, purulent matters are secreted of variouskinds; which are infectious the first time they are applied to the skinbeneath the cuticle, or swallowed with the saliva into the stomach. Thiscontagion acts not by its being absorbed into the circulation, but by thesympathies, or associated actions, between the part first stimulated by thecontagious matter and the other parts of the system. Thus in the naturalsmall-pox the contagion is swallowed with the saliva, and by its stimulusinflames the stomach; this variolous inflammation of the stomach increasesevery day, like the circle round the puncture of an inoculated arm, till itbecomes great enough to disorder the circles of irritative and sensitivemotions, and thus produces fever-fits, with sickness and vomiting. Lastly, after the cold paroxysm, or fit of torpor, of the stomach has increased fortwo or three successive days, an inflammation of the skin commences inpoints; which generally first appear upon the face, as the associatedactions between the skin of the face and that of the stomach have been morefrequently exerted together than those of any other parts of the externalsurface. Contagious matters, as those of the measles and small-pox, do not act uponthe system at the same time; but the progress of that which was lastreceived is delayed, till the action of the former infection ceases. Allkinds of matter, even that from common ulcers, are probably contagious thefirst time they are inserted beneath the cuticle or swallowed into thestomach; that is, as they were formed by certain morbid actions of theextremities of the vessels, they have the power to excite similar morbidactions in the extremities of other vessels, to which they are applied; andthese by sympathy, or associations of motion, excite similar morbid actionsin distant parts of the system, without entering the circulation; and hencethe blood of a patient in the small-pox will not give that disease byinoculation to others. When the new fibres or vessels become again absorbed into the circulation, the inflammation ceases; which is promoted, after sufficient evacuations, by external stimulants and bandages: but where the action of the vessels isvery great, a mortification of the part is liable to ensue, owing to theexhaustion of sensorial power; which however occurs in weak people withoutmuch pain, and without very violent previous inflammation; and, likepartial paralysis, may be esteemed one mode of natural death of old people, a part dying before the whole. * * * * * SECT. XXXIV. DISEASES OF VOLITION. I. 1. _Volition defined. Motions termed involuntary are caused by volition. Desires opposed to each other. Deliberation. Ass between two hay-cocks. Saliva swallowed against one's desire. Voluntary motions distinguished from those associated with sensitive motions. _ 2. _Pains from excess, and from defect of motion. No pain is felt during vehement voluntary exertion; as in cold fits of ague, labour-pains, strangury, tenesmus, vomiting, restlessness in fevers, convulsion of a wounded muscle. _ 3. _Of holding the breath and screaming in pain; why swine and dogs cry out in pain, and not sheep and horses. Of grinning and biting in pain; why mad animals bite others. _ 4. _Epileptic convulsions explained, why the fits begin with quivering of the under jaw, biting the tongue, and setting the teeth; why the convulsive motions are alternately relaxed. The phenomenon of laughter explained. Why children cannot tickle themselves. How some have died from immoderate laughter. _ 5. _Of cataleptic spasms, of the locked jaw, of painful cramps. _ 6. _Syncope explained. Why no external objects are perceived in syncope. _ 7. _Of palsy and apoplexy from violent exertions. Case of Mrs. Scot. From dancing, scating, swimming. Case of Mr. Nairn. Why palsies are not always immediately preceded by violent exertions. Palsy and epilepsy from diseased livers. Why the right arm more frequently paralytic than the left. How paralytic limbs regain their motions. _ II. _Diseases of the sensual motions from excess or defect of voluntary exertion. _ 1. _Madness. _ 2. _Distinguished from delirium. _ 3. _Why mankind more liable to insanity than brutes. _ 4. _Suspicion. Want of shame, and of cleanliness. _ 5. _They bear cold, hunger, and fatigue. Charles XII. Of Sweden. _ 6. _Pleasureable delirium, and insanity. Child riding on a stick. Pains of martyrdom not felt. _ 7. _Dropsy. _ 8. _Inflammation cured by insanity. _ III. 1. _Pain relieved by reverie. Reverie is an exertion of voluntary and sensitive motions. _ 2. _Case of reverie. _ 3. _Lady supposed to have two souls. _ 4. _Methods of relieving pain. _ I. 1. Before we commence this Section on Diseased Voluntary Motions, it maybe necessary to premise, that the word volition is not used in this workexactly in its common acceptation. Volition is said in Section V. To bearthe same analogy to desire and aversion, which sensation does to pleasureand pain. And hence that, when desire or aversion produces any action ofthe muscular fibres, or of the organs of sense, they are termed volition;and the actions produced in consequence are termed voluntary actions. Whence it appears, that motions of our muscles or ideas may be produced inconsequence of desire or aversion without our having the power to preventthem, and yet these motions may be termed voluntary, according to ourdefinition of the word; though in common language they would be calledinvoluntary. The objects of desire and aversion are generally at a distance, whereasthose of pleasure and pain are immediately acting upon our organs. Hence, before desire or aversion are exerted, so as to cause any actions, there isgenerally time for deliberation; which consists in discovering the means toobtain the object of desire, or to avoid the object of aversion; or inexamining the good or bad consequences, which may result from them. In thiscase it is evident, that we have a power to delay the proposed action, orto perform it; and this power of choosing, whether we shall act or not, isin common language expressed by the word volition, or will. Whereas in thiswork the word volition means simply the active state of the sensorialfaculty in producing motion in consequence of desire or aversion: whetherwe have the power of restraining that action, or not; that is, whether weexert any actions in consequence of opposite desires or aversions, or not. For if the objects of desire or aversion are present, there is no necessityto investigate or compare the _means_ of obtaining them, nor do we alwaysdeliberate about their consequences; that is, no deliberation necessarilyintervenes, and in consequence the power of choosing to act or not is notexerted. It is probable, that this twofold use of the word volition in alllanguages has confounded the metaphysicians, who have disputed about freewill and necessity. Whereas from the above analysis it would appear, thatduring our sleep, we use no voluntary exertions at all; and in our wakinghours, that they are the consequence of desire or aversion. To will is to act in consequence of desire; but to desire means to desiresomething, even if that something be only to become free from the pain, which causes the desire; for to desire nothing is not to desire; the worddesire, therefore, includes both the action and the object or motive; forthe object and motive of desire are the same thing. Hence to desire withoutan object, that is, without a motive, is a solecism in language. As if oneshould ask, if you could eat without food, or breathe without air. From this account of volition it appears, that convulsions of the muscles, as in epileptic fits, may in the common sense of that word be termedinvoluntary; because no deliberation is interposed between the desire oraversion and the consequent action; but in the sense of the word, as abovedefined, they belong to the class of voluntary motions, as delivered inVol. II. Class III. If this use of the word be discordant to the ear of thereader, the term morbid voluntary motions, or motions in consequence ofaversion, may be substituted in its stead. If a person has a desire to be cured of the ague, and has at the same timean aversion (or contrary desire) to swallowing an ounce of Peruvian bark;he balances desire against desire, or aversion against aversion; and thushe acquires the power of choosing, which is the common acceptation of theword _willing_. But in the cold fit of ague, after having discovered thatthe act of shuddering, or exerting the subcutaneous muscles, relieves thepain of cold; he immediately exerts this act of volition, and shudders, assoon as the pain and consequent aversion return, without any deliberationintervening; yet is this act, as well as that of swallowing an ounce of thebark, caused by volition; and that even though he endeavours in vain toprevent it by a weaker contrary volition. This recalls to our minds thestory of the hungry ass between two hay-stacks, where the two desires aresupposed so exactly to counteract each other, that he goes to neither ofthe stacks, but perishes by want. Now as two equal and opposite desires arethus supposed to balance each other, and prevent all action, it follows, that if one of these hay-stacks was suddenly removed, that the ass wouldirresistibly be hurried to the other, which in the common use of the wordmight be called an involuntary act; but which, in our acceptation of it, would be classed amongst voluntary actions, as above explained. Hence to deliberate is to compare opposing desires or aversions, and thatwhich is the most interesting at length prevails, and produces action. Similar to this, where two pains oppose each other, the stronger or moreinteresting one produces action; as in pleurisy the pain from suffocationwould produce expansion of the lungs, but the pain occasioned by extendingthe inflamed membrane, which lines the chest, opposes this expansion, andone or the other alternately prevails. When any one moves his hand quickly near another person's eyes, theeye-lids instantly close; this act in common language is termedinvoluntary, as we have not time to deliberate or to exert any contrarydesire or aversion, but in this work it would be termed a voluntary act, because it is caused by the faculty of volition, and after a few trials thenictitation can be prevented by a contrary or opposing volition. The power of opposing volitions is best exemplified in the story of MutiusScævola, who is said to have thrust his hand into the fire before Porcenna, and to have suffered it to be consumed for having failed him in his attempton the life of that general. Here the aversion for the loss of same, or theunsatisfied desire to serve his country, the two prevalent enthusiasms atthat time, were more powerful than the desire of withdrawing his hand, which must be occasioned by the pain of combustion; of these opposingvolitions Vincit amor patriæ, laudumque immensa cupido. If any one is told not to swallow his saliva for a minute, he soon swallowsit contrary to his will, in the common sense of that word; but this also isa voluntary action, as it is performed by the faculty of volition, and isthus to be understood. When the power of volition is exerted on any of oursenses, they become more acute, as in our attempts to hear small noises inthe night. As explained in Section XIX. 6. Hence by our attention to thefauces from our desire not to swallow our saliva; the fauces become moresensible; and the stimulus of the saliva is followed by greater sensation, and consequent desire of swallowing it. So that the desire or volition inconsequence of the increased sensation of the saliva is more powerful, thanthe previous desire not to swallow it. See Vol. II. Deglutitio invita. Inthe same manner if a modest man wishes not to want to make water, when heis confined with ladies in a coach or an assembly-room; that very act ofvolition induces the circumstance, which he wishes to avoid, as aboveexplained; insomuch that I once saw a partial insanity, which might becalled a voluntary diabetes, which was occasioned by the fear (andconsequent aversion) of not being able to make water at all. It is further necessary to observe here, to prevent any confusion ofvoluntary, with sensitive, or associate motions, that in all the instancesof violent efforts to relieve pain, those efforts are at first voluntaryexertions; but after they have been frequently repeated for the purpose ofrelieving certain pains, they become associated with those pains, and ceaseat those times to be subservient to the will; as in coughing, sneezing, andstrangury. Of these motions those which contribute to remove or dislodgethe offending cause, as the actions of the abdominal muscles in parturitionor in vomiting, though they were originally excited by volition, are inthis work termed sensitive motions; but those actions of the muscles ororgans of sense, which do not contribute to remove the offending cause, asin general convulsions or in madness, are in this work termed voluntarymotions, or motions in consequence of aversion, though in common languagethey are called involuntary ones. Those sensitive unrestrainable actions, which contribute to remove the cause of pain are uniformly and invariablyexerted, as in coughing or sneezing; but those motions which are exerted inconsequence of aversion without contributing to remove the painful cause, but only to prevent the sensation of it, as in epileptic, or catalepticfits, are not uniformly and invariably exerted, but change from one set ofmuscles to another, as will be further explained; and may by this criterionalso be distinguished from the former. At the same time those motions, which are excited by perpetual stimulus, orby association with each other, or immediately by pleasureable or painfulsensation, may properly be termed involuntary motions, as those of theheart and arteries; as the faculty of volition seldom affects those, exceptwhen it exists in unnatural quantity, as in maniacal people. 2. It was observed in Section XIV. On the Production of Ideas, that thoseparts of the system, which are usually termed the organs of sense, areliable to be excited into pain by the excess of the stimulus of thoseobjects, which are by nature adapted to affect them; as of too great light, sound, or pressure. But that these organs receive no pain from the defector absence of these stimuli, as in darkness or silence. But that our otherorgans of perception, which have generally been called appetites, as ofhunger, thirst, want of heat, want of fresh air, are liable to be affectedwith pain by the defect, as well as by the excess of their appropriatedstimuli. This excess or defect of stimulus is however to be considered only as theremote cause of the pain, the immediate cause being the excess or defect ofthe natural action of the affected part, according to Sect. IV. 5. Henceall the pains of the body may be divided into those from excess of motion, and those from defect of motion; which distinction is of great importancein the knowledge and the cure of many diseases. For as the pains fromexcess of motion either gradually subside, or are in general succeeded byinflammation; so those from defect of motion either gradually subside, orare in general succeeded by convulsion, or madness. These pains are easilydistinguishable from each other by this circumstance, that the former areattended with heat of the pained part, or of the whole body; whereas thelatter exists without increase of heat in the pained part, and is generallyattended with coldness of the extremities of the body; which is the truecriterion of what have been called nervous pains. Thus when any acrid material, as snuff or lime, falls into the eye, painand inflammation and heat are produced from the excess of stimulus; butviolent hunger, hemicrania, or the clavus hystericus, are attended withcoldness of the extremities, and defect of circulation. When we are exposedto great cold, the pain we experience from the deficiency of heat isattended with a quiescence of the motions of the vascular system; so thatno inflammation is produced, but a great desire of heat, and a tremulousmotion of the subcutaneous muscles, which is properly a convulsion inconsequence of this pain from defect of the stimulus of heat. It was before mentioned, that as sensation consists in certain movements ofthe sensorium, beginning at some of the extremities of it, and propagatedto the central parts of it; so volition consists of certain other movementsof the sensorium, commencing in the central parts of it, and propagated tosome of its extremities. This idea of these two great powers of motion inthe animal machine is confirmed from observing, that they never exist in agreat degree or universally at the same time; for while we strongly exertour voluntary motions, we cease to feel the pains or uneasinesses, whichoccasioned us to exert them. Hence during the time of fighting with fists or swords no pain is felt bythe combatants, till they cease to exert themselves. Thus in the beginningof ague-fits the painful sensation of cold is diminished, while the patientexerts himself in the shivering and gnashing of his teeth. He then ceasesto exert himself, and the pain of cold returns; and he is thus perpetuallyinduced to reiterate these exertions, from which he experiences a temporaryrelief. The same occurs in labour-pains, the exertion of the parturientwoman relieves the violence of the pains for a time, which recur again soonafter she has ceased to use those exertions. The same is true in many otherpainful diseases, as in the strangury, tenesmus, and the efforts ofvomiting; all these disagreeable sensations are diminished or removed for atime by the various exertions they occasion, and recur alternately withthose exertions. The restlessness in some fevers is an almost perpetual exertion of thiskind, excited to relieve some disagreeable sensations; the reciprocalopposite exertions of a wounded worm, the alternate emprosthotonos andopisthotonos of some spasmodic diseases, and the intervals of allconvulsions, from whatever cause, seem to be owing to this circumstance ofthe laws of animation; that great or universal exertion cannot exist at thesame time with great or universal sensation, though they can existreciprocally; which is probably resolvable into the more general law, thatthe whole sensorial power being expended in one mode of exertion, there isnone to spare for any other. Whence syncope, or temporary apoplexy, succeeds to epileptic convulsions. 3. Hence when any violent pain afflicts us, of which we can neither avoidnor remove the cause, we soon learn to endeavour to alleviate it, byexerting some violent voluntary effort, as mentioned above; and arenaturally induced to use those muscles for this purpose, which have been inthe early periods of our lives most frequently or most powerfully exerted. Now the first muscles, which infants use most frequently, are those ofrespiration; and on this account we gain a habit of holding our breath, atthe same time that we use great efforts to exclude it, for this purpose ofalleviating unavoidable pain; or we press out our breath through a smallaperture of the larynx, and scream violently, when the pain is greater thanis relievable by the former mode of exertion. Thus children scream torelieve any pain either of body or mind, as from anger, or fear of beingbeaten. Hence it is curious to observe, that those animals, who have morefrequently exerted their muscles of respiration violently, as in talking, barking, or grunting, as children, dogs, hogs, scream much more, when theyare in pain, than those other animals, who use little or no language intheir common modes of life; as horses, sheep, and cows. The next most frequent or most powerful efforts, which infants are firsttempted to produce, are those with the muscles in biting hard substances;indeed the exertion of these muscles is very powerful in commonmastication, as appears from the pain we receive, if a bit of bone isunexpectedly found amongst our softer food; and further appears from theiracting to so great mechanical disadvantage, particularly when we bite withthe incisores, or canine teeth; which are first formed, and thence arefirst used to violent exertion. Hence when a person is in great pain, the cause of which he cannot remove, he sets his teeth firmly together, or bites some substance between themwith great vehemence, as another mode of violent exertion to produce atemporary relief. Thus we have a proverb where no help can be had in pain, "to grin and abide;" and the tortures of hell are said to be attended with"gnashing of teeth. " Hence in violent spasmodic pains I have seen people bite not only theirtongues, but their arms or fingers, or those of the attendants, or anyobject which was near them; and also strike, pinch, or tear, others orthemselves, particularly the part of their own body, which is painful atthe time. Soldiers, who die of painful wounds in battle, are said in Homerto bite the ground. Thus also in the bellon, or colica saturnina, thepatients are said to bite their own flesh, and dogs in this disease to biteup the ground they lie upon. It is probable that the great endeavours tobite in mad dogs, and the violence of other mad animals, is owing to thesame cause. 4. If the efforts of our voluntary motions are exerted with still greaterenergy for the relief of some disagreeable sensation, convulsions areproduced; as the various kinds of epilepsy, and in some hysteric paroxysms. In all these diseases a pain, or disagreeable sensation is produced, frequently by worms, or acidity in the bowels, or by a diseased nerve inthe side, or head, or by the pain of a diseased liver. In some constitutions a more intolerable degree of pain is produced in somepart at a distance from the cause by sensitive association, as beforeexplained; these pains in such constitutions arise to so great a degree, that I verily believe no artificial tortures could equal some, which I havewitnessed; and am confident life would not have long been preserved, unlessthey had been soon diminished or removed by the universal convulsion of thevoluntary motions, or by temporary madness. In some of the unfortunate patients I have observed, the pain has risen toan inexpressible degree, as above described, before the convulsions havesupervened; and which were preceded by screaming, and grinning; in others, as in the common epilepsy, the convulsion has immediately succeeded thecommencement of the disagreeable sensations; and as a stupor frequentlysucceeds the convulsions, they only seemed to remember that a pain at thestomach preceded the fit, or some other uneasy feel; or more frequentlyretained no memory at all of the immediate cause of the paroxysm. But evenin this kind of epilepsy, where the patient does not recollect anypreceding pain, the paroxysms generally are preceded by a quivering motionof the under jaw, with a biting of the tongue; the teeth afterwards becomepressed together with vehemence, and the eyes are then convulsed, beforethe commencement of the universal convulsion; which are all efforts torelieve pain. The reason why these convulsive motions are alternately exerted andremitted was mentioned above, and in Sect. XII. 1. 3. When the exertionsare such as give a temporary relief to the pain, which excites them, theycease for a time, till the pain is again perceived; and then new exertionsare produced for its relief. We see daily examples of this in the loudreiterated laughter of some people; the pleasureable sensation, whichexcites this laughter, arises for a time so high as to change its name andbecome painful: the convulsive motions of the respiratory muscles relievethe pain for a time; we are, however, unwilling to lose the pleasure, andpresently put a stop to this exertion, and immediately the pleasure recurs, and again as instantly rises into pain. All of us have felt the pain ofimmoderate laughter; children have been tickled into convulsions of thewhole body; and others have died in the act of laughing; probably from aparalysis succeeding the long continued actions of the muscles ofrespiration. Hence we learn the reason, why children, who are so easily excited to laughby the tickling of other people's fingers, cannot tickle themselves intolaughter. The exertion of their hands in the endeavour to tickle themselvesprevents the necessity of any exertion of the respiratory muscles torelieve the excess of pleasurable affection. See Sect. XVII. 3. 5. Chrysippus is recorded to have died laughing, when an ass was invited tosup with him. The same is related of one of the popes, who, when he wasill, saw a tame monkey at his bedside put on the holy thiara. Hall. Phys. T. III. P. 306. There are instances of epilepsy being produced by laughing recorded by VanSwieten, T. III. 402 and 308. And it is well known, that many people havedied instantaneously from the painful excess of joy, which probably mighthave been prevented by the exertions of laughter. Every combination of ideas, which we attend to, occasions pain or pleasure;those which occasion pleasure, furnish either social or selfish pleasure, either malicious or friendly, or lascivious, or sublime pleasure; that is, they give us pleasure mixed with other emotions, or they give us unmixedpleasure, without occasioning any other emotions or exertions at the sametime. This unmixed pleasure, if it be great, becomes painful, like allother animal motions from stimuli of every kind; and if no other exertionsare occasioned at the same time, we use the exertion of laughter to relievethis pain. Hence laughter is occasioned by such wit as excites simplepleasure without any other emotion, such as pity, love, reverence. Forsublime ideas are mixed with admiration, beautiful ones with love, new oneswith surprise; and these exertions of our ideas prevent the action oflaughter from being necessary to relieve the painful pleasure abovedescribed. Whence laughable wit consists of frivolous ideas, withoutconnections of any consequence, such as puns on words, or on phrases, incongruous junctions of ideas; on which account laughter is so frequent inchildren. Unmixed pleasure less than that, which causes laughter, causes sleep, as insinging children to sleep, or in slight intoxication from wine or food. SeeSect. XVIII. 12. 5. If the pains, or disagreeable sensations, above described do not obtaina temporary relief from these convulsive exertions of the muscles, thoseconvulsive exertions continue without remission, and one kind of catalepsyis produced. Thus when a nerve or tendon produces great pain by its beinginflamed or wounded, the patient sets his teeth firmly together, and grinsviolently, to diminish the pain; and if the pain is not relieved by thisexertion, no relaxation of the maxillary muscles takes place, as in theconvulsions above described, but the jaws remain firmly fixed together. This locked jaw is the most frequent instance of cataleptic spasm, becausewe are more inclined to exert the muscles subservient to mastication fromtheir early obedience to violent efforts of volition. But in the case related in Sect. XIX. On Reverie, the cataleptic lady hadpain in her upper teeth; and pressing one of her hands vehemently againsther cheek-bone to diminish this pain, it remained in that attitude forabout half an hour twice a day, till the painful paroxysm was over. I have this very day seen a young lady in this disease, (with which she hasfrequently been afflicted, ) she began to-day with violent pain shootingfrom one side of the forehead to the occiput, and after various struggleslay on the bed with her fingers and wrists bent and stiff for about twohours; in other respects she seemed in a syncope with a natural pulse. Shethen had intervals of pain and of spasm, and took three grains of opiumevery hour till she had taken nine grains, before the pains and spasmceased. There is, however, another species of fixed spasm, which differs from theformer, as the pain exists in the contracted muscle, and would seem ratherto be the consequence than the cause of the contraction, as in the cramp inthe calf of the leg, and in many other parts of the body. In these spasms it should seem, that the muscle itself is first thrown intocontraction by some disagreeable sensation, as of cold; and that then theviolent pain is produced by the great contraction of the muscular fibresextending its own tendons, which are said to be sensible to extension only;and is further explained in Sect. XVIII. 15. 6. Many instances have been given in this work, where after violent motionsexcited by irritation, the organ has become quiescent to less, and even tothe great irritation, which induced it into violent motion; as afterlooking long at the sun or any bright colour, they cease to be seen; andafter removing from bright day-light into a gloomy room, the eye cannot atfirst perceive the objects, which stimulate it less. Similar to this is thesyncope, which succeeds after the violent exertions of our voluntarymotions, as after epileptic fits, for the power of volition acts in thiscase as the stimulus in the other. This syncope is a temporary palsy, orapoplexy, which ceases after a time, the muscles recovering their power ofbeing excited into action by the efforts of volition; as the eye in thecircumstance above mentioned recovers in a little time its power of seeingobjects in a gloomy room; which were invisible immediately after coming outof a stronger light. This is owing to an accumulation of sensorial powerduring the inaction of those fibres, which were before accustomed toperpetual exertions, as explained in Sect. XII. 7. 1. A slighter degree ofthis disease is experienced by every one after great fatigue, when themuscles gain such inability to further action, that we are obliged to restthem for a while, or to summon a greater power of volition to continuetheir motions. In all the syncopes, which I have seen induced after convulsive fits, thepulse has continued natural, though the organs of sense, as well as thelocomotive muscles, have ceased to perform their functions; for it isnecessary for the perception of objects, that the external organs of senseshould be properly excited by the voluntary power, as the eye-lids must beopen, and perhaps the muscles of the eye put into action to distend, andthence give greater pellucidity to the cornea, which in syncope, as indeath, appears flat and less transparent. The tympanum of the ear also seems to require a voluntary exertion of itsmuscles, to gain its due tension, and it is probable the other externalorgans of sense require a similar voluntary exertion to adapt them to thedistinct perception of objects. Hence in syncope as in sleep, as the powerof volition is suspended, no external objects are perceived. See Sect. XVIII. 5. During the time which the patient lies in a fainting fit, thespirit of animation becomes accumulated; and hence the muscles in a whilebecome irritable by their usual stimulation, and the fainting fit ceases. See Sect. XII. 7. 1. 7. If the exertion of the voluntary motions has been still more energetic, the quiescence, which succeeds, is so complete, that they cannot again beexcited into action by the efforts of the will. In this manner the palsy, and apoplexy (which is an universal palsy) are frequently produced afterconvulsions, or other violent exertions; of this I shall add a fewinstances. Platernus mentions some, who have died apoplectic from violent exertions indancing; and Dr. Mead, in his Essay on Poisons, records a patient in thehydrophobia, who at one effort broke the cords which bound him, and at thesame instant expired. And it is probable, that those, who have expired fromimmoderate laughter, have died from this paralysis consequent to violentexertion. Mrs. Scott of Stafford was walking in her garden in perfecthealth with her neighbour Mrs. ----; the latter accidentally fell into amuddy rivulet, and tried in vain to disengage herself by the assistance ofMrs. Scott's hand. Mrs. Scott exerted her utmost power for many minutes, first to assist her friend, and next to prevent herself from being pulledinto the morass, as her distressed companion would not disengage her hand. After other assistance was procured by their united screams, Mrs. Scottwalked to a chair about twenty yards from the brook, and was seized with anapoplectic stroke: which continued many days, and terminated in a totalloss of her right arm, and her speech; neither of which she ever afterperfectly recovered. It is said, that many people in Holland have died after skating too long ortoo violently on their frozen canals; it is probable the death of these, and of others, who have died suddenly in swimming, has been owing to thisgreat quiescence or paralysis; which has succeeded very violent exertions, added to the concomitant cold, which has had greater effect after thesufferers had been heated and exhausted by previous exercise. I remember a young man of the name of Nairne at Cambridge, who walking onthe edge of a barge fell into the river. His cousin and fellow-student ofthe same name, knowing the other could not swim, plunged into the waterafter him, caught him by his clothes, and approaching the bank by avehement exertion propelled him safe to the land, but that instant, seized, as was supposed, by the cramp, or paralysis, sunk to rise no more. Thereason why the cramp of the muscles, which compose the calf of the leg, isso liable to affect swimmers, is, because these muscles have very weakantagonists, and are in walking generally elongated again after theircontraction by the weight of the body on the ball of the toe, which is verymuch greater than the resistance of the water in swimming. See SectionXVIII. 15. It does not follow that every apoplectic or paralytic attack is immediatelypreceded by vehement exertion; the quiescence, which succeeds exertion, andwhich is not so great as to be termed paralysis, frequently recursafterwards at certain periods; and by other causes of quiescence, occurringwith those periods, as was explained in treating of the paroxysms ofintermitting fevers; the quiescence at length, becomes so great as to beincapable of again being removed by the efforts of volition, and completeparalysis is formed. See Section XXXII. 3. 2. Many of the paralytic patients, whom I have seen, have evidently haddiseased livers from the too frequent potation of spirituous liquors; someof them have had the gutta rosea on their faces and breasts; which has insome degree receded either spontaneously, or by the use of externalremedies, and the paralytic stroke has succeeded; and as in severalpersons, who have drank much vinous spirits, I have observed epileptic fitsto commence at about forty or fifty years of age, without any hereditarytaint, from the stimulus, as I believed, of a diseased liver; I was inducedto ascribe many paralytic cases to the same source; which were notevidently the effect of age, or of unacquired debility. And the accountgiven before of dropsies, which very frequently are owing to a paralysis ofthe absorbent system, and are generally attendant on free drinkers ofspirituous liquors, confirmed me in this opinion. The disagreeable irritation of a diseased liver produces exertions andconsequent quiescence; these by the accidental concurrence of other causesof quiescence, as cold, solar or lunar periods, inanition, the want oftheir usual portion of spirit of wine, at length produces paralysis. This is further confirmed by observing, that the muscles, we mostfrequently, or most powerfully exert, are most liable to palsy; as those ofthe voice and of articulation, and of those paralytics which I have seen, amuch greater proportion have lost the use of their right arm; which is somuch more generally exerted than the left. I cannot dismiss this subject without observing, that after a paralyticstroke, if the vital powers are not much injured, that the patient has allthe movements of the affected limb to learn over again, just as in earlyinfancy; the limb is first moved by the irritation of its muscles, as instretching, (of which a case was related in Section VII. 1. 3. ) or by theelectric concussion; afterwards it becomes obedient to sensation, as inviolent danger or fear; and lastly, the muscles become again associatedwith volition, and gradually acquire their usual habits of acting together. Another phænomenon in palsies is, that when the limbs of one side aredisabled, those of the other are in perpetual motion. This can only beexplained from conceiving that the power of motion, whatever it is, orwherever it resides, and which is capable of being exhausted by fatigue, and accumulated in rest, is now less expended, whilst one half of the bodyis capable of receiving its usual proportion of it, and is hence derivedwith greater ease or in greater abundance into the limbs, which remainunaffected. II. 1. The excess or defect of voluntary exertion produces similar effectsupon the sensual motions, or ideas of the mind, as those already mentionedupon the muscular fibres. Thus when any violent pain, arising from thedefect of some peculiar stimulus, exists either in the muscular or sensualsystems of fibres, and which cannot be removed by acquiring the defectivestimulus; as in some constitutions convulsions of the muscles are producedto procure a temporary relief, so in other constitutions vehement voluntaryexertions of the ideas of the mind are produced for the same purpose; forduring this exertion, like that of the muscles, the pain either vanishes oris diminished: this violent exertion constitutes madness; and in many casesI have seen the madness take place, and the convulsions cease, andreciprocally the madness cease, and the convulsions supervene. See SectionIII. 5. 8. 2. Madness is distinguishable from delirium, as in the latter the patientknows not the place where he resides, nor the persons of his friends orattendants, nor is conscious of any external objects, except when spoken towith a louder voice, or stimulated with unusual force, and even then hesoon relapses into a state of inattention to every thing about him. Whilstin the former he is perfectly sensible to every thing external, but has thevoluntary powers of his mind intensely exerted on some particular object ofhis desire or aversion, he harbours in his thoughts a suspicion of allmankind, lest they should counteract his designs; and while he keeps hisintentions, and the motives of his actions profoundly secret; he isperpetually studying the means of acquiring the object of his wish, or ofpreventing or revenging the injuries he suspects. 3. A late French philosopher, Mr. Helvetius, has deduced almost all ouractions from this principle of their relieving us from the ennui or tædiumvitæ; and true it is, that our desires or aversions are the motives of allour voluntary actions; and human nature seems to excel other animals in themore facil use of this voluntary power, and on that account is more liableto insanity than other animals. But in mania this violent exertion ofvolition is expended on mistaken objects, and would not be relieved, thoughwe were to gain or escape the objects, that excite it. Thus I have seen twoinstances of madmen, who conceived that they had the itch, and several havebelieved they had the venereal infection, without in reality having asymptom of either of them. They have been perpetually thinking upon thissubject, and some of them were in vain salivated with design of convincingthem to the contrary. 4. In the minds of mad people those volitions alone exist, which areunmixed with sensation; immoderate suspicion is generally the firstsymptom, and want of shame, and want of delicacy about cleanliness. Suspicion is a voluntary exertion of the mind arising from the pain offear, which it is exerted to relieve: shame is the name of a peculiardisagreeable sensation, see Fable of the Bees, and delicacy aboutcleanliness arises from another disagreeable sensation. And therefore arenot found in the minds of maniacs, which are employed solely in voluntaryexertions. Hence the most modest women in this disease walk naked amongstmen without any kind of concern, use obscene discourse, and have nodelicacy about their natural evacuations. 5. Nor are maniacal people more attentive to their natural appetites, or tothe irritations which surround them, except as far as may respect theirsuspicions or designs; for the violent and perpetual exertions of theirvoluntary powers of mind prevents their perception of almost every otherobject, either of irritation or of sensation. Hence it is that they bearcold, hunger, and fatigue, with much greater pertinacity than in theirsober hours, and are less injured by them in respect to their generalhealth. Thus it is asserted by historians, that Charles the Twelfth ofSweden slept on the snow, wrapped only in his cloak, at the siege ofFrederickstad, and bore extremes of cold and hunger, and fatigue, underwhich numbers of his soldiers perished; because the king was insane withambition, but the soldier had no such powerful stimulus to preserve hissystem from debility and death. 6. Besides the insanities arising from exertions in consequence of pain, there is also a pleasurable insanity, as well as a pleasurable delirium; asthe insanity of personal vanity, and that of religious fanaticism. Whenagreeable ideas excite into motion the sensorial power of sensation, andthis again causes other trains of agreeable ideas, a constant stream ofpleasurable ideas succeeds, and produces pleasurable delirium. So when thesensorial power of volition excites agreeable ideas, and the pleasure thusproduced excites more volition in its turn, a constant flow of agreeablevoluntary ideas succeeds; which when thus exerted in the extremeconstitutes insanity. Thus when our muscular actions are excited by our sensations of pleasure, it is termed play; when they are excited by our volition, it is termedwork; and the former of these is attended with less fatigue, because themuscular actions in play produce in their turn more pleasurable sensation;which again has the property of producing more muscular action. Anagreeable instance of this I saw this morning. A little boy, who was tiredwith walking, begged of his papa to carry him. "Here, " says the reverenddoctor, "ride upon my gold-headed cane;" and the pleased child, putting itbetween his legs, gallopped away with delight, and complained no more ofhis fatigue. Here the aid of another sensorial power, that of pleasurablesensation, superadded vigour to the exertion of exhausted volition. Whichcould otherwise only have been excited by additional pain, as by the lashof slavery. On this account where the whole sensorial power has beenexerted on the contemplation of the promised joys of heaven, the saints ofall persecuted religions have borne the tortures of martyrdom withotherwise unaccountable firmness. 7. There are some diseases, which obtain at least a temporary relief fromthe exertions of insanity; many instances of dropsies being thus for a timecured are recorded. An elderly woman labouring with ascites I twice sawrelieved for some weeks by insanity, the dropsy ceased for several weeks, and recurred again alternating with the insanity. A man afflicted withdifficult respiration on lying down, with very irregular pulse, andoedematous legs, whom I saw this day, has for above a week been muchrelieved in respect to all those symptoms by the accession of insanity, which is shewn by inordinate suspicion, and great anger. In cases of common temporary anger the increased action of the arterialsystem is seen by the red skin, and increased pulse, with the immediateincrease of muscular activity. A friend of mine, when he was painfullyfatigued by riding on horseback, was accustomed to call up ideas into hismind, which used to excite his anger or indignation, and thus for a time atleast relieved the pain of fatigue. By this temporary insanity, the effectof the voluntary power upon the whole of his system was increased; as inthe cases of dropsy above mentioned, it would appear, that the increasedaction of the voluntary faculty of the sensorium affected the absorbentsystem, as well as the secerning one. 8. In respect to relieving inflammatory pains, and removing fever, I haveseen many instances, as mentioned in Sect. XII. 2. 4. One lady, whom Iattended, had twice at some years interval a locked jaw, which relieved apain on her sternum with peripneumony. Two other ladies I saw, who towardsthe end of violent peripneumony, in which they frequently lost blood, wereat length cured by insanity supervening. In the former the increasedvoluntary exertion of the muscles of the jaw, in the latter that of theorgans of sense, removed the disease; that is, the disagreeable sensation, which had produced the inflammation, now excited the voluntary power, andthese new voluntary exertions employed or expended the superabundantsensorial power, which had previously been exerted on the arterial system, and caused inflammation. Another case, which I think worth relating, was of a young man abouttwenty; he had laboured under an irritative fever with debility for threeor four weeks, with very quick and very feeble pulse, and other usualsymptoms of that species of typhus, but at this time complained much andfrequently of pain of his legs and feet. When those who attended him werenearly in despair of his recovery, I observed with pleasure an insanity ofmind supervene: which was totally different from delirium, as he knew hisfriends, calling them by their names, and the room in which he lay, butbecame violently suspicious of his attendants, and calumniated withvehement oaths his tender mother, who sat weeping by his bed. On this hispulse became slower and firmer, but the quickness did not for some timeintirely cease, and he gradually recovered. In this case the introductionof an increased quantity of the power of volition gave vigour to thosemovements of the system, which are generally only actuated by the power ofirritation, and of association. Another case I recollect of a young man, about twenty-five, who had thescarlet-fever, with very quick pulse, and an universal eruption on hisskin, and was not without reason esteemed to be in great danger of hislife. After a few days an insanity supervened, which his friends mistookfor delirium, and he gradually recovered, and the cuticle peeled off. Fromthese and a few other cases I have always esteemed insanity to be afavourable sign in fevers, and have cautiously distinguished it fromdelirium. III. Another mode of mental exertion to relieve pain, is by producing atrain of ideas not only by the efforts of volition, as in insanity; but bythose of sensation likewise, as in delirium and sleep. This mental effortis termed reverie, or somnambulation, and is described more at large inSect. XIX. On that subject. But I shall here relate another case of thatwonderful disease, which fell yesterday under my eye, and to which I haveseen many analogous alienations of mind, though not exactly similar in allcircumstances. But as all of them either began or terminated with pain orconvulsion, there can be no doubt but that they are of epileptic origin, and constitute another mode of mental exertion to relieve some painfulsensation. 1. Master A. About nine years old, had been seized at seven every morningfor ten days with uncommon fits, and had had slight returns in theafternoon. They were supposed to originate from worms, and had been in vainattempted to be removed by vermifuge purges. As his fit was expected atseven yesterday morning, I saw him before that hour; he was asleep, seemedfree from pain, and his pulse natural. About seven he began to complain ofpain about his navel, or more to the left side, and in a few minutes hadexertions of his arms and legs like swimming. He then for half an hourhunted a pack of hounds; as appeared by his hallooing, and calling the dogsby their names, and discoursing with the attendants of the chase, describing exactly a day of hunting, which (I was informed) he hadwitnessed a year before, going through all the most minute circumstances ofit; calling to people, who were then present, and lamenting the absence ofothers, who were then also absent. After this scene he imitated, as he layin bed, some of the plays of boys, as swimming and jumping. He then sung anEnglish and then an Italian song; part of which with his eyes open, andpart with them closed, but could not be awakened or excited by anyviolence, which it was proper to use. After about an hour he came suddenly to himself with apparent surprise, andseemed quite ignorant of any part of what had passed, and after beingapparently well for half an hour, he suddenly fell into a great stupor, with slower pulse than natural, and a slow moaning respiration, in which hecontinued about another half hour, and then recovered. The sequel of this disease was favourable; he was directed one grain ofopium at six every morning, and then to rise out of bed; at half past sixhe was directed fifteen drops of laudanum in a glass of wine and water. Thefirst day the paroxysm became shorter, and less violent. The dose of opiumwas increased to one-half more, and in three or four days the fits lefthim. The bark and filings of iron were also exhibited twice a day; and Ibelieve the complaint returned no more. 2. In this paroxysm it must be observed, that he began with pain, and endedwith stupor, in both circumstances resembling a fit of epilepsy. And thattherefore the exertions both of mind and body, both the voluntary ones, andthose immediately excited by pleasurable sensation, were exertions torelieve pain. The hunting scene appeared to be rather an act of memory than ofimagination, and was therefore rather a voluntary exertion, though attendedwith the pleasurable eagerness, which was the consequence of those ideasrecalled by recollection, and not the cause of them. These ideas thus voluntarily recollected were succeeded by sensations ofpleasure, though his senses were unaffected by the stimuli of visible oraudible objects; or so weakly excited by them as not to produce sensationor attention. And the pleasure thus excited by volition produced otherideas and other motions in consequence of the sensorial power of sensation. Whence the mixed catenations of voluntary and sensitive ideas and muscularmotions in reverie; which, like every other kind of vehement exertion, contribute to relieve pain, by expending a large quantity of sensorialpower. Those fits generally commence during sleep, from whence I suppose they havebeen thought to have some connection with sleep, and have thence beentermed Somnambulism; but their commencement during sleep is owing to ourincreased excitability by internal sensations at that time, as explained inSect. XVIII. 14. And 15. , and not to any similitude between reverie andsleep. 3. I was once concerned for a very elegant and ingenious young lady, whohad a reverie on alternate days, which continued nearly the whole day; andas in her days of disease she took up the same kind of ideas, which she hadconversed about on the alternate day before, and could recollect nothing ofthem on her well-day; she appeared to her friends to possess two minds. This case also was of epileptic kind, and was cured, with some relapses, byopium administered before the commencement of the paroxysm. 4. Whence it appears, that the methods of relieving inflammatory pains, isby removing all stimulus, as by venesection, cool air, mucilaginous diet, aqueous potation, silence, darkness. The methods of relieving pains from defect of stimulus is by supplying thepeculiar stimulus required, as of food, or warmth. And the general method of relieving pain is by exciting into action somegreat part of the system for the purpose of expending a part of thesensorial power. This is done either by exertion of the voluntary ideas andmuscles, as in insanity and convulsion; or by exerting both voluntary andsensitive motions, as in reverie; or by exciting the irritative motions bywine or opium internally, and by the warm bath or blisters externally; orlastly, by exciting the sensitive ideas by good news, affecting stories, oragreeable passions. * * * * * SECT. XXXV. DISEASES OF ASSOCIATION. I. 1. _Sympathy or consent of parts. Primary and secondary parts of an associated train of motions reciprocally affect each other. Parts of irritative trains of motion affect each other in four ways. Sympathies of the skin and stomach. Flushing of the face after a meal. Eruption of the small-pox on the face. Chilness after a meal. _ 2. _Vertigo from intoxication. _ 3. _Absorption from the lungs and pericardium by emetics. In vomiting the actions of the stomach are decreased, not increased. Digestion strengthened after an emetic. Vomiting from deficiency of sensorial power. _ 4. _Dyspnoea from cold bathing. Slow pulse from digitalis. Death from gout in the stomach. _ II. 1. _Primary and secondary parts of sensitive associations affect each other. Pain from gall-stone, from urinary stone, Hemicrania. Painful epilepsy. _ 2. _Gout and red face from inflamed liver. Shingles from inflamed kidney. _ 3. _Coryza from cold applied to the feet. Pleurisy. Hepatitis. _ 4. _Pain of shoulders from inflamed liver. _ III. _Diseases from the associations of ideas. _ I. 1. Many synchronous and successive motions of our muscular fibres, andof our organs of sense, or ideas, become associated so as to formindissoluble tribes or trains of action, as shewn in Section X. OnAssociate Motions. Some constitutions more easily establish theseassociations, whether by voluntary, sensitive, or irritative repetitions, and some more easily lose them again, as shewn in Section XXXI. OnTemperaments. When the beginning of such a train of actions becomes by any meansdisordered, the succeeding part is liable to become disturbed inconsequence, and this is commonly termed sympathy or consent of parts bythe writers of medicine. For the more clear understanding of thesesympathies we must consider a tribe or train of actions as divided into twoparts, and call one of them the primary or original motions, and the otherthe secondary or sympathetic ones. The primary and secondary parts of a train of irritative actions mayreciprocally affect each other in four different manners. 1. They may bothbe exerted with greater energy than natural. 2. The former may act withgreater, and the latter with less energy. 3. The former may act with less, and the latter with greater energy. 4. They may both act with less energythan natural. I shall now give an example of each kind of these modes ofaction, and endeavour to shew, that though the primary and secondary partsof these trains or tribes of motion are connected by irritativeassociation, or their previous habits of acting together, as described inSect. XX. On Vertigo. Yet that their acting with similar or dissimilardegrees of energy, depends on the greater or less quantity of sensorialpower, which the primary part of the train expends in its exertions. The actions of the stomach constitute so important a part of theassociations of both irritative and sensitive motions, that it is said tosympathize with almost every part of the body; the first example, which Ishall adduce to shew that both the primary and secondary parts of a trainof irritative associations of motion act with increased energy, is takenfrom the consent of the skin with this organ. When the action of the fibresof the stomach is increased, as by the stimulus of a full meal, theexertions of the cutaneous arteries of the face become increased by theirirritative associations with those of the stomach, and a glow or flushingof the face succeeds. For the small vessels of the skin of the face havingbeen more accustomed to the varieties of action, from their frequentexposure to various degrees of cold and heat become more easily excitedinto increased action, than those of the covered parts of our bodies, andthus act with more energy from their irritative or sensitive associationswith the stomach. On this account in small-pox the eruption in consequenceof the previous affection of the stomach breaks out a day sooner on theface than on the hands, and two days sooner than on the trunk, and recedesin similar times after maturation. But secondly, in weaker constitutions, that is, in those who possess lesssensorial power, so much of it is expended in the increased actions of thefibres of the stomach excited by the stimulus of a meal, that a sense ofchilness succeeds instead of the universal glow above mentioned; and thusthe secondary part of the associated train of motions is diminished inenergy, in consequence of the increased activity of the primary part of it. 2. Another instance of a similar kind, where the secondary part of thetrain acts with less energy in consequence of the greater exertions of theprimary part, is the vertigo attending intoxication; in this circumstanceso much sensorial power is expended on the stomach, and on its nearest ormore strongly associated motions, as those of the subcutaneous vessels, andprobably of the membranes of some internal viscera, that the irritativemotions of the retina become imperfectly exerted from deficiency ofsensorial power, as explained in Sect. XX. And XXI. 3. On Vertigo and onDrunkenness, and hence the staggering inebriate cannot completely balancehimself by such indistinct vision. 3. An instance of the third circumstance, where the primary part of a trainof irritative motions acts with less, and the secondary part with greaterenergy, may be observed by making the following experiment. If a personlies with his arms and shoulders out of bed, till they become cold, atemporary coryza or catarrh is produced; so that the passage of thenostrils becomes totally obstructed; at least this happens to many people;and then on covering the arms and shoulders, till they become warm, thepassage of the nostrils ceases again to be obstructed, and a quantity ofmucus is discharged from them. In this case the quiescence of the vesselsof the skin of the arms and shoulders, occasioned by exposure to cold air, produces by irritative association an increased action of the vessels ofthe membrane of the nostrils; and the accumulation of sensorial powerduring the torpor of the arms and shoulders is thus expended in producing atemporary coryza or catarrh. Another instance may be adduced from the sympathy or consent of the motionsof the stomach with other more distant links of the very extensive tribesor trains of irritative motions associated with them, described in Sect. XX. On Vertigo. When the actions of the fibres of the stomach arediminished or inverted, the actions of the absorbent vessels, which take upthe mucus from the lungs, pericardium, and other cells of the body, becomeincreased, and absorb the fluids accumulated in them with greater avidity, as appears from the exhibition of foxglove, antimony, or other emetics incases of anasarca, attended with unequal pulse and difficult respiration. That the act of nausea and vomiting is a decreased exertion of the fibresof the stomach may be thus deduced; when an emetic medicine isadministered, it produces the pain of sickness, as a disagreeable taste inthe mouth produces the pain of nausea; these pains, like that of hunger, orof cold, or like those, which are usually termed nervous, as the head-achor hemicrania, do not excite the organ into greater action; but in thiscase I imagine the pains of sickness or of nausea counteract or destroy thepleasurable sensation, which seems necessary to digestion, as shewn inSect. XXXIII. 1. 1. The peristaltic motions of the fibres of the stomachbecome enfeebled by the want of this stimulus of pleasurable sensation, andin consequence stop for a time, and then become inverted; for they cannotbecome inverted without being previously stopped. Now that this inversionof the trains of motion of the fibres of the stomach is owing to thedeficiency of pleasurable sensation is evinced from this circumstance, thata nauseous idea excited by words will produce vomiting as effectually us anauseous drug. Hence it appears, that the act of nausea or vomiting expends less sensorialpower than the usual peristaltic motions of the stomach in the digestion ofour aliment; and that hence there is a greater quantity of sensorial powerbecomes accumulated in the fibres of the stomach, and more of it inconsequence to spare for the action of those parts of the system, which arethus associated with the stomach, as of the whole absorbent series ofvessels, and which are at the same time excited by their usual stimuli. From this we can understand, how after the operation of an emetic thestomach becomes more irritable and sensible to the stimulus, and thepleasure of food; since as the sensorial power becomes accumulated duringthe nausea and vomiting, the digestive power is afterwards exerted moreforceably for a time. It should, however, be here remarked, that thoughvomiting is in general produced by the defect of this stimulus ofpleasurable sensation, as when a nauseous drug is administered; yet in longcontinued vomiting, as in sea-sickness, or from habitual dram-drinking, itarises from deficiency of sensorial power, which in the former case isexhausted by the increased exertion of the irritative ideas of vision, andin the latter by the frequent application of an unnatural stimulus. 4. An example of the fourth circumstance above mentioned, where both theprimary and secondary parts of a train of motions proceed with energy lessthan natural, may be observed in the dyspnoea, which occurs in going into avery cold bath, and which has been described and explained in Sect. XXXII. 3. 2. And by the increased debility of the pulsations of the heart and arteriesduring the operation of an emetic. Secondly, from the slowness andintermission of the pulsations of the heart from the incessant efforts tovomit occasioned by an overdose of digitalis. And thirdly, from the totalstoppage of the motions of the heart, or death, in consequence of thetorpor of the stomach, when affected with the commencement or cold paroxysmof the gout. See Sect. XXV. 17. II. 1. The primary and secondary parts of the trains of sensitiveassociation reciprocally affect each other in different manners. 1. Theincreased sensation of the primary part may cease, when that of thesecondary part commences. 2. The increased action of the primary part maycease, when that of the secondary part commences. 3. The primary part mayhave increased sensation, and the secondary part increased action. 4. Theprimary part may have increased action, and the secondary part increasedsensation. Examples of the first mode, where the increased sensation of the primarypart of a train of sensitive association ceases, when that of the secondarypart commences, are not unfrequent; as this is the general origin of thosepains, which continue some time without being attended with inflammation, such as the pain at the pit of the stomach from a stone at the neck of thegall-bladder, and the pain of strangury in the glans penis from a stone atthe neck of the urinary bladder. In both these cases the part, which isaffected secondarily, is believed to be much more sensible than the partprimarily affected, as described in the catalogue of diseases, Class II. 1. 1. 11. And IV. 2. 2. 2. And IV. 2. 2. 4. The hemicrania, or nervous headach, as it is called, when it originatesfrom a decaying tooth, is another disease of this kind; as the pain of thecarious tooth always ceases, when the pain over one eye and templecommences. And it is probable, that the violent pains, which induceconvulsions in painful epilepsies, are produced in the same manner, from amore sensible part sympathizing with a diseased one of less sensibility. See Catalogue of Diseases, Class IV. 2. 2. 8. And III. 1. 1. 6. The last tooth, or dens sapientiæ, of the upper jaw most frequently decaysfirst, and is liable to produce pain over the eye and temple of that side. The last tooth of the under-jaw is also liable to produce a similarhemicrania, when it begins to decay. When a tooth in the upper-jaw is thecause of the headach, a slighter pain is sometimes perceived on thecheek-bone. And when a tooth in the lower-jaw is the cause of headach, apain sometimes affects the tendons of the muscles of the neck, which areattached near the jaws. But the clavus hystericus, or pain about the middleof the parietal bone on one side of the head, I have seen produced by thesecond of the molares, or grinders, of the under-jaw; of which I shallrelate the following case. See Class IV. 2. 2. 8. Mrs. ----, about 30 years of age, was seized with great pain about themiddle of the right parietal bone, which had continued a whole day before Isaw her, and was so violent as to threaten to occasion convulsions. Notbeing able to detect a decaying tooth, or a tender one, by examination withmy eye, or by striking them with a tea-spoon, and fearing bad consequencesfrom her tendency to convulsion, I advised her to extract the last tooth ofthe under-jaw on the affected side; which was done without any good effect. She was then directed to lose blood, and to take a brisk cathartic; andafter that had operated, about 60 drops of laudanum were given her, withlarge doses of bark; by which the pain was removed. In about a fortnightshe took a cathartic medicine by ill advice, and the pain returned withgreater violence in the same place; and, before I could arrive, as shelived 30 miles from me, she suffered a paralytic stroke; which affected herlimbs and her face on one side, and relieved the pain of her head. About a year afterwards I was again called to her on account of a pain asviolent as before exactly on the same part of the other parietal bone. Onexamining her mouth I found the second molaris of the under-jaw on the sidebefore affected was now decayed, and concluded, that this tooth hadoccasioned the stroke of the palsy by the pain and consequent exertion ithad caused. On this account I earnestly entreated her to allow the soundmolaris of the same jaw opposite to the decayed one to be extracted; whichwas forthwith done, and the pain of her head immediately ceased, to theastonishment of her attendants. In the cases above related of the pain existing in a part distant from theseat of the disease, the pain is owing to defect of the usual motions ofthe painful part. This appears from the coldness, paleness, and emptinessof the affected vessels, or of the extremities of the body in general, andfrom there being no tendency to inflammation. The increased action of theprimary part of these associated motions, as of the hepatic termination ofthe bile-duct; from the stimulus of a gall-stone, or of the interiortermination of the urethra from the stimulus of a stone in the bladder, orlastly, of a decaying tooth in hemicrania, deprives the secondary part ofthese associated motions, namely, the exterior terminations of thebile-duct or urethra, or the pained membranes of the head in hemicrania, oftheir natural share of sensorial power: and hence the secondary parts ofthese sensitive trains of association become pained from the deficiency oftheir usual motions, which is accompanied with deficiency of secretions andof heat. See Sect. IV. 5. XII. 5. 3. XXXIV. 1. Why does the pain of the primary part of the association cease, when thatof the secondary part commences? This is a question of intricacy, butperhaps not inexplicable. The pain of the primary part of these associatedtrains of motion was owing to too great stimulus, as of the stone at theneck of the bladder, and was consequently caused by too great action of thepained part. This greater action than natural of the primary part of theseassociated motions, by employing or expending the sensorial power ofirritation belonging to the whole associated train of motions, occasionedtorpor, and consequent pain in the secondary part of the associated train;which was possessed of greater sensibility than the primary part of it. Nowthe great pain of the secondary part of the train, as soon as it commences, employs or expends the sensorial power of sensation belonging to the wholeassociated train of motions; and in consequence the motions of the primarypart, though increased by the stimulus of an extraneous body, cease to beaccompanied with pain or sensation. If this mode of reasoning be just it explains a curious fact, why when twoparts of the body are strongly stimulated, the pain is felt only in one ofthem, though it is possible by voluntary attention it may be alternatelyperceived in them both. In the same manner, when two new ideas arepresented to us from the stimulus of external bodies, we attend to but oneof them at a time. In other words, when one set of fibres, whether of themuscles or organs of sense, contract so strongly as to excite muchsensation; another set of fibres contracting more weakly do not excitesensation at all, because the sensorial power of sensation is pre-occupiedby the first set of fibres. So we cannot will more than one effect at once, though by associations previously formed we can move many fibres incombination. Thus in the instances above related, the termination of the bile duct inthe duodenum, and the exterior extremity of the urethra, are more sensiblethan their other terminations. When these parts are deprived of their usualmotions by deficiency of sensorial power, as above explained, they becomepainful according to law the fifth in Section IV. And the less painoriginally excited by the stimulus of concreted bile, or of a stone attheir other extremities ceases to be perceived. Afterwards, however, whenthe concretions of bile, or the stone on the urinary bladder, become morenumerous or larger, the pain from their increased stimulus becomes greaterthan the associated pain; and is then felt at the neck of the gall bladderor urinary bladder; and the pain of the glans penis, or at the pit of thestomach, ceases to be perceived. 2. Examples of the second mode, where the increased action of the primarypart of a train of sensitive association ceases, when that of the secondarypart commences, are also not unfrequent; as this is the usual manner of thetranslation of inflammations from internal to external parts of the system, such as when an inflammation of the liver or stomach is translated to themembranes of the foot, and forms the gout; or to the skin of the face, andforms the rosy drop; or when an inflammation of the membranes of thekidneys is translated to the skin of the loins, and forms one kind ofherpes, called shingles; in these cases by whatever cause the originalinflammation may have been produced, as the secondary part of the train ofsensitive association is more sensible, it becomes exerted with greaterviolence than the first part of it; and by both its increased pain, and theincreased motion of its fibres, so far diminishes or exhausts the sensorialpower of sensation; that the primary part of the train being less sensibleceases both to feel pain, and to act with unnatural energy. 3. Examples of the third mode, where the primary part of a train ofsensitive association of motions may experience increased sensation, andthe secondary part increased action, are likewise not unfrequent; as it isin this manner that most inflammations commence. Thus, after standing sometime in snow, the feet become affected with the pain of cold, and a commoncoryza, or inflammation of the membrane of the nostrils, succeeds. It isprobable that the internal inflammations, as pleurisies, or hepatitis, which are produced after the cold paroxysm of fever, originate in the samemanner from the sympathy of those parts with some others, which werepreviously pained from quiescence; as happens to various parts of thesystem during the cold fits of fevers. In these cases it would seem, thatthe sensorial power of sensation becomes accumulated during the pain ofcold, as the torpor of the vessels occasioned by the defect of heatcontributes to the increase or accumulation of the sensorial power ofirritation, and that both these become exerted on some internal part, whichwas not rendered torpid by the cold which affected the external parts, norby its association with them; or which sooner recovered its sensibility. This requires further consideration. 4. An example of the fourth mode, or where the primary part of a sensitiveassociation of motions may have increased action, and the secondary partincreased sensation, may be taken from the pain of the shoulder, whichattends inflammation of the membranes of the liver, see Class IV. 2. 2. 9. ;in this circumstance so much sensorial power seems to be expended in theviolent actions and sensations of the inflamed membranes of the liver, thatthe membranes associated with them become quiescent to their usual stimuli, and painful in consequence. There may be other modes in which the primary and secondary parts of thetrains of associated sensitive motions may reciprocally affect each other, as may be seen by looking over Class IV. In the catalogue of diseases; allwhich may probably be resolved into the plus and minus of sensorial power, but we have not yet had sufficient observations made upon them with a viewto this doctrine. III. The associated trains of our ideas may have sympathies, and theirprimary and secondary parts affect each other in some manner similar tothose above described; and may thus occasion various curious phenomena notyet adverted to, besides those explained in the Sections on Dreams, Reveries, Vertigo, and Drunkenness; and may thus disturb the deductions ofour reasonings, as well as the streams of our imaginations; present us withfalse degrees of fear, attach unfounded value to trivial circumstances;give occasion to our early prejudices and antipathies; and thus embarrassthe happiness of our lives. A copious and curious harvest might be reapedfrom this province of science, in which, however, I shall not at presentwield my sickle. * * * * * SECT. XXXVI. OF THE PERIODS OF DISEASES. I. _Muscles excited by volition soon cease to contract, or by sensation, or by irritation, owing to the exhaustion of sensorial power. Muscles subjected to less stimulus have their sensorial power accumulated. Hence the periods of some fevers. Want of irritability after intoxication. _ II. 1. _Natural actions catenated with daily habits of life. _ 2. _With solar periods. Periods of sleep. Of evacuating the bowels. _ 3. _Natural actions catenated with lunar periods. Menstruation. Venereal orgasm of animals. Barrenness. _ III. _Periods of diseased animal actions from stated returns of nocturnal cold, from solar and lunar influence. Periods of diurnal fever, hectic fever, quotidian, tertian, quartan fever. Periods of gout, pleurisy, of fevers with arterial debility, and with arterial strength, Periods of rhaphania, of nervous cough, hemicrania, arterial hæmorrhages, hæmorrhoids, hæmoptoe, epilepsy, palsy, apoplexy, madness. _ IV. _Critical days depend on lunar periods. Lunar periods in the small pox. _ I. If any of our muscles be made to contract violently by the power ofvolition, as those of the fingers, when any one hangs by his hands on aswing, fatigue soon ensues; and the muscles cease to act owing to thetemporary exhaustion of the spirit of animation; as soon as this is againaccumulated in the muscles, they are ready to contract again by the effortsof volition. Those violent muscular actions induced by pain become in the same mannerintermitted and recurrent; as in labour-pains, vomiting, tenesmus, strangury; owing likewise to the temporary exhaustion of the spirit ofanimation, as above mentioned. When any stimulus continues long to act with unnatural violence, so as toproduce too energetic action of any of our moving organs, those motionssoon cease, though the stimulus continues to act; as in looking long on abright object, as on an inch-square of red silk laid on white paper in thesunshine. See Plate I. In Sect. III. 1. On the contrary, where less of the stimulus of volition, sensation, orirritation, have been applied to a muscle than usual; there appears to bean accumulation of the spirit of animation in the moving organ; by which itis liable to act with greater energy from less quantity of stimulus, thanwas previously necessary to excite it into so great action; as after havingbeen immersed in snow the cutaneous vessels of our hands are excited intostronger action by the stimulus of a less degree of heat, than wouldpreviously have produced that effect. From hence the periods of some fever-fits may take their origin, eithersimply, or by their accidental coincidence with lunar and solar periods, orwith the diurnal periods of heat and cold, to be treated of below; forduring the cold fit at the commencement of a fever, from whatever causethat cold fit may have been induced, it follows, 1. That the spirit ofanimation must become accumulated in the parts, which exert during thiscold fit less than their natural quantity of action. 2. If the causeproducing the cold fit does not increase, or becomes diminished; the partsbefore benumbed or inactive become now excitable by smaller stimulus, andare thence thrown into more violent action than is natural; that is a hotfit succeeds the cold one. 3. By the energetic action of the system duringthe hot fit, if it continues long, an exhaustion of the spirit of animationtakes place; and another cold fit is liable to succeed, from the movingsystem not being excitable into action from its usual stimulus. Thisinirritability of the system from a too great previous stimulus, andconsequent exhaustion of sensorial power, is the cause of the generaldebility, and sickness, and head-ach, some hours after intoxication. Andhence we see one of the causes of the periods of fever-fits; which howeverare frequently combined with the periods of our diurnal habits, or of heatand cold, or of solar or lunar periods. When besides the tendency to quiescence occasioned by the expenditure ofsensorial power during the hot fit of fever, some other cause of torpor, asthe solar or lunar periods, is necessary to the introduction of a secondcold fit; the fever becomes of the intermittent kind; that is, there is aspace of time intervenes between the end of the hot fit, and thecommencement of the next cold one. But where no exteriour cause isnecessary to the introduction of the second cold fit; no such interval ofhealth intervenes; but the second cold fit commences, as soon as thesensorial power is sufficiently exhausted by the hot fit; and the feverbecomes continual. II. 1. The following are natural animal actions, which are frequentlycatenated with our daily habits of life, as well as excited by theirnatural irritations. The periods of hunger and thirst become catenated withcertain portions of time, or degrees of exhaustion, or other diurnal habitsof life. And if the pain of hunger be not relieved by taking food at theusual time, it is liable to cease till the next period of time or otherhabits recur; this is not only true in respect to our general desire offood, but the kinds of it also are governed by this periodical habit;insomuch that beer taken to breakfast will disturb the digestion of those, who have been accustomed to tea; and tea taken at dinner will disagree withthose, who have been accustomed to beer. Whence it happens, that those, whohave weak stomachs, will be able to digest more food, if they take theirmeals at regular hours; because they have both the stimulus of the alimentthey take, and the periodical habit, to assist their digestion. The periods of emptying the bladder are not only dependent on the acrimonyor distention of the water in it, but are frequently catenated withexternal cold applied to the skin, as in cold bathing, or washing thehands; or with other habits of life, as many are accustomed to empty thebladder before going to bed, or into the house after a journey, and thiswhether it be full or not. Our times of respiration are not only governed by the stimulus of the bloodin the lungs, or our desire of fresh air, but also by our attention to thehourly objects before us. Hence when a person is earnestly contemplating anidea of grief, he forgets to breathe, till the sensation in his lungsbecomes very urgent; and then a sigh succeeds for the purpose of moreforceably pushing forwards the blood, which is accumulated in the lungs. Our times of respiration are also frequently governed in part by our wantof a steady support for the actions of our arms, and hands, as in threadinga needle, or hewing wood, or in swimming; when we are intent upon theseobjects, we breathe at the intervals of the exertion of the pectoralmuscles. 2. The following natural animal actions are influenced by solar periods. The periods of sleep and of waking depend much on the solar period, for weare inclined to sleep at a certain hour, and to awake at a certain hour, whether we have had more or less fatigue during the day, if within certainlimits; and are liable to wake at a certain hour, whether we went to bedearlier or later, within certain limits. Hence it appears, that those whocomplain of want of sleep, will be liable to sleep better or longer, ifthey accustom themselves to go to rest, and to rise, at certain hours. The periods of evacuating the bowels are generally connected with some partof the solar day, as well as with the acrimony or distention occasioned bythe feces. Hence one method of correcting costiveness is by endeavouring toestablish a habit of evacuation at a certain hour of the day, asrecommended by Mr. Locke, which may be accomplished by using dailyvoluntary efforts at those times, joined with the usual stimulus of thematerial to be evacuated. 3. The following natural animal actions are connected with lunar periods. 1. The periods of female menstruation are connected with lunar periods togreat exactness, in some instances even to a few hours. These do notcommence or terminate at the full or change, or at any other particularpart of the lunation, but after they have commenced at any part of it, theycontinue to recur at that part with great regularity, unless disturbed bysome violent circumstance, as explained in Sect. XXXII. No. 6. Their returnis immediately caused by deficient venous absorption, which is owing to thewant of the stimulus, designed by nature, of amatorial copulation, or ofthe growing fetus. When the catamenia returns sooner than the period oflunation, it shows a tendency of the constitution to inirritability; thatis to debility, or deficiency of sensorial power, and is to be relieved bysmall doses of steel and opium. The venereal orgasm of birds and quadrupeds seems to commence, or returnabout the most powerful lunations at the vernal or autumnal equinoxes; butif it be disappointed of its object, it is said to recur at monthlyperiods; in this respect resembling the female catamenia. Whence it isbelieved, that women are more liable to become pregnant at or about thetime of their catamenia, than at the intermediate times; and on thisaccount they are seldom much mistaken in their reckoning of nine lunarperiods from the last menstruation; the inattention to this may sometimeshave been the cause of supposed barrenness, and is therefore worth theobservation of those, who wish to have children. III. We now come to the periods of diseased animal actions. The periods offever-fits, which depend on the stated returns of nocturnal cold, arediscussed in Sect. XXXII. 3. Those, which originate or recur at solar orlunar periods, are also explained in Section XXXII. 6. These we shall hereenumerate; observing, however, that it is not more surprising, that theinfluence of the varying attractions of the sun and moon, should raise theocean into mountains, than that it should affect the nice sensibilities ofanimal bodies; though the manner of its operation on them is difficult tobe understood. It is probable however, that as this influence graduallylessens during the course of the day, or of the lunation, or of the year, some actions of our system become less and less; till at length a totalquiescence of some part is induced; which is the commencement of theparoxysms of fever, of menstruation, of pain with decreased action of theaffected organ, and of consequent convulsion. 1. A diurnal fever in some weak people is distinctly observed to come ontowards evening, and to cease with a moist skin early in the morning, obeying the solar periods. Persons of weak constitutions are liable to getinto better spirits at the access of the hot fit of this evening fever; andare thence inclined to sit up late; which by further enfeebling themincreases the disease; whence they lose their strength and their colour. 2. The periods of hectic fever, supposed to arise from absorption ofmatter, obeys the diurnal periods like the above, having the exacerbescencetowards evening, and its remission early in the morning, with sweats, ordiarrhoea, or urine with white sediment. 3. The periods of quotidian fever are either catenated with solar time, andreturn at the intervals of twenty-four hours; or with lunar time, recurringat the intervals of about twenty-five hours. There is great use in knowingwith what circumstances the periodical return or new morbid motions areconjoined, as the most effectual times of exhibiting the proper medicinesare thus determined. So if the torpor, which ushers in an ague fit, iscatenated with the lunar day: it is known, when the bark or opium must begiven, so as to exert its principal effect about the time of the expectedreturn. Solid opium should be given about an hour before the expected coldfit; liquid opium and wine about half an hour; the bark repeatedly for sixor eight hours previous to the expected return. 4. The periods of tertian fevers, reckoned from the commencement of onecold fit to the commencement of the next cold fit, recur with solarintervals of forty-eight hours, or with lunar ones of about fifty hours. When these of recurrence begin one or two hours earlier than the solarperiod, it shews, that the torpor or cold fit is produced by less externalinfluence; and therefore that it is more liable to degenerate into a feverwith only remissions; so when menstruation recurs sooner than the period oflunation, it shews a tendency of the habit to torpor of inirritability. 5. The periods of quartan fevers return at solar intervals of seventy-twohours, or at lunar ones of about seventy-four hours and an half. This kindof ague appears most in moist cold autumns, and in cold countries repletewith marshes. It is attended with greater debility, and its cold accessmore difficult to prevent. For where there is previously a deficiency ofsensorial power, the constitution is liable to run into greater torpor fromany further diminution of it; two ounces of bark and some steel should begiven on the day before the return of the cold paroxysm, and a pint of wineby degrees a few hours before its return, and thirty drops of laudanum onehour before the expected cold fit. 6. The periods of the gout generally commence about an hour beforesun-rise, which is usually the coldest part of the twenty-four hours. Thegreater periods of the gout seem also to observe the solar influence, returning about the same season of the year. 7. The periods of the pleurisy recur with exacerbation of the pain andfever about sun-set, at which time venesection is of most service. The samemay be observed of the inflammatory rheumatism, and other fevers witharterial strength, which seem to obey solar periods; and those withdebility seem to obey lunar ones. 8. The periods of fevers with arterial debility seem to obey the lunar day, having their access daily nearly an hour later; and have sometimes twoaccesses in a day, resembling the lunar effects upon the tides. 9. The periods of rhaphania, or convulsions of the limbs from rheumaticpains, seem to be connected with solar influence, returning at nearly thesame hour for weeks together, unless disturbed by the exhibition ofpowerful doses of opium. So the periods of Tussis ferina, or violent cough with slow pulse, callednervous cough, recurs by solar periods. Five grains of opium, given at thetime the cough commenced disturbed the period, from seven in the evening toeleven, at which time it regularly returned for some days, during whichtime the opium was gradually omitted. Then 120 drops of laudanum were givenan hour before the access of the cough, and it totally ceased. The laudanumwas continued a fortnight, and then gradually discontinued. 10. The periods of hemicrania, and of painful epilepsy, are liable to obeylunar periods, both in their diurnal returns, and in their greater periodsof weeks, but are also induced by other exciting causes. 11. The periods of arterial hæmorrhages seem to return at solar periodsabout the same hour of the evening or morning. Perhaps the venoushæmorrhages obey the lunar periods, as the catamenia, and hæmorrhoids. 12. The periods of the hæmorrhoids, or piles, in some recur monthly, inothers only at the greater lunar influence about the equinoxes. 13. The periods of hæmoptoe sometimes obey solar influence, recurring earlyin the morning for several days; and sometimes lunar periods, recurringmonthly; and sometimes depend on our hours of sleep. See Class I. 2. 1. 9. 14. Many of the first periods of epileptic fits obey the monthly lunationwith some degree of accuracy; others recur only at the most powerfullunations before the vernal equinox, and after the autumnal one; but whenthe constitution has gained a habit of relieving disagreeable sensations bythis kind of exertion, the fit recurs from any slight cause. 15. The attack of palsy and apoplexy are known to recur with greatfrequency about the equinoxes. 16. There are numerous instances of the effect of the lunations upon theperiods of insanity, whence the name of lunatic has been given to thoseafflicted with this disease. IV. The critical days, in which fevers are supposed to terminate, haveemployed the attention of medical philosophers from the days of Hippocratesto the present time. In whatever part of a lunation a fever commences, which owes either its whole cause to solar and lunar influence, or to thisin conjunction with other causes; it would seem, that the effect would bethe greatest at the full and new moon, as the tides rise highest at thosetimes, and would be the least at the quadratures; thus if a fever-fitshould commence at the new or full moon, occasioned by the solar and lunarattraction diminishing some chemical affinity of the particles of blood, and thence decreasing their stimulus on our sanguiferous system, asmentioned in Sect. XXXII. 6. This effect will daily decrease for the firstseven days, and will then increase till about the fourteenth day, and willagain decrease till about the twenty-first day, and increase again till theend of the lunation. If a fever-fit from the above cause should commence onthe seventh day after either lunation, the reverse of the abovecircumstances would happen. Now it is probable, that those fevers, whosecrisis or terminations are influenced by lunations, may begin at one orother of the above times, namely at the changes or quadratures; thoughsufficient observations have not been made to ascertain this circumstance. Hence I conclude, that the small-pox and measles have their critical days, not governed by the times required for certain chemical changes in theblood, which affect or alter the stimulus of the contagious matter, butfrom the daily increasing or decreasing effect of this lunar link ofcatenation, as explained in Section XVII. 3. 3. And as other feversterminate most frequently about the seventh, fourteenth, twenty-first, orabout the end of four weeks, when no medical assistance has disturbed theirperiods, I conclude, that these crises, or terminations, are governed byperiods of the lunations; though we are still ignorant of their manner ofoperation. In the distinct small-pox the vestiges of lunation are very apparent, afterinoculation a quarter of a lunation precedes the commencement of the fever, another quarter terminates with the complete eruption, another quarter withthe complete maturation, and another quarter terminates the completeabsorption of a material now rendered inoffensive to the constitution. * * * * * SECT. XXXVII. OF DIGESTION, SECRETION, NUTRITION. I. _Crystals increase by the greater attraction of their sides. Accretion by chemical precipitations, by welding, by pressure, by agglutination. _ II. _Hunger, digestion, why it cannot be imitated out of the body. Lacteals absorb by animal selection or appetency. _ III. _The glands and pores absorb nutritious particles by animal selection. Organic particles of Buffon. Nutrition applied at the time of elongation of fibres. Like inflammation. _ IV. _It seems easier to have preserved animals than to reproduce them. Old age and death from inirritability. Three causes of this. Original fibres of the organs of sense and muscles unchanged. _ V. _Art of producing long life. _ I. The larger crystals of saline bodies may be conceived to arise from thecombination of smaller crystals of the same form, owing to the greaterattractions of their sides than of their angles. Thus if four cubes werefloating in a fluid, whose friction or resistance is nothing, it is certainthe sides of these cubes would attract each other stronger than theirangles; and hence that these four smaller cubes would so arrange themselvesas to produce one larger one. There are other means of chemical accretion, such as the depositions ofdissolved calcareous or siliceous particles, as are seen in the formationof the stalactites of limestone in Derbyshire, or of calcedone in Cornwall. Other means of adhesion are produced by heat and pressure, as in thewelding of iron-bars; and other means by simple pressure, as in forcing twopieces of caoutchou, or elastic gum, to adhere; and lastly, by theagglutination of a third substance penetrating the pores of the other two, as in the agglutination of wood by means of animal gluten. Though theultimate particles of animal bodies are held together during life, as wellas after death, by their specific attraction of cohesion, like all othermatter; yet it does not appear, that their original organization wasproduced by chemical laws, and their production and increase must thereforeonly be looked for from the laws of animation. II. When the pain of hunger requires relief, certain parts of the materialworld, which surround us, when applied to our palates, excite into actionthe muscles of deglutition; and the material is swallowed into the stomach. Here the new aliment becomes mixed with certain animal fluids, andundergoes a chemical process, termed digestion; which however chemistry hasnot yet learnt to imitate out of the bodies of living animals orvegetables. This process seems very similar to the saccharine process inthe lobes of farinaceous seeds, as of barley, when it begins to germinate;except that, along with the sugar, oil and mucilage are also produced;which form the chyle of animals, which is very similar to their milk. The reason, I imagine, why this chyle-making, or saccharine process, hasnot yet been imitated by chemical operations, is owing to the materialsbeing in such a situation in respect to warmth, moisture, and motion; thatthey will immediately change into the vinous or acetous fermentation;except the new sugar be absorbed by the numerous lacteal or lymphaticvessels, as soon as it is produced; which is not easy to imitate in thelaboratory. These lacteal vessels have mouths, which are irritated into action by thestimulus of the fluid, which surrounds them; and by animal selection, orappetency, they absorb such part of the fluid as is agreeable to theirpalate; those parts, for instance, which are already converted into chyle, before they have time to undergo another change by a vinous or acetousfermentation. This animal absorption of fluid is almost visible to thenaked eye in the action of the puncta lacrymalia; which imbibe the tearsfrom the eye, and discharge them again into the nostrils. III. The arteries constitute another reservoir of a changeful fluid; fromwhich, after its recent oxygenation in the lungs, a further animalselection of various fluids is absorbed by the numerous glands; theseselect their respective fluids from the blood, which is perpetuallyundergoing a chemical change; but the selection by these glands, like thatof the lacteals, which open their mouths into the digesting aliment in thestomach, is from animal appetency, not from chemical affinity; secretioncannot therefore be imitated in the laboratory, as it consists in aselection of part of a fluid during the chemical change of that fluid. The mouths of the lacteals, and lymphatics, and the ultimate terminationsof the glands, are finer than can easily be conceived; yet it is probable, that the pores, or interstices of the parts, or coats, which constitutethese ultimate vessels, may still have greater tenuity; and that thesepores from the above analogy must posses a similar power of irritability, and absorb by their living energy the particles of fluid adapted to theirpurposes, whether to replace the parts abraded or dissolved, or to elongateand enlarge themselves. Not only every kind of gland is thus endued withits peculiar appetency, and selects the material agreeable to its tastefrom the blood, but every individual pore acquires by animal selection thematerial, which it wants; and thus nutrition seems to be performed in amanner so similar to secretion; that they only differ in the one retaining, and the other parting again with the particles, which they have selectedfrom the blood. This way of accounting for nutrition from stimulus, and the consequentanimal selection of particles, is much more analogous to other phenomena ofthe animal microcosm, than by having recourse to the microscopicanimalcula, or organic particles of Buffon, and Needham; which beingalready compounded must themselves require nutritive particles to continuetheir own existence. And must be liable to undergo a change by ourdigestive or secretory organs; otherwise mankind would soon resemble bytheir theory the animals, which they feed upon. He, who is nourished bybeef or venison, would in time become horned; and he, who feeds on pork orbacon, would gain a nose proper for rooting into the earth, as well as forthe perception of odours. The whole animal system may be considered as consisting of the extremitiesof the nerves, or of having been produced from them; if we except perhapsthe medullary part of the brain residing in the head and spine, and in thetrunks of the nerves. These extremities of the nerves are either of thoseof locomotion, which are termed muscular fibres; or of those of sensation, which constitute the immediate organs of sense, and which have also theirpeculiar motions. Now as the fibres, which constitute the bones andmembranes, possessed originally sensation and motion; and are liable againto possess them, when they become inflamed; it follows, that those were, when first formed, appendages to the nerves of sensation or locomotion, orwere formed from them. And that hence all these solid parts of the body, asthey have originally consisted of extremities of nerves, require anapposition of nutritive particles of a similar kind, contrary to theopinion of Buffon and Needham above recited. Lastly, as all these filaments have possessed, or do possess, the power ofcontraction, and of consequent inertion or elongation; it seems probable, that the nutritive particles are applied during their times of elongation;when their original constituent particles are removed to a greater distancefrom each other. For each muscular or sensual fibre may be considered as arow or string of beads; which approach, when in contraction, and recededuring its rest or elongation; and our daily experience shews us, thatgreat action emaciates the system, and that it is repaired during rest. Something like this is seen out of the body; for if a hair, or a singleuntwisted fibre of flax or silk, be soaked in water; it becomes longer andthicker by the water, which is absorbed into its pores. Now if a hair couldbe supposed to be thus immersed in a solution of particles similar tothose, which compose it; one may imagine, that it might be thus increasedin weight and magnitude; as the particles of oak-bark increase thesubstance of the hides of beasts in the process of making leather. Imention these not as philosophic analogies, but as similes to facilitateour ideas, how an accretion of parts may be effected by animal appetences, or selections, in a manner somewhat similar to mechanical or chemicalattractions. If those new particles of matter, previously prepared by digestion andsanguification, only supply the places of those, which have been abraded bythe actions of the system, it is properly termed nutrition. If they areapplied to the extremities of the nervous fibrils, or in such quantity asto increase the length or crassitude of them, the body becomes at the sametime enlarged, and its growth is increased, as well as its deficiencesrepaired. In this last case something more than a simple apposition or selection ofparticles seems to be necessary; as many parts of the system during itsgrowth are caused to recede from those, with which they were before incontact; as the ends of the bones, or cartilages, recede from each other, as their growth advances: this process resembles inflammation, as appearsin ophthalmy, or in the production of new flesh in ulcers, where oldvessels are enlarged, and new ones produced; and like that is attended withsensation. In this situation the vessels become distended with blood, andacquire greater sensibility, and may thus be compared to the erection ofthe penis, or of the nipples of the breasts of women; while new particlesbecome added at the same time; as in the process of nutrition abovedescribed. When only the natural growth of the various parts of the body are produced, a pleasurable sensation attends it, as in youth, and perhaps in those, whoare in the progress of becoming fat. When an unnatural growth is theconsequence, as in inflammatory diseases, a painful sensation attends theenlargement of the system. IV. This apposition of new parts, as the old ones disappear, selected fromthe aliment we take, first enlarges and strengthens our bodies for twentyyears, for another twenty years it keeps us in health and vigour, and addsstrength and solidity to the system; and then gradually ceases to nourishus properly, and for another twenty years we gradually sink into decay, andfinally cease to act, and to exist. On considering this subject one should have imagined at first view, that itmight have been easier for nature to have supported her progeny for ever inhealth and life, than to have perpetually reproduced them by the wonderfuland mysterious process of generation. But it seems our bodies by long habitcease to obey the stimulus of the aliment, which should support us. Afterwe have acquired our height and solidity we make no more new parts, and thesystem obeys the irritations, sensations, volitions; and associations, with, less and less energy, till the whole sinks into inaction. Three causes may conspire to render our nerves less excitable, which havebeen already mentioned, 1. If a stimulus be greater than natural, itproduces too great an exertion of the stimulated organ, and in consequenceexhausts the spirit of animation; and the moving organ ceases to act, eventhough the stimulus be continued. And though rest will recruit thisexhaustion, yet some degree of permanent injury remains, as is evidentafter exposing the eyes long to too strong a light. 2. If excitationsweaker than natural be applied, so as not to excite the organ into action, (as when small doses of aloe or rhubarb are exhibited, ) they may begradually increased, without exciting the organ into action; which willthus acquire a habit of disobedience to the stimulus; thus by increasingthe dose by degrees, great quantities of opium or wine may be taken withoutintoxication. See Sect. XII. 3. 1. 3. Another mode, by which life is gradually undermined, is when irritativemotions continue to be produced in consequence of stimulus, but are notsucceeded by sensation; hence the stimulus of contagious matter is notcapable of producing fever a second time, because it is not succeeded bysensation. See Sect. XII. 3. 6. And hence, owing to the want of the generalpleasurable sensation, which ought to attend digestion and glandularsecretion, an irksomeness of life ensues; and, where this is in greaterexcess, the melancholy of old age occurs, with torpor or debility. From hence I conclude, that it is probable that the fibrillæ, or movingfilaments at the extremities of the nerves of sense, and the fibres whichconstitute the muscles (which are perhaps the only parts of the system thatare endued with contractile life) are not changed, as we advance in years, like the other parts of the body; but only enlarged or elongated with ourgrowth; and in consequence they become less and less excitable into action. Whence, instead of gradually changing the old animal, the generation of atotally new one becomes necessary with undiminished excitability; whichmany years will continue to acquire new parts, or new solidity, and thenlosing its excitability in time, perish like its parent. V. From this idea the art of preserving long health and life may bededuced; which must consist in using no greater stimulus, whether of thequantity or kind of our food and drink, or of external circumstances, suchas heat, and exercise, and wakefulness, than is sufficient to preserve usin vigour; and gradually, as we grow old to increase the stimulus of ouraliment, as the irritability of our system increases. The debilitating effects ascribed by the poet MARTIAL to the excessive useof warm bathing in Italy, may with equal propriety be applied to the warmrooms of England; which, with the general excessive stimulus of spirituousor fermented liquors, and in some instances of immoderate venery, contribute to shorten our lives. _Balnea, vina, venus, corrumpunt corpora nostra_, _At faciunt vitam balnea, vina, venus!_ Wine, women, warmth, against our lives combine; But what is life without warmth, women, wine! * * * * * SECT. XXXVIII. OF THE OXYGENATION OF THE BLOOD IN THE LUNGS, AND IN THE PLACENTA. I. _Blood absorbs oxygene from the air, whence phosphoric acid changes its colour, gives out heat, and some phlogistic material, and acquires an ethereal spirit, which is dissipated in fibrous motion. _ II. _The placenta is a pulmonary organ like the gills of fish. Oxygenation of the blood from air, from water, by lungs, by gills, by the placenta; necessity of this oxygenation to quadrupeds, to fish, to the foetus in utero. Placental vessels inserted into the arteries of the mother. Use of cotyledons in cows. Why quadrupeds have not sanguiferous lochia. Oxygenation of the chick in the egg, of feeds. _ III. _The liquor amnii is not excrementitious. It is nutritious. It is found in the esophagus and stomach, and forms the meconium. Monstrous births without heads. Question of Dr. Harvey. _ I. From the recent discoveries of many ingenious philosophers it appears, that during respiration the blood imbibes the vital part of the air, calledoxygene, through the membranes of the lungs; and that hence respiration maybe aptly compared to a slow combustion. As in combustion the oxygene of theatmosphere unites with some phlogistic or inflammable body, and forms anacid (as in the production of vitriolic acid from sulphur, or carbonic acidfrom charcoal, ) giving out at the same time a quantity of the matter ofheat; so in respiration the oxygene of the air unites with the phlogisticpart of the blood, and probably produces phosphoric or animal acid, changing the colour of the blood from a dark to a bright red; and probablysome of the matter of heat is at the same time given out according to thetheory of Dr. Crawford. But as the evolution of heat attends almost allchemical combinations, it is probable, that it also attends the secretionsof the various fluids from the blood; and that the constant combinations orproductions of new fluids by means of the glands constitute the moregeneral source of animal heat; this seems evinced by the universalevolution of the matter of heat in the blush of shame or of anger; in whichat the same time an increased secretion of the perspirable matter occurs;and the partial evolution of it from topical inflammations, as in gout orrheumatism, in which there is a secretion of new blood-vessels. Some medical philosophers have ascribed the heat of animal bodies to thefriction of the particles of the blood against the sides of the vessels. But no perceptible heat has ever been produced by the agitation of water, or oil, or quicksilver, or other fluids; except those fluids have undergoneat the same time some chemical change, as in agitating milk or wine, tillthey become sour. Besides the supposed production of phosphoric acid, and change of colour ofthe blood, and the production of carbonic acid, there would appear to besomething of a more subtile nature perpetually acquired from theatmosphere; which is too fine to be long contained in animal vessels, andtherefore requires perpetual renovation; and without which life cannotcontinue longer than a minute or two; this ethereal fluid is probablysecreted from the blood by the brain, and perpetually dissipated in theactions of the muscles and organs of sense. That the blood acquires something from the air, which is immediatelynecessary to life, appears from an experiment of Dr. Hare (Philos. Transact. Abridged, Vol. III. P. 239. ) who found, "that birds, mice, &c. Would live as long again in a vessel, where he had crowded in double thequantity of air by a condensing engine, than they did when confined in airof the common density. " Whereas if some kind of deleterious vapour only wasexhaled from the blood in respiration; the air, when condensed into halfits compass, could not be supposed to receive so much of it. II. Sir Edward Hulse, a physician of reputation at the beginning of thepresent century, was of opinion, that the placenta was a respiratory organ, like the gills of fish; and not an organ to supply nutriment to the foetus;as mentioned in Derham's Physico-theology. Many other physicians seem tohave espoused the same opinion, as noticed by Haller. Elem. Physiologiæ, T. 1. Dr. Gipson published a defence of this theory in the Medical Essays ofEdinburgh, Vol. I. And II. Which doctrine is there controverted at large bythe late Alexander Monro; and since that time the general opinion has been, that the placenta is an organ of nutrition only, owing perhaps rather tothe authority of so great a name, than to the validity of the argumentsadduced in its support. The subject has lately been resumed by Dr. JamesJeffray, and by Dr. Forester French, in their inaugural dissertations atEdinburgh and at Cambridge; who have defended the contrary opinion in anable and ingenious manner; and from whose Theses I have extracted many ofthe following remarks. First, by the late discoveries of Dr. Priestley, M. Lavoisier, and otherphilosophers, it appears, that the basis of atmospherical air, calledoxygene, is received by the blood through the membranes of the lungs; andthat by this addition the colour of the blood is changed from a dark to alight red. Secondly, that water possesses oxygene also as a part of itscomposition, and contains air likewise in its pores; whence the blood offish receives oxygene from the water, or from the air it contains, by meansof their gills, in the same manner as the blood is oxygenated in the lungsof air-breathing animals; it changes its colour at the same time from adark to a light red in the vessels of their gills, which constitute apulmonary organ adapted to the medium in which they live. Thirdly, that theplacenta consists of arteries carrying the blood to its extremities, and avein bringing it back, resembling exactly in structure the lungs and gillsabove mentioned; and that the blood changes its colour from a dark to alight red in passing through these vessels. This analogy between the lungs and gills of animals, and the placenta ofthe fetus, extends through a great variety of other circumstances; thusair-breathing creatures and fish can live but a few minutes without air orwater; or when they are confined in such air or water, as has been spoiledby their own respiration; the same happens to the fetus, which, as soon asthe placenta is separated from the uterus, must either expand its lungs, and receive air, or die. Hence from the structure, as well as the use ofthe placenta, it appears to be a respiratory organ, like the gills of fish, by which the blood in the fetus becomes oxygenated. From the terminations of the placental vessels not being observed to bleedafter being torn from the uterus, while those of the uterus effuse a greatquantity of florid arterial blood, the terminations of the placentalvessels would seem to be inserted into the arterial ones of the mother; andto receive oxygenation from the passing currents of her blood through theircoats or membranes; which oxygenation is proved by the change of the colourof the blood from dark to light red in its passage from the placentalarteries to the placental vein. The curious structure of the cavities or lacunæ of the placenta, demonstrated by Mr. J. Hunter, explain this circumstance. That ingeniousphilosopher has shewn, that there are numerous cavities of lacunæ formed onthat side of the placenta, which is in contact with the uterus; thosecavities or cells are filled with blood from the maternal arteries, whichopen into them; which blood is again taken up by the maternal veins, and isthus perpetually changed. While the terminations of the placental arteriesand veins are spread in fine reticulation on the sides of these cells. Andthus, as the growing fetus requires greater oxygenation, an apparatus isproduced resembling exactly the air-cells of the lungs. In cows, and other ruminating animals, the internal surface of the uterusis unequal like hollow cups, which have been called cotyledons; and intothese cavities the prominencies of the numerous placentas, with which thefetus of those animals is furnished, are inserted, and strictly adhere;though they may be extracted without effusion of blood. These inequalitiesof the uterus, and the numerous placentas in consequence, seem to bedesigned for the purpose of expanding a greater surface for theterminations of the placental vessels for the purpose of receivingoxygenation from the uterine ones; as the progeny of this class of animalsare more completely formed before their nativity, than that of thecarnivorous classes, and must thence in the latter weeks of pregnancyrequire greater oxygenation. Thus calves and lambs can walk about in a fewminutes after their birth; while puppies and kittens remain many dayswithout opening their eyes. And though on the separation of the cotyledonsof ruminating animals no blood is effused, yet this is owing clearly to thegreater power of contraction of their uterine lacunæ or alveoli. SeeMedical Essays, Vol. V. Page 144. And from the same cause they are notliable to a sanguiferous menstruation. The necessity of the oxygenation of the blood in the fetus is fartherillustrated by the analogy of the chick in the egg; which appears to haveits blood oxygenated at the extremities of the vessels surrounding theyolk; which are spread on the air-bag at the broad end of the egg, and mayabsorb oxygene through that moist membrane from the air confined behind it;and which is shewn by experiments in the exhausted receiver to bechangeable though the shell. This analogy may even be extended to the growing seeds of vegetables; whichwere shewn by Mr. Scheele to require a renovation of the air over thewater, in which they were confined. Many vegetable seeds are surroundedwith air in their pods or receptacles, as peas, the fruit of staphylea, andlichnis vesicaria; but it is probable, that those seeds, after they areshed, as well as the spawn of fish, by the situation of the former on ornear the moist and aerated surface of the earth, and of the latter in theever-changing and ventilated water, may not be in need of an apparatus forthe oxygenation of their first blood, before the leaves of one, and thegills of the other, are produced for this purpose. III. 1. There are many arguments, besides the strict analogy between theliquor amnii and the albumen ovi, which shew the former to be a nutritivefluid; and that the fetus in the latter months of pregnancy takes it intoits stomach; and that in consequence the placenta is produced for someother important purpose. First, that the liquor amnii is not an excrementitious fluid is evinced, because it is found in greater quantity, when the fetus is young, decreasing after a certain period till birth. Haller asserts, "that in someanimals but a small quantity of this fluid remains at the birth. In theeggs of hens it is consumed on the eighteenth day, so that at the exclusionof the chick scarcely any remains. In rabbits before birth there is none. "Elem. Physiol. Had this been an excrementitious fluid, the contrary wouldprobably have occurred. Secondly, the skin of the fetus is covered with awhitish crust or pellicle, which would seem to preclude any idea of theliquor amnii being produced by any exsudation of perspirable matter. And itcannot consist of urine, because in brute animals the urachus passes fromthe bladder to the alantois for the express purpose of carrying off thatfluid; which however in the human fetus seems to be retained in thedistended bladder, as the feces are accumulated in the bowels of allanimals. 2. The nutritious quality of the liquid, which surrounds the fetus, appearsfrom the following considerations. 1. It is coagulable by heat, by nitrousacid, and by spirit of wine, like milk, serum of blood, and other fluids, which daily experience evinces to be nutritious. 2. It has a saltish tasteaccording to the accurate Baron Haller, not unlike the whey of milk, whichit even resembles in smell. 3. The white of the egg which constitutes thefood of the chick, is shewn to be nutritious by our daily experience;besides the experiment of its nutritious effects mentioned by Dr. Fordycein his late Treatise on Digestion, p. 178; who adds, that it much resemblesthe essential parts of the serum of blood. 3. A fluid similar to the fluid, with which the fetus is surrounded, exceptwhat little change may be produced by a beginning digestion, is found inthe stomach of the fetus; and the white of the egg is found, in the samemanner in the stomach of the chick. Numerous hairs, similar to those of its skin, are perpetually found amongthe contents of the stomach in new-born calves; which must therefore havelicked themselves before their nativity. Blasii Anatom. See Sect. XVI. 2. On Instinct. The chick in the egg is seen gently to move in its surrounding fluid, andto open and shut its mouth alternately. The same has been observed inpuppies. Haller's El. Phys. I. 8. P. 201. A column of ice has been seen to reach down the oesophagus from the mouthto the stomach in a frozen fetus; and this ice was the liquor amnii frozen. The meconium, or first fæces, in the bowels of new-born infants evince, that something has been digested; and what could this be but the liquoramnii together with the recrements of the gastric juice and gall, whichwere necessary for its digestion? There have been recorded some monstrous births of animals without heads, and consequently without mouths, which seem to have been delivered ondoubtful authority, or from inaccurate observation. There are two of suchmonstrous productions however better attested; one of a human fetus, mentioned by Gipson in the Scots Medical Essays; which having the gulaimpervious was furnished with an aperture into the wind-pipe, whichcommunicated below into the gullet; by means of which the liquor amniimight be taken into the stomach before nativity without danger ofsuffocation, while the fetus had no occasion to breathe. The othermonstrous fetus is described by Vander Wiel, who asserts, that he saw amonstrous lamb, which had no mouth; but instead of it was furnished with anopening in the lower part of the neck into the stomach. Both theseinstances evidently favour the doctrine of the fetus being nourished by themouth; as otherwise there had been no necessity for new or unnaturalapertures into the stomach, when the natural ones were deficient? From these facts and observations we may safely infer, that the fetus inthe womb is nourished by the fluid which surrounds it; which during thefirst period of gestation is absorbed by the naked lacteals; and isafterwards swallowed into the stomach and bowels, when these organs areperfected; and lastly that the placenta is an organ for the purpose ofgiving due oxygenation to the blood of the fetus; which is more necessary, or at least more frequently necessary, than even the supply of food. The question of the great Harvey becomes thus easily answered. "Why is notthe fetus in the womb suffocated for want of air, when it remains thereeven to the tenth month without respiration: yet if it be born in theseventh or eighth month, and has once respired, it becomes immediatelysuffocated for want of air, if its respiration be obstructed?" For further information on this subject, the reader is referred to theTentamen Medicum of Dr. Jeffray, printed at Edinburgh in 1786. And it ishoped that Dr. French will some time give his theses on this subject to thepublic. * * * * * SECT. XXXIX. OF GENERATION. Felix, qui causas altà caligine mersas Pandit, et evolvit tenuissima vincula rerum. I. _Habits of acting and feeling of individuals attend the soul into a future life, and attend the new embryon at the time of its production. The new speck of entity absorbs nutriment, and receives oxygene. Spreads the terminations of its vessels on cells, which communicate with the arteries of the uterus; sometimes with those of the peritoneum. Afterwards it swallows the liquor amnii, which it produces by its irritation from the uterus, or peritoneum. Like insects in the heads of calves and sheep. Why the white of egg is of two consistencies. Why nothing is found in quadrupeds similar to the yolk, nor in most vegetable seeds. _ II. 1. _Eggs of frogs and fish impregnated out of their bodies. Eggs of fowls which are not fecundated, contain only the nutriment for the embryon. The embryon is produced by the male, and the nutriment by the female. Animalcula in semine. Profusion of nature's births. _ 2. _Vegetables viviparous. Buds and bulbs have each a father but no mother. Vessels of the leaf and bud inosculate. The paternal offspring exactly resembles the parent. _ 3. _Insects impregnated for six generations. Polypus branches like buds. Creeping roots. Viviparous flowers. Tænia, volvox. Eve from Adam's rib. Semen not a stimulus to the egg. _ III. 1. _Embryons not originally created within other embryons. Organized matter is not so minute. _ 2. _All the parts of the embryon are not formed in the male parent. Crabs produce their legs, worms produce their heads and tails. In wens, cancers, and inflammations, new vessels are formed. Mules partake of the forms of both parents. Hair and nails grow by elongation, not by distention. _ 3. _Organic particles of Buffon. _ IV. 1. _Rudiment of the embryon a simple living filament, becomes a living ring, and then a living tube. _ 2. _It acquires irritabilities, and sensibilities with new organizations, as in wounded snails, polypi, moths, gnats, tadpoles. Hence new parts are acquired by addition not by distention. _ 3. _All parts of the body grow if not confined. _ 4. _Fetuses deficient at their extremities, or have a duplicature of parts. Monstrous births. Double parts of vegetables. _ 5. _Mules cannot be formed by distention of the seminal ens. _ 6. _Families of animals from a mixture of their orders. Mules imperfect. _ 7. _Animal appetency like chemical affinity. Vis fabricatrix and medicatrix of nature. _ 8. _The changes of animals before and after nativity. Similarity of their structure. Changes in them from lust, hunger, and danger. All warm-blooded animals derived from one living filament. Cold-blooded animals, insects, worms, vegetables, derived also from one living filament. Male animals have teats. Male pigeon gives milk. The world itself generated. The cause of causes. A state of probation and responsibility. _ V. 1. _Efficient cause of the colours of birds eggs, and of hair and feathers, which become white in snowy countries. Imagination of the female colours the egg. Ideas or motions of the retina imitated by the extremities of the nerves of touch, or rete mucosum. _ 2. _Nutriment supplied by the female of three kinds. Her imagination can only affect the first kind. Mules how produced, and mulattoes. Organs of reproduction why deficient in mules. Eggs with double yolks. _ VI. 1. _Various secretions produced by the extremities of the vessels, as in the glands. Contagious matter. Many glands affected by pleasurable ideas, as those which secrete the semen. _ 2. _Snails and worms are hermaphrodite, yet cannot impregnate themselves. Final cause of this. _ 3. _The imagination of the male forms the sex. Ideas, or motions of the nerves of vision or of touch, are imitated by the ultimate extremities of the glands of the testes, which mark the sex. This effect of the imagination belongs only to the male. The sex of the embryon is not owing to accident. _ 4. _Causes of the changes in animals from imagination as in monsters. From the male. From the female. _ 5. _Miscarriages from fear. _ 6. _Power of the imagination of the male over the colour, form, and sex of the progeny. An instance of. _ 7. _Act of generation accompanied with ideas of the male or female form. Art of begetting beautiful children of either sex. _ VII. _Recapitulation. _ VIII. _Conclusion. Of cause and effect. The atomic philosophy leads to a first cause. _ I. The ingenious Dr. Hartley in his work on man, and some otherphilosophers, have been of opinion, that our immortal part acquires duringthis life certain habits of action or of sentiment, which become for everindissoluble, continuing after death in a future state of existence; andadd, that if these habits are of the malevolent kind, they must render thepossessor miserable even in heaven. I would apply this ingenious idea tothe generation or production of the embryon, or new animal, which partakesso much of the form and propensities of the parent. Owing to the imperfection of language the offspring is termed a _new_animal, but is in truth a branch or elongation of the parent; since a partof the embryon-animal is, or was, a part of the parent; and therefore instrict language it cannot be said to be entirely _new_ at the time of itsproduction; and therefore it may retain some of the habits of theparent-system. At the earliest period of its existence the embryon, as secreted from theblood of the male, would seem to consist of a living filament with certaincapabilities of irritation, sensation, volition, and association; and alsowith some acquired habits or propensities peculiar to the parent: theformer of these are in common with other animals; the latter seem todistinguish or produce the kind of animal, whether man or quadruped, withthe similarity of feature or form to the parent. It is difficult to beconceived, that a living entity can be separated or produced from the bloodby the action of a gland; and which shall afterwards become an animalsimilar to that in whose vessels it is formed; even though we shouldsuppose with some modern theorists, that the blood is alive; yet everyother hypothesis concerning generation rests on principles still moredifficult to our comprehension. At the time of procreation this speck of entity is received into anappropriated nidus, in which it must acquire two circumstances necessary toits life and growth; one of these is food or sustenance, which is to bereceived by the absorbent mouths of its vessels; and the other is that partof atmospherical air, or of water, which by the new chemistry is termedoxygene, and which affects the blood by passing through the coats of thevessels which contain it. The fluid surrounding the embryon in its newhabitation, which is called liquor amnii, supplies it with nourishment; andas some air cannot but be introduced into the uterus along with a newembryon, it would seem that this same fluid would for a short time, supposefor a few hours, supply likewise a sufficient quantity of the oxygene forits immediate existence. On this account the vegetable impregnation of aquatic plants is performedin the air; and it is probable that the honey-cup or nectary of vegetablesrequires to be open to the air, that the anthers and stigmas of the flowermay have food of a more oxygenated kind than the common vegetablesap-juice. On the introduction of this primordium of entity into the uterus theirritation of the liquor amnii, which surrounds it, excites the absorbentmouths of the new vessels into action; they drink up a part of it, and apleasurable sensation accompanies this new action; at the same time thechemical affinity of the oxygene acts through the vessels of the rubescentblood; and a previous want, or disagreeable sensation, is relieved by thisprocess. As the want of this oxygenation of the blood is perpetual, (as appears fromthe incessant necessity of breathing by lungs or gills, ) the vessels becomeextended by the efforts of pain or desire to seek this necessary object ofoxygenation, and to remove the disagreeable sensation, which that wantoccasions. At the same time new particles of matter are absorbed, orapplied to these extended vessels, and they become permanently elongated, as the fluid in contact with them soon loses the oxygenous part, which itat first possessed, which was owing to the introduction of air along withthe embryon. These new blood-vessels approach the sides of the uterus, andpenetrate with their fine terminations into the vessels of the mother; oradhere to them, acquiring oxygene through their coats from the passingcurrents of the arterial blood of the mother. See Sect. XXXVIII. 2. This attachment of the placental vessels to the internal side of the uterusby their own proper efforts appears further illustrated by the manyinstances of extra-uterine fetuses, which have thus attached or insertedtheir vessels into the peritoneum; or on the viscera, exactly in the samemanner as they naturally insert or attach them to the uterus. The absorbent vessels of the embryon continue to drink up nourishment fromthe fluid in which they swim, or liquor amnii; and which at first needs noprevious digestive preparation; but which, when the whole apparatus ofdigestion becomes complete, is swallowed by the mouth into the stomach, andbeing mixed with saliva, gastric juice, bile, pancreatic juice, and mucusof the intestines, becomes digested, and leaves a recrement, which producesthe first feces of the infant, called meconium. The liquor amnii is secreted into the uterus, as the fetus requires it, andmay probably be produced by the irritation of the fetus as an extraneousbody; since a similar fluid is acquired from the peritoneum in cases ofextra-uterine gestation. The young caterpillars of the gadfly placed in theskins of cows, and the young of the ichneumon-fly placed in the backs ofthe caterpillars on cabbages, seem to produce their nourishment by theirirritating the sides of their nidus. A vegetable secretion and concretionis thus produced on oak-leaves by the gall-insect, and by the cynips in thebedeguar of the rose; and by the young grasshopper on many plants, by whichthe animal surrounds itself with froth. But in no circumstance isextra-uterine gestation so exactly resembled as by the eggs of a fly, whichare deposited in the frontal sinus of sheep and calves. These eggs float insome ounces of fluid collected in a thin pellicle or hydatide. This bag offluid compresses the optic nerve on one side, by which the vision beingless distinct in that eye, the animal turns in perpetual circles towardsthe side affected, in order to get a more accurate view of objects; for thesame reason as in squinting the affected eye is turned away from the objectcontemplated. Sheep in the warm months keep their noses close to the groundto prevent this fly from so readily getting into their nostrils. The liquor amnii is secreted into the womb as it is required, not only inrespect to quantity, but, as the digestive powers of the fetus becomeformed, this fluid becomes of a different consistence and quality, till itis exchanged for milk after nativity. Haller. Physiol. V. 1. In the egg thewhite part, which is analogous to the liquor amnii of quadrupeds, consistsof two distinct parts; one of which is more viscid, and probably moredifficult of digestion, and more nutritive than the other; and this latteris used in the last week of incubation. The yolk of the egg is a stillstronger or more nutritive fluid, which is drawn up into the bowels of thechick just at its exclusion from the shell, and serves it for nourishmentfor a day or two, till it is able to digest, and has learnt to choose theharder seeds or grains, which are to afford it sustenance. Nothinganalogous to this yolk is found in the fetus of lactiferous animals, as themilk is another nutritive fluid ready prepared for the young progeny. The yolk therefore is not necessary to the spawn of fish, the eggs ofinsects, or for the seeds of vegetables; as their embryons have probablytheir food presented to them as soon as they are excluded from theirshells, or have extended their roots. Whence it happens that some insectsproduce a living progeny in the spring and summer, and eggs in the autumn;and some vegetables have living roots or buds produced in the place ofseeds, as the polygonum viviparum, and magical onions. See Botanic Garden, p. 11. Art. Anthoxanthum. There seems however to be a reservoir of nutriment prepared for some seedsbesides their cotyledons or seed-leaves, which may be supposed in somemeasure analogous to the yolk of the egg. Such are the saccharine juices ofapples, grapes and other fruits, which supply nutrition to the seeds afterthey fall on the ground. And such is the milky juice in the centre of thecocoa-nut, and part of the kernel of it; the same I suppose of all othermonocotyledon seeds, as of the palms, grasses, and lilies. II. 1. The process of generation is still involved in impenetrableobscurity, conjectures may nevertheless be formed concerning some of itscircumstances. First, the eggs of fish and frogs are impregnated, afterthey leave the body of the female; because they are deposited in a fluid, and are not therefore covered with a hard shell. It is however remarkable, that neither frogs nor fish will part with their spawn without the presenceof the male; on which account female carp and gold-fish in small ponds, where there are no males, frequently die from the distention of theirgrowing spawn. 2. The eggs of fowls, which are laid without beingimpregnated, are seen to contain only the yolk and white, which areevidently the food or sustenance for the future chick. 3. As thecicatricula of these eggs is given by the cock, and is evidently therudiment of the new animal; we may conclude, that the embryon is producedby the male, and the proper food and nidus by the female. For if the femalebe supposed to form an equal part of the embryon, why should she form thewhole of the apparatus for nutriment and for oxygenation? the male in manyanimals is larger, stronger, and digests more food than the female, andtherefore should contribute as much or more towards the reproduction of thespecies; but if he contributes only half the embryon and none of theapparatus for sustenance and oxygenation, the division is unequal; thestrength of the male, and his consumption of food are too great for theeffect, compared with that of the female, which is contrary to the usualcourse of nature. In objection to this theory of generation it may be said, if the animalculain femine, as seen by the microscope, be all of them rudiments ofhomunculi, when but one of them can find a nidus, what a waste nature hasmade of her productions? I do not assert that these moving particles, visible by the microscope, are homunciones; perhaps they may be thecreatures of stagnation or putridity, or perhaps no creatures at all; butif they are supposed to be rudiments of homunculi, or embryons, such aprofusion of them corresponds with the general efforts of nature to providefor the continuance of her species of animals. Every individual treeproduces innumerable seeds, and every individual fish innumerable spawn, insuch inconceivable abundance as would in a short space of time crowd theearth and ocean with inhabitants; and these are much more perfect animalsthan the animalcula in femine can be supposed to be, and perish inuncounted millions. This argument only shews, that the productions ofnature are governed by general laws; and that by a wise superfluity ofprovision she has ensured their continuance. 2. That the embryon is secreted or produced by the male, and not by theconjunction of fluids from both male and female, appears from the analogyof vegetable seeds. In the large flowers, as the tulip, there is nosimilarity of apparatus between the anthers and the stigma: the seed isproduced according to the observations of Spallanzani long before theflowers open, and in consequence long before it can be impregnated, likethe egg in the pullet. And after the prolific dust is shed on the stigma, the seed becomes coagulated in one point first, like the cicatricula of theimpregnated egg. See Botanic Garden, Part I. Additional note 38. Now inthese simple products of nature, if the female contributed to produce thenew embryon equally with the male, there would probably have been somevisible similarity of parts for this purpose, besides those necessary forthe nidus and sustenance of the new progeny. Besides in many flowers themales are more numerous than the females, or than the separate uterinecells in their germs, which would shew, that the office of the male was atleast as important as that of the female; whereas if the female, besidesproducing the egg or seed, was to produce an equal part of the embryon, theoffice of reproduction would be unequally divided between them. Add to this, that in the most simple kind of vegetable reproduction, I meanthe buds of trees, which are their viviparous offspring, the leaf isevidently the parent of the bud, which rises in its bosom, according to theobservation of Linnaeus. This leaf consists of absorbent vessels, andpulmonary ones, to obtain its nutriment, and to impregnate it with oxygene. This simple piece of living organization is also furnished with a power ofreproduction; and as the new offspring is thus supported adhering to itsfather, it needs no mother to supply it with a nidus, and nutriment, andoxygenation; and hence no female leaf has existence. I conceive that the vessels between the bud and the leaf communicate orinosculate; and that the bud is thus served with vegetable blood, that is, with both nutriment and oxygenation, till the death of the parent-leaf inautumn. And in this respect it differs from the fetus of viviparousanimals. Secondly, that then the bark-vessels belonging to the dead-leaf, and in which I suppose a kind of manna to have been deposited, become nowthe placental vessels, if they may be so called, of the new bud. From thevernal sap thus produced of one sugar-maple-tree in New-York and inPennsylvania, five or six pounds of good sugar may be made annually withoutdestroying the tree. Account of maple-sugar by B. Rushes. London, Phillips. (See Botanic Garden, Part I. Additional note on vegetable placentation. ) These vessels, when the warmth of the vernal sun hatches the young bud, serve it with a saccharine nutriment, till it acquires leaves of its own, and shoots a new system of absorbents down the bark and root of the tree, just as the farinaceous or oily matter in seeds, and the saccharine matterin fruits, serve their embryons with nutriment, till they acquire leavesand roots. This analogy is as forceable in so obscure a subject, as it iscurious, and may in large buds, as of the horse-chesnut, be almost seen bythe naked eye; if with a penknife the remaining rudiment of the last year'sleaf, and of the new bud in its bosom, be cut away slice by slice. Theseven ribs of the last year's leaf will be seen to have arisen from thepith in seven distinct points making a curve; and the new bud to have beenproduced in their centre, and to have pierced the alburnum and cortex, andgrown without the assistance of a mother. A similar process may be seen ondissecting a tulip-root in winter; the leaves, which inclosed the lastyear's flower-stalk, were not necessary for the flower; but each of thesewas the father of a new bud, which may be now found at its base; and which, as it adheres to the parent, required no mother. This paternal offspring of vegetables, I mean their buds and bulbs, isattended with a very curious circumstance; and that is, that they exactlyresemble their parents, as is observable in grafting fruit-trees, and inpropagating flower-roots; whereas the seminal offspring of plants, beingsupplied with nutriment by the mother, is liable to perpetual variation. Thus also in the vegetable class dioicia, where the male flowers areproduced on one tree, and the female ones on another; the buds of the maletrees uniformly produce either male flowers, or other buds similar tothemselves; and the buds of the female trees produce either female flowers, or other buds similar to themselves; whereas the seeds of these treesproduce either male or female plants. From this analogy of the productionof vegetable buds without a mother, I contend that the mother does notcontribute to the formation of the living ens in animal generation, but isnecessary only for supplying its nutriment and oxygenation. There is another vegetable fact published by M. Koelreuter, which he calls"a complete metamorphosis of one natural species of plants into another, "which shews, that in seeds as well as in buds, the embryon proceeds fromthe male parent, though the form of the subsequent mature plant is in partdependant on the female. M. Koelreuter impregnated a stigma of thenicotiana rustica with the farina of the nicotiana paniculata, and obtainedprolific seeds from it. With the plants which sprung from these seeds, herepeated the experiment, impregnating them with the farina of the nicotianapaniculata. As the mule plants which he thus produced were prolific, hecontinued to impregnate them for many generations with the farina of thenicotiana paniculata, and they became more and more like the male parent, till he at length obtained six plants in every respect perfectly similar tothe nicotiana paniculata; and in no respect resembling their female parentthe nicotiana rustica. _Blumenbach_ on Generation. 3. It is probable that the insects, which are said to require but oneimpregnation for six generations, as the aphis (see Amenit. Academ. )produce their progeny in the manner above described, that is, without amother, and not without a father; and thus experience a lucina sineconcubitu. Those who have attended to the habits of the polypus, which isfound in the stagnant water of our ditches in July, affirm, that the youngones branch out from the side of the parent like the buds of trees, andafter a time separate themselves from them. This is so analogous to themanner in which the buds of trees appear to be produced, that these polypimay be considered as all male animals, producing embryons, which require nomother to supply them with a nidus, or with nutriment, and oxygenation. This lateral or lineal generation of plants, not only obtains in the budsof trees, which continue to adhere to them, but is beautifully seen in thewires of knot-grass, polygonum aviculare, and in those of strawberries, fragaria vesca. In these an elongated creeping bud is protruded, and, whereit touches the ground, takes root, and produces a new plant derived fromits father, from which it acquires both nutriment and oxygenation; and inconsequence needs no maternal apparatus for these purposes. In viviparousflowers, as those of allium magicum, and polygonum viviparum, the anthersand the stigmas become effete and perish; and the lateral or paternaloffspring succeeds instead of seeds, which adhere till they aresufficiently mature, and then fall upon the ground, and take root likeother bulbs. The lateral production of plants by wires, while each new plant is thuschained to its parent, and continues to put forth another and another, asthe wire creeps onward on the ground, is exactly resembled by thetape-worm, or tænia, so often found in the bowels, stretching itself in achain quite from the stomach to the rectum. Linnæus asserts, "that it growsold at one extremity, while it continues to generate young ones at theother, proceeding ad infinitum, like a root of grass. The separate jointsare called gourd-worms, and propagate new joints like the parent withoutend, each joint being furnished with its proper mouth, and organs ofdigestion. " Systema naturæ. Vermes tenia. In this animal there evidentlyappears a power of reproduction without any maternal apparatus for thepurpose of supplying nutriment and oxygenation to the embryon, as itremains attached to its father till its maturity. The volvox globator, which is a transparent animal, is said by Linnæus to bear within it sonsand grand-sons to the fifth generation. These are probably living fetuses, produced by the father, of different degrees of maturity, to be detruded atdifferent periods of time, like the unimpregnated eggs of various sizes, which are found in poultry; and as they are produced without any knowncopulation, contribute to evince, that the living embryon in other ordersof animals is formed by the male-parent, and not by the mother, as oneparent has the power to produce it. This idea of the reproduction of animals from a single living filament oftheir fathers, appears to have been shadowed or allegorized in the curiousaccount in sacred writ of the formation of Eve from a rib of Adam. From all these analogies I conclude, that the embryon is produced solely bythe male, and that the female supplies it with a proper nidus, withsustenance, and with oxygenation; and that the idea of the semen of themale constituting only a stimulus to the egg of the female, exciting itinto life, (as held by some philosophers) has no support from experiment oranalogy. III. 1. Many ingenious philosophers have found so great difficulty inconceiving the manner of the reproduction of animals, that they havesupposed all the numerous progeny, to have existed in miniature in theanimal originally created; and that these infinitely minute forms are onlyevolved or distended, as the embryon increases in the womb. This idea, besides its being unsupported by any analogy we are acquainted with, ascribes a greater tenuity to organized matter, than we can readily admit;as these included embryons are supposed each of them to consist of thevarious and complicate parts of animal bodies: they must possess a muchgreater degree of minuteness, than that which was ascribed to the devilsthat tempted St. Anthony; of whom 20, 000 were said to have been able todance a saraband on the point of the finest needle without incommoding eachother. 2. Others have supposed, that all the parts of the embryon are formed inthe male, previous to its being deposited in the egg or uterus; and that itis then only to have its parts evolved or distended as mentioned above; butthis is only to get rid of one difficulty by proposing another equallyincomprehensible: they found it difficult to conceive, how the embryoncould be formed in the uterus or egg, and therefore wished it to be formedbefore it came thither. In answer to both these doctrines it may beobserved, 1st, that some animals, as the crab-fish, can reproduce a wholelimb, as a leg which has been broken off; others, as worms and snails, canreproduce a head, or a tail, when either of them has been cut away; andthat hence in these animals at least a part can be formed anew, whichcannot be supposed to have existed previously in miniature. Secondly, there are new parts or new vessels produced in many diseases, ason the cornea of the eye in ophthalmy, in wens and cancers, which cannot besupposed to have had a prototype or original miniature in the embryon. Thirdly, how could mule-animals be produced, which partake of the forms ofboth the parents, if the original embryon was a miniature existing in thesemen of the male parent? if an embryon of the male ass was only expanded, no resemblance to the mare could exist in the mule. This mistaken idea of the extension of parts seems to have had its risefrom the mature man resembling the general form of the fetus; and fromthence it was believed, that the parts of the fetus were distended into theman; whereas they have increased 100 times in weight, as well as 100 timesin size; now no one will call the additional 99 parts a distention of theoriginal one part in respect to weight. Thus the uterus during pregnancy isgreatly enlarged in thickness and solidity as well as in capacity, andhence must have acquired this additional size by accretion of new parts, not by an extension of the old ones; the familiar act of blowing up thebladder of an animal recently slaughtered has led our imaginations to applythis idea of distention to the increase of size from natural growth; whichhowever must be owing to the apposition of new parts; as it is evinced fromthe increase of weight along with the increase of dimension; and is evenvisible to our eyes in the elongation of our hair from the colour of itsends; or when it has been dyed on the head; and in the growth of our nailsfrom the specks sometimes observable on them; and in the increase of thewhite crescent at their roots, and in the growth of new flesh in wounds, which consists of new nerves as well as of new blood-vessels. 3. Lastly, Mr. Buffon has with great ingenuity imagined the existence ofcertain organic particles, which are supposed to be partly alive, andpartly mechanic springs. The latter of these were discovered by Mr. Needhamin the milt or male organ of a species of cuttle fish, called calmar; theformer, or living animalcula, are found in both male and female secretions, in the infusions of seeds, as of pepper, in the jelly of roasted veal, andin all other animal and vegetable substances. These organic particles hesupposes to exist in the spermatic fluids of both sexes, and that they arederived thither from every part of the body, and must therefore resemble, as he supposes, the parts from whence they are derived. These organicparticles he believes to be in constant activity, till they become mixed inthe womb, and then they instantly join and produce an embryon or fetussimilar to the two parents. Many objections might be adduced to this fanciful theory, I shall onlymention two. First, that it is analogous to no known animal laws. Andsecondly, that as these fluids, replete with organic particles derived bothfrom the male and female organs, are supposed to be similar; there is noreason why the mother should not produce a female embryon without theassistance of the male, and realize the lucina sine concubitu. IV. 1. I conceive the primordium, or rudiment of the embryon, as secretedfrom the blood of the parent, to consist of a simple living filament as amuscular fibre; which I suppose to be an extremity of a nerve ofloco-motion, as a fibre of the retina is an extremity of a nerve ofsensation; as for instance one of the fibrils, which compose the mouth ofan absorbent vessel; I suppose this living filament, of whatever form itmay be, whether sphere, cube, or cylinder, to be endued with the capabilityof being excited into action by certain kinds of stimulus. By the stimulusof the surrounding fluid, in which it is received from the male, it maybend into a ring; and thus form the beginning of a tube. Such movingfilaments, and such rings, are described by those, who have attended tomicroscopic animalcula. This living ring may now embrace or absorb anutritive particle of the fluid, in which it swims; and by drawing it intoits pores, or joining it by compression to its extremities, may increaseits own length or crassitude; and by degrees the living ring may become aliving tube. 2. With this new organization, or accretion of parts, new kinds ofirritability may commence; for so long as there was but one living organ, it could only be supposed to possess irritability; since sensibility may beconceived to be an extension of the effect of irritability over the rest ofthe system. These new kinds of irritability and of sensibility inconsequence of new organization, appear from variety of facts in the moremature animal; thus the formation of the testes, and consequent secretionof the semen, occasion the passion of lust; the lungs must be previouslyformed before their exertions to obtain fresh air can exist; the throat oroesophagus must be formed previous to the sensation or appetites of hungerand thirst; one of which seems to reside at the upper end, and the other atthe lower end of that canal. Thus also the glans penis, when it is distended with blood, acquires a newsensibility, and a new appetency. The same occurs to the nipples of thebreasts of female animals, when they are distended with blood, they acquirethe new appetency of giving milk. So inflamed tendons and membranes, andeven bones, acquire new sensations; and the parts of mutilated animals, asof wounded snails, and polypi, and crabs, are reproduced; and at the sametime acquire sensations adapted to their situations. Thus when the head ofa snail is reproduced after decollation with a sharp rasor, those curioustelescopic eyes are also reproduced, and acquire their sensibility tolight, as well as their adapted muscles for retraction on the approach ofinjury. With every new change, therefore, of organic form, or addition of organicparts, I suppose a new kind of irritability or of sensibility to beproduced; such varieties of irritability or of sensibility exist in ouradult state in the glands; every one of which is furnished with anirritability, or a taste, or appetency, and a consequent mode of actionpeculiar to itself. In this manner I conceive the vessels of the jaws to produce those of theteeth, those of the fingers to produce the nails, those of the skin toproduce the hair; in the same manner as afterwards about the age of pubertythe beard and other great changes in the form of the body, and dispositionof the mind, are produced in consequence of the new secretion of semen; forif the animal is deprived of this secretion those changes do not takeplace. These changes I conceive to be formed not by elongation ordistention of primeval stamina, but by apposition of parts; as the maturecrab-fish, when deprived of a limb, in a certain space of time has power toregenerate it; and the tadpole puts forth its feet long after its exclusionfrom the spawn; and the caterpillar in changing into a butterfly acquires anew form, with new powers, new sensations, and new desires. The natural history of butterflies, and moths, and beetles, and gnats, isfull of curiosity; some of them pass many months, and others even years, intheir caterpillar or grub state; they then rest many weeks without food, suspended in the air, buried in the earth, or submersed in water; andchange themselves during this time into an animal apparently of a differentnature; the stomachs of some of them, which before digested vegetableleaves or roots, now only digest honey; they have acquired wings for thepurpose of seeking this new food, and a long proboscis to collect it fromflowers, and I suppose a sense of smell to detect the secret places inflowers, where it is formed. The moths, which fly by night, have a muchlonger proboscis rolled up under their chins like a watch spring; whichthey extend to collect the honey from flowers in their sleeping state; whenthey are closed, and the nectaries in consequence more difficult to beplundered. The beetle kind are furnished with an external covering of ahard material to their wings, that they may occasionally again make holesin the earth, in which they passed the former state of their existence. But what most of all distinguishes these new animals is, that they are newfurnished with the powers of reproduction; and that they now differ fromeach other in sex, which does not appear in their caterpillar or grubstate. In some of them the change from a caterpillar into a butterfly ormoth seems to be accomplished for the sole purpose of their propagation;since they immediately die after this is finished, and take no food in theinterim, as the silk-worm in this climate; though it is possible, it mighttake honey as food, if it was presented to it. For in general it wouldseem, that food of a more stimulating kind, the honey of vegetables insteadof their leaves, was necessary for the purpose of the seminal reproductionof these animals, exactly similar to what happens in vegetables; in thesethe juices of the earth are sufficient for their purpose of reproduction bybuds or bulbs; in which the new plant seems to be formed by irritativemotions, like the growth of their other parts, as their leaves or roots;but for the purpose of seminal or amatorial reproduction, where sensationis required, a more stimulating food becomes necessary for the anther, andstigma; and this food is honey; as explained in Sect. XIII. On VegetableAnimation. The gnat and the tadpole resemble each other in their change from natantanimals with gills into aerial animals with lungs; and in their change ofthe element in which they live; and probably of the food, with which theyare supported; and lastly, with their acquiring in their new state thedifference of sex, and the organs of seminal or amatorial reproduction. While the polypus, who is their companion in their former state of life, not being allowed to change his form and element, can only propagate likevegetable buds by the same kind of irritative motions, which produces thegrowth of his own body, without the seminal or amatorial propagation, whichrequires sensation; and which in gnats and tadpoles seems to require achange both of food and of respiration. From hence I conclude, that with the acquisition of new parts, newsensations, and new desires, as well as new powers, are produced; and thisby accretion to the old ones, and not by distention of them. And finally, that the most essential parts of the system, as the brain for the purposeof distributing the power of life, and the placenta for the purpose ofoxygenating the blood, and the additional absorbent vessels for the purposeof acquiring aliment, are first formed by the irritations above mentioned, and by the pleasurable sensations attending those irritations, and by theexertions in consequence of painful sensations, similar to those of hungerand suffocation. After these an apparatus of limbs for future uses, or forthe purpose of moving the body in its present natant state, and of lungsfor future respiration, and of testes for future reproduction, are formedby the irritations and sensations, and consequent exertions of the partspreviously existing, and to which the new parts are to be attached. 3. In confirmation of these ideas it may be observed, that all the parts ofthe body endeavour to grow, or to make additional parts to themselvesthroughout our lives; but are restrained by the parts immediatelycontaining them; thus, if the skin be taken away, the fleshy parts beneathsoon shoot out new granulations, called by the vulgar proud flesh. If theperiosteum be removed, a similar growth commences from the bone. Now in thecase of the imperfect embryon, the containing or confining parts are notyet supposed to be formed, and hence there is nothing to restrain itsgrowth. 4. By the parts of the embryon being thus produced by new apportions, manyphenomena both of animal and vegetable productions receive an easierexplanation; such as that many fetuses are deficient at the extremities, asin a finger or a toe, or in the end of the tongue, or in what is called ahare-lip with deficiency of the palate. For if there should be a deficiencyin the quantity of the first nutritive particles laid up in the egg for thereception of the first living filament, the extreme parts, as being lastformed, must shew this deficiency by their being imperfect. This idea of the growth of the embryon accords also with the production ofsome monstrous births, which consist of a duplicature of the limbs, aschickens with four legs; which could not occur, if the fetus was formed bythe distention of an original stamen, or miniature. For if there should bea superfluity of the first nutritive particles laid up in the egg for thefirst living filament; it is easy to conceive, that a duplicature of someparts may be formed. And that such superfluous nourishment sometimesexists, is evinced by the double yolks in some eggs, which I suppose werethus formed previous to their impregnation by the exuberant nutriment ofthe hen. This idea is confirmed by the analogy of the monsters in the vegetableworld also; in which a duplicate or triplicate production of various partsof the flower is observable, as a triple nectary in some columbines, and atriple petal in some primroses; and which are supposed to be produced byabundant nourishment. 5. If the embryon be received into a fluid, whose stimulus is different insome degree from the natural, as in the production of mule-animals, the newirritabilities or sensibilities acquired by the increasing or growingorganized parts may differ, and thence produce parts not similar to thefather, but of a kind belonging in part to the mother; and thus, though theoriginal stamen or living ens was derived totally from the father, yet newirritabilities or sensibilities being excited, a change of formcorresponding with them will be produced. Nor could the production of mulesexist, if the stamen or miniature of all the parts of the embryon ispreviously formed in the male semen, and is only distended by nourishmentin the female uterus. Whereas this difficulty ceases, if the embryon besupposed to consist of a living filament, which acquires or makes new partswith new irritabilities, as it advances in its growth. The form, solidity, and colour, of the particles of nutriment laid up forthe reception of the first living filament, as well as their peculiar kindof stimulus, may contribute to produce a difference in the form, solidity, and colour of the fetus, so as to resemble the mother, as it advances inlife. This also may especially happen during the first state of theexistence of the embryon, before it has acquired organs, which can changethese first nutritive particles, as explained in No. 5. 2. Of this Section. And as these nutritive particles are supposed to be similar to those, whichare formed for her own nutrition, it follows that the fetus should so farresemble the mother. This explains, why hereditary diseases may be derived either from the maleor female parent, as well as the peculiar form of either of their bodies. Some of these hereditary diseases are simply owing to a deficient activityof a part of the system, as of the absorbent vessels, which open into thecells or cavities of the body, and thus occasion dropsies. Others are atthe same time owing to an increase of sensation, as in scrophula andconsumption; in these the obstruction of the fluids is first caused by theinirritability of the vessels, and the inflammation and ulcers whichsucceed, are caused by the consequent increase of sensation in theobstructed part. Other hereditary diseases, as the epilepsy, and otherconvulsions, consist in too great voluntary exertions in consequence ofdisagreeable sensation in some particular diseased part. Now as the pains, which occasion these convulsions, are owing to defect of the action of thediseased part, as shewn in Sect. XXXIV. It is plain, that all thesehereditary diseases may have their origin either from defectiveirritability derived from the father, or from deficiency of the stimulus ofthe nutriment derived from the mother. In either case the effect would besimilar; as a scrophulous race is frequently produced among the poor fromthe deficient stimulus of bad diet, or of hunger; and among the rich, by adeficient irritability from their having been long accustomed to too greatstimulus, as of vinous spirit. 6. From this account of reproduction it appears, that all animals have asimilar origin, viz. From a single living filament; and that the differenceof their forms and qualities has arisen only from the differentirritabilities and sensibilities, or voluntarities, or associabilities, ofthis original living filament; and perhaps in some degree from thedifferent forms of the particles of the fluids, by which it has been atfirst stimulated into activity. And that from hence, as Linnæus hasconjectured in respect to the vegetable world, it is not impossible, butthe great variety of species of animals, which now tenant the earth, mayhave had their origin from the mixture of a few natural orders. And thatthose animal and vegetable mules, which could continue their species, havedone so, and constitute the numerous families of animals and vegetableswhich now exist; and that those mules, which were produced with imperfectorgans of generation, perished without reproduction, according to theobservation of Aristotle; and are the animals, which we now call mules. SeeBotanic Garden, Part II. Note on Dianthus. Such a promiscuous intercourse of animals is said to exist at this day inNew South Wales by Captain Hunter. And that not only amongst the quadrupedsand birds of different kinds, but even amongst the fish, and, as hebelieves, amongst the vegetables. He speaks of an animal between theopossum and the kangaroo, from the size of a sheep to that of a rat. Manyfish seemed to partake of the shark; some with a shark's head andshoulders, and the hind part of a shark; others with a shark's head and thebody of a mullet; and some with a shark's head and the flat body of asting-ray. Many birds partake of the parrot; some have the head, neck, andbill of a parrot, with long straight feet and legs; others with legs andfeet of a parrot, with head and neck of a sea gull. Voyage to South Walesby Captain John Hunter, p. 68. 7. All animals therefore, I contend, have a similar cause of theirorganization, originating from a single living filament, endued indeed withdifferent kinds of irritabilities and sensibilities, or of animalappetencies; which exist in every gland, and in every moving organ of thebody, and are as essential to living organization as chemical affinitiesare to certain combinations of inanimate matter. If I might be indulged to make a simile in a philosophical work, I shouldsay, that the animal appetencies are not only perhaps less numerousoriginally than the chemical affinities; but that like these latter, theychange with every new combination; thus vital air and azote, when combined, produce nitrous acid; which now acquires the property of dissolving silver;so with every new additional part to the embryon, as of the throat orlungs, I suppose a new animal appetency to be produced. In this early formation of the embryon from the irritabilities, sensibilities, and associabilities, and consequent appetencies, the facultyof volition can scarcely be supposed to have had its birth. For about whatcan the fetus deliberate, when it has no choice of objects? But in the moreadvanced state of the fetus, it evidently possesses volition; as itfrequently changes its attitude, though it seems to sleep the greatest partof its time; and afterwards the power of volition contributes to change oralter many parts of the body during its growth to manhood, by our earlymodes of exertion in the various departments of life. All these facultiesthen constitute the vis fabricatrix, and the vis conservatrix, as well asthe vis medicatrix of nature, so much spoken of, but so little understoodby philosophers. 8. When we revolve in our minds, first, the great changes, which we seenaturally produced in animals after their nativity, as in the production ofthe butterfly with painted wings from the crawling caterpillar; or of therespiring frog from the subnatant tadpole; from the feminine boy to thebearded man, and from the infant girl to the lactescent woman; both whichchanges may be prevented by certain mutilations of the glands necessary toreproduction. Secondly, when we think over the great changes introduced into variousanimals by artificial or accidental cultivation, as in horses, which wehave exercised for the different purposes of strength or swiftness, incarrying burthens or in running races; or in dogs, which have beencultivated for strength and courage, as the bull-dog; or for acuteness ofhis sense or smell, as the hound and spaniel; or for the swiftness of hisfoot, as the greyhound; or for his swimming in the water, or for drawingsnow-sledges, as the rough-haired dogs of the north; or lastly, as aplay-dog for children, as the lap-dog; with the changes of the forms of thecattle, which have been domesticated from the greatest antiquity, ascamels, and sheep; which have undergone so total a transformation, that weare now ignorant from what species of wild animals they had their origin. Add to these the great changes of shape and colour, which we daily seeproduced in smaller animals from our domestication of them, as rabbits, orpigeons; or from the difference of climates and even of seasons; thus thesheep of warm climates are covered with hair instead of wool; and the haresand partridges of the latitudes, which are long buried in snow, becomewhite during the winter months; add to these the various changes producedin the forms of mankind, by their early modes of exertion; or by thediseases occasioned by their habits of life; both of which becamehereditary, and that through many generations. Those who labour at theanvil, the oar, or the loom, as well as those who carry sedan-chairs, orwho have been educated to dance upon the rope, are distinguishable by theshape of their limbs; and the diseases occasioned by intoxication deformthe countenance with leprous eruptions, or the body with tumid viscera, orthe joints with knots and distortions. Thirdly, when we enumerate the great changes produced in the species ofanimals before their nativity; these are such as resemble the form orcolour of their parents, which have been altered by the cultivation oraccidents above related, and are thus continued to their posterity. Or theyare changes produced by the mixture of species as in mules; or changesproduced probably by the exuberance of nourishment supplied to the fetus, as in monstrous births with additional limbs; many of these enormities ofshape are propagated, and continued as a variety at least, if not as a newspecies of animal. I have seen a breed of cats with an additional claw onevery foot; of poultry also with an additional claw, and with wings totheir feet; and of others without rumps. Mr. Buffon mentions a breed ofdogs without tails, which are common at Rome and at Naples, which hesupposes to have been produced by a custom long established of cuttingtheir tails close off. There are many kinds of pigeons, admired for theirpeculiarities, which are monsters thus produced and propagated. And tothese must be added, the changes produced by the imagination of the maleparent, as will be treated of more at large in No. VI. Of this Section. When we consider all these changes of animal form, and innumerable others, which may be collected from the books of natural history; we cannot but beconvinced, that the fetus or embryon is formed by apposition of new parts, and not by the distention of a primordial nest of germs, included onewithin another, like the cups of a conjurer. Fourthly, when we revolve in our minds the great similarity of structure, which obtains in all the warm-blooded animals, as well quadrupeds, birds, and amphibious animals, as in mankind; from the mouse and bat to theelephant and whale; one is led to conclude, that they have alike beenproduced from a similar living filament. In some this filament in itsadvance to maturity has acquired hands and fingers, with a fine sense oftouch, as in mankind. In others it has acquired claws or talons, as intygers and eagles. In others, toes with an intervening web, or membrane, asin seals and geese. In others it has acquired cloven hoofs, as in cows andswine; and whole hoofs in others, as in the horse. While in the bird kindthis original living filament has put forth wings instead of arms or legs, and feathers instead of hair. In some it has protruded horns on theforehead instead of teeth in the fore part of the upper jaw; in otherstushes instead of horns; and in others beaks instead of either. And allthis exactly as is daily seen in the transmutations of the tadpole, whichacquires legs and lungs, when he wants them; and loses his tail, when it isno longer of service to him. Fifthly, from their first rudiment, or primordium, to the termination oftheir lives, all animals undergo perpetual transformations; which are inpart produced by their own exertions in consequence of their desires andaversions, of their pleasures and their pains, or of irritations, or ofassociations; and many of these acquired forms or propensities aretransmitted to their posterity. See Sect. XXXI. 1. As air and water are supplied to animals in sufficient profusion, the threegreat objects of desire, which have changed the forms of many animals bytheir exertions to gratify them, are those of lust, hunger, and security. Agreat want of one part of the animal world has consisted in the desire ofthe exclusive possession of the females; and these have acquired weapons tocombat each other for this purpose, as the very thick, shield-like, hornyskin on the shoulder of the boar is a defence only against animals of hisown species, who strike obliquely upwards, nor are his tushes for otherpurposes, except to defend himself, as he is not naturally a carnivorousanimal. So the horns of the stag are sharp to offend his adversary, but arebranched for the purpose of parrying or receiving the thrusts of hornssimilar to his own, and have therefore been formed for the purpose ofcombating other stags for the exclusive possession of the females; who areobserved, like the ladies in the times of chivalry, to attend the car ofthe victor. The birds, which do not carry food to their young, and do not thereforemarry, are armed with spurs for the purpose of fighting for the exclusivepossession of the females, as cocks and quails. It is certain that theseweapons are not provided for their defence against other adversaries, because the females of these species are without this armour. The finalcause of this contest amongst the males seems to be, that the strongest andmost active animal should propagate the species, which should thence becomeimproved. Another great want consists in the means of procuring food, which hasdiversified the forms of all species of animals. Thus the nose of the swinehas become hard for the purpose of turning up the soil in search of insectsand of roots. The trunk of the elephant is an elongation of the nose forthe purpose of pulling down the branches of trees for his food, and fortaking up water without bending his knees. Beasts of prey have acquiredstrong jaws or talons. Cattle have acquired a rough tongue and a roughpalate to pull off the blades of grass, as cows and sheep. Some birds haveacquired harder beaks to crack nuts, as the parrot. Others have acquiredbeaks adapted to break the harder seeds, as sparrows. Others for the softerseeds of flowers, or the buds of trees, as the finches. Other birds haveacquired long beaks to penetrate the moister soils in search of insects orroots, as woodcocks; and others broad ones to filtrate the water of lakes, and to retain aquatic insects. All which seem to have been graduallyproduced during many generations by the perpetual endeavour of thecreatures to supply the want of food, and to have been delivered to theirposterity with constant improvement of them for the purposes required. The third great want amongst animals is that of security, which seems muchto have diversified the forms of their bodies and the colour of them; theseconsist in the means of escaping other animals more powerful thanthemselves. Hence some animals have acquired wings instead of legs, as thesmaller birds, for the purpose of escape. Others great length of fin, or ofmembrane, as the flying fish, and the bat. Others great swiftness of foot, as the hare. Others have acquired hard or armed shells, as the tortoise andthe echinus marinus. Mr. Osbeck, a pupil of Linnæus, mentions the American frog fish, LophiusHistrio, which inhabits the large floating islands of sea-weed about theCape of Good Hope, and has fulcra resembling leaves, that the fishes ofprey may mistake it for the sea-weed, which it inhabits. Voyage to China, p. 113. The contrivances for the purposes of security extend even to vegetables, asis seen in the wonderful and various means of their concealing or defendingtheir honey from insects, and their seeds from birds. On the other handswiftness of wing has been acquired by hawks and swallows to pursue theirprey; and a proboscis of admirable structure has been acquired by the bee, the moth, and the humming bird, for the purpose of plundering the nectariesof flowers. All which seem to have been formed by the original livingfilament, excited into action by the necessities of the creatures, whichpossess them, and on which their existence depends. From thus meditating on the great similarity of the structure of thewarm-blooded animals, and at the same time of the great changes theyundergo both before and after their nativity; and by considering in howminute a portion of time many of the changes of animals above describedhave been produced; would it be too bold to imagine, that in the greatlength of time, since the earth began to exist, perhaps millions of agesbefore the commencement of the history of mankind, would it be too bold toimagine, that all warm-blooded animals have arisen from one livingfilament, which THE GREAT FIRST CAUSE endued with animality, with the powerof acquiring new parts, attended with new propensities, directed byirritations, sensations, volitions, and associations; and thus possessingthe faculty of continuing to improve by its own inherent activity, and ofdelivering down those improvements by generation to its posterity, worldwithout end! Sixthly, The cold-blooded animals, as the fish-tribes, which are furnishedwith but one ventricle of the heart, and with gills instead of lungs, andwith fins instead of feet or wings, bear a great similarity to each other;but they differ, nevertheless, so much in their general structure from thewarm-blooded animals, that it may not seem probable at first view, that thesame living filament could have given origin to this kingdom of animals, asto the former. Yet are there some creatures, which unite or partake of boththese orders of animation, as the whales and seals; and more particularlythe frog, who changes from an aquatic animal furnished with gills to anaerial one furnished with lungs. The numerous tribes of insects without wings, from the spider to thescorpion, from the flea to the lobster; or with wings, from the gnat andthe ant to the wasp and the dragon-fly, differ so totally from each other, and from the red-blooded classes above described, both in the forms oftheir bodies, and their modes of life; besides the organ of sense, whichthey seem to possess in their antennæ or horns, to which it has beenthought by some naturalists, that other creatures have nothing similar;that it can scarcely be supposed that this nation of animals could havebeen produced by the same kind of living filament, as the red-bloodedclasses above mentioned. And yet the changes which many of them undergo intheir early state to that of their maturity, are as different, as oneanimal can be from another. As those of the gnat, which passes his earlystate in water, and then stretching out his new wings, and expanding hisnew lungs, rises in the air; as of the caterpillar, and bee-nymph, whichfeed on vegetable leaves or farina, and at length bursting from theirself-formed graves, become beautiful winged inhabitants of the skies, journeying from flower to flower, and nourished by the ambrosial food ofhoney. There is still another class of animals, which are termed vermes byLinnæus, which are without feet, or brain, and are hermaphrodites, asworms, leeches, snails, shell-fish, coralline insects, and sponges; whichpossess the simplest structure of all animals, and appear totally differentfrom those already described. The simplicity of their structure, however, can afford no argument against their having been produced from a livingfilament as above contended. Last of all the various tribes of vegetables are to be enumerated amongstthe inferior orders of animals. Of these the anthers and stigmas havealready been shewn to possess some organs of sense, to be nourished byhoney, and to have the power of generation like insects, and have thencebeen announced amongst the animal kingdom in Sect. XIII. And to these mustbe added the buds and bulbs which constitute the viviparous offspring ofvegetation. The former I suppose to be beholden to a single living filamentfor their seminal or amatorial procreation; and the latter to the samecause for their lateral or branching generation, which they possess incommon with the polypus, tænia, and volvox; and the simplicity of which isan argument in favour of the similarity of its cause. Linnæus supposes, in the Introduction to his Natural Orders, that very fewvegetables were at first created, and that their numbers were increased bytheir intermarriages, and adds, suadent hæc Creatoris leges a simplicibusad composita. Many other changes seem to have arisen in them by theirperpetual contest for light and air above ground, and for food or moisturebeneath the soil. As noted in Botanic Garden, Part II. Note on Cuscuta. Other changes of vegetables from climate, or other causes, are remarked inthe Note on Curcuma in the same work. From these one might be led toimagine, that each plant at first consisted of a single bulb or flower toeach root, as the gentianella and daisy; and that in the contest for airand light new buds grew on the old decaying flower stem, shooting downtheir elongated roots to the ground, and that in process of ages tall treeswere thus formed, and an individual bulb became a swarm of vegetables. Other plants, which in this contest for light and air were too slender torise by their own strength, learned by degrees to adhere to theirneighbours, either by putting forth roots like the ivy, or by tendrils likethe vine, or by spiral contortions like the honeysuckle; or by growing uponthem like the misleto, and taking nourishment from their barks; or by onlylodging or adhering on them, and deriving nourishment from the air, astillandsia. Shall we then say that the vegetable living filament was originallydifferent from that of each tribe of animals above described? And that theproductive living filament of each of those tribes was different originallyfrom the other? Or, as the earth and ocean were probably peopled withvegetable productions long before the existence of animals; and manyfamilies of these animals long before other families of them, shall weconjecture that one and the same kind of living filaments is and has beenthe cause of all organic life? This idea of the gradual formation and improvement of the animal worldaccords with the observations of some modern philosophers, who havesupposed that the continent of America has been raised out of the ocean ata later period of time than the other three quarters of the globe, whichthey deduce from the greater comparative heights of its mountains, and theconsequent greater coldness of its respective climates, and from the lesssize and strength of its animals, as the tygers and allegators comparedwith those of Asia or Africa. And lastly, from the less progress in theimprovements of the mind of its inhabitants in respect to voluntaryexertions. This idea of the gradual formation and improvement of the animal worldseems not to have been unknown to the ancient philosophers. Plato havingprobably observed the reciprocal generation of inferior animals, as snailsand worms, was of opinion, that mankind with all other animals wereoriginally hermaphrodites during the infancy of the world, and were inprocess of time separated into male and female. The breasts and teats ofall male quadrupeds, to which no use can be now assigned, adds perhaps someshadow of probability to this opinion. Linnæus excepts the horse from themale quadrupeds, who have teats; which might have shewn the earlier originof his exigence; but Mr. J. Hunter asserts, that he has discovered thevestiges of them on his sheath, and has at the same time enriched naturalhistory with a very curious fact concerning the male pigeon; at the time ofhatching the eggs both the male and female pigeon undergo a great change intheir crops; which thicken and become corrugated, and secrete a kind ofmilky fluid, which coagulates, and with which alone they for a few daysfeed their young, and afterwards feed them with this coagulated fluid mixedwith other food. How this resembles the breasts of female quadrupeds afterthe production of their young! and how extraordinary, that the male shouldat this time give milk as well as the female! See Botanic Garden, Part II. Note on Curcuma. The late Mr. David Hume, in his posthumous works, places the powers ofgeneration much above those of our boasted reason; and adds, that reasoncan only make a machine, as a clock or a ship, but the power of generationmakes the maker of the machine; and probably from having observed, that thegreatest part of the earth has been formed out of organic recrements; asthe immense beds of limestone, chalk, marble, from the shells of fish; andthe extensive provinces of clay, sandstone, ironstone, coals, fromdecomposed vegetables; all which have been first produced by generation, orby the secretions of organic life; he concludes that the world itself mighthave been generated, rather than created; that is, it might have beengradually produced from very small beginnings, increasing by the activityof its inherent principles, rather than by a sudden evolution of the wholeby the Almighty fire. --What a magnificent idea of the infinite power of THEGREAT ARCHITECT! THE CAUSE OF CAUSES! PARENT OF PARENTS! ENS ENTIUM! For if we may compare infinities, it would seem to require a greaterinfinity of power to cause the causes of effects, than to cause the effectsthemselves. This idea is analogous to the improving excellence observablein every part of the creation; such as in the progressive increase of thesolid or habitable parts of the earth from water; and in the progressiveincrease of the wisdom and happiness of its inhabitants; and is consonantto the idea of our present situation being a state of probation, which byour exertions we may improve, and are consequently responsible for ouractions. V. 1. The efficient cause of the various colours of the eggs of birds, andof the air and feathers of animals, is a subject so curious, that I shallbeg to introduce it in this place. The colours of many animals seem adaptedto their purposes of concealing themselves either to avoid danger, or tospring upon their prey. Thus the snake and wild cat, and leopard, are socoloured as to resemble dark leaves and their lighter interstices; birdsresemble the colour of the brown ground, or the green hedges, which theyfrequent; and moths and butterflies are coloured like the flowers whichthey rob of their honey. Many instances are mentioned of this kind inBotanic Garden, p. 2. Note on Rubia. These colours have, however, in some instances another use, as the blackdiverging area from the eyes of the swan; which, as his eyes are placedless prominent than those of other birds, for the convenience of puttingdown his head under water, prevents the rays of light from being reflectedinto his eye, and thus dazzling his sight, both in air and beneath thewater; which must have happened, if that surface had been white like therest of his feathers. There is a still more wonderful thing concerning these colours adapted tothe purpose of concealment; which is, that the eggs of birds are socoloured as to resemble the colour of the adjacent objects and theirinterfaces. The eggs of hedge-birds are greenish with dark spots; those ofcrows and magpies, which are seen from beneath through wicker nests, arewhite with dark spots; and those of larks and partridges are russet orbrown, like their nests or situations. A thing still more astonishing is, that many animals in countries coveredwith snow become white in winter, and are said to change their colour againin the warmer months, as bears, hares, and partridges. Our domesticatedanimals lose their natural colours, and break into great variety, ashorses, dogs, pigeons. The final cause of these colours is easilyunderstood, as they serve some purposes of the animal, but the efficientcause would seem almost beyond conjecture. First, the choroid coat of the eye, on which the semitransparent retina isexpanded, is of different colour in different animals; in those which feedon grass it is green; from hence there would appear some connexion betweenthe colour of the choroid coat and of that constantly painted on the retinaby the green grass. Now, when the ground becomes covered with snow, itwould seem, that that action of the retina, which is called whiteness, being constantly excited in the eye, may be gradually imitated by theextremities of the nerves of touch, or rete mucosum of the skin. And if itbe supposed, that the action of the retina in producing the perception ofany colour consists in so disposing its own fibres or surface, as toreflect those coloured rays only, and transmit the others likesoap-bubbles; then that part of the retina, which gives us the perceptionof snow, must at that time be white; and that which gives us the perceptionof grass, must be green. Then if by the laws of imitation, as explained in Section XII. 3. 3. AndXXXIX. 6. The extremities of the nerves of touch in the rete mucosum beinduced into similar action, the skin or feathers, or hair, may in likemanner so dispose their extreme fibres, as to reflect white; for it isevident, that all these parts were originally obedient to irritativemotions during their growth, and probably continue to be so; that thoseirritative motions are not liable in a healthy state to be succeeded bysensation; which however is no uncommon thing in their diseased state, orin their infant state, as in plica polonica, and in very youngpen-feathers, which are still full of blood. It was shewn in Section XV. On the Production of Ideas, that the movingorgan of sense in some circumstances resembled the object which producedthat motion. Hence it may be conceived, that the rete mucosum, which is theextremity of the nerves of touch, may by imitating the motions of theretina become coloured. And thus, like the fable of the camelion, allanimals may possess a tendency to be coloured somewhat like the coloursthey most frequently inspect, and finally, that colours may be thus givento the egg-shell by the imagination of the female parent; which shell ispreviously a mucous membrane, indued with irritability, without which itcould not circulate its fluids, and increase in its bulk. Nor is this morewonderful than that a single idea of imagination mould in an instant colourthe whole surface of the body of a bright scarlet, as in the blush ofshame, though by a very different process. In this intricate subjectnothing but loose analogical conjectures can be had, which may however leadto future discoveries; but certain it is that both the change of the colourof animals to white in the winters of snowy countries, and the spots onbirds eggs, must have some efficient cause; since the uniformity of theirproduction shews it cannot arise from a fortuitous concurrence ofcircumstances; and how is this efficient cause to be detected, orexplained, but from its analogy to other animal facts? 2. The nutriment supplied by the female parent in viviparous animals totheir young progeny may be divided into three kinds, corresponding with theage of the new creature. 1. The nutriment contained in the ovum aspreviously prepared for the embryon in the ovary. 2. The liquor amniiprepared for the fetus in the uterus, and in which it swims; and lastly, the milk prepared in the pectoral glands for the new born-child. There isreason to conclude that variety of changes may be produced in the newanimal from all these sources of nutriment, but particularly from the firstof them.. The organs of digestion and of sanguification in adults, and afterwardsthose of secretion, prepare or separate the particles proper fornourishment from other combinations of matter, or recombine them into newkinds of matter, proper to excite into action the filaments, which absorbor attract them by animal appetency. In this process we must attend notonly to the action of the living filament which receives a nutritiveparticle to its bosom, but also to the kind of particle, in respect toform, or size, or colour, or hardness, which is thus previously preparedfor it by digestion, sanguification, and secretion. Now as the firstfilament of entity cannot be furnished with the preparative organs abovementioned, the nutritive particles, which are at first to be received byit, are prepared by the mother; and deposited in the ovum ready for itsreception. These nutritive particles must be supposed to differ in somerespects, when thus prepared by different animals. They may differ in size, solidity, colour, and form; and yet may be sufficiently congenial to theliving filament, to which they are applied, as to excite its activity bytheir stimulus, and its animal appetency to receive them, and to combinethem with itself into organization. By this first nutriment thus prepared for the embryon is not meant theliquor amnii, which is produced afterwards, nor the larger exterior partsof the white of the egg; but the fluid prepared, I suppose, in the ovary ofviviparous animals, and that which immediately surrounds the cicatricula ofan impregnated egg, and is visible to the eye in a boiled one. Now these ultimate particles of animal matter prepared by the glands of themother may be supposed to resemble the similar ultimate particles, whichwere prepared for her own nourishment; that is, to the ultimate particlesof which her own organization consists. And that hence when these becomecombined with a new embryon, which in its early state is not furnished withstomach, or glands, to alter them; that new embryon will bear someresemblance to the mother. This seems to be the origin of the compound forms of mules, which evidentlypartake of both parents, but principally of the male parent. In thisproduction of chimeras the antients seem to have indulged their fancies, whence the sphinxes, griffins, dragons, centaurs, and minotaurs, which arevanished from modern credulity. It would seem, that in these unnatural conjunctions, when the nutrimentdeposited by the female was so ill adapted to stimulate the living filamentderived from the male into action, and to be received; or embraced by it, and combined with it into organization, as not to produce the organsnecessary to life, as the brain, or heart, or stomach, that no mule wasproduced. Where all the parts necessary to life in these compound animalswere formed sufficiently perfect, except the parts of generation, thoseanimals were produced which are now called mules. The formation of the organs of sexual generation, in contradistinction tothat by lateral buds, in vegetables, and in some animals, as the polypus, the tænia, and the volvox, seems the chef d'oeuvre, the master-piece ofnature; as appears from many flying insects, as in moths and butterflies, who seem to undergo a general change of their forms solely for the purposeof sexual reproduction, and in all other animals this organ is not completetill the maturity of the creature. Whence it happens that, in thecopulation of animals of different species, the parts necessary to life arefrequently completely formed; but those for the purpose of generation aredefective, as requiring a nicer organization; or more exact coincidence ofthe particles of nutriment to the irritabilities or appetencies of theoriginal living filament. Whereas those mules, where all the parts could beperfectly formed, may have been produced in early periods of time, and mayhave added to the numbers of our various species of animals, as beforeobserved. As this production of mules is a constant effect from the conjunction ofdifferent species of animals, those between the horse and the female assalways resembling the horse more than the ass; and those, on the contrary, between the male ass and the mare, always resembling the ass more than themare; it cannot be ascribed to the imagination of the male animal whichcannot be supposed to operate so uniformly; but to the form of the firstnutritive particles, and to their peculiar stimulus exciting the livingfilament to select and combine them with itself. There is a similaruniformity of effect in respect to the colour of the progeny producedbetween a white man, and a black woman, which, if I am well informed, isalways of the mulatto kind, or a mixture of the two; which may perhaps beimputed to the peculiar form of the particles of nutriment supplied to theembryon by the mother at the early period of its existence, and theirpeculiar stimulus; as this effect, like that of the mule progeny abovetreated of, is uniform and consistent, and cannot therefore be ascribed tothe imagination of either of the parents. Dr. Thunberg observes, in his Journey to the Cape of Good Hope, that thereare some families, which have descended from blacks in the female line forthree generations. The first generation proceeding from an European, whomarried a tawny slave, remains tawny, but approaches to a white complexion;but the children of the third generation, mixed with Europeans, becomequite white, and are often remarkably beautiful. V. I. P. 112. When the embryon has produced a placenta, and furnished itself with vesselsfor selection of nutritious particles, and for oxygenation of them, nogreat change in its form or colour is likely to be produced by theparticles of sustenance it now takes from the fluid, in which it isimmersed; because it has now acquired organs to alter or new combine them. Hence it continues to grow, whether this fluid, in which it swims, beformed by the uterus or by any other cavity of the body, as inextra-uterine gestation; and which would seem to be produced by thestimulus of the fetus on the sides of the cavity, where it is found, asmentioned before. And thirdly, there is still less reason to expect anyunnatural change to happen to the child after its birth from the differenceof the milk it now takes; because it has acquired a stomach, and lungs, andglands, of sufficient power to decompose and recombine the milk; and thusto prepare from it the various kinds of nutritious particles, which theappetencies of the various fibrils or nerves may require. From all this reasoning I would conclude, that though the imagination ofthe female may be supposed to affect the embryon by producing a differencein its early nutriment; yet that no such power can affect it after it hasobtained a placenta, and other organs; which may select or change the food, which is presented to it either in the liquor amnii, or in the milk. Now asthe eggs in pullets, like the seeds in vegetables, are produced gradually, long before they are impregnated, it does not appear how any sudden effectof imagination of the mother at the time of impregnation can produce anyconsiderable change in the nutriment already thus laid up for the expectedor desired embryon. And that hence any changes of the embryon, except thoseuniform ones in the production of mules and mulattoes, more probably dependon the imagination of the male parent. At the same time it seems manifest, that those monstrous births, which consist in some deficiencies only, orsome redundancies of parts, originate from the deficiency or redundance ofthe first nutriment prepared in the ovary, or in the part of the eggimmediately surrounding the cicatricula, as described above; and whichcontinues some time to excite the first living filament into action, afterthe simple animal is completed; or ceases to excite it, before the completeform is accomplished. The former of these circumstances is evinced by theeggs with double yolks, which frequently happen to our domesticatedpoultry, and which, I believe, are so formed before impregnation, but whichwould be well worth attending to, both before and after impregnation; as itis probable, something valuable on this subject might be learnt from them. The latter circumstance, or that of deficiency of original nutriment, maybe deduced from reverse analogy. There are, however, other kinds of monstrous births, which neither dependon deficiency of parts, or supernumerary ones; nor are owing to theconjunction of animals of different species; but which appear to be newconformations, or new dispositions of parts in respect to each other, andwhich, like the variation of colours and forms of our domesticated animals, and probably the sexual parts of all animals, may depend on the imaginationof the male parent, which we now come to consider. VI. 1. The nice actions of the extremities of our various glands areexhibited in their various productions, which are believed to be made bythe gland, and not previously to exist as such in the blood. Thus the glands, which constitute the liver, make bile; those of thestomach make gastric acid; those beneath the jaw, saliva; those of theears, ear-wax; and the like. Every kind of gland must possess a peculiarirritability, and probably a sensibility, at the early state of itsexistence; and must be furnished with a nerve of sense, or of motion, toperceive, and to select, and to combine the particles, which compose thefluid it secretes. And this nerve of sense which perceives the differentarticles which compose the blood, must at least be conceived to be as fineand subtile an organ, as the optic or auditory nerve, which perceive lightor sound. See Sect. XIV. 9. But in nothing is this nice action of the extremities of the blood-vesselsso wonderful, as in the production of contagious matter. A small drop ofvariolous contagion diffused in the blood, or perhaps only by beinginserted beneath the cuticle, after a time, (as about a quarter of alunation, ) excites the extreme vessels of the skin into certain motions, which produce a similar contagious material, filling with it a thousandpustules. So that by irritation, or by sensation in consequence ofirritation, or by association of motions, a material is formed by theextremities of certain cutaneous vessels, exactly similar to thestimulating material, which caused the irritation, or consequent sensation, or association. Many glands of the body have their motions, and in consequence theirsecreted fluids, affected by pleasurable or painful ideas, since they arein many instances influenced by sensitive associations, as well as by theirritations of the particles of the passing blood. Thus the idea of meat, excited in the minds of hungry dogs, by their sense of vision, or of smell, increases the discharge of saliva, both in quantity and viscidity; as isseen in its hanging down in threads from their mouths, as they stand rounda dinner-table. The sensations of pleasure, or of pain, of peculiar kinds, excite in the same manner a great discharge of tears; which appear also tobe more saline at the time of their secretion, from their inflaming theeyes and eye-lids. The paleness from fear, and the blush of shame, and ofjoy, are other instances of the effects of painful, or pleasurablesensations, on the extremities of the arterial system. It is probable, that the pleasurable sensation excited in the stomach byfood, as well as its irritation, contributes to excite into action thegastric glands, and to produce a greater secretion of their fluids. Thesame probably occurs in the secretion of bile; that is, that thepleasurable sensation excited in the stomach, affects this secretion bysensitive association, as well as by irritative association. And lastly it would seem, that all the glands in the body have theirsecreted fluids affected, in quantity and quality, by the pleasurable orpainful sensations, which produce or accompany those secretions. And thatthe pleasurable sensations arising from these secretions may constitute theunnamed pleasure of exigence, which is contrary to what is meant by tediumvitæ, or ennui; and by which we sometimes feel ourselves happy, withoutbeing able to ascribe it to any mental cause, as after an agreeable meal, or in the beginning of intoxication. Now it would appear, that no secretion or excretion of fluid is attendedwith so much agreeable sensation, as that of the semen; and it would thencefollow, that the glands, which perform this secretion, are more likely tobe much affected by their catenations with pleasurable sensations. Thiscircumstance is certain, that much more of this fluid is produced in agiven time, when the object of its exclusion is agreeable to the mind. 2. A forceable argument, which shews the necessity of pleasurable sensationto copulation, is, that the act cannot be performed without it; it iseasily interrupted by the pain of fear or bashfulness; and no efforts ofvolition or of irritation can effect this process, except such as inducepleasurable ideas or sensations. See Sect. XXXIII. 1. 1. A curious analogical circumstance attending hermaphrodite insects, assnails and worms, still further illustrates this theory; if the snail orworm could have impregnated itself, there might have been a saving of alarge male apparatus; but as this is not so ordered by nature, but eachsnail and worm reciprocally receives and gives impregnation, it appears, that a pleasurable excitation seems also to have been required. This wonderful circumstance of many insects being hermaphrodites, and atthe same time not having power to impregnate themselves, is attended to byDr. Lister, in his Exercitationes Anatom. De Limacibus, p. 145; who, amongst many other final causes, which he adduces to account for it, adds, ut tam tristibus et frigidis animalibus majori cum voluptate perficiaturvenus. There is, however, another final cause, to which this circumstance may beimputed: it was observed above, that vegetable buds and bulbs, which areproduced without a mother, are always exact resemblances of their parent;as appears in grafting fruit-trees, and in the flower-buds of the dioiceousplants, which are always of the same sex on the same tree; hence thosehermaphrodite insects, if they could have produced young without a mother, would not have been, capable of that change or improvement, which is seenin all other animals, and in those vegetables, which are procreated by themale embryon received and nourished by the female. And it is henceprobable, that if vegetables could only have been produced by buds andbulbs, and not by sexual generation, that there would not at this time haveexisted one thousandth part of their present number of species; which haveprobably been originally mule-productions; nor could any kind ofimprovement or change have happened to them, except by the difference ofsoil or climate. 3. I conclude, that the imagination of the male at the time of copulation, or at the time of the secretion of the semen, may so affect this secretionby irritative or sensitive association, as described in No. 5. 1. Of thissection, as to cause the production of similarity of form and of features, with the distinction of sex; as the motions of the chissel of the turnerimitate or correspond with those of the ideas of the artist. It is not hereto be understood, that the first living fibre, which is to form an animal, is produced with any similarity of form to the future animal; but withpropensities, or appetences, which shall produce by accretion of parts thesimilarity of form, feature, or sex, corresponding to the imagination ofthe father. Our ideas are movements of the nerves of sense, as of the optic nerve inrecollecting visible ideas, suppose of a triangular piece of ivory. Thefine moving fibres of the retina act in a manner to which I give the nameof white; and this action is confined to a defined part of it; to whichfigure I give the name of triangle. And it is a preceding pleasurablesensation existing in my mind, which occasions me to produce thisparticular motion of the retina, when no triangle is present. Now it isprobable, that the acting fibres of the ultimate terminations of thesecreting apertures of the vessels of the testes, are as fine as those ofthe retina; and that they are liable to be thrown into that peculiaraction, which marks the sex of the secreted embryon, by sympathy with thepleasurable motions of the nerves of vision or of touch; that is, withcertain ideas of imagination. From hence it would appear, that the worldhas long been mistaken in ascribing great power to the imagination of thefemale, whereas from this account of it, the real power of imagination, inthe act of generation, belongs solely to the male. See Sect. XII. 3. 3. It may be objected to this theory, that a man may be supposed to have inhis mind, the idea of the form and features of the female, rather than hisown, and therefore there should be a greater number of female births. Onthe contrary, the general idea of our own form occurs to every one almostperpetually, and is termed consciousness of our existence, and thus mayeffect, that the number of males surpasses that of females. See Sect. XV. 3. 4. And XVIII. 13. And what further confirms this idea is, that the malechildren most frequently resemble the father in form, or feature, as wellas in sex; and the female most frequently resemble the mother, in feature, and form, as well as in sex. It may again be objected, if a female child sometimes resembles the father, and a male child the mother, the ideas of the father, at the time ofprocreation, must suddenly change from himself to the mother, at the veryinstant, when the embryon is secreted or formed. This difficulty ceaseswhen we consider, that it is as easy to form an idea of feminine featureswith male organs of reproduction, or of male features with female ones, asthe contrary; as we conceive the idea of a sphinx or mermaid as easily andas distinctly as of a woman. Add to this, that at the time of procreationthe idea of the male organs, and of the female features, are often bothexcited at the same time, by contact, or by vision. I ask, in my turn, is the sex of the embryon produced by accident?Certainly whatever is produced has a cause; but when this cause is toominute for our comprehension, the effect is said in common language tohappen by chance, as in throwing a certain number on dice. Now what causecan occasionally produce the male or female character of the embryon, butthe peculiar actions of those glands, which form the embryon? And what caninfluence or govern these actions of the gland, but its associations orcatenations with other sensitive motions? Nor is this more extraordinary, than that the catenations of irritative motions with the apparentvibrations of objects at sea should produce sickness of the stomach; orthat a nauseous story should occasion vomiting. 4. An argument, which evinces the effect of imagination on the firstrudiment of the embryon, may be deduced from the production of somepeculiar monsters. Such, for instance, as those which have two heads joinedto one body, and those which have two bodies joined to one head; of whichfrequent examples occur amongst our domesticated quadrupeds, and poultry. It is absurd to suppose, that such forms could exist in primordial germs, as explained in No. IV. 4. Of this section. Nor is it possible, that suchdeformities could be produced by the growth of two embryons, or livingfilaments; which should afterwards adhere together; as the head and tailpart of different polypi are said to do (Blumenbach on Generation, Cadel, London); since in that case one embryon, or living filament, must havebegun to form one part first, and the other another part first. But suchmonstrous conformations become less difficult to comprehend, when they areconsidered as an effect of the imagination, as before explained, on theliving filament at the time of its secretion; and that such duplicature oflimbs were produced by accretion of new parts, in consequence ofpropensities, or animal appetencies thus acquired from the male parent. For instance, I can conceive, if a turkey-cock should behold a rabbit, or afrog, at the time of procreation, that it might happen, that a forcible oreven a pleasurable idea of the form of a quadruped might so occupy hisimagination, as to cause a tendency in the nascent filament to resemblesuch a form, by the apposition of a duplicature of limbs. Experiments onthe production of mules and monsters would be worthy the attention of aSpallanzani, and might throw much light upon this subject, which at presentmust be explained by conjectural analogies. The wonderful effect of imagination, both in the male and female parent, isshewn in the production of a kind of milk in the crops both of the male andfemale pigeons after the birth of their young, as observed by Mr. Hunter, and mentioned before. To this should be added, that there are someinstances of men having had milk secreted in their breasts, and who havegiven suck to children, as recorded by Mr. Buffon. This effect ofimagination, of both the male and female parent, seems to have beenattended to in very early times; Jacob is said not only to have placed rodsof trees, in part stripped of their bark, so as to appear spotted, but alsoto have placed spotted lambs before the flocks, at the time of theircopulation. Genesis, chap. Xxx. Verse 40. 5. In respect to the imagination of the mother, it is difficult tocomprehend, how this can produce any alteration in the fetus, except byaffecting the nutriment laid up for its first reception, as described inNo. V. 2. Of this section, or by affecting the nourishment or oxygenationwith which she supplies it afterwards. Perpetual anxiety may probablyaffect the secretion of the liquor amnii into the uterus, as it enfeeblesthe whole system; and sudden fear is a frequent cause of miscarriage; forfear, contrary to joy, decreases for a time the action of the extremitiesof the arterial system; hence sudden paleness succeeds, and a shrinking orcontraction of the vessels of the skin, and other membranes. By thiscircumstance, I imagine, the terminations of the placental vessels aredetached from their adhesions, or insertions, into the membrane of theuterus; and the death of the child succeeds, and consequent miscarriage. Of this I recollect a remarkable instance, which could be ascribed to noother cause, and which I shall therefore relate in few words. A healthyyoung woman, about twenty years of age, had been about five monthspregnant, and going down into her cellar to draw some beer, was frighted bya servant boy starting up from behind the barrel, where he had concealedhimself with design to alarm the maid-servant, for whom he mistook hismistress. She came with difficulty up stairs, began to flood immediately, and miscarried in a few hours. She has since borne several children, norever had any tendency to miscarry of any of them. 6. In respect to the power of the imagination of the male over the form, colour, and sex of the progeny, the following instances have fallen undermy observation, and may perhaps be found not very unfrequent, if they weremore attended to. I am acquainted with a gentleman, who has one child withdark hair and eyes, though his lady and himself have light hair and eyes;and their other four children are like their parents. On observing thisdissimilarity of one child to the others he assured me, that he believed itwas his own imagination, that produced the difference; and related to methe following story. He said, that when his lady lay in of her third child, he became attached to a daughter of one of his inferior tenants, andoffered her a bribe for her favours in vain; and afterwards a greaterbribe, and was equally unsuccessful; that the form of this girl dwelt muchin his mind for some weeks, and that the next child, which was thedark-ey'd young lady above mentioned, was exceedingly like, in bothfeatures and colour, to the young woman who refused his addresses. To this instance I must add, that I have known two families, in which, onaccount of an intailed estate in expectation, a male heir was most eagerlydesired by the father; and on the contrary, girls were produced to theseventh in one, and to the ninth in another; and then they had each of thema son. I conclude, that the great desire of a male heir by the fatherproduced rather a disagreeable than an agreeable sensation; and that hisideas dwelt more on the fear of generating a female, than on thepleasurable sensations or ideas of his own male form or organs at the timeof copulation, or of the secretion of the semen; and that hence the idea ofthe female character was more present to his mind than that of the maleone; till at length in despair of generating a male these ideas ceased, andthose of the male character presided at the genial hour. 7. Hence I conclude, that the act of generation cannot exist without beingaccompanied with ideas, and that a man must have at that time either ageneral idea of his own male form, or of the form of his male organs; or anidea of the female form, or of her organs; and that this marks the sex, andthe peculiar resemblances of the child to either parent. From whence itwould appear, that the phalli, which were hung round the necks of the Romanladies, or worn in their hair, might have effect in producing a greaterproportion of male children; and that the calipædia, or art of begettingbeautiful children, and of procreating either males or females, may betaught by affecting the imagination of the male-parent; that is, by thefine extremities of the seminal glands, imitating the actions of the organsof sense either of sight or touch. But the manner of accomplishing thiscannot be unfolded with sufficient delicacy for the public eye; but may beworth the attention of those, who are seriously interested in theprocreation of a male or female child. _Recapitulation. _ VII. 1. A certain quantity of nutritive particles are produced by thefemale parent before impregnation, which require no further digestion, secretion, or oxygenation. Such are seen in the unimpregnated eggs ofbirds, and in the unimpregnated seed-vessels of vegetables. 2. A living filament is produced by the male, which being inserted amidstthese first nutritive particles, is stimulated into action by them; and inconsequence of this action, some of the nutritive particles are embraced, and added to the original living filament; in the same manner as commonnutrition is performed in the adult animal. 3. Then this new organization, or additional part, becomes stimulated bythe nutritive particles in its vicinity, and sensation is now superadded toirritation; and other particles are in consequence embraced, and added tothe living filament; as is seen in the new granulations of flesh in ulcers. By the power of association, or by irritation, the parts already producedcontinue their motions, and new ones are added by sensation, as abovementioned; and lastly by volition, which last sensorial power is proved toexist in the fetus in its maturer age, because it has evidently periods ofactivity and of sleeping; which last is another word for a temporarysuspension of volition. The original living filament may be conceived to possess a power ofrepulsing the particles applied to certain parts of it, as well as ofembracing others, which stimulate other parts of it; as these powers existin different parts of the mature animal; thus the mouth of every glandembraces the particles or fluid, which suits its appetency; and itsexcretory duct repulses those particles, which are disagreeable to it. 4. Thus the outline or miniature of the new animal is produced gradually, but in no great length of time; because the original nutritive particlesrequire no previous preparation by digestion, secretion, and oxygenation:but require simply the selection and apposition, which is performed by theliving filament. Mr. Blumenbach says, that he possesses a human fetus ofonly five weeks old, which is the size of a common bee, and has all thefeatures of the face, every finger, and every toe, complete; and in whichthe organs of generation are distinctly seen. P. 76. In another fetus, whose head was not larger than a pea, the whole of the basis of the skullwith all its depressions, apertures, and processes, were marked in the mostsharp and distinct manner, though without any ossification. Ib. 5. In some cases by the nutriment originally deposited by the mother thefilament acquires parts not exactly similar to those of the father, as inthe production of mules and mulattoes. In other cases, the deficiency ofthis original nutriment causes deficiencies of the extreme parts of thefetus, which are last formed, as the fingers, toes, lips. In other cases, aduplicature of limbs are caused by the superabundance of this originalnutritive fluid, as in the double yolks of eggs, and the chickens from themwith four legs and four wings. But the production of other monsters, asthose with two heads, or with parts placed in wrong situations, seems toarise from the imagination of the father being in some manner imitated bythe extreme vessels of the seminal glands; as the colours of the spots oneggs, and the change of the colour of the hair and feathers of animals bydomestication, may be caused in the same manner by the imagination of themother. 6. The living filament is a part of the father, and has therefore certainpropensities, or appetencies, which belong to him; which may have beengradually acquired during a million of generations, even from the infancyof the habitable earth; and which now possesses such properties, as wouldrender, by the apposition of nutritious particles, the new fetus exactlysimilar to the father; as occurs in the buds and bulbs of vegetables, andin the polypus, and tænia or tape-worm. But as the first nutriment issupplied by the mother, and therefore resembles such nutritive particles, as have been used for her own nutriment or growth, the progeny takes inpart of the likeness of the mother. Other similarity of the excitability, or of the form of the male parent, such as the broad or narrow shoulders, or such as constitute certainhereditary diseases, as scrophula, epilepsy, insanity, have their originproduced in one or perhaps two generations; as in the progeny of those whodrink much vinous spirits; and those hereditary propensities cease again, as I have observed, if one or two sober generations succeed; otherwise thefamily becomes extinct. This living filament from the father is also liable to have itspropensities, or appetencies, altered at the time of its production by theimagination of the male parent; the extremities of the seminal glandsimitating the motions of the organs of sense; and thus the sex of theembryon is produced; which may be thus made a male or a female by affectingthe imagination of the father at the time of impregnation. See Sect. XXXIX. 6. 3. And 7. 7. After the fetus is thus completely formed together with its umbilicalvessels and placenta, it is now supplied with a different kind of food, asappears by the difference of consistency of the different parts of thewhite of the egg, and of the liquor amnii, for it has now acquired organsfor digestion or secretion, and for oxygenation, though they are as yetfeeble; which can in some degree change, as well as select, the nutritiveparticles, which are now presented to it. But may yet be affected by thedeficiency of the quantity of nutrition supplied by the mother, or by thedegree of oxygenation supplied to its placenta by the maternal blood. The augmentation of the complete fetus by additional particles of nutrimentis not accomplished by distention only, but by apposition to every partboth external and internal; each of which acquires by animal appetenciesthe new addition of the particles which it wants. And hence the enlargedparts are kept similar to their prototypes, and may be said to be extended;but their extension must be conceived only as a necessary consequence ofthe enlargement of all their parts by apposition of new particles. Hence the new apposition of parts is not produced by capillary attraction, because the whole is extended; whereas capillary attraction would rathertend to bring the sides of flexible tubes together, and not to distendthem. Nor is it produced by chemical affinities, for then a solution ofcontinuity would succeed, as when sugar is dissolved in water; but it isproduced by an animal process, which is the consequence of irritation, orsensation; and which may be termed animal appetency. This is further evinced from experiments, which have been instituted toshew, that a living muscle of an animal body requires greater force tobreak it, than a similar muscle of a dead body. Which evinces, that besidesthe attraction of cohesion, which all matter possesses, and besides thechemical attractions of affinities, which hold many bodies together, thereis an animal adhesion, which adds vigour to these common laws of theinanimate world. 8. At the nativity of the child it deposits the placenta or gills, and byexpanding its lungs acquires more plentiful oxygenation from the currentsof air, which it must now continue perpetually to respire to the end of itslife; as it now quits the liquid element, in which it was produced, andlike the tadpole, when it changes into a frog, becomes an aerial animal. 9. As the habitable parts of the earth have been, and continue to be, perpetually increasing by the production of sea-shells and corallines, andby the recrements of other animals, and vegetables; so from the beginningof the existence of this terraqueous globe, the animals, which inhabit it, have constantly improved, and are still in a state of progressiveimprovement. This idea of the gradual generation of all things seems to have been asfamiliar to the ancient philosophers as to the modern ones; and to havegiven rise to the beautiful hieroglyphic figure of the [Greek: proton ôon], or first great egg, produced by NIGHT, that is, whose origin is involved inobscurity, and animated by [Greek: eros], that is, by DIVINE LOVE; fromwhence proceeded all things which exist. _Conclusion. _ VIII. 1. Cause and effect may be considered as the progression, orsuccessive motions, of the parts of the great system of Nature. The stateof things at this moment is the effect of the state of things, whichexisted in the preceding moment; and the cause of the state of things, which shall exist in the next moment. These causes and effects may be more easily comprehended, if motion beconsidered as a change of the figure of a group of bodies, as proposed inSect. XIV. 2. 2. Inasmuch as our ideas of visible or tangible objects aremore distinct, than our abstracted ideas of their motions. Now the changeof the configuration of the system of nature at this moment must be aneffect of the preceding configuration, for a change of configuration cannotexist without a previous configuration; and the proximate cause of everyeffect must immediately precede that effect. For example, a moving ivoryball could not proceed onwards, unless it had previously began to proceed;or unless an impulse had been previously given it; which previous motion orimpulse constitutes a part of the last situation of things. As the effects produced in this moment of time become causes in the next, we may consider the progressive motions of objects as a chain of causesonly; whose first link proceeded from the great Creator, and which haveexisted from the beginning of the created universe, and are perpetuallyproceeding. 2. These causes may be conveniently divided into two kinds, efficient andinert causes, according with the two kinds of entity supposed to exist inthe natural world, which may be termed matter and spirit, as proposed inSect. I. And further treated of in Sect. XIV. The efficient causes ofmotion, or new configuration, consist either of the principle of generalgravitation, which actuates the sun and planets; or of the principle ofparticular gravitation, as in electricity, magnetism, heat; or of theprinciple of chemical affinity, as in combustion, fermentation, combination; or of the principle of organic life, as in the contraction ofvegetable and animal fibres. The inert causes of motion, or newconfiguration, consist of the parts of matter, which are introduced withinthe spheres of activity of the principles above described. Thus, when anapple falls on the ground, the principle of gravitation is the efficientcause, and the matter of the apple the inert cause. If a bar of iron beapproximated to a magnet, it may be termed the inert cause of the motion, which brings these two bodies into contact; while the magnetic principlemay be termed the efficient cause. In the same manner the fibres, whichconstitute the retina, may be called the inert cause of the motions of thatorgan in vision, while the sensorial power may be termed the efficientcause. 3. Another more common distribution of the perpetual chain of causes andeffects, which constitute the motions, or changing configurations, of thenatural world, is into active and passive. Thus, if a ball in motionimpinges against another ball at rest, and communicates its motion to it, the former ball is said to act, and the latter to be acted upon. In thissense of the words a magnet is said to attract iron; and the prick of aspur to stimulate a horse into exertion; so that in this view of the worksof nature all things may be said either simply to exist, or to exist ascauses, or to exist as effects; that is, to exist either in an active orpassive state. This distribution of objects, and their motions, or changes of position, has been found so convenient for the purposes of common life, that on thisfoundation rests the whole construction or theory of language. The names ofthe things themselves are termed by grammarians Nouns, and their modes ofexistence are termed Verbs. The nouns are divided into substantives, whichdenote the principal things spoken of; and into adjectives, which denotesome circumstances, or less kinds of things, belonging to the former. Theverbs are divided into three kinds, such as denote the existence of thingssimply, as, to be; or their existence in an active state, as, to eat; ortheir existence in a passive state, as, to be eaten. Whence it appears, that all languages consist only of nouns and verbs, with theirabbreviations for the greater expedition of communicating our thoughts; asexplained in the ingenious work of Mr. Horne Tooke, who has unfolded by asingle flash of light the whole theory of language, which had so long lainburied beneath the learned lumber of the schools. Diversions of Purley. Johnson. London. 4. A third division of causes has been into proximate and remote; thesehave been much spoken of by the writers on medical subjects, but withoutsufficient precision. If to proximate and remote causes we add proximateand remote effects, we shall include four links of the perpetual chain ofcausation; which will be more convenient for the discussion of manyphilosophical subjects. Thus if a particle of chyle be applied to the mouth of a lacteal vessel, itmay be termed the remote cause of the motions of the fibres, which composethe mouth of that lacteal vessel; the sensorial power is the proximatecause; the contraction of the fibres of the mouth of the vessel is theproximate effect; and their embracing the particle of chyle is the remoteeffect; and these four links of causation constitute absorption. Thus when we attend to the rising sun, first the yellow rays of lightstimulate the sensorial power residing in the extremities of the opticnerve, this is the remote cause. 2. The sensorial power is excited into astate of activity, this is the proximate cause. 3. The fibrous extremitiesof the optic nerve are contracted, this is the proximate effect. 4. Apleasurable or painful sensation is produced in consequence of thecontraction of these fibres of the optic nerve, this is the remote effect;and these four links of the chain of causation constitute the sensitiveidea, or what is commonly termed the sensation of the rising sun. 5. Other causes have been announced by medical writers under the names ofcausa procatarctica, and causa proegumina, and causa sine quâ non. Allwhich are links more or less distant of the chain of remote causes. To these must be added the final cause, so called by many authors, whichmeans the motive, for the accomplishment of which the preceding chain ofcauses was put into action. The idea of a final cause, therefore, includesthat of a rational mind, which employs means to effect its purposes; thusthe desire of preserving himself from the pain of cold, which he hasfrequently experienced, induces the savage to construct his hut; the fixingstakes into the ground for walls, branches of trees for rafters, and turffor a cover, are a series of successive voluntary exertions; which are somany means to produce a certain effect. This effect of preserving himselffrom cold, is termed the final cause; the construction of the hut is theremote effect; the action of the muscular fibres of the man, is theproximate effect; the volition, or activity of desire to preserve himselffrom cold, is the proximate cause; and the pain of cold, which excited thatdesire, is the remote cause. 6. This perpetual chain of causes and effects, whose first link is rivettedto the throne of GOD, divides itself into innumerable diverging branches, which, like the nerves arising from the brain, permeate the most minute andmost remote extremities of the system, diffusing motion and sensation tothe whole. As every cause is superior in power to the effect, which it hasproduced, so our idea of the power of the Almighty Creator becomes moreelevated and sublime, as we trace the operations of nature from cause tocause, climbing up the links of these chains of being, till we ascend tothe Great Source of all things. Hence the modern discoveries in chemistry and in geology, by having tracedthe causes of the combinations of bodies to remoter origins, as well asthose in astronomy, which dignify the present age, contribute to enlargeand amplify our ideas of the power of the Great First Cause. And had thoseancient philosophers, who contended that the world was formed from atoms, ascribed their combinations to certain immutable properties received fromthe hand of the Creator, such as general gravitation, chemical affinity, oranimal appetency, instead of ascribing them to a blind chance; the doctrineof atoms, as constituting or composing the material world by the variety oftheir combinations, so far from leading the mind to atheism, wouldstrengthen the demonstration of the existence of a Deity, as the firstcause of all things; because the analogy resulting from our perpetualexperience of cause and effect would have thus been exemplified throughuniversal nature. _The heavens declare the glory of _GOD_, and the firmament sheweth hishandywork! One day telleth another, and one night certifieth another; theyhave neither speech nor language, yet their voice is gone forth into alllands, and their words into the ends of the world. Manifold are thy works, _O LORD!_ in wisdom hast thou made them all. _ Psal. Xix. Civ. * * * * * SECT. XL. On the OCULAR SPECTRA of Light and Colours, by Dr. R. W. Darwin, of Shrewsbury. Reprinted, by Permission, from the Philosophical Transactions, Vol. LXXVI. P. 313. _Spectra of four kinds. _ 1. _Activity of the retina in vision. _ 2. _Spectra from defect of sensibility. _ 3. _Spectra from excess of sensibility_. 4. _Of direct ocular spectra. _ 5. _Greater stimulus excites the retina into spasmodic action. _ 6. _Of reverse ocular spectra. _ 7. _Greater stimulus excites the retina into various successive spasmodic actions. _ 8. _Into fixed spasmodic action. _ 9. _Into temporary paralysis. _ 10. _Miscellaneous remarks;_ 1. _Direct and reverse spectra at the same time. A spectral halo. Rule to predetermine the colours of spectra. _ 2. _Variation of spectra from extraneous light. _ 3. _Variation of spectra in number, figure, and remission. _ 4. _Circulation of the blood in the eye is visible. _ 5. _A new way of magnifying objects. Conclusion. _ When any one has long and attentively looked at a bright object, as at thesetting sun, on closing his eyes, or removing them, an image, whichresembles in form the object he was attending to, continues some time to bevisible; this appearance in the eye we shall call the ocular spectrum ofthat object. These ocular spectra are of four kinds: 1st, Such as are owing to a lesssensibility of a defined part of the retina; or _spectra from defect ofsensibility. _ 2d, Such as are owing to a greater sensibility of a definedpart of the retina; or _spectra from excess of sensibility_. 3d, Such asresemble their object in its colour as well as form; which may be termed_direct ocular spectra_. 4th, Such as are of a colour contrary to that oftheir object; which may be termed _reverse ocular spectra_. The laws of light have been most successfully explained by the greatNewton, and the perception of visible objects has been ably investigated bythe ingenious Dr. Berkeley and M. Malebranche; but these minute phenomenaof vision have yet been thought reducible to no theory, though manyphilosophers have employed a considerable degree of attention upon them:among these are Dr. Jurin, at the end of Dr. Smith's Optics; M. Æpinus, inthe Nov. Com. Petropol. V. 10. ; M. Beguelin, in the Berlin Memoires, V. II. 1771; M. D'Arcy, in the Histoire de l'Acad. Des Scienc. 1765; M. De laHire; and, lastly, the celebrated M. De Buffon, in the Memoires de l'Acad. Des Scien. Who has termed them accidental colours, as if subjected to noestablished laws, Ac. Par. 1743. M. P. 215. I must here apprize the reader, that it is very difficult for differentpeople to give the same names to various shades of colours; whence, in thefollowing pages, something must be allowed, if on repeating the experimentsthe colours here mentioned should not accurately correspond with his ownnames of them. I. _Activity of the Retina in Vision. _ From the subsequent experiments it appears, that the retina is in an activenot in a passive state during the existence of these ocular spectra; and itis thence to be concluded, that all vision is owing to the activity of thisorgan. 1. Place a piece of red silk, about an inch in diameter, as in plate 1, atSect. III. 1. , on a sheet of white paper, in a strong light; look steadilyupon it from about the distance of half a yard for a minute; then closingyour eyelids cover them with your hands, and a green spectrum will be seenin your eyes, resembling in form the piece of red silk: after some time, this spectrum will disappear and shortly reappear; and this alternatelythree or four times, if the experiment is well made, till at length itvanishes entirely. 2. Place on a sheet of white paper a circular piece of blue silk, aboutfour inches in diameter, in the sunshine; cover the center of this with acircular piece of yellow silk, about three inches in diameter; and thecenter of the yellow silk with a circle of pink silk, about two inches indiameter; and the center of the pink silk with a circle of green silk, about one inch in diameter; and the centre of this with a circle of indigo, about half an inch in diameter; make a small speck with ink in the verycenter of the whole, as in plate 3, at Sect. III. 3. 6. ; look steadily fora minute on this central spot, and then closing your eyes, and applyingyour hand at about an inch distance before them, so as to prevent too muchor too little light from passing through the eyelids, you will see the mostbeautiful circles of colours that imagination can conceive, which are mostresembled by the colours occasioned by pouring a drop or two of oil on astill lake in a bright day; but these circular irises of colours are notonly different from the colours of the silks above mentioned, but are atthe same time perpetually changing as long as they exist. 3. When any one in the dark presses either corner of his eye with hisfinger, and turns his eye away from his finger, he will see a circle ofcolours like those in a peacock's tail: and a sudden flash of light isexcited in the eye by a stroke on it. (Newton's Opt. Q. 16. ) 4. When any one turns round rapidly on one foot, till he becomes dizzy, andfalls upon the ground, the spectra of the ambient objects continue topresent themselves in rotation, or appear to librate, and he seems tobehold them for some time still in motion. From all these experiments it appears, that the spectra in the eye are notowing to the mechanical impulse of light impressed on the retina, nor toits chemical combination with that organ, nor to the absorption andemission of light, as is observed in many bodies; for in all these casesthe spectra must either remain uniformly, or gradually diminish; andneither their alternate pretence and evanescence as in the firstexperiment, nor the perpetual changes of their colours as in the second, nor the flash of light or colours in the pressed eye as in the third, northe rotation or libration of the spectra as in the fourth, could exist. It is not absurd to conceive, that the retina may be stimulated intomotion, as well as the red and white muscles which form our limbs andvessels; since it consists of fibres, like those, intermixed with itsmedullary substance. To evince this structure, the retina of an ox's eyewas suspended in a glass of warm water, and forcibly torn in a few places;the edges of these parts appeared jagged and hairy, and did not contract, and become smooth like simple mucus, when it is distended till it breaks;which shews that it consists of fibres; and that its fibrous constructionbecame still more distinct to the sight, by adding some caustic alkali tothe water, as the adhering mucus was first eroded, and the hair-like fibresremained floating in the vessel. Nor does the degree of transparency of theretina invalidate the evidence of its fibrous structure, since Leeuwenhoekhas shewn that the crystalline humour itself consists of fibres. (ArcanaNaturæ, V. 1. P. 70. ) Hence it appears, that as the muscles have larger fibres intermixed with asmaller quantity of nervous medulla, the organ of vision has a greaterquantity of nervous medulla intermixed with smaller fibres; and it isprobable that the locomotive muscles, as well as the vascular ones, ofmicroscopic animals have much greater tenuity than these of the retina. And besides the similar laws, which will be shewn in this paper to governalike the actions of the retina and of the muscles, there are many otheranalogies which exist between them. They are both originally excited intoaction by irritations, both are nearly in the same quantity of time, arealike strengthened or fatigued by exertion, are alike painful if excitedinto action when they are in an inflamed state, are alike liable toparalysis, and to the torpor of old age. II. OF SPECTRA FROM DEFECT OF SENSIBILITY. _The retina is not so easily excited into action by less irritation after having been lately subjected to greater. _ 1. When any one passes from the bright daylight into a darkened room, theirises of his eyes expand themselves to their utmost extent in a fewseconds of time; but it is very long before the optic nerve, after havingbeen stimulated by the greater light of the day, becomes sensible of theless degree of it in the room; and, if the room is not too obscure, theirises will again contract themselves in some degree, as the sensibility ofthe retina returns. 2. Place about half an inch square of white paper on a black hat, andlooking steadily on the center of it for a minute, remove your eyes to asheet of white paper; and after a second or two a dark square will be seenon the white paper, which will continue some time. A similar dark squarewill be seen in the closed eye, if light be admitted through the eyelids. So after looking at any luminous object of a small size, as at the sun, fora short time, so as not much to fatigue the eyes, this part of the retinabecomes less sensible to smaller quantities of light; hence, when the eyesare turned on other less luminous parts of the sky, a dark spot is seenresembling the shape of the sun, or other luminous object which we lastbeheld. This is the source of one kind of the dark-coloured _muscævolitantes_. If this dark spot lies above the center of the eye, we turnour eyes that way, expecting to bring it into the center of the eye, thatwe may view it more distinctly; and in this case the dark spectrum seems tomove upwards. If the dark spectrum is found beneath the centre of the eye, we pursue it from the same motive, and it seems to move downwards. This hasgiven rise to various conjectures of something floating in the aqueoushumours of the eyes; but whoever, in attending to these spots, keeps hiseyes unmoved by looking steadily at the corner of a cloud, at the same timethat he observes the dark spectra, will be thoroughly convinced, that theyhave no motion but what is given to them by the movement of our eyes inpursuit of them. Sometimes the form of the spectrum, when it has beenreceived from a circular luminous body, will become oblong; and sometimesit will be divided into two circular spectra, which is not owing to ourchanging the angle made by the two optic axises, according to the distanceof the clouds or other bodies to which the spectrum is supposed to becontiguous, but to other causes mentioned in No. X. 3. Of this section. Theapparent size of it will also be variable according to its supposeddistance. As these spectra are more easily observable when our eyes are a littleweakened by fatigue, it has frequently happened, that people of delicateconstitutions have been much alarmed at them, fearing a beginning decay oftheir sight, and have thence fallen into the hands of ignorant oculists;but I believe they never are a prelude to any other disease of the eye, andthat it is from habit alone, and our want of attention to them, that we donot see them on all objects every hour of our lives. But as the nerves ofvery weak people lose their sensibility, in the same manner as theirmuscles lose their activity, by a small time of exertion, it frequentlyhappens, that sick people in the extreme debility of fevers are perpetuallyemployed in picking something from the bed-clothes, occasioned by theirmistaking the appearance of these _muscæ volitantes_ in their eyes. Benvenuto Celini, an Italian artist, a man of strong abilities, relates, that having passed the whole night on a distant mountain with somecompanions and a conjurer, and performed many ceremonies to raise thedevil, on their return in the morning to Rome, and looking up when the sunbegan to rise, they saw numerous devils run on the tops of the houses, asthey passed along; so much were the spectra of their weakened eyesmagnified by fear, and made subservient to the purposes of fraud orsuperstition. (Life of Ben. Celini. ) 3. Place a square inch of white paper on a large piece of straw-colouredsilk; look steadily some time on the white paper, and then move the centreof your eyes on the silk, and a spectrum of the form of the paper willappear on the silk, of a deeper yellow than the other part of it: for thecentral part of the retina, having been some time exposed to the stimulusof a greater quantity of white light, is become less sensible to a smallerquantity of it, and therefore sees only the yellow rays in that part of thestraw-coloured silk. Facts similar to these are observable in other parts of our system: thus, if one hand be made warm, and the other exposed to the cold, and then bothof them immersed in subtepid water, the water is perceived warm to onehand, and cold to the other; and we are not able to hear weak sounds forsome time after we have been exposed to loud ones; and we feel a chillinesson coming into an atmosphere of temperate warmth, after having been sometime confined in a very warm room: and hence the stomach, and other organsof digestion, of those who have been habituated to the greater stimulus ofspirituous liquor, are not excited into their due action by the lessstimulus of common food alone; of which the immediate consequence isindigestion and hypochondriacism. III. OF SPECTRA FROM EXCESS OF SENSIBILITY. _The retina is more easily excited into action by greater irritation after having been lately subjected to less. _ 1. If the eyes are closed, and covered perfectly with a hat, for a minuteor two, in a bright day; on removing the hat a red or crimson light is seenthrough the eyelids. In this experiment the retina, after being some timekept in the dark, becomes so sensible to a small quantity of light, as toperceive distinctly the greater quantity of red rays than of others whichpass through the eyelids. A similar coloured light is seen to pass throughthe edges of the fingers, when the open hand is opposed to the flame of acandle. 2. If you look for some minutes steadily on a window in the beginning ofthe evening twilight, or in a dark day, and then move your eyes a little, so that those parts of the retina, on which the dark frame-work of thewindow was delineated, may now fall on the glass part of it, many luminouslines, representing the frame-work, will appear to lie across the glasspanes: for those parts of the retina, which were before least stimulated bythe dark frame-work, are now more sensible to light than the other parts ofthe retina which were exposed to the more luminous parts of the window, 3. Make with ink on white paper a very black spot, about half an inch indiameter, with a tail about an inch in length, so as to represent atadpole, as in plate 2, at Sect. III. 3. 3. ; look steadily for a minute onthis spot, and, on moving the eye a little, the figure of the tadpole willbe seen on the white part of the paper, which figure of the tadpole willappear whiter or more luminous than the other parts of the white paper; forthe part of the retina on which the tadpole was delineated, is now moresensible to light, than the other parts of it, which were exposed to thewhite paper. This experiment is mentioned by Dr. Irwin, but is not by himascribed to the true cause, namely, the greater sensibility of that part ofthe retina which has been exposed to the black spot, than of the otherparts which had received the white field of paper, which is put beyond adoubt by the next experiment. 4. On closing the eyes after viewing the black spot on the white paper, asin the foregoing experiment, a red spot is seen of the form of the blackspot: for that part of the retina, on which the black spot was delineated, being now more sensible to light than the other parts of it, which wereexposed to the white paper, is capable of perceiving the red rays whichpenetrate the eyelids. If this experiment be made by the light of a tallowcandle, the spot will be yellow instead of red; for tallow candles aboundmuch with yellow light, which passes in greater quantity and force throughthe eyelids than blue tight; hence the difficulty of distinguishing blueand green by this kind of candle light. The colour of the spectrum maypossibly vary in the daylight, according to the different colour of themeridian or the morning or evening light. M. Beguelin, in the Berlin Memoires, V. II. 1771, observes, that, when heheld a book so that the sun shone upon his half-closed eyelids, the blackletters, which he had long inspected, became red, which must have been thusoccasioned. Those parts of the retina which had received for some time theblack letters, were so much more sensible than those parts which had beenopposed to the white paper, that to the former the red light, which passedthrough the eyelids, was perceptible. There is a similar story told, Ithink, in de Voltaire's Historical Works, of a Duke of Tuscany, who wasplaying at dice with the general of a foreign army, and, believing he sawbloody spots upon the dice, portended dreadful events, and retired inconfusion. The observer, after looking for a minute on the black spots of adie, and carelessly closing his eyes, on a bright day; would see the imageof a die with red spots upon it, as above explained. 5. On emerging from a dark cavern, where we have long continued, the lightof a bright day becomes intolerable to the eye for a considerable time, owing to the excess of sensibility existing in the eye, after having beenlong exposed to little or no stimulus. This occasions us immediately tocontract the iris to its smallest aperture, which becomes again graduallydilated, as the retina becomes accustomed to the greater stimulus of thedaylight. The twinkling of a bright star, or of a distant candle in the night, isperhaps owing to the same cause. While we continue to look upon theseluminous objects, their central parts gradually appear paler, owing to thedecreasing sensibility of the part of the retina exposed to their light;whilst, at the same time, by the unsteadiness of the eye, the edges of themare perpetually falling on parts of the retina that were just beforeexposed to the darkness of the night, and therefore tenfold more sensibleto light than the part on which the star or candle had been for some timedelineated. This pains the eye in a similar manner as when we come suddenlyfrom a dark room into bright daylight, and gives the appearance of brightscintillations. Hence the stars twinkle most when the night is darkest, anddo not twinkle through telescopes, as observed by Musschenbroeck; and itwill afterwards be seen why this twinkling is sometimes of differentcolours when the object is very bright, as Mr. Melvill observed in lookingat Sirius. For the opinions of others on this subject, see Dr. Priestley'svaluable History of Light and Colours, p. 494. Many facts observable in the animal system are similar to these; as the hotglow occasioned by the usual warmth of the air, or our clothes, on comingout of a cold bath; the pain of the fingers on approaching the fire afterhaving handled snow; and the inflamed heels from walking in snow. Hencethose who have been exposed to much cold have died on being brought to afire, or their limbs have become so much inflamed as to mortify. Hence muchfood or wine given suddenly to those who have almost perished by hunger hasdestroyed them; for all the organs of the famished body are now become somuch more irritable to the stimulus of food and wine, which they have longbeen deprived of, that inflammation is excited, which terminates ingangrene or fever. IV. OF DIRECT OCULAR SPECTRA. _A quantity of stimulus somewhat greater than natural excites the retina into spasmodic action, which ceases in a few seconds. _ A certain duration and energy of the stimulus of light and colours excitesthe perfect action of the retina in vision; for very quick motions areimperceptible to us, as well as very slow ones, as the whirling of a top, or the shadow on a sun-dial. So perfect darkness does not affect the eye atall; and excess of light produces pain, not vision. 1. When a fire-coal is whirled round in the dark, a lucid circle remains aconsiderable time in the eye; and that with so much vivacity of light, thatit is mistaken for a continuance of the irritation of the object. In thesame manner, when a fiery meteor shoots across the night, it appears toleave a long lucid train behind it, part of which, and perhaps sometimesthe whole, is owing to the continuance of the action of the retina afterhaving been thus vividly excited. This is beautifully illustrated by thefollowing experiment: fix a paper sail, three or four inches in diameter, and made like that of a smoke jack, on a tube of pasteboard; on lookingthrough the tube at a distant prospect, some disjointed parts of it will beseen through the narrow intervals between the sails; but as the fly beginsto revolve, these intervals appear larger; and when it revolves quicker, the whole prospect is seen quite as distinct as if nothing intervened, though less luminous. [Illustration: Fig. 3. ] 2. Look through a dark tube, about half a yard long, at the area of ayellow circle of half an inch diameter, lying upon a blue area of doublethat diameter, for half a minute; and on closing your eyes the colours ofthe spectrum will appear similar to the two areas, as in fig. 3. ; but ifthe eye is kept too long upon them, the colours of the spectrum will be thereverse of those upon the paper, that is, the internal circle will becomeblue, and the external area yellow; hence some attention is required inmaking this experiment. 3. Place the bright flame of a spermaceti candle before a black object inthe night; look steadily at it for a short time, till it is observed tobecome somewhat paler; and on closing the eyes, and covering themcarefully, but not so as to compress them, the image of the blazing candlewill continue distinctly to be visible. 4. Look steadily, for a short time, at a window in a dark day, as in Exp. 2. Sect. III. And then closing your eyes, and covering them with yourhands, an exact delineation of the window remains for some time visible inthe eye. This experiment requires a little practice to make it succeedwell; since, if the eyes are fatigued by looking too long on the window, orthe day be too bright, the luminous parts of the window will appear dark inthe spectrum, and the dark parts of the frame-work will appear luminous, asin Exp. 2. Sect. III. And it is even difficult for many, who first try thisexperiment, to perceive the spectrum at all; for any hurry of mind, or eventoo great attention to the spectrum itself, will disappoint them, till theyhave had a little experience in attending to such small sensations. The spectra described in this section, termed direct ocular spectra, areproduced without much fatigue of the eye; the irritation of the luminousobject being soon withdrawn, or its quantity of light being not so great asto produce any degree of uneasiness in the organ of vision; whichdistinguishes them from the next class of ocular spectra, which are theconsequence of fatigue. These direct spectra are best observed in suchcircumstances that no light, but what comes from the object, can fall uponthe eye; as in looking through a tube, of half a yard long, and an inchwide, at a yellow paper on the side of a room, the direct spectrum waseasily produced on closing the eye without taking it from the tube; but ifthe lateral light is admitted through the eyelids, or by throwing thespectrum on white paper, it becomes a reverse spectrum, as will beexplained below. The other senses also retain for a time the impressions that have been madeupon them, or the actions they have been excited into. So if a hard body ispressed upon the palm of the hand, as is practised in tricks oflegerdemain, it is not easy to distinguish for a few seconds whether itremains or is removed; and tastes continue long to exist vividly in themouth, as the smoke of tobacco, or the taste of gentian, after the sapidmaterial is withdrawn. V. _A quantity of stimulus somewhat greater than the last mentioned excites the retina into spasmodic action, which ceases and recurs alternately. _ 1. On looking for a time on the setting sun, so as not greatly to fatiguethe sight, a yellow spectrum is seen when the eyes are closed and covered, which continues for a time, and then disappears and recurs repeatedlybefore it entirely vanishes. This yellow spectrum of the sun when theeyelids are opened becomes blue; and if it is made to fall on the greengrass, or on other coloured objects, it varies its own colour by anintermixture of theirs, as will be explained in another place. 2. Place a lighted spermaceti candle in the night about one foot from youreye, and look steadily on the centre of the flame, till your eye becomesmuch more fatigued than in Sect. IV. Exp. 3. ; and on closing your eyes areddish spectrum will be perceived, which will cease and returnalternately. The action of vomiting in like manner ceases, and is renewed by intervals, although the emetic drug is thrown up with the first effort: so after-painscontinue some time after parturition; and the alternate pulsations of theheart of a viper are renewed for some time after it is cleared from itsblood. VI. OF REVERSE OCULAR SPECTRA. _The retina, after having been excited into action by a stimulus somewhat greater them the last mentioned, falls into opposite spasmodic action. _ The actions of every part of animal bodies may be advantageously comparedwith each other. This strict analogy contributes much to the investigationof truth; while those looser analogies, which compare the phenomena ofanimal life with those of chemistry or mechanics, only serve to mislead ourinquiries. When any of our larger muscles have been in long or in violent action, andtheir antagonists have been at the same time extended, as soon as theaction of the former ceases, the limb is stretched the contrary way for ourease, and a pandiculation or yawning takes place. By the following observations it appears, that a similar circumstanceobtains in the organ of vision; after it has been fatigued by one kind ofaction, it spontaneously falls into the opposite kind. 1. Place a piece of coloured silk, about an inch in diameter, on a sheet ofwhite paper, about half a yard from your eyes; look steadily upon it for aminute; then remove your eyes upon another part of the white paper, and aspectrum will be seen of the form of the silk thus inspected, but of acolour opposite to it. A spectrum nearly similar will appear if the eyesare closed, and the eyelids shaded by approaching the hand near them, so asto permit some, but to prevent too much light falling on them. Red silk produced a green spectrum. Green produced a red one. Orange produced blue. Blue produced orange. Yellow produced violet. Violet produced yellow. That in these experiments the colours of the spectra are the reverse of thecolours which occasioned them, may be seen by examining the third figure inSir Isaac Newton's Optics, L. II. P. 1, where those thin laminæ of air, which reflected yellow, transmitted violet; those which reflected red, transmitted a blue green; and so of the rest, agreeing with the experimentsabove related. 2. These reverse spectra are similar to a colour, formed by a combinationof all the primary colours except that with which the eye has been fatiguedin making the experiment: thus the reverse spectrum of red must be such agreen as would be produced by a combination of all the other prismaticcolours. To evince this fact the following satisfactory experiment wasmade. The prismatic colours were laid on a circular pasteboard wheel, aboutfour inches in diameter, in the proportions described in Dr. Priestley'sHistory of Light and Colours, pl. 12. Fig. 83. Except that the redcompartment was entirely left out, and the others proportionably extendedso as to complete the circle. Then, as the orange is a mixture of red andyellow, and as the violet is a mixture of red and indigo, it becamenecessary to put yellow on the wheel instead of orange, and indigo insteadof violet, that the experiment might more exactly quadrate with the theoryit was designed to establish or confute; because in gaining a greenspectrum from a red object, the eye is supposed to have become insensibleto red light. This wheel, by means of an axis, was made to whirl like atop; and on its being put in motion, a green colour was produced, corresponding with great exactness to the reverse spectrum of red. 3. In contemplating any one or these reverse spectra in the closed andcovered eye, it disappears and re-appears several times successively, tillat length it entirely vanishes, like the direct spectra in Sect. V. ; butwith this additional circumstance, that when the spectrum becomes faint orevanescent, it is instantly revived by removing the hand from before theeyelids, so as to admit more light: because then not only the fatigued partof the retina is inclined spontaneously to fall into motions of a contrarydirection, but being still sensible to all other rays of light, except thatwith which it was lately fatigued, is by these rays at the same timestimulated into those motions which form the reverse spectrum. From these experiments there is reason to conclude, that the fatigued partof the retina throws itself into a contrary mode of action, like oscitationor pandiculation, as soon as the stimulus which has fatigued it iswithdrawn; and that it still remains sensible, that is, liable to beexcited into action by any other colours at the same time, except thecolour with which it has been fatigued. VII. _The retina after having been excited into action by a stimulus somewhat greater than the last mentioned falls into various successive spasmodic actions. _ 1. On looking at the meridian sun as long as the eyes can well bear itsbrightness, the disk first becomes pale, with a luminous crescent, whichseems to librate from one edge of it to the other, owing to theunsteadiness of the eye; then the whole phasis of the sun becomes blue, surrounded with a white halo; and on closing the eyes, and covering themwith the hands, a yellow spectrum is seen, which in a little time changesinto a blue one. M. De la Hire observed, after looking at the bright sun, that theimpression in his eye first assumed a yellow appearance, and then green, and then blue; and wishes to ascribe these appearances to some affection ofthe nerves. (Porterfield on the Eye, Vol. I. P. 313. ) 2. After looking steadily on about an inch square of pink silk, placed onwhite paper, in a bright sunshine, at the distance of a foot from my eyes, and closing and covering my eyelids, the spectrum of the silk was at firsta dark green, and the spectrum of the white paper became of a pink. Thespectra then both disappeared; and then the internal spectrum was blue; andthen, after a second disappearance, became yellow, and lastly pink, whilstthe spectrum of the field varied into red and green. These successions of different coloured spectra were not exactly the samein the different experiments, though observed, as near as could be, withthe same quantity of light, and other similar circumstances; owing, Isuppose, to trying too many experiments at a time; so that the eye was notquite free from the spectra of the colours which were previously attendedto. The alternate exertions of the retina in the preceding section resembledthe oscitation or pandiculation of the muscles, as they were performed indirections contrary to each other, and were the consequence of fatiguerather than of pain. And in this they differ from the successive dissimilarexertions of the retina, mentioned in this section, which resemble inminiature the more violent agitations of the limbs in convulsive diseases, as epilepsy, chorea S. Viti, and opisthotonos; all which diseases areperhaps, at first, the consequence of pain, and have their periodsafterwards established by habit. VIII. _The retina, after having been excited into action by a stimulus somewhat greater than the last mentioned, falls into a fixed spasmodic action, which continues for some days. _ 1. After having looked long at the meridian sun, in making some of thepreceding experiments, till the disks faded into a pale blue, I frequentlyobserved a bright blue spectrum of the sun on other objects all the nextand the succeeding day, which constantly occurred when I attended to it, and frequently when I did not previously attend to it. When I closed andcovered my eyes, this appeared of a dull yellow; and at other times mixedwith the colours of other objects on which it was thrown. It may beimagined, that this part of the retina was become insensible to whitelight, and thence a bluish spectrum became visible on all luminous objects;but as a yellowish spectrum was also seen in the closed and covered eye, there can remain no doubt of this being the spectrum of the sun. A similarappearance was observed by M. Æpinus, which he acknowledges he could giveno account of. (Nov. Com. Petrop. V. 10. P. 2. And 6. ) The locked jaw, and some cataleptic spasms, are resembled by thisphenomenon; and from hence we may learn the danger to the eye by inspectingvery luminous objects too long a time. IX. _A quantity of stimulus greater than the preceding induces a temporaryparalysis of the organ of vision. _ 1. Place a circular piece of bright red silk, about half an inch indiameter, on the middle of a sheet of white paper; lay them on the floor ina bright sunshine, and fixing your eyes steadily on the center of the redcircle, for three or four minutes, at the distance of four or six feet fromthe object, the red silk will gradually become paler, and finally cease toappear red at all. 2. Similar to these are many other animal facts; as purges, opiates, andeven poisons, and contagious matter, cease to stimulate our system, afterwe have been habituated to their use. So some people sleep undisturbed by aclock, or even by a forge hammer in their neighbourhood: and not onlycontinued irritations, but violent exertions of any kind, are succeeded bytemporary paralysis. The arm drops down after violent action, and continuesfor a time useless; and it is probable, that those who have perishedsuddenly in swimming, or in scating on the ice, have owed their deaths tothe paralysis, or extreme fatigue, which succeeds every violent andcontinued exertion. X. MISCELLANEOUS REMARKS. There were some circumstances occurred in making these experiments, whichwere liable to alter the results of them, and which I shall here mentionfor the assistance of others, who may wish to repeat them. 1. _Of direct and inverse spectra existing at the same time_; _ofreciprocal direct spectra_; _of a combination of direct and inversespectra_; _of a spectral halo_; _rules to pre-determine the colours ofspectra_. a. When an area, about six inches square, of bright pink Indian paper, hadbeen viewed on an area, about a foot square, of white writing paper, theinternal spectrum in the closed eye was green, being the reverse spectrumof the pink paper; and the external spectrum was pink, being the directspectrum of the pink paper. The same circumstance happened when theinternal area was white, and external one pink; that is, the internalspectrum was pink, and the external one green. All the same appearancesoccurred when the pink paper was laid on a black hat. b. When six inches square of deep violet polished paper was viewed on afoot square of white writing paper, the internal spectrum was yellow, beingthe reverse spectrum of the violet paper, and the external one was violet, being the direct spectrum of the violet paper. c. When six inches square of pink paper was viewed on a foot square of bluepaper, the internal spectrum was blue, and the external spectrum was pink;that is, the internal one was the direct spectrum of the external object, and the external one was the direct spectrum of the internal object, instead of their being each the reverse spectrum of the objects theybelonged to. d. When six inches square of blue paper were viewed on a foot square ofyellow paper, the interior spectrum became a brilliant yellow, and theexterior one a brilliant blue. The vivacity of the spectra was owing totheir being excited both by the stimulus of the interior and exteriorobjects; so that the interior yellow spectrum was both the reverse spectrumof the blue paper, and the direct one of the yellow paper; and the exteriorblue spectrum was both the reverse spectrum of the yellow paper, and thedirect one of the blue paper. e. When the internal area was only a square half-inch of red paper, laid ona square foot of dark violet paper, the internal spectrum was green, with areddish-blue halo. When the red internal paper was two inches square, theinternal spectrum was a deeper green, and the external one redder. When theinternal paper was six inches square, the spectrum of it became blue, andthe spectrum of the external paper was red. f. When a square half-inch of blue paper was laid on a six-inch square ofyellow paper, the spectrum of the central paper in the closed eye wasyellow, incircled with a blue halo. On looking long on the meridian sun, the disk fades into a pale blue surrounded with a whitish halo. These circumstances, though they very much perplexed the experiments tillthey were investigated, admit of a satisfactory explanation; for while therays from the bright internal object in exp. A. Fall with their full forceon the center of the retina, and, by fatiguing that part of it, induce thereverse spectrum, many scattered rays, from the same internal pink paper, fall on the more external parts of the retina, but not in such quantity asto occasion much fatigue, and hence induce the direct spectrum of the pinkcolour in those parts of the eye. The same reverse and direct spectra occurfrom the violet paper in exp. B. : and in exp. C. The scattered rays fromthe central pink paper produce a direct spectrum of this colour on theexternal parts of the eye, while the scattered rays from the external bluepaper produce a direct spectrum of that colour on the central part of theeye, instead of these parts of the retina falling reciprocally into theirreverse spectra. In exp. D. The colours being the reverse of each other, the scattered rays from the exterior object falling on the central parts ofthe eye, and there exciting their direct spectrum, at the same time thatthe retina was excited into a reverse spectrum by the central object, andthis direct and reverse spectrum being of similar colour, the superiorbrilliancy of this spectrum was produced. In exp. E. The effect of variousquantities of stimulus on the retina, from the different respective sizesof the internal and external areas, induced a spectrum of the internal areain the center of the eye, combined of the reverse spectrum of that internalarea and the direct one of the external area, in various shades of colour, from a pale green to a deep blue, with similar changes in the spectrum ofthe external area. For the same reasons, when an internal bright object wassmall, as in exp. F. Instead of the whole of the spectrum of the externalobject being reverse to the colour of the internal object, only a kind ofhalo, or radiation of colour, similar to that of the internal object, wasspread a little way on the external spectrum. For this internal blue areabeing so small, the scattered rays from it extended but a little way on theimage of the external area of yellow paper, and could therefore produceonly a blue halo round the yellow spectrum in the center. If any one should suspect that the scattered rays from the exteriorcoloured object do not intermix with the rays from the interior colouredobject, and thus affect the central part of the eye, let him look throughan opake tube, about two feet in length, and an inch in diameter, at acoloured wall of a room with one eye, and with the other eye naked; and hewill find, that by shutting out the lateral light, the area of the wallseen through a tube appears as if illuminated by the sunshine, comparedwith the other parts of it; from whence arises the advantage of lookingthrough a dark tube at distant paintings. Hence we may safely deduce the following rules to determine before-hand thecolours of all spectra. 1. The direct spectrum without any lateral light isan evanescent representation of its object in the unfatigued eye. 2. Withsome lateral light it becomes of a colour combined of the direct spectrumof the central object, and of the circumjacent objects, in proportion totheir respective quantity and brilliancy. 3. The reverse spectrum withoutlateral light is a representation in the fatigued eye of the form of itsobjects, with such a colour as would be produced by all the primarycolours, except that of the object. 4. With lateral light the colour iscompounded of the reverse spectrum of the central object, and the directspectrum of the circumjacent objects, in proportion to their respectivequantity and brilliancy. 2. _Variation and vivacity of the spectra occasioned by extraneous light. _ The reverse spectrum, as has been before explained, is similar to a colour, formed by a combination of all the primary colours, except that with whichthe eye has been fatigued in making the experiment: so the reverse spectrumof red is such a green as would be produced by a combination of all theother prismatic colours. Now it must be observed, that this reversespectrum of red is therefore the direct spectrum of a combination of allthe other prismatic colours, except the red; whence, on removing the eyefrom a piece of red silk to a sheet of white paper, the green spectrum, which is perceived, may either be called the reverse spectrum of the redsilk, or the direct spectrum of all the rays from the white paper, exceptthe red; for in truth it is both. Hence we see the reason why it is noteasy to gain a direct spectrum of any coloured object in the day-time, where there is much lateral light, except of very bright objects, as of thesetting sun, or by looking through an opake tube; because the lateralexternal light falling also on the central part of the retina, contributesto induce the reverse spectrum, which is at the same time the directspectrum of that lateral light, deducting only the colour of the centralobject which we have been viewing. And for the same reason, it is difficultto gain the reverse spectrum, where there is no lateral light to contributeto its formation. Thus, in looking through an opake tube on a yellow wall, and closing my eye, without admitting any lateral light, the spectra wereall at first yellow; but at length changed into blue. And on looking in thesame manner on red paper, I did at length get a green spectrum; but theywere all at first red ones: and the same after looking at a candle in thenight. The reverse spectrum was formed with greater facility when the eye wasthrown from the object on a sheet of white paper, or when light wasadmitted through the closed eyelids; because not only the fatigued part ofthe retina was inclined spontaneously to fall into motions of a contrarydirection; but being still sensible to all other rays of light except thatwith which it was lately fatigued, was by these rays stimulated at the sametime into those motions which form the reverse spectrum. Hence, when, thereverse spectrum of any colour became faint, it was wonderfully revived byadmitting more light through the eyelids, by removing the hand from beforethem: and hence, on covering the closed eyelids, the spectrum would oftencease for a time, till the retina became sensible to the stimulus of thesmaller quantity of light, and then it recurred. Nor was the spectrum onlychanged in vivacity, or in degree, by this admission of light through theeyelids; but it frequently happened, after having viewed bright objects, that the spectrum in the closed and covered eye was changed into a thirdspectrum, when light was admitted through the eyelids: which third spectrumwas composed of such colours as could pass through the eyelids, exceptthose of the object. Thus, when an area of half an inch diameter of pinkpaper was viewed on a sheet of white paper in the sunshine, the spectrumwith closed and covered eyes was green; but on removing the hands frombefore the closed eyelids, the spectrum became yellow, and returnedinstantly again to green, as often as the hands were applied to cover theeyelids, or removed from them: for the retina being now insensible to redlight, the yellow rays passing through the eyelids in greater quantity thanthe other colours, induced a yellow spectrum; whereas if the spectrum wasthrown on white paper, with the eyes open, it became only a lighter green. Though a certain quantity of light facilitates the formation of the reversespectrum, a greater quantity prevents its formation, as the more powerfulstimulus excites even the fatigued parts of the eye into action; otherwisewe should see the spectrum of the last viewed object as often as we turnour eyes. Hence the reverse spectra are best seen by gradually approachingthe hand near the closed eyelids to a certain distance only, which must bevaried with the brightness of the day, or the energy of the spectrum. Addto this, that all dark spectra, as black, blue, or green, if light beadmitted through the eyelids, after they have been some time covered, givereddish spectra, for the reasons given in Sect. III. Exp. 1. From these circumstances of the extraneous light coinciding with thespontaneous efforts of the fatigued retina to produce a reverse spectrum, as was observed before, it is not easy to gain a direct spectrum, except ofobjects brighter than the ambient light; such as a candle in the night, thesetting sun, or viewing a bright object through an opake tube; and then thereverse spectrum is instantaneously produced by the admission of someexternal light; and is as instantly converted again to the direct spectrumby the exclusion of it. Thus, on looking at the setting sun, on closing theeyes, and covering them, a yellow spectrum is seen, which is the directspectrum of the setting sun; but on opening the eyes on the sky, the yellowspectrum is immediately changed into a blue one, which is the reversespectrum of the yellow sun, or the direct spectrum of the blue sky, or acombination of both. And this is again transformed into a yellow one onclosing the eyes, and so reciprocally, as quick as the motions of theopening and closing eyelids. Hence, when Mr. Melvill observed thescintillations of the star Sirius to be sometimes coloured, these wereprobably the direct spectrum of the blue sky on the parts of the retinafatigued by the white light of the star. (Essays Physical and Literary, p. 81. V. 2. ) When a direct spectrum is thrown on colours darker than itself, it mixeswith them; as the yellow spectrum of the setting sun, thrown on the greengrass, becomes a greener yellow. But when a direct spectrum is thrown oncolours brighter than itself, it becomes instantly changed into the reversespectrum, which mixes with those brighter colours. So the yellow spectrumof the setting sun thrown on the luminous sky becomes blue, and changeswith the colour or brightness of the clouds on which it appears. But thereverse spectrum mixes with every kind of colour on which it is thrown, whether brighter than itself or not; thus the reverse spectrum, obtained byviewing a piece of yellow silk, when thrown on white paper, was a lucidblue green; when thrown on black Turkey leather, becomes a deep violet. Andthe spectrum of blue silk, thrown on white paper, was a light yellow; onblack silk was an obscure orange; and, the blue spectrum, obtained fromorange-coloured silk, thrown on yellow, became a green. In these cases the retina is thrown into activity or sensation by thestimulus of external colours, at the same time that it continues theactivity or sensation which forms the spectra; in the same manner as theprismatic colours, painted on a whirling top, are seen to mix together. When these colours of external objects are brighter than the directspectrum which is thrown upon them, they change it into the reversespectrum, like the admission of external light on a direct spectrum, asexplained above. When they are darker than the direct spectrum, they mixwith it, their weaker stimulus being inefficient to induce the reversespectrum. 3. _Variation of spectra in respect to number, and figure, and remission. _ [Illustration: Fig. 4. ] When we look long and attentively at any object, the eye cannot always bekept entirely motionless; hence, on inspecting a circular area of red silkplaced on white paper, a lucid crescent or edge is seen to librate on oneside or other of the red circle: for the exterior parts of the retinasometimes falling on the edge of the central silk, and sometimes on thewhite paper, are less fatigued with red light than the central part of theretina, which is constantly, exposed to it; and therefore, when they fallon the edge of the red silk, they perceive it more vividly. Afterwards, when the eye becomes fatigued, a green spectrum in the form of a crescentis seen to librate on one side or other of the central circle, as by theunsteadiness of the eye a part of the fatigued retina falls on the whitepaper; and as by the increasing fatigue of the eye the central part of thesilk appears paler, the edge on which the unfatigued part of the retinaoccasionally falls will appear of a deeper red than the original silk, because it is compared with the pale internal part of it. M. De Buffon inmaking this experiment observed, that the red edge of the silk was not onlydeeper coloured than the original silk; but, on his retreating a littlefrom it, it became oblong, and at length divided into two, which must havebeen owing to his observing it either before or behind the point ofintersection of the two optic axises. Thus, if a pen is held up before adistant candle, when we look intensely at the pen two candles are seenbehind it; when we look intensely at the candle two pens are seen. If thesight be unsteady at the time of beholding the sun, even though one eyeonly be used, many images of the sun will appear, or luminous lines, whenthe eye is closed. And as some parts of these will be more vivid thanothers, and some parts of them will be produced nearer the center of theeye than others, these will disappear sooner than the others; and hence thenumber and shape of these spectra of the sun will continually vary, as longas they exist. The cause of some being more vivid than others, is theunsteadiness of the eye of the beholder, so that some parts of the retinahave been longer exposed to the sunbeams. That some parts of a complicatedspectrum fade and return before other parts of it, the following experimentevinces. Draw three concentric circles; the external one an inch and a halfin diameter, the middle one an inch, and the internal one half an inch;colour the external and internal areas blue, and the remaining one yellow, as in Fig. 4. ; after having looked about a minute on the center of thesecircles, in a bright light, the spectrum of the external area appears firstin the closed eye, then the middle area, and lastly the central one; andthen the central one disappears, and the others in inverted order. Ifconcentric circles of more colours are added, it produces the beautifulever changing spectrum in Sect. I. Exp. 2. From hence it would seem, that the center of the eye produces quickerremissions of spectra, owing perhaps to its greater sensibility; that is, to its more energetic exertions. These remissions of spectra bear someanalogy to the tremors of the hands, and palpitations of the heart, of weakpeople: and perhaps a criterion of the strength of any muscle or nerve maybe taken from the time it can be continued in exertion. 4. _Variation of spectra in respect to brilliancy; the visibility of thecirculation of the blood in the eye. _ 1. The meridian or evening light makes a difference in the colours of somespectra; for as the sun descends, the red rays, which are less refrangibleby the convex atmosphere, abound in great quantity. Whence the spectrum ofthe light parts of a window at this time, or early in the morning, is red;and becomes blue either a little later or earlier; and white in themeridian day; and is also variable from the colour of the clouds or skywhich are opposed to the window. 2. All these experiments are liable to be confounded, if they are made toosoon after each other, as the remaining spectrum will mix with the newones. This is a very troublesome circumstance to painters, who are obligedto look long upon the same colour; and in particular to those whose eyes, from natural debility, cannot long, continue the same kind of exertion. Forthe same reason, in making these experiments, the result becomes muchvaried if the eyes, after viewing any object, are removed on other objectsfor but an instant of time, before we close them to view the spectrum; forthe light from the object, of which we had only a transient view, in thevery time of closing our eyes acts as a stimulus on the fatigued retina;and for a time prevents the defined spectrum from appearing, or mixes itsown spectrum with it. Whence, after the eyelids are closed, either a darkfield, or some unexpected colours, are beheld for a few seconds, before thedesired spectrum becomes distinctly visible. 3. The length of time taken up in viewing an object, of which we are toobserve the spectrum, makes a great difference in the appearance of thespectrum, not only in its vivacity, but in its colour; as the directspectrum of the central object, or of the circumjacent ones, and also thereverse spectra of both, with their various combinations, as well as thetime of their duration in the eye, and of their remissions or alternations, depend upon the degree of fatigue the retina is subjected to. The Chevalierd'Arcy constructed a machine by which a coal of fire was whirled round inthe dark, and found, that when a luminous body made a revolution in eightthirds of time, it presented to the eye a complete circle of fire; fromwhence he concludes, that the impression continues on the organ about theseventh part of a second. (Mem. De l'Acad. Des Sc. 1765. ) This, however, isonly to be considered as the shortest time of the duration of these directspectra; since in the fatigued eye both the direct and reverse spectra, with their intermissions, appear to take up many seconds of time, and seemvery variable in proportion to the circumstances of fatigue or energy. 4. It sometimes happens, if the eyeballs have been rubbed hard with thefingers, that lucid sparks are seen in quick motion amidst the spectrum weare attending to. This is similar to the flashes of fire from a stroke onthe eye in fighting, and is resembled by the warmth and glow, which appearsupon the skin after friction, and is probably owing to an acceleration ofthe arterial blood into the vessels emptied by the previous pressure. Bybeing accustomed to observe such small sensations in the eye, it is easy tosee the circulation of the blood in this organ. I have attended to thisfrequently, when I have observed my eyes more than commonly sensible toother spectra. The circulation may be seen either in both eyes at a time, or only in one of them; for as a certain quantity of light is necessary toproduce this curious phenomenon, if one hand be brought nearer the closedeyelids than the other, the circulation in that eye will for a timedisappear. For the easier viewing the circulation, it is sometimesnecessary to rub the eyes with a certain degree of force after they areclosed, and to hold the breath rather longer than is agreeable, which, byaccumulating more blood in the eye, facilitates the experiment; but ingeneral it may be seen distinctly after having examined other spectra withyour back to the light, till the eyes become weary; then having coveredyour closed eyelids for half a minute, till the spectrum is faded awaywhich you were examining, turn your face to the light, and removing yourhands from the eyelids, by and by again shade them a little, and thecirculation becomes curiously distinct. The streams of blood are howevergenerally seen to unite, which shews it to be the venous circulation, owing, I suppose, to the greater opacity of the colour of the blood inthese vessels; for this venous circulation is also much more easily seen bythe microscope in the tail of a tadpole. 5. _Variation of spectra in respect to distinctness and size; with a newway of magnifying objects. _ 1. It was before observed, that when the two colours viewed together wereopposite to each other, as yellow and blue, red and green, &c. According tothe table of reflections and transmissions of light in Sir Isaac Newton'sOptics, B. II. Fig. 3. The spectra of those colours were of all others themost brilliant, and best defined; because they were combined of the reversespectrum of one colour, and of the direct spectrum of the other. Hence, inbooks printed with small types, or in the minute graduation ofthermometers, or of clock-faces, which are to be seen at a distance, if theletters or figures are coloured with orange, and the ground with indigo; orthe letters with red, and the ground with green; or any other lucid colouris used for the letters, the spectrum of which is similar to the colour ofthe ground; such letters will be seen much more distinctly, and with lessconfusion, than in black or white: for as the spectrum of the letter is thesame colour with the ground on which they are seen, the unsteadiness of theeye in long attending to them will not produce coloured lines by the edgesof the letters, which is the principal cause of their confusion. The beautyof colours lying in vicinity to each other, whose spectra are thusreciprocally similar to each colour, is owing to this greater ease that theeye experiences in beholding them distinctly; and it is probable, in theorgan of hearing, a similar circumstance may constitute the pleasure ofmelody. Sir Isaac Newton observes, that gold and indigo were agreeable whenviewed together; and thinks there may be some analogy between thesensations of light and sound. (Optics, Qu. 14. ) In viewing the spectra of bright objects, as of an area of red silk of halfan inch diameter on white paper, it is easy to magnify it to tenfold itssize: for if, when the spectrum is formed, you still keep your eye fixed onthe silk area, and remove it a few inches further from you, a green circleis seen round the red silk: for the angle now subtended by the silk is lessthan it was when the spectrum was formed, but that of the spectrumcontinues the same, and our imagination places them at the same distance. Thus when you view a spectrum on a sheet of white paper, if you approachthe paper to the eye, you may diminish it to a point; and if the paper ismade to recede from the eye, the spectrum will appear magnified inproportion to the distance. [Illustration: Fig. 5. ] I was surprised, and agreeably amused, with the following experiment. Icovered a paper about four inches square with yellow, and with a pen filledwith a blue colour wrote upon the middle of it the word BANKS in capitals, as in Fig. 5, and sitting with my back to the sun, fixed my eyes for aminute exactly on the center of the letter N in the middle of the word;after closing my eyes, and shading them somewhat with my hand, the word wasdistinctly seen in the spectrum in yellow letters on a blue field; andthen, on opening my eyes on a yellowish wall at twenty feet distance, themagnified name of BANKS appeared written on the wall in golden characters. _Conclusion. _ It was observed by the learned M. Sauvage (Nosol. Method. Cl. VIII. Ord. I. ) that the pulsations of the optic artery might be perceived by lookingattentively on a white wall well illuminated. A kind of net-work, darkerthan the other parts of the wall, appears and vanishes alternately withevery pulsation. This change of the colour of the wall he well ascribes tothe compression of the retina by the diastole of the artery. The variouscolours produced in the eye by the pressure of the finger, or by a strokeon it, as mentioned by Sir Isaac Newton, seem likewise to originate fromthe unequal pressure on various parts of the retina. Now as Sir IsaacNewton has shewn, that all the different colours are reflected ortransmitted by the laminæ of soap bubbles, or of air, according to theirdifferent thickness or thinness, is it not probable, that the effect of theactivity of the retina may be to alter its thickness or thinness, so asbetter to adapt it to reflect or transmit the colours which stimulate itinto action? May not muscular fibres exist in the retina for this purpose, which may be less minute than the locomotive muscles of microscopicanimals? May not these muscular actions of the retina constitute thesensation of light and colours; and the voluntary repetitions of them, whenthe object is withdrawn, constitute our memory of them? And lastly, may notthe laws of the sensations of light, here investigated, be applicable toall our other senses, and much contribute to elucidate many phenomena ofanimal bodies both in their healthy and diseased state; and thus renderthis investigation well worthy the attention of the physician, themetaphysician, and the natural philosopher? November 1, 1785. * * * * * Dum, Liber! astra petis volitans trepidantibus alis, Irruis immemori, parvula gutta, mari. Me quoque, me currente rotâ revolubilis ætas Volverit in tenebras, --i, Liber, ipse sequor. * * * * * INDEX TO THE SECTIONS OF PART FIRST. A. Abortion from fear, xxxix. 6. 5. Absorbent vessels, xxiii. 3. Xxix. 1. ---- regurgitate their fluids, xxix. 2. ---- their valves, xxix. 2. ---- communicate with vena portarum, xxvii. 2. Absorption of solids, xxxiii. 3. 1. Xxxvii. ---- of fluids in anasarca, xxxv. 1. 3. Accumulation of sensorial power, iv. 2. Xii. 5. 2. Activity of system too great, cure of, xii. 6. ---- too small, cure of, xii. 7. Age, old, xii. 3. 1. Xxxvii. 4. Ague-fit, xii. 7. 1. Xxxii. 3. 4. Xxxii. 9. ---- how cured by bark, xii. 3. 4. ---- periods, how occasioned, xii. 2. 3. Xxxii. 3. 4. Ague cakes, xxxii. 7. Xxxii. 9. Air, sense of fresh, xiv. 8. ---- injures ulcers, xxviii. 2. ---- injected into veins, xxxii. 5. Alcohol deleterious, xxx. 3. Alliterations, why agreeable, xxii. 2. Aloes in lessened doses, xii. 3. 1. American natives indolent, xxxi. 2. ---- narrow shouldered, xxxi. 1. Analogy intuitive, xvii. 3. 7. Animals less liable to madness, xxxiii. 1. ---- less liable to contagion, xxxiii. 1. ---- how to teach, xxii. 3. 2. ---- their similarity to each other, xxxix. 4. 8. ---- their changes after nativity, xxxix. 4. 8. ---- their changes before nativity, xxxix. 4. 8. ---- less liable to contagious diseases, why, xxxiii. 1. 5. ---- less liable to delirium and insanity, why, xxxiii. 1. 5. ---- easier to preserve than to reproduce, xxxvii. ---- food, distaste of, xxviii. 1. ---- appetency, xxxix. 4. 7. Antipathy, x. 2. 2. Aphthæ, xxviii. Apoplexy, xxxiv. 1. 7. ---- not from deficient irritation, xxxii. 2. 1. Appetites, xi. 2. 2. Xiv. 8. Architecture, xxii. 2. Xvi. 10. Arts, fine, xxii. 2. Asparagus, its smell in urine, xxix. Association defined, ii. 2. 11. Iv. 7. V. 2. ---- associate motions, x. ---- stronger than irritative ones, xxiv. 2. 8. ---- formed before nativity, xi. 3. ---- with irritative ones, xxiv. 2. 8. ---- with retrograde ones, xxv. 7. Xxv. 10. Xxv. 15. ---- diseases from, xxxv. Asthma, xviii. 15. Attention, language of, xvi. 8. 6. Atrophy, xxviii. Aversion, origin of, xi. 2. 3. B. Balance ourselves by vision, xx. 1. Bandage increases absorption, xxxiii. 3. 2. Barrenness, xxxvi. 2. 3. Battement of sounds, xx. 7. Bath, cold. See Cold Bath. Beauty, sense of, xvi. 6. Xxii. 2. Bile-ducts, xxx. ---- stones, xxx. 1. 3. ---- regurgitates into the blood, xxiv. 2. 7. ---- vomiting of, xxx. 1. 3. Birds of passage, xvi. 12. ---- nests of, xvi. 13. ---- colour of their eggs, xxxix. 5. Biting in pain, xxxiv. 1. 3. ---- of mad animals, xxxiv. 1. 3. Black spots on dice appear red, xl. 3. Bladder, communication of with the intestines, xxix. 3. ---- of fish, xxiv. 1. 4. Blood, transfusion of in nervous fevers, xxxii. 4. ---- deficiency of, xxxii. 2. And 4. ---- from the vena portarum into the intestines, xxvii. 2. ---- its momentum, xxxii. 5. 2. ---- momentum increased by venesection, xxxii. 5. 4. ---- drawn in nervous pains, xxxii. 5. 4. ---- its oxygenation, xxxviii. Breasts of men, xiv. 8. Breathing, how learnt, xvi. 4. Brutes differ from men, xi. 2. 3. Xvi. 17. Brutes. See Animals. Buxton bath, why it feels warm, xii. 2. 1. Xxxii. 3. 3. C. Capillary vessels are glands, xxvi. 1. Catalepsy, xxxiv. 1. 5. Catarrh from cold skin, xxxv. 1. 3. Xxxv. 2. 3. ---- from thin caps in sleep, xviii. 15. Catenation of motions defined, ii. 2. 11. Iv. 7. ---- cause of them, xvii. 1. 3. ---- described, xvii. ---- continue some time after their production, xvii. 1. 3. ---- voluntary ones dissevered in sleep, xvii. 1. 12. Xvii. 3. 7. Cathartics, external, their operation, xxix. 7. 6. Causation, animal, defined, ii. 2. 11. Iv. 7. Cause of causes, xxxix. 4. 8. Causes inert and efficient, xxxix. 8. 2. ---- active and passive, xxxix. 8. 3. ---- proximate and remote, xxxix. 8. 4. Chick in the egg, oxygenation of, xxxviii. 2. Child riding on a stick, xxxiv. 2. 6. Chilness after meals, xxi. 3. Xxxv. 1. 1. Cholera, case of, xxv. 13. Circulation in the eye visible, xl. 10. 4. Cold in the head, xii. 6. 5. ---- perceived by the teeth, xxxii. 3. 1. Xiv. 6. ---- air, uses of in fevers, xxxii. 3. 3. ---- feet, produces coryza, xxxv. 2. 3. Xxxv. 1. 3. ---- bath, why it strengthens, xxxii. 3. 2. ---- short and cold breathing in it, xxxii. 3. 2. ---- produces a fever-fit, xxxii. 3. 2. ---- fit of fever the consequence of hot fit, xxxii. 9. 3. ---- bathing in pulmonary hæmorrhage, xxvii. 1. ---- fits of fever, xxxii. 4. Xxxii. 9. Xvii. 3. 3. Colours of animals, efficient cause of, xxxix. 5. 1. ---- of eggs from female imagination, xxxix. 5. 1. ---- of the choroid coat of the eye, xxxix. 5. 1. ---- of birds nests, xvi. 13. Comparing ideas, xv. 3. Consciousness, xv. 3. 4. ---- in dreams, xviii. 13. Consent of parts. See Sympathy. Consumption, its temperament, xxxi. 1. And 2. ---- of dark-eyed patients, xxvii. 2. ---- of light-eyed patients, xxviii. 2. ---- is contagious, xxxiii. 2. 7. Contagion, xii. 3. 6. Xix. 9. Xxxiii. 2. 6. And 8. Xxii. 3. 3. ---- does not enter the blood, xxxiii. 2. 10. Xxii. 3. 3. Contraction and attraction, iv. 1. ---- of fibres produces sensation, iv. 5. Xii. 1. 6. ---- continues some time, xii. 1. 5. ---- alternates with relaxation, xii. 1. 3. Convulsion, xvii. 1. 8. Xxxiv. 1. 1. And 4. Iii. 5. 8. ---- of particular muscles, xvii. 1. 8. ---- periods of, xxxvi. 3. 9. Coryza. See Catarrh. Cough, nervous, periods of, xxxvi. 3. 9. Cramp, xviii. 15. Xxxiv. 1. 7. Critical days from lunations, xxxvi. 4. D. Darkish room, why we see well in it, xii. 2. 1. Debility sensorial and stimulatory, xii. 2. 1. ---- direct and indirect of Dr. Brown, xii. 2. 1. Xxxii. 3. 2. ---- See Weakness. ---- from drinking spirits, cure of, xii. 7. 8. ---- in fevers, cure of, xii. 7. 8. Deliberation, what, xxxiv. 1. Delirium, two kinds of, xxxiii. 1. 4. Xxxiv. 2. 2. ---- cases of, iii. 5. 8. ---- prevented by dreams, xviii. 2. Desire, origin of, xi. 2. 3. Diabetes explained, xxix. 4. ---- with bloody urine, xxvii. 2. ---- in the night, xviii. 15. Diarrhoea, xxix. 4. Digestion, xxxiii. 1. Xxxvii. ---- strengthened by emetics, xxxv. 1. 3. ---- strengthened by regular hours, why, xxxvi. 2. 1. Digitalis, use of in dropsy, xxix. 5. 2. Distention acts as a stimulus, xxxii. 4. ---- See Extension. Distinguishing, xv. 3. Diurnal circle of actions, xxv. 4. Doubting, xv. 3. Dreams, viii. 1. 2. Xiv. 2. 5. ---- their inconsistency, xviii. 17. ---- no surprise in them, xviii. 17. ---- much novelty of combination, xviii. 9. Dropsies explained, xxix. 5. 1. Dropsy cured by insanity, xxxiv. 2. 7. ---- cure of, xxix. 5. 2. Drunkards weak till next day, xvii. 1. 7. ---- stammer, and stagger, and weep, xii. 4. 1. Xxi. 4. ---- see objects double, why, xxi. 7. ---- become delirious, sleepy, stupid, xxi. 5. Drunkenness. See Intoxication, xxi. ---- diminished by attention, xxi. 8. Dyspnoea in cold bath, xxxii. 3. 2. E. Ear, a good one, xvi. 10. ---- noise in, xx. 7. Eggs of frogs, fish, fowl, xxxix. 2. ---- of birds, why spotted, xxxix. 5. ---- with double yolk, xxxix. 4. 4. Electricity, xii. 1. Xiv. 9. ---- jaundice cured by it, xxx. 1. 2. Embryon produced by the male, xxxix. 2. ---- consists of a living fibre, xxxix. 4. ---- absorbs nutriment, receives oxygen, xxxix. 1. ---- its actions and sensations, xvi. 2. Emetic. See Vomiting. Emotions, xi. 2. 2. Ennui, or tædium vitæ, xxxiv. 2. 3. Xxxiii. 1. 1. Xxxix. 6. Epileptic fits explained, xxxiv. 1. 4. Xxvii. 2. ---- in sleep, why, xviii. 14. & 15. Equinoxial lunations, xxxii. 6. Excitability perpetually varies, xii. 1. 7. ---- synonymous to quantity of sensorial power, xii. 1. 7. Exercise, its use, xxxii. 5. 3. Exertion of sensorial power defined, xii. 2. 1. Existence in space, xiv. 2. 5. Extension, sense of, xiv. 7. Eyes become black in some epilepsies, xxvii. 2. F. Face, flushing of after dinner, xxxv. 1. 1. ---- why first affected in small-pox, xxxv. 1. 1. ---- red from inflamed liver, xxxv. 2. 2. Fainting fits, xii. 7. 1. Xiv. 7. Fear, language of, xvi. 8. 1. ---- a cause of fever, xxxii. 8. ---- cause of, xvii. 3. 7. Fetus. See Embryon, xvi. 2. Xxxix. 1. Fevers, irritative, xxxii. 1. ---- intermittent, xxxii. 1. Xxxii. 3. ---- sensitive, xxxiii. 1. ---- not an effort of nature for relief, xxxii. 10. ---- paroxysms of, xii. 7. 1. Xii. 2. 3. Xii. 3. 5. ---- why some intermit and not others, xxxvi. 1. ---- cold fits of, xxxii. 4. Xxxii. 9. Xvii. 3. 3. ---- periods of, xxxvi. 3. ---- have solar or lunar periods, xxxii. 6. ---- source of the symptoms of, xxxii. 1. ---- prostration of strength in, xii. 4. 1. Xxxii. 3. 2. ---- cure of, xii. 6. 1. ---- how cured by the bark, xii. 3. 4. ---- cured by increased volition, xii. 2. 4. Xxxiv. 2. 8. ---- best quantity of stimulus in, xii. 7. 8. Fibres. See Muscles. Fibres, their mobility, xii. 1. 7. Xii. 1. 1. ---- contractions of, vi. Xii. 1. 1. ---- four classes of their motions, vi. ---- their motions distinguished from sensorial ones, v. 3. Figure, xiv. 2. 2. Iii. 1. Fish, their knowledge, xvi. 14. Foxglove, its use in dropsies, xxix. 5. 2. ---- overdose of, xxv. 17. Free-will, xv. 3. 7. G. Gall-stone, xxv. 17. ---- See Bile-stones. Generation, xxxiii. 1. Xxxix. Gills of fish, xxxviii. 2. Glands, xxiii. 2. ---- conglobate glands, xxiii. 3. ---- have their peculiar stimulus, xi. 1. ---- their senses, xiv. 9. Xxxix. 6. ---- invert their motions, xxv. 7. ---- increase their motions, xxv. 7. Golden rule for exhibiting wine, xii. 7. 8. ---- for leaving off wine, xii. 7. 8. Gout from inflamed liver, xxxv. 2. 2. Xviii. 16. Xxiv. 2. 8. ---- in the stomach, xxiv. 2. 8. Xxv. 17. ---- why it returns after evacuations, xxxii. 4. ---- owing to vinous spirit only, xxi. 10. ---- periods of, xxxvi. 3. 6. Grinning in pain, xxxiv. 1. 3. Gyration on one foot, xx. 5. And 6. H. Habit defined, ii. 2. 11. Iv. 7. Hæmorrhages, periods of, xxxvi. 3. 11. ---- from paralysis of veins, xxvii. 1. And 2. Hair and nails, xxxix. 3. 2. ---- colour of, xxxix. 5. 1. Harmony, xxii. 2. Head-achs, xxxv. 2. 1. Hearing, xiv. 4. Heat, sense of, xiv. 6. Xxxii. 3. 1. ---- produced by the glands, xxxii. 3. ---- external and internal, xxxii. 3. 1. ---- atmosphere of heat, xxxii. 3. 1. ---- increases during sleep, xviii. 15. Hemicrania, xxxv. 2. 1. ---- from decaying teeth, xxxv. 2. 1. Hepatitis, cause of, xxxv. 2. 3. Hereditary diseases, xxxix. 7. 6. Hermaphrodite insects, xxxix. 5. Herpes, xxviii. 2. ---- from inflamed kidney, xxxv. 2. 2. Hilarity from diurnal fever, xxxvi. 3. 1. Hunger, sense of, xiv. 8. Hydrophobia, xxii. 3. 3. Hypochondriacism, xxxiii. 1. 1. Xxxiv. 2. 3. I. Ideas defined, ii. 2. 7. ---- are motions of the organs of sense, iii. 4. Xviii. 5. Xviii. 10. Xviii. 6. ---- analogous to muscular motions, iii. 5. ---- continue some time, xx. 6. ---- new ones cannot be invented, iii. 6. 1. ---- abstracted ones, iii. 6. 4. ---- inconsistent trains of, xviii. 17. ---- perish with the organ of sense, iii. 4. 4. ---- painful from inflammation of the organ, iii. 5. 5. ---- irritative ones, vii. 1. 4. Vii. 3. 2. Xv. 2. Xx. 7. ---- of resemblance, contiguity, causation, viii. 3. 2. X. 3. 3. ---- resemble the figure and other properties of bodies, xiv. 2. 2. ---- received in tribes, xv. 1. ---- of the same sense easier combined, xv. 1. 1. ---- of reflection, xv. 1. 6. Ii. 2. 12. Ideal presence, xv. 1. 7. Identity, xv. 3. 5. Xviii. 13. Iliac passion, xxv. 15. Imagination, viii. 1. 2. Xv. 1. 7. Xv. 2. 2. ---- of the male forms the sex, xxxix. 6. Imitation, origin of, xii. 3. 3. Xxxix. 5. Xxii. 3. Xvi. 7. Immaterial beings, xiv. 1. Xiv. 2. 4. Impediment of speech, xvii. 1. 10. Xvii. 2. 10. Infection. See Contagion. Inflammation, xii. 2. 3. Xxxiii. 2. 2. ---- great vascular exertion in, xii. 2. 1. ---- not from pains from defect of stimulus, xxxiii. 2. 3. ---- of parts previously insensible, xii. 3. 7. ---- often distant from its cause, xxiv. 2. 8. ---- observes solar days, xxxii. 6. ---- of the eye, xxxiii. 3. 1. ---- of the bowels prevented by their continued action in sleep, xviii. 2. Inoculation with blood, xxxiii. 2. 10. Insane people, their great strength, xii. 2. 1. Insanity (see Madness) pleasurable one, xxxiv. 2. 6. Insects, their knowledge, xvi. 15. And 16. ---- in the heads of calves, xxxix. 1. ---- class of, xxxix. 4. 8. Instinctive actions defined, xvi. 1. Intestines, xxv. 3. Intoxication relieves pain, why, xxi. 3. ---- from food after fatigue, xxi. 2. ---- diseases from it, xxi. 10. ---- See Drunkenness. Intuitive analogy, xvii. 3. 7. Invention, xv. 3. 3. Irritability increases during sleep, xviii. 15. Itching, xiv. 9. J. Jaundice from paralysis of the liver, xxx. 1. 2. ---- cured by electricity, xxx. 1. 2. Jaw-locked, xxxiv. 1. 5. Judgment, xv. 3. K. Knowledge of various animals, xvi. 11. L. Lachrymal sack, xvi. 8. Xxiv. 2. 2. And 7. Lacteals, paralysis of, xxviii. ---- See Absorbents. Lady playing on the harpsichord, xvii. 2. ---- distressed for her dying bird, xvii. 2. 10. Language, natural, its origin, xvi. 7. & 8. ---- of various passions described, xvi. 8. ---- artificial, of various animals, xvi. 9. ---- theory of, xxxix. 8. 3. Lapping of puppies, xvi. 4. Laughter explained, xxxiv. 1. 4. ---- from tickling, xvii. 3. 5. Xxxiv. 1. 4. ---- from frivolous ideas, xxxiv. 1. 4. Xviii. 12. Life, long, art of producing, xxxvii. Light has no momentum, iii. 3. 1. Liquor amnii, xvi. 2. Xxxviii. 2. ---- is nutritious, xxxviii. 3. ---- frozen, xxxviii. 3. Liver, paralysis of, xxx. 1. 4. ---- large of geese, xxx. 1. 6. Love, sentimental, its origin, xvi. 6. ---- animal, xiv. 8. Xvi. 5. Lunar periods affect diseases, xxxii. 6. Lust, xiv. 8. Xvi. 5. Lymphatics, paralysis of, xxviii. ---- See Absorbents. M. Mad-dog, bite of, xxii. 3. 3. Madness, xxxiv. 2. 1. Xii. 2. 1. Magnetism, xii. 1. 1. Magnifying objects, new way of, xl. 10. 5. Male animals have teats, xxxix. 4. 8. ---- pigeons give milk, xxxix. 4. 8. Man distinguished from brutes, xi. 2. 3. Xvi. 17. Material world, xiv. 1. Xiv. 2. 5. Xviii. 7. Matter, penetrability of, xiv. 2. 3. ---- purulent, xxxiii. 2. 4. Measles, xxxiii. 2. 9. Membranes, xxvi. 2. Memory defined, ii. 2. 10. Xv. 1. 7. Xv. 3. Menstruation by lunar periods, xxxii. 6. Miscarriage from fear, xxxix. 6. 5. Mobility of fibres, xii. 1. 7. Momentum of the blood, xxxii. 5. 2. ---- sometimes increased by venesection, xxxii. 5. 4. Monsters, xxxix. 4. 4. And 5. 2. ---- without heads, xxxviii. 3. Moon and sun, their influence, xxxii. 6. Mortification, xxxiii. 3. 3. Motion is either cause or effect, i. Xiv. 2. 2. ---- primary and secondary, i. ---- animal, i. Iii. 1. ---- propensity to, xxii. 1. ---- animal, continue some time after their production, xvii. 1. 3. ---- defined, a variation of figure, iii. 1. Xiv. 2. 2. Xxxix. 8. Mucus, experiments on, xxvi. 1. ---- secretion of, xxvi. 2. Mules, xxxix. 4. 5. And 6. Xxxix. 5. 2. Mule plants, xxxix. 2. Muscæ volitantes, xl. 2. Muscles constitute an organ of sense, xiv. 7. Ii. 2. 4. ---- stimulated by extension, xi. 1. Xiv. 7. ---- contract by spirit of animation, xii. 1. 1. And 3. Music, xvi. 10. Xxii. 2. Musical time, why agreeable, xii. 3. 3. N. Nausea, xxv. 6. Nerves and brain, ii. 2. 3. ---- extremities of form the whole system, xxxvii. 3. ---- are not changed with age, xxxvii. 4. Nervous pains defined, xxxiv. 1. 1. Number defined, xiv. 2. 2. Nutriment for the embryon, xxxix. 5. 2. Nutrition owing to stimulus, xxxvii. 3. ---- by animal selection, xxxvii. 3. ---- when the fibres are elongated, xxxvii. 3. ---- like inflammation, xxxvii. 3. O. Objects long viewed become faint, iii. 3. 2. Ocular spectra, xl. Oil externally in diabætes, xxix. 4. Old age from inirritability, xxxvii. Opium is stimulant, xxxii. 2. 2. ---- promotes absorption after evacuation, xxxiii. 3. 1. ---- in increasing doses, xii. 3. 1. Organs of sense, ii. 2. 5. And 6. Organs when destroyed cease to produce ideas, iii. 4. 4. Organic particles of Buffon, xxxvii. 3. Xxxix. 3. 3. Organ-pipes, xx. 7. Oxygenation of the blood, xxxviii. P. Pain from excess and defect of motion, iv. 5. Xii. 5. 3. Xxxiv. 1. Xxxv. 2. 1. ---- not felt during exertion, xxxiv. 1. 2. ---- from greater contraction of fibres, xii. 1. 6. ---- from accumulation of sensorial power, xii. 5. 3. ---- from light, pressure, heat, caustics, xiv. 9. ---- in epilepsy, xxxv. 2. 1. ---- distant from its cause, xxiv. 2. 8. ---- from stone in the bladder, xxxv. 2. 1. ---- of head and back from defect, xxxii. 3. ---- from a gall-stone, xxxv. 2. 1. Xxv. 17. ---- of the stomach in gout, xxv. 17. ---- of shoulder in hepatitis, xxxv. 2. 4. ---- produces volition, iv. 6. Paleness in cold fit, xxxii. 3. 2. Palsies explained, xxxiv. 1. 7. Paralytic limbs stretch from irritation, vii. 1. 3. ---- patients move their sound limb much, xii. 5. 1. Paralysis from great exertion, xii. 4. 6. ---- from less exertion, xii. 5. 6. ---- of the lacteals, xxviii. ---- of the liver, xxx. 1. 4. ---- of the right arm, why, xxxiv. 1. 7. ---- of the veins, xxvii. 2. Particles of matter will not approach, xii. 1. 1. Passions, xi. 2. 2. ---- connate, xvi. 1. Pecking of chickens, xvi. 4. Perception defined, ii. 2. 8. Xv. 3. 1. Periods of agues, how formed, xxxii. 3. 4. ---- of diseases, xxxvi. ---- of natural actions and of diseased actions, xxxvi. Perspiration in fever-fits, xxxii. 9. See Sweat. Petechiæ, xxvii. 2. Pigeons secrete milk in their stomachs, xxxix. 4. 8. Piles, xxvii. 2. Placenta a pulmonary organ, xxxviii. 2. Pleasure of life, xxxiii. 1. Xxxix. 5. ---- from greater fibrous contractions, xii. 1. 6. ---- what kind causes laughter, xxxiv. 1. 4. ---- what kind causes sleep, xxxiv. 1. 4. Pleurisy, periods of, xxxvi. 3. 7. ---- cause of, xxxv. 2. 3. Prometheus, story of, xxx. 3. Prostration of strength in fevers, xii. 4. 1. Pupils of the eyes large, xxxi. 1. Pulse quick in fevers with debility, xii. 1. 4. Xii. 5. 4. Xxxii. 2. 1. ---- in fevers with strength, xxxii. 2. ---- from defect of blood, xxxii. 2. 3. Xii. 1. 4. ---- weak from emetics, xxv. 17. Q. Quack advertisements injurious. Preface. Quadrupeds have no sanguiferous lochia, xxxviii. 2. ---- have nothing similar to the yolk of egg, xxxix. 1. R. Rhaphania, periods of, xxxvi. 3. 9. Reason, ix. 1. 2. Xv. 3. Reasoning, xv. 3. Recollection, ii. 2. 10. Ix. 1. 2. Xv. 2. 3. Relaxation and bracing, xxxii. 3. 2. Repetition, why agreeable, xii. 3. 3. Xxii. 2. Respiration affected by attention, xxxvi. 2. 1. Restlessness in fevers, xxxiv. 1. 2. Retrograde motions, xii. 5. 5. Xxv. 6. Xxix. 11. ---- of the stomach, xxv. 6. ---- of the skin, xxv. 9. ---- of fluids, how distinguished, xxix. 8. ---- how caused, xxix. 11. 5. ---- vegetable motions, xxix. 9. Retina is fibrous, iii. 2. Xl. 1. ---- is active in vision, iii. 3. Xl. 1. ---- excited into spasmodic motions, xl. 7. ---- is sensible during sleep, xviii. 5. Xix. 8. Reverie, xix. 1. Xxxiv. 3. ---- case of a sleep-walker, xix. 2. ---- is an epileptic disease, xix. 9. Rhymes in poetry, why agreeable, xxii. 2. Rheumatism, three kinds of, xxvi. 3. Rocking young children, xxi. 3. Ruminating animals, xxv. 1. S. Saliva produced by mercury, xxiv. 1. ---- by food, xxiv. 1. 1. ---- by ideas, xxiv. 1. 2. And 5. ---- by disordered volition, xxiv. 1. 7. Schirrous tumours revive, xii. 2. 2. Screaming in pain, xxxiv. 1. 3. Scrophula, its temperament, xxxi. 1. ---- xxviii. 2. Xxxix. 4. 5. Scurvy of the lungs, xxvii. 2. Sea-sickness, xx. 4. ---- stopped by attention, xx. 5. Secretion, xxxiii. 1. Xxxvii. ---- increased during sleep, xviii. 16. Seeds require oxygenation, xxxviii. 2. Sensation defined, ii. 2. 9. V. 2. Xxxix. 8. 4. ---- diseases of, xxxiii. ---- from fibrous contractions, iv. 5. Xii. 1. 6. ---- in an amputated limb, iii. 6. 3. ---- affects the whole sensorium, xi. 2. ---- produces volition, iv. 6. Sensibility increases during sleep, xviii. 15. Sensitive motions, viii. Xxxiii. 2. Xxxiv. 1. ---- fevers of two kinds, xxxiii. 1. 2. ---- ideas, xv. 2. 2. Sensorium defined, ii. 2. 1. Senses correct one another, xviii. 7. ---- distinguished from appetites, xxxiv. 1. 1. Sensorial power. See Spirit of Animation. ---- great expence of in the vital motions, xxxii. 3. 2. ---- two kinds of excited in sensitive fevers, xxxiii. 1. 3. ---- powers defined, v. 1. ---- motions distinguished from fibrous motions, v. 3. ---- not much, accumulated in sleep, xviii. 2. ---- powers, accumulation of, xii. 5. 1. ---- exhaustion of, xii. 4. 1. ---- wasted below natural in hot fits, xxxii. 9. 3. ---- less exertion of produces pain, xii. 5. 3. ---- less quantity of it, xii. 5. 4. Sensual motions distinguished from muscular, ii. 2. 7. Sex owing to the imagination of the father, xxxix. 7. 6. Xxxix. 6. 3. Xxxix. 6. 7. Xxxix. 5. Shingles from inflamed kidney, xxxv. 2. 2. Shoulders broad, xxxi. 1. Xxxix. 7. 6. Shuddering from cold, xxxiv. 1. 1. And 2. Sight, its accuracy in men, xvi. 6. Skin, skurf on it, xxvi. 1. Sleep suspends volition, xviii. 1. ---- defined, xviii. 21. ---- remote causes, xviii. 20. ---- sensation continues in it, xviii. 2. ---- from food, xxi. 1. ---- from rocking, uniform sounds, xxi. 1. ---- from wine and opium, xxi. 3. ---- why it invigorates, xii. 5. 1. ---- pulse slower and fuller, xxxii. 2. 2. ---- interrupted, xxvii. 2. ---- from breathing less oxygene, xviii. 20. ---- from being whirled on a millstone, xviii. 20. ---- from application of cold, xviii. 20. ---- induced by regular hours, xxxvi. 2. 2. Sleeping animals, xii. 2. 2. Sleep-walkers. See Reverie, xix. 1. Small-pox, xxxiii. 2. 6. Xxxix. 6. 1. ---- eruption first on the face, why, xxxv. 1. 1. Xxxiii. 2. 10. ---- the blood will not infect, xxxiii. 2. 10. ---- obeys lunations, xxxvi. 4. Smell, xiv. 5. Xvi. 5. Smiling, origin of, xvi. 8. 4. Solidity, xiv. 2. 1. Somnambulation. See Reverie, xix. 1. Space, xiv. 2. 2. Spasm, doctrine of, xxxii. 10. Spectra, ocular, xl. ---- mistaken for spectres, xl. 2. ---- vary from long inspection, iii. 3. 5. Spirit of animation. See Sensorial Power. ---- of animation causes fibrous contraction, iv. 2. Ii. 2. 1. Xiv. 2. 4. ---- possesses solidity, figure, and other properties of matter, xiv. 2. 4. Spirits and angels, xiv. 2. 4. Stammering explained, xvii. 1. 10. Xvii. 2. 10. Stimulus defined, ii. 2. 13. Iv. 4. Xii. 2. 1. ---- of various kinds, xi. 1. ---- with lessened effect, xii. 3. 1. ---- with greater effect, xii. 3. 3. ---- ceases to produce sensation, xii. 3. 6. Stomach and intestines, xxv. ---- inverted by great stimulus, xxv. 6. ---- its actions decreased in vomiting, xxxv. 1. 3. ---- a blow on it occasions death, xxv. 17. Stools black, xxvii. 2. Strangury, xxxv. 2. 1. Sucking before nativity, xvi. 4. Suckling children, sense of, xiv. 8. Suggestion defined, ii. 2. 10. Xv. 2. 4. Sun and moon, their influence, xxxii. 6. Surprise, xvii. 3. 7. Xviii. 17. Suspicion attends madness, xxxiv. 2. 4. Swallowing, act of, xxv. 1. Xvi. 4. Sweat, cold, xxv. 9. Xxix. 6. ---- in hot fit of fever, xxxii. 9. ---- in a morning, why, xviii. 15. Sweaty hands cured by lime, xxix. 4. 9. Swinging and rocking, why agreeable, xxi. 3. Sympathy, xxxv. 1. Syncope, xii. 7. 1. Xxxiv. 1. 6. T. Tædium vitæ. See Ennui. Tape-worm, xxxix. 2. 3. Taste, sense of, xiv. 5. Tears, secretion of, xxiv. ---- from grief, xvi. 8. 2. ---- from tender pleasure, xvi. 8. 3. ---- from stimulus of nasal duct, xvi. 8. Xxiv. 2. 4. ---- by volition, xxiv. 2. 6. Teeth decaying cause headachs, xxxv. 2. 1. Temperaments, xxxi. Theory of medicine, wanted. Preface. Thirst, sense of, xiv. 8. ---- why in dropsies, xxix. 5. Tickle themselves, children cannot, xvii. 3. 5. Tickling, xiv. 9. Time, xiv. 2. 2. Xviii. 12. ---- lapse of, xv. 3. 6. ---- poetic and musical, why agreeable, xxii. 2. ---- dramatic, xviii. 12. Tooth-edge, xvi. 10. Iii. 4. 3. Xxii. 3. 3. Touch, sense of, xiv. 2. 1. ---- liable to vertigo, xxi. 9. ---- of various animals, xvi. 6. Trains of motions inverted, xii. 5. 5. Transfusion of blood in nervous fever, xxxii. 4. Translations of matter, xxix. 7. Typhus, best quantity of stimulus in, xii. 7. 8. ---- periods of observe lunar days, xxxii. 6. U. Ulcers, art of healing, xxxiii. 3. 2. ---- of the lungs, why difficult to heal, xxviii. 2. Uniformity in the fine arts, why agreeable, xxii. 2. Urine pale in intoxication, xxi. 6. ---- paucity of in anasarca, why, xxix. 5. ---- its passage from intestines to bladder, xxix. 3. ---- copious during sleep, xviii. 15. V. Variation, perpetual, of irritability, xii. 2. 1. Vegetable buds are inferior animals, xiii. 1. ---- exactly resemble their parents, xxxix. ---- possess sensation and volition, xiii. 2. ---- have associate and retrograde motions, xiii. 4. Xxix. 9. ---- their anthers and stigmas are alive, xiii. 5. ---- have organs of sense and ideas, xiii. 5. ---- contend for light and air, xxxix. 4. 8. ---- duplicature of their flowers, xxxix. 4. 4. Veins are absorbents, xxvii. 1. ---- paralysis of, xxvii. 1. Venereal orgasm of brutes, xxxii. 6. Venesection in nervous pains, xxxii. 5. 4. Verbs of three kinds, xv. 3. 4. Verses, their measure, xxii. 2. Vertigo, xx. ---- defined, xx. 11. ---- in looking from a tower, xx. 1. ---- in a ship at sea, xx. 4. ---- of all the senses, xxi. 9. ---- by intoxication, xxxv. 1. 2. Vibratory motions perceived after sailing, xx. 5. Xx. 10. Vinegar makes the lips pale, xxvii. 1. Vis medicatrix of nature, xxxix. 4. 7. Vision, sense of, xiv. 3. Volition defined, v. 2. Xxxiv. 1. ---- affects the whole sensorium, xi. 2. ---- diseases of, xxxiv. Voluntarity, xi. 2. 4. Voluntary motions, ix. Xxxiv. 1. Voluntary ideas, xv. 2. 3. ---- criterion of, xi. 2. 3. Xxxiv. 1. Vomiting from vertigo, xx. 8. ---- from drunkenness, xx. 8. Xxi. 6. ---- by intervals, xxv. 8. ---- by voluntary efforts, xxv. 6. ---- of two kinds, xxxv. 1. 3. ---- in cold fit of fever, xxxii. 9. 1. ---- stopped by quicksilver, xxv. 16. ---- weakens the pulse, xxv. 17. W. Waking, how, xviii. 14. Walking, how learnt, xvi. 3. Warmth in sleep, why, xviii. 15. Weakness defined, xii. 1. 3. Xii. 2. 1. Xxxii. 3. 2. ---- cure of, xii. 7. 8. ---- See Debility. Wit producing laughter, xxxiv. 1. 4. World generated, xxxix. 4. 8. * * * * * END OF THE FIRST VOLUME.