Transcriber's Note

 The punctuation and spelling from the original text have been faithfully preserved. Only obvious typographical errors have been corrected. 

[Illustration: An artificial lake, nearly dry and partly filled withrubbish, has become a breeding-ground for dangerous mosquitoes. ]

 American Nature Series

 Group IV. Working with Nature

 INSECTS AND DISEASE

 A POPULAR ACCOUNT OF THE WAY IN WHICH INSECTS MAY SPREAD OR CAUSE SOME OF OUR COMMON DISEASES

 WITH MANY ORIGINAL ILLUSTRATIONS FROM PHOTOGRAPHS

 BY

 RENNIE W. DOANE, A. B. 

 _Assistant Professor of Entomology Leland Stanford Junior University_

 LONDON

 CONSTABLE & COMPANY LIMITED

 1910

 COPYRIGHT, 1910, BY

 HENRY HOLT AND COMPANY

 _Published August, 1910_

 THE QUINN & BODEN CO. PRESS

 RAHWAY, N. J. 

PREFACE

The subject of preventive medicine is one that is attracting world-wideattention to-day. We can hardly pick up a newspaper or magazine withoutseeing the subject discussed in some of its phases, and during the lastfew years several books have appeared devoted wholly or in part to theways of preventing rather than curing many of our ills. 

Looking over the titles of these articles and books the reader will atonce be impressed with the importance that is being given to the subjectof the relation of insects to some of our common diseases. As many ofthese maladies are caused by minute parasites or microbes thezoölogists, biologists and physicians are studying with untiring zeal tolearn what they can in regard to the development and habits of theseorganisms, and the entomologists are doing their part by studying inminute detail the structure and life-history of the insects that areconcerned. Thus many important facts are being learned, many importantobservations made. The results of the best of these investigations arealways published in technical magazines or papers that are usuallyaccessible only to the specialist. 

This little book is an attempt to bring together and place inuntechnical form the most important of these facts gathered from sourcesmany of which are at present inaccessible to the general reader, perhapseven to many physicians and entomologists. 

In order that the reader who is not a specialist in medicine orentomology may more readily understand the intimate biological relationsof the animals and parasites to be discussed it seems desirable to callattention first to their systematic relations and to review some of theimportant general facts in regard to their structure and life-history. This, it is believed, will make even the most complex specialinterrelations of some of these organisms readily understandable by all. Those who are already more or less familiar with these things may findthe bibliography of use for more extended reading. 

My thanks are due to Prof. V. L. Kellogg for reading the manuscript andoffering helpful suggestions and criticisms. 

Unless otherwise credited the pictures are from photographs taken by theauthor in the laboratory and field. As many of these are pictures oflive specimens it is believed that they will be of interest as showingthe insects, not as we think they should be, but as they actually are. Mr. J. H. Paine has given me valuable aid in preparing these photographs. 

 R. W. D. 

 Stanford University, California, March, 1910. 

CONTENTS

CHAPTER I PAGE

PARASITISM AND DISEASE 1

Definition of a parasite, 1; examples among various animals, 2; _Parasitism_, 3; effect on the parasite, 4; how a harmlesskind may become harmful, 5; immunity, 6; _Diseases caused byparasites_, 7; ancient and modern views, 7; _Infectious and contagiousdiseases_, 8; examples, 9; importance of distinguishing, 9; _Effect of the parasite on the host_, 9; microbes everywhere, 10;importance of size, 11; numbers, 11; location, 11; mechanicalinjury, 12; morphological injury, 13; physiological effect, 13;the point of view, 14. 

CHAPTER II

BACTERIA AND PROTOZOA 15

_Bacteria_, 15; border line between plants and animals, 15;most bacteria not harmful, 15; a few cause disease, 15; howthey multiply, 15; parasitic and non-parasitic kinds, 17; how akind normally harmless may become harmful, 18; effect of thebacteria on the host, 18; methods of dissemination, 18; _Protozoa_, 19; _Amoeba_, 19; its lack of special organs, 19; whereit lives, 19; growth and reproduction, 19; _Classes of Protozoa_, 20; the amoeba-like forms, 20; the flagellate forms, 20; importanceof these, 21; the ciliated forms, 22; the Sporozoa or spore-forming kinds, 22; these most important, 23; abundance, 23; adaptability, 23; commoncharacters, 24; ability to resist unfavorable conditions, 24. 

CHAPTER III

TICKS AND MITES 26

_Ticks_, 26; general characters, 27; mouth-parts, 27; habits, 27; life-history, 27; _Ticks and disease_, 28; _Texas fever_, 28; itsoccurrence in the north, 28; carried by a tick, 29; loss andmethods of control, 31; other diseases of cattle carried by ticks, 31; _Rocky Mountain spotted fever_, 32; its occurrence, 32;probably caused by parasites, 32; relation of ticks to this disease, 33; _Relapsing Fever_, 33; its occurrence, 34; transmittedby ticks, 34; _Mites_, 35; _Face-mites_, 35; _Itch-mites_, 36;_Harvest-mites_, 37. 

CHAPTER IV

HOW INSECTS CAUSE OR CARRY DISEASE 40

Numbers, 40; importance, 41; losses caused by insects, 41;loss of life, 42; _The flies_, 43; horse-flies, 43; stable-flies, 44;surra, 45; nagana, 45; black-flies, 46; punkies, 46; screw-wormflies, 47; blow-flies, 48; flesh-flies, 48; fly larvæ in intestinalcanal, 49; bot-flies, 50; _Fleas_, 52; jigger-flea, 53; _Bedbugs_, 54;_Lice_, 54; _How insects may carry disease_, 55; in a mechanicalway, 55; as one of the necessary hosts of the parasite, 56. 

CHAPTER V

HOUSE-FLIES OR TYPHOID-FLIES 57

The old attitude toward the house-fly, 57; its present standing, 58; reasons for the change, 58; _Structure_, 59; head andmouth-parts, 60; thorax and wings, 61; feet, 62; _How theycarry bacteria_, 62; _Life-history_, 63; eggs, 63; ordinarily laid inmanure, 63; other places, 63; habits of the larvæ, 64; habits ofthe adults, 64; places they visit, 65; _Flies and typhoid_, 65;patients carrying the germs before and after they have had thedisease, 65; how the flies get these on their body and distributethem, 66; results of some observations and experiments, 66;_Flies and other diseases_, 68; flies and cholera, 68; flies andtuberculosis, 69; possibility of their carrying other diseases, 70;_Fighting flies_, 71; screens not sufficient, 71; the larger problem, 71; the manure pile, 72; outdoor privies, 72; garbage can, 72; coöperation necessary, 72; city ordinances, 73; an expert'sopinion of the house-fly, 73; _Other flies_, 75; habits of severalmuch the same but do not enter house as much, 75; the smallhouse-fly, 75; stable-flies, 75; these may spread disease, 75. 

CHAPTER VI

MOSQUITOES 76

Numbers, 76; interest and importance, 76; eggs, 77; always in water, 77;time of hatching, 77; _Larvæ_, 78; live only in water, 78; head andmouth-parts of larvæ, 78; what they feed on, 78; breathing apparatus, 79; growth of the larvæ, 80; _Pupæ_, 80; active but takes no food, 80;breathing tubes, 80; how the adult issues, 81; _The Adult_, 81; male andfemale, 81; how mosquitoes "sing" and how the song is heard, 82; thepalpi, 82; _The Mouth-parts_, 83; needles for piercing, 83; _How themosquito bites_, 84; secretion from the salivary gland, 84; why malescannot bite, 84; blood not necessary for either sex, 84; _The Thorax_, 85; the legs, 85; the wings, 85; the balancers, 85; the breathing pores, 86; _The abdomen_, 86; _The digestive system_, 86; _The salivaryglands_, 87; their importance, 87; effects of a mosquito bite, 87;probable function of the saliva, 88; _How mosquitoes breathe_, 89;_Blood_, 90; in body cavity, 90; heart, 90; _Classification_, 91;_Anopheles_, 91; distinguishing characters, 92; eggs, 92; where thelarvæ are found, 93; _Yellow fever mosquito_, 94; its importance, 94;the adult, 95; habits, 95; habits of the larvæ, 95; _Other species_, 96;some in fresh water, others in brackish water, 96; Natural enemies ofmosquitoes, 97; how natural enemies of mosquitoes control their numbers, 98; mosquitoes in Hawaii, 98; _Enemies of the adults_, 99; _Enemies ofthe larvæ and pupæ_, 100; _Fighting mosquitoes_, 101; fighting theadult, 102; _Fighting the larvæ_, 103; domestic or local species, 104;draining and treating with oil, 104; combatting salt-marsh species bydraining, 105; by minnows or oil, 105. 

CHAPTER VII

MOSQUITOES AND MALARIA 106

Early reference to malaria, 106; its general distribution, 106;theories in regard to its cause, 107; insects early suspected, 107;_The parasite that causes malaria_, 108; studies of the parasite, 108; _Life-history in human host_, 109; its effect on the host, 110;the search for the sexual generation, 111; _The parasite in themosquito_, 112; review of whole life-history, 115; malaria transmittedonly by mosquitoes, 115; _Summary_, 117; experimental proof, 118. 

CHAPTER VIII

MOSQUITOES AND YELLOW FEVER 120

A disease of tropical or semi-tropical countries, 120; outbreaks in theUnited States, 120; parasite that causes the disease not known, 121;formerly regarded as a contagious disease, 122; _The yellow fevercommission_, 123; Dr. Finlay's claim, 124; experiments made by thecommission, 125; summary of results, 129; what it means, 130; _resultsin Havana_, 131; _the fight in New Orleans_, 132; _In the Panama canalzone_, 135; _in Rio de Janeiro_, 136; claims of the French commission, 138; _habits of stegomyia_, 139; breeding habits, 139; possible resultsof war against the mosquitoes, 139; Danger of this disease in thePacific Islands, 140. 

CHAPTER IX

FLEAS AND PLAGUE 142

Great scourges, 142; the "black death, " 142; old conditionsand new, 143; _How plague was controlled in San Francisco_, 143; _Indian Plague commission_, 144; Dr. Simond's claim, 145; The advisory committee and the new commission, 146;_Results of Dr. Verjbitski's experiments_, 147; _Results of variousinvestigations_, 150; _structure and habits of fleas_, 151; feedinghabits, 152; _Common species of fleas_, 153; _Ground squirrels andplague_, 155; squirrel fleas, 156; _Remedies for fleas_, 157; catsand dogs, 159. 

CHAPTER X

OTHER DISEASES, MOSTLY TROPICAL, KNOWN OR THOUGHT TOBE TRANSMITTED BY INSECTS 161

_Sleeping Sickness_, 161; its occurrence in Africa, 161; caused by aProtozoan parasite, 162; the tsetse-fly, 163; _Elephantiasis_, 164;caused by parasitic worms, 164; their development, 165; how they aretransferred to man, 165; effect on the patient, 166; _Dengue_, 168;other names, 168; probably transmitted by mosquitoes, 170;_Mediterranean fever_, 171; cause, 171; may be conveyed by mosquitoes, 171; _Leprosy_, 171; caused by a bacteria parasite, 171; possibilitiesof flies, mosquitoes and other insects transmitting the disease, 172;_Kala-azar_, 173; transmitted by the bedbug, 173; _Oriental sore_, 174;the parasite may be carried by insects, 174. 

BIBLIOGRAPHY 175

Parasites and parasitism, 175; Protozoa, 176; Bacteria, 177; Insects anddisease, 178; Mosquitoes--systematic and general, 179; Mosquito anatomy, 182; Mosquitoes--life-history and habits, 183; Mosquito fighting, 183;Mosquitoes and disease, 185; Malaria, 186; Yellow fever, 189; Dengue, 192; Filarial diseases and elephantiasis, 193; Leprosy, 193; Plague, 194; Fleas, 198; Typhoid fever, 199; House-flies--anatomy, life-history, habits, 200; House-flies and typhoid, 202; House-fly and variousdiseases, 203; Human myiasis, 207; Stomoxys and other flies, 208;tsetse-flies, 209; Trypanosomes and Trypanosomiasis, 210; Sleepingsickness, 211; Rocky mountain fever and ticks, 212; Ticks and variousdiseases, 213; Kala-azar and bedbugs, 216; Text or reference books, 216;Miscellaneous articles, 218. 

ILLUSTRATIONS

 AN ARTIFICIAL LAKE, NEARLY DRY AND PARTLY FILLED WITH RUBBISH, HAS BECOME A BREEDING-GROUND FOR DANGEROUS MOSQUITOES _Frontispiece_

 PAGE

 FIG. 1. A LAMPREY 2

 FIG. 2. _Sacculina_ 2

 FIG. 3. _Trichina spiralis_ 2

 FIG. 4. AN EXTERNAL PARASITE, A BIRD-LOUSE (_Lipeurus ferox_) 3

 FIG. 5. AN INTERNAL PARASITE, A TACHINA FLY (_Blepharipeza adusta_) 3

 FIG. 6. WORK OF AN INTERNAL PARASITE, PUSS-MOTH LARVA PARASITIZED BY A SMALL ICHNEUMON FLY 3

 FIG. 7. TYPHOID FEVER BACILLI 20

 FIG. 8. _Amoeba_ 20

 FIG. 9. _Euglina virdis_ 21

 FIG. 10. _Spirocheta duttoni_ 21

 FIG. 11. _Paramoecium_ 22

 FIG. 12. _Vorticella_ 22

 FIG. 13. PATHOGENIC PROTOZOA; A GROUP OF INTESTINAL PARASITES 22

 FIG. 14. CASTOR-BEAN TICK (_Ixodes ricinus_) 28

 FIG. 15. TEXAS FEVER TICK 28

 FIG. 16. TEXAS FEVER TICK (_Margaropus annulatus_) 29

 FIG. 17. _Amblyomma variegatum_ 29

 FIG. 18. _Ornithodoros moubata_ 36

 FIG. 19. THE FOLLICLE MITE (_Demodex folliculorum_) 36

 FIG. 20. ITCH-MITE (_Sarcoptes scabiei_) 37

 FIG. 21. HARVEST-MITES OR "JIGGERS" 37

 FIG. 22. HORSE-FLY (_Tabanus punctifer_) 44

 FIG. 23. STABLE-FLY (_Stomoxys calcitrans_) 44

 FIG. 24. A BLACK-FLY (_Simulium sp. _) 45

 FIG. 25. SCREW-WORM FLY (_Chrysomyia macellaria_) 45

 FIG. 26. BLOW-FLY (_Calliphora vomitoria_) 45

 FIG. 27. BLUE-BOTTLE FLY (_Lucilia sericata_) 50

 FIG. 28. FLESH-FLY (_Sarcophaga sp. _) 50

 FIG. 29. "THE LITTLE HOUSE-FLY" (_Homalomyia canicularis_) 51

 FIG. 30. HORSE BOT-FLY (_Gastrophilus equi. _) 51

 FIG. 31. OXWARBLE FLY (_Hypoderma lineata_) 51

 FIG. 32. SHEEP BOT-FLY (_Gastrophilus nasalis_) 51

 FIG. 33. CHIGO OR JIGGER-FLEA, MALE (_Dermatophilus penetrans_) 54

 FIG. 34. CHIGO, FEMALE DISTENDED WITH EGGS 54

 FIG. 35. BEDBUG (_Cimex lectularis_) 55

 FIG. 36. BODY-LOUSE (_Pediculus vestimenti_) 55

 FIG. 37. ONE USE FOR THE HOUSE-FLY 57

 FIG. 38. THE HOUSE-FLY (_Musca domestica_) 58

 FIG. 39. HEAD OF HOUSE-FLY SHOWING EYES, ANTENNÆ AND MOUTH-PARTS 60

 FIG. 40. PROBOSCIS OF HOUSE-FLY, SIDE VIEW 60

 FIG. 41. LOBES AT END OF PROBOSCIS OF HOUSE-FLY SHOWING CORRUGATED RIDGES 61

 FIG. 42. WING OF HOUSE-FLY 61

 FIG. 43. WING OF STABLE-FLY (_Stomoxys calcitrans_) 62

 FIG. 44. WING OF HOUSE-FLY SHOWING PARTICLES OF DIRT ADHERING TO IT 62

 FIG. 45. LAST THREE SEGMENTS OF LEG OF HOUSE-FLY 62

 FIG. 46. FOOT OF HOUSE-FLY 63

 FIG. 47. LARVA OF HOUSE-FLY 63

 FIG. 48. BARN-YARD FILLED WITH MANURE 64

 FIG. 49. DIRTY STALLS 65

 FIG. 50. PUPA OF HOUSE-FLY 76

 FIG. 51. HEAD OF STABLE-FLY 76

 FIG. 52. MASS OF MOSQUITO EGGS (_Theobaldia incidens_) 76

 FIG. 53. MOSQUITO EGGS AND LARVÆ (_T. Incidens_) 77

 FIG. 54. MOSQUITO LARVA (_T. Incidens_), DORSAL VIEW 77

 FIG. 55. EGGS, LARVÆ AND PUPÆ OF MOSQUITOES (_T. Incidens_) 78

 FIG. 56. LARVA OF MOSQUITO (_T. Incidens_) 78

 FIG. 57. MOSQUITO LARVÆ AND PUPÆ (_T. Incidens_) 79

 FIG. 58. ANOPHELES LARVÆ (_A. Maculipennis_) 79

 FIG. 59. MOSQUITO PUPÆ (_T. Incidens_) 80

 FIG. 60. MOSQUITO PUPA (_T. Incidens_) 80

 FIG. 61. MOSQUITO LARVÆ AND PUPÆ (_T. Incidens_) 80

 FIG. 62. A FEMALE MOSQUITO (_T. Incidens_) 81

 FIG. 63. A MALE MOSQUITO (_T. Incidens_) 81

 FIG. 64. HEAD AND THORAX OF FEMALE MOSQUITO (_Ochlerotatus lativittatus_) 82

 FIG. 65. HEAD AND THORAX OF MALE MOSQUITO (_O. Lativittatus_) 82

 FIG. 66. HEAD OF FEMALE MOSQUITO 83

 FIG. 67. CROSS-SECTION OF PROBOSCIS OF FEMALE AND MALE MOSQUITO 83

 FIG. 68. WING OF MOSQUITO (_O. Lativittatus_) 86

 FIG. 69. END OF MOSQUITO WING HIGHLY MAGNIFIED 86

 FIG. 70. DIAGRAM TO SHOW THE ALIMENTARY CANAL AND SALIVARY GLANDS OF A MOSQUITO 87

 FIG. 71. SALIVARY GLANDS OF MOSQUITOES 87

 FIG. 72. HEADS OF CULICINÆ MOSQUITOES 90

 FIG. 73. HEADS OF ANOPHELINÆ MOSQUITOES 90

 FIG. 74. WING OF _Anopheles maculipennis_ 90

 FIG. 75. WING OF _Theobaldia incidens_ 90

 FIG. 76. A NON-MALARIAL MOSQUITO (_T. Incidens_), MALE, STANDING ON THE WALL 91

 FIG. 77. FEMALE OF SAME 91

 FIG. 78. A MALARIAL MOSQUITO (_A. Maculipennis_), MALE, STANDING ON THE WALL 91

 FIG. 79. FEMALE OF SAME 91

 FIG. 80. EGG OF _Anopheles_, SIDE VIEW 92

 FIG. 81. EGG OF ANOPHELES, DORSAL VIEW 92

 FIG. 82. ANOPHELES LARVÆ 92

 FIG. 83. ANOPHELES LARVÆ 93

 FIG. 84. ANOPHELES LARVA, DORSAL VIEW 93

 FIG. 85. ANOPHELES PUPÆ RESTING AT SURFACE OF WATER 93

 FIG. 86. SALT-MARSH MOSQUITO (_Ochlerotatus lativittatus_); MALE 98

 FIG. 87. SALT-MARSH MOSQUITO (_O. Lativittatus_); FEMALE 98

 FIG. 88. TOP-MINNOW (_Mollienisia latipinna_) 99

 FIG. 89. DRAGON-FLIES 99

 FIG. 90. THE YOUNG (NYMPH) OF A DRAGON-FLY 100

 FIG. 91. THE CAST SKIN (_exuvæ_) OF A DRAGON-FLY NYMPH 100

 FIG. 92. DIVING-BEETLES AND BACK-SWIMMERS 101

 FIG. 93. KILLIFISH (_Fundulus heteroliatus_) 102

 FIG. 94. STICKLEBACK (_Apeltes quadracus_) 102

 FIG. 95. AN OLD WATERING-TROUGH, AN EXCELLENT BREEDING-PLACE FOR MOSQUITOES 103

 FIG. 96. HORSE AND CATTLE TRACKS IN MUD FILLED WITH WATER 108

 FIG. 97. A MALARIAL MOSQUITO (_Anopheles maculipennis_) MALE 108

 FIG. 98. A MALARIAL MOSQUITO (_A. Maculipennis_) FEMALE 109

 FIG. 99. DIAGRAM TO ILLUSTRATE THE LIFE-HISTORY OF THE MALARIAL PARASITE 110

 FIG. 100. MALARIAL MOSQUITO (_A. Maculipennis_) ON THE WALL 111

 FIG. 101. MALARIAL MOSQUITO (_A. Maculipennis_) STANDING ON A TABLE 111

 FIG. 102. SALT-MARSH MOSQUITO (_O. Lativittatus_) STANDING ON A TABLE 118

 FIG. 103. ANOPHELES HANGING FROM THE CEILING 118

 FIG. 104. YELLOW FEVER MOSQUITO (_Stegomyia calopus_) 122

 FIG. 105. RAT-FLEA (_Læmopsylla cheopis_); MALE 152

 FIG. 106. RAT-FLEA (_L. Cheopis_); FEMALE 152

 FIG. 107. HEAD OF RAT-FLEA SHOWING MOUTH-PARTS 153

 FIG. 108. HUMAN-FLEA (_Pulex irritans_); MALE 153

 FIG. 109. HUMAN-FLEA (_P. Irritans_); FEMALE 156

 FIG. 110. MOUSE-FLEA (_Ctenopsyllus musculi_); FEMALE 156

 FIG. 111. TRYPANOSOMA GAMBIENSE 164

 FIG. 112. TSETSE-FLY 164

INSECTS AND DISEASE

CHAPTER I

PARASITISM AND DISEASE

PARASITES

The dictionary says that a parasite is a living organism, either animalor plant, that lives in or on some other organism from which it derivesits nourishment for a whole or part of its existence. This definitionwill serve as well as any, as it seems to include all the forms thatmight be classed as parasites. As a general thing, however, we areaccustomed to think of a parasite as working more or less injury to itshost, or perhaps we had better say that if it does not cause anyirritation or ill effects its presence is not noted and we do not thinkof it at all. 

As a matter of fact the number of parasitic organisms that are actuallydetrimental to the welfare of their hosts is comparatively small whilethe number of forms both large and small that lead parasitic lives inor on various hosts, usually doing no appreciable harm, often perhapswithout the host being aware of their presence, is very great indeed. 

Few of the higher animals live parasitic lives. The nearest approach toa true parasite among the vertebrates is the lamprey-eel (Fig. 1) whichattaches itself to the body of a fish and sucks the blood or eats theflesh. Among the Crustaceans, the group that includes the lobsters andcrabs, we find many examples of parasites, the most extraordinary ofwhich is the curious crab known as _Sacculina_ (Fig. 2). In its earlystages this creature is free-swimming and looks not unlike other youngcrabs. But it soon attaches itself to another crab and begins to live atthe expense of its host. Then it commences to undergo remarkable changesand finally becomes a mere sac-like organ with a number of long slenderroot-like processes penetrating and taking nourishment from the body ofthe unfortunate crab-host. 

The worms furnish many well-known examples of parasites, whole groups ofthem being especially adapted to parasitic life. The tapeworms, commonin many animals and often occurring in man, the roundworms of which thetrichina (Fig. 3) that causes "measly" pork is a representative, arefamiliar examples. These and a host of others all show a very highdegree of specialization fitting them for their peculiar lives in theirhosts. 

[Illustration: FIG. 1--A lamprey. (After Goode. )]

[Illustration: FIG. 2--_Sacculina_; _A_, parasite attached to a crab;_B_, the active larval condition; _C_, the adult removed from its host. (After Haeckel. )]

[Illustration: FIG. 3--_Trichina spiralis_ encysted in muscle of a pig. (From Kellogg's Elementary Zoöl. )]

[Illustration: FIG. 4--An external parasite, a bird-louse (_Lipeurusferox_). ]

[Illustration: FIG. 5--A tachina fly (_Blepharipeza adusta_) the larvaof which is an internal parasite. ]

[Illustration: FIG. 6--Work of an internal parasite, puss-moth larvaparasitized by a small ichneumon fly. ]

From among the insects may be selected interesting examples of almostall kinds and degrees of parasitism, temporary, permanent, external, internal (Figs. 4, 5, 6). Among them is found, too, that curiouscondition known as hyperparasitism where one animal, itself a parasite, is preyed upon by a still smaller parasite. 

 "The larger fleas have smaller fleas Upon their backs to bite um, These little fleas still smaller fleas And so _ad infinitum_. "

Coming now to the minute, microscopic, one-celled animals, the Protozoa, we find entire groups of them that are living parasitic lives, dependingwholly on one or more hosts for their existence. Many of these have avery remarkable life-history, living part of the time in one host, partin another. The malarial parasite and others that cause some of thediseases of man and domestic animals are among the most important ofthese. 

PARASITISM

Among all these parasites, from the highest to the lowest the processthat has fitted them for a parasitic life has been one of degeneration. While they may be specialized to an extreme degree in one direction theyare usually found to have some of the parts or organs, which in closelyrelated forms are well developed, atrophied or entirely wanting. As arule this is a distinct advantage rather than a disadvantage to theparasite, for those parts or organs that are lost would be useless oreven in the way in its special mode of life. 

Then, too, the parasite often gives up all its independence and becomeswholly dependent on its host or hosts not only for its food but for itsdissemination from one animal to another, in order that the species maynot perish with the host. But in return for all this it has gained alife of ease, free from most of the dangers that beset the moreindependent animals, and is thus able to devote its whole time andenergy to development and the propagation of the species. 

We are accustomed to group the parasites that we know into two classes, as harmful or injurious and as harmless, the latter including all thosekinds that do not ordinarily affect our well-being in any way. But sucha classification is not always satisfactory or safe, for certainorganisms that to-day or under present conditions are not harmful may, on account of a great increase in numbers or change of conditions, become of prime importance to-morrow. An animal that is well and strongmay harbor large numbers of parasites which are living at the expense ofsome of the host's food or energy or comfort, yet the loss is so smallthat it is not noticed and the intruders, if they are thought of at all, are classed as harmless. Or we may at times even look upon them asbeneficial in one way or another. "A reasonable amount of fleas is goodfor a dog. They keep him from brooding on being a dog. "

But should these parasites for some reason or other increase rapidlythey might work great harm to the host. Even David Harum would limit thenumber of fleas on a dog. Or the animal might become weakened from somecause so that the drain on its resources made by the parasites, eventhough they did not increase in numbers, would materially affect it. 

Perhaps the most serious way in which parasites that are usuallyharmless may become of great importance is illustrated by theirintroduction into new regions or, as is more often the case, by theintroduction of new hosts into the region where the parasites are found. Under normal conditions the animals of a given region are usually immuneto the parasites of the same region. That is, they actually repel themand do not suffer them to exist in or on their bodies, or they aretolerant toward them. In the latter case the parasites live at theexpense of the host, but the host has become used to their being there, adapted to them, and the injury that they do, if any, is negligible. 

But when a new animal comes into the region from some other locality theparasites may be extremely dangerous to it. There are many strikingexamples of this. Most of the people living in what is known as theyellow fever belt are immune to the fever. They will not develop it evenunder conditions that would surely mean infection for a person fromoutside this zone. Certain of our common diseases which we regard as oflittle consequence become very serious matters when introduced among apeople that has never known them before. The cattle of the southernstates are immune to the Texas fever, but let northern cattle be sentsouth or let the ticks which transmit the disease be taken north wherethey can get on cattle there, and the results are disastrous. 

Another striking example and one that is attracting world-wide attentionjust now is the trypanosome that is causing such devastation among theinhabitants of central Africa. With the advent of white men into thisregion and the consequent migration of the natives along the traderoutes this parasite, which is the cause of sleeping sickness, is beingintroduced into new regions and thousands upon thousands of people aredying as a result of its ravages. 

DISEASES CAUSED BY PARASITES

Some two hundred years ago, after it became known that minute animalparasites were associated with certain diseases and were the cause ofthem, it rapidly came to be believed that all our ills were in some waycaused by such parasites, known or unknown. Further study andinvestigation failed to reveal the intruders in many instances and so itbegan to be doubted whether after all they were responsible for muchthat had been laid at their doors. Then after it was discovered thatminute plant parasites, bacteria, were responsible for many diseasesthey in turn began to be accused of being the cause of most of the illsthat the flesh is heir to. 

In later years we have come to adopt what seems to be a more reasonableview, for we can see and definitely prove that neither of these extremeviews was correct but that there was much truth in each of them. To-daywe recognize that certain diseases, such as typhoid, cholera, tuberculosis and many others, are caused by the presence of bacteria inthe body, and it is just as definitely known that such maladies asmalaria and sleeping sickness are caused by animal parasites. 

Then there is a long list of other epidemic diseases, such as smallpox, measles and scarlet fever, the exact cause of which has not beendetermined. Many of these are believed to be due to micro-organisms ofsome kind, and if so they will almost certainly sooner or later befound. Curiously enough most of the diseases in this last class and manyof those in the first are contagious, while all that are caused byanimal parasites are, as far as is known, infectious but not contagious. 

INFECTIOUS AND CONTAGIOUS DISEASES

It is important that we keep in mind this distinction. By contagiousdiseases are meant those that are transmitted by contact with thediseased person either directly, by touch, or indirectly by the use ofthe same articles, by the breath or effluvial emanations from the bodyor other sources. Small-pox, measles, influenza, etc. , are examples ofthis group. By infectious diseases are meant those which aredisseminated indirectly, that is, in a roundabout way by means of wateror food or other substances taken into or introduced into the body insome way. Typhoid, malaria, and yellow fever, cholera and others areexamples of this class. Thus it is evident that all of the contagiousdiseases may be infectious, but many of the infectious diseases are notas a rule contagious, although some of them may become so underfavorable conditions. 

Just one example will show the importance of knowing whether a diseaseis contagious or infectious. Until a few years ago it was believed thatyellow fever was highly contagious and every precaution was taken tokeep the disease from spreading by keeping the infected region in strictquarantine. This often meant much hardship and suffering and always agreat financial loss. We now know that it is infectious only and notcontagious, and that all this quarantine was unnecessary. The wholefight in controlling an outbreak of yellow fever or in preventing suchan outbreak is now directed against the mosquito, the sole agent bywhich the disease can be transmitted from one person to another. 

EFFECT OF THE PARASITE ON THE HOST

We have seen how a few parasites in or on an animal do not as a ruleproduce any appreciable ill effects. This is of course a most fortunatething for us, for the parasitic germs are everywhere. 

There is perhaps "more truth than poetry" in the following newspaperjingle:

 "Sing a song of microbes, Dainty little things, Eyes and ears and horns and tails, Claws and fangs and stings. Microbes in the carpet, Microbes in the wall, Microbes in the vestibule, Microbes in the hall. Microbes on my money, Microbes in my hair, Microbes on my meat and bread, Microbes everywhere. Microbes in the butter, Microbes in the cheese, Microbes on the knives and forks, Microbes in the breeze. Friends are little microbes, Enemies are big, Life among the microbes is-- Nothing '_infra dig_. ' Fussy little microbes, Millions at a birth, Make our flesh and blood and bones, Keep us on the earth. "

While of course most of these microbes are to be regarded as absolutelyharmless and some as very useful, many have the power to do much injuryif the proper conditions for their rapid development should at any timeexist. While the size of the parasite is always a factor in the damagethat it may do to the host the factor of numbers is perhaps of stillgreater importance because of the power of very rapid multiplicationpossessed by so many of the smaller forms. 

Certain minute parasites in the blood may cause little or noinconvenience, but should they begin to multiply too rapidly some of thecapillaries may be filled up and trouble thus result. Or take some ofthe larger forms. A few intestinal worms may cause no appreciable effecton the host, but as soon as their numbers increase serious conditionsmay come about simply by the presence of the great masses in the hosteven if they were not robbing it of its nourishment. Many instances areknown where such worms have formed masses that completely clogged up thealimentary canal. Such injuries as these may be regarded as mechanicalinjuries. Some parasites injure the host only when they are laying theireggs or reproducing the young. These may clog up passages or some ofthem may be carried to some more sensitive part of the body where thedamage is done. The guinea-worm of southwestern Asia and of Africa livesin the body of its host for nearly a year sometimes attaining a greatlength and migrating through the connective tissue to different parts ofthe body causing no particular inconvenience until it is ready to layits eggs when it comes to the surface and then great suffering mayresult. The African eye-worm is another example of a parasite causingmechanical injury only at certain times. It works in the tissues of thebody sometimes for a long while, doing no harm unless it finds its wayto the connective tissue of the eyeball. 

It is known that many of the germs which cause diseases cannot get intothe body unless the protecting membranes have first been injured in someway. Thus the germs that cause plague and lockjaw find their way intothe system principally through abrasions of the skin. Many physicianshave come to believe that the typhoid fever germ cannot get into thebody from the intestine where it is taken with our food or drink unlessthe walls of the intestine have been injured in some way. It is wellknown that of the many parasites that inhabit the alimentary canal somerasp the surface and others bore through into the body cavity. This initself may not be a serious thing, but if the mechanical injury thuscaused opens the way for malignant germs, baneful results may follow. Even that popular disease appendicitis is believed to be due sometimesto the injury caused by the work of parasites in the appendix. 

Parasites may cause morphological or structural changes in the tissuesof their hosts. The stimulation caused by their presence may result inswellings or excresences or other abnormal growths. Interesting examplesof this are to be found in the way in which pearls are formed in variousmollusks. In the pearl oysters of Ceylon occur some of the best pearls. If these are carefully sectioned there may usually be found at thecenter the remains of certain cestode larvæ whose presence in the oystercaused it to deposit the nacreous layers that make up the pearl. Otherparasites cause similar growths in various shellfish. The greatenlargements of the arms or legs or other parts of the body seen inpatients affected with elephantiasis is an abnormal growth due to thepresence of the parasitic filaræ in some of the lymph-glands where theyhave come to rest. 

Finally, the parasite may exert a direct physiological effect on thehost. This is evident when the parasite demands and takes a portion ofthe nourishment that would otherwise go to the building up of the host. Sometimes this is of little importance, but at other times it may be amatter of life or death to the infected animal. The physiologicaleffect produced may be due to the toxins or poisonous matters that aregiven off by the parasite while it is living in the host's body. Thus itis believed that the malarial patients usually suffer less from theactual loss of red blood-corpuscles that are destroyed by the parasitethan they do from the effects of the poisonous excretions that arepoured into the circulation when the thousands of corpuscles break torelease the parasites. 

One other point in regard to the relation of the parasite to its hostand this part of the subject may be dismissed. From our standpoint welook upon the presence of parasites in the body as an abnormalcondition. From a biological standpoint their presence there isperfectly normal; it is a necessary part of their life. We think thatthey have no business there, but from the viewpoint of the parasitestheir whole business is to be just there. If they are not, they perish. And when we take a dose of quinine or other drug we are killing ordriving from their homes millions of these little creatures who havetaken up their abode with us for the time being. But they interfere withour health and comfort, so they must go. 

CHAPTER II

BACTERIA AND PROTOZOA

BACTERIA

On the border line between the plant and the animal worlds are manyforms which possess some of the characteristics of both. Indeed when anattempt is made to separate all known organisms into two groups one isimmediately confronted with difficulties. In looking over the text-booksof Botany we will find that certain low forms are discussed there asbelonging with the plants, and on turning to the manuals of Zoölogy wewill find that the same organisms are placed among the lowest forms ofanimals. The question is of course of little actual importance fromcertain points of view. It serves, however, to show the close relationof all forms of life, and from a medical standpoint it may be of verygreat importance owing to the difference in the life-habits, methods ofreproduction and methods of transmission of many of the forms that causedisease. We have already seen that none of the diseases that are causedby animal parasites is contagious, while many of those caused bybacteria are both contagious and infectious. 

Just over on the plant side of this indefinite border line are theminute organisms known as bacteria. Their numbers are infinite and theyare found everywhere. The majority of them are beneficial to mankind inone way or another, but some of them cause certain of the diseases thatwe will have to discuss later so attention may be called here to a fewof the important facts in regard to their organization and life-historyin order that we may better understand how they may be so easilytransferred from one host to another. 

Although these bacilli are so extremely minute (Fig. 7), some of them sosmall that they cannot be seen with the most powerful microscopes, theydiffer in size, shape, methods of division and spore-formation. Eachspecies makes a characteristic growth on gelatin, agar or other mediaupon which it may be cultivated. In this way as well as by theinoculation of animals the presence of the ultramicroscopic kinds may bedemonstrated. 

The method of reproduction is very simple. They increase to a certainpoint in size, then divide. This growth and division takes place veryrapidly. Twenty to thirty minutes is sufficient time in some cases fora just-divided cell to attain full size and divide again. Thus in a fewdays time the number of bacteria resulting from a single individualwould be inconceivable if they should all develop. 

Fortunately for us, however, they do not all multiply so rapidly as thisand besides there are natural checks, not the least of which are thesubstances given off by the bacteria themselves in their growth anddevelopment. Such excretions often serve to inhibit furthermultiplication. Sometimes, though not often, they form spores which notonly provide for a more rapid multiplication, but enable the organism tolive under conditions that would otherwise prove fatal to it. 

Bacteria may be conveniently grouped under two heads: those that liveupon dead organic matter, known as the saprophytic forms, and those thatare found in living plants or animals, the true parasites. Such agrouping is not always entirely satisfactory, for many of the kinds thatlive saprophytically under normal conditions may become parasitic ifopportunity offers, and also many of those that are usually regarded asparasitic may be grown in cultures of agar or other media, under whichconditions they may be regarded as living saprophytically. 

It is this power of easily adapting themselves to different conditionsthat makes many of the kinds dangerous. The bacillus which causestetanus or lockjaw will illustrate this. It is a rather common bacillusin soil in many localities. As long as it remains there it is of nospecial importance, but if it is introduced into the body through ascratch or any other wound it becomes a very serious matter. 

We may say, then, that the effect the bacillus has on the host dependslargely on the host. Not only does it depend on what the host is, butthe particular condition of the host at the time of infection is ofimportance. Children are subject to many diseases that adults seldomhave. Hunger, thirst, fatigue, exposure and other factors may make aperson susceptible to the actions of certain bacteria that would beharmless under other conditions. 

The minute size and great numbers of the bacteria make theirdissemination a comparatively simple matter. They may be carried in theair as minute particles of dust; they may be carried in water or milk;they may be carried on the clothing or on the person from one host toanother, or they may be disseminated in scores of other ways. In otherchapters, particularly the one dealing with the house-fly and typhoid, we shall see how it is that insects are often important factors inspreading some of the most dreaded of the bacterial diseases. 

THE PROTOZOA

The Protozoa, or one-celled animals, belonged to an unknown world beforethe invention of the microscope. The first of these instruments enabledthe early observers to see some of the larger and more conspicuousmembers of the group and each improvement of the microscope has enabledus to see more and more of them and to study in detail not only thestructure but to follow the life-history of many of them. 

_The Amoeba. _ With some, as the common amoeba (Fig. 8), a minutelittle form that is to be found in the slime at the bottom of almost anybody of water, the life-history is extremely simple. The organism itselfconsists of a minute particle of protoplasm, a single cell with nodefinite shape or body-wall and no specialized organs or apparatus forcarrying on the life-functions. It lives in the slime or ooze in freshor salt water, takes its food by simply flowing over the particle thatis to be ingested, grows to a certain limit of size, then divides intotwo more or less equal parts, each part becoming a new animal that goeson with its development as did the parent form. This process of growthand division may go on for many generations, but cannot continueindefinitely unless there is a conjugation of two separate individuals. This process of conjugation is just the opposite to that of division. Two amoeba flow together and become one. It seems to rejuvenate theorganism so that it is able to go on with its division and thus fulfilits life-mission which is the same for these lowly animals as with thehigher, that of perpetuating the species. 

_Classes of Protozoa. _ The group or Phylum Protozoa is divided into foursmaller groups or classes. The amoeba belongs to the lowest of these, the Rhizopoda. Rhizopoda means "root-footed, " and the name is applied tothese animals because most of them move about by means of root-likeprocesses known as pseudopodia or "false feet. " This is by far thelargest class and contains thousands of forms, mostly living in saltwater but there are many fresh-water species. They are non-parasitic, but some of them by their presence in the body may cause such diseasesas dysentery, etc. 

[Illustration: FIG. 7--Typhoid Fever bacilli. (After Muir andRitchie. )]

[Illustration: FIG. 8--_Amoeba_, showing the forms assumed by a singleindividual in four successive changes. (From Kellogg's ElementaryZoöl. )]

[Illustration: FIG. 9--_Euglina virdis. _ (After Saville Kent. )]

[Illustration: FIG. 10--_Spirocheta duttoni_, × 4500. (After Breinl andCarter. )]

The next class which may be known as the whip-bearers (_Mastigophora_)includes those Protozoa that move by fine undulating processes calledflagella. One of the common representatives of this class is the littlegreen _Euglena_ (Fig. 9), whose presence in standing ponds and puddlesoften imparts a greenish color to the water. Then in the salt water nearthe surface there are often myriads of minute _Noctiluca_ whosewonderfully phosphorescent little bodies glow like coals of fire whenthe water is disturbed at night. Although this class contains fewerforms than the preceding some of these have within recent years beenfound to be of great importance because they live as parasites on manand other animals. The trypanosome whose presence in the blood andtissues of the patient causes that dreadful disease which ends insleeping sickness belongs here as well as do several other similar kindsthat produce serious troubles for various mammals and birds. TheSpirochæta, about which there has been so much recent discussion, alsobelong here. These are simple spiral-like forms (Fig. 10), that aresometimes classed with the simple plants, bacteria, but Nuttall andothers have shown very definitely that they should be classed with thesimplest animals, the Protozoans. These are the cause of relapsingfevers in man and of several diseases of domestic animals. It isbelieved by certain eminent zoölogists that when the germ that causesyellow fever is discovered it will be found to belong to this group. 

The members of the class Infusoria, so called because they were earlyfound to be abundant in various infusions, are characterized by numerousfine cilia or hair-like organs by means of which the organism movesabout and procures its food. The well-known "slipper animalcule"(_Paramoecium_) (Fig. 11), and the "bell-animalcule" (_Vorticella_)(Fig. 12) are two common representatives. The _Paramoecia_ were theanimals mostly used by Jennings in his wonderfully interestingexperiments on the behavior of these lowly forms of life. He showed thatthey always reacted in a certain definite way in response to particularstimuli, and he was led to believe that he could see "what must beconsidered the beginnings of intelligence and of many other qualitiesfound in the higher animals. " A species of _Vorticella_ was probably thefirst Protozoan that was ever observed. An old Dutch microscopist, Antonvon Leeuwenhoek, in 1675, while studying with lenses of his ownmanufacture, discovered and described forms which undoubtedly belong tothis genus. Few if any of the Infusoria are pathogenic, although someare said to be associated with certain intestinal diseases both in manand the lower animals (Fig. 13). 

[Illustration: FIG. 11--_Paramoecium. _ (From Kellogg's ElementaryZoöl. )]

[Illustration: FIG. 12--_Vorticella_, one individual with the stalkcoiled, the other with the stalk extended. (From Kellogg's ElementaryZoöl. )]

[Illustration: FIG. 13--Pathogenic Protozoa; a group of intestinalparasites. _A_, _B_, _Megastoma entericum_, _C_, _Balantidum entozoon_. (After Calkins. )]

The last class, the Sporozoa, or the spore-forming animals, while smallin the number of known species, only about three hundred kinds beingknown, is extremely important. A number of diseases in man and otheranimals are due to the presence of these Sporozoans, for they are allparasitic. Few if any animals are exempt from their attacks. They evenattack other minute Protozoa. One hundred and fifty-seven species havebeen recorded as attacking insects, one hundred species attack birds, fifty-two reptiles, eighty crustaceans, twenty-two fish, and so throughthe list. Ten have been recorded as attacking man. In some instances theparasite is always present in the host and some hosts may harbor severaldifferent species of Sporozoa. 

Very little work had been done on this group of parasites prior to 1900. Since that time most of the species that we now know have beendiscovered, and within the last few years the life-histories of many ofthese have been worked out quite completely. No other group of animalsis being studied more to-day by both the physicians and biologists. 

The Sporozoa vary greatly in appearance, organization and life-history. They are so very plastic that they can adapt themselves readily to theirvarious hosts, hence we have a great variety of forms. But they allagree in certain characters; all take their food and oxygen and carry onexcretory processes by osmosis, _i. E. _, through the body-wall; all arecapable of some kind of locomotion, some have one or more flagella, others move by a pseudopod movement. Some are capable of moving fromcell to cell in the body as do the white blood-corpuscles. They allagree in the production of spores--hence the name. 

At certain stages in their development the nucleus within the body ofthe organism divides again and again until there are a great manydaughter nuclei, each accompanied by a small mass of protoplasm, ofteninclosed in a little sac or cyst of its own. This is the process ofspore-formation and we see that from a single individual we may have bydivision, not two animals as in the amoeba, but a score or more ofthem. The little cysts or capsules that inclose them enable them toresist without injury many vicissitudes that would otherwise destroythem. They may dry up or freeze or lie for a long time in the ground orwater until the time comes when they are introduced into another host. 

The class Sporozoa is divided into five small groups or orders. Nearlyall of these contain forms that are of more or less importance, but theones that live in the blood-cells (_Hæmosporidiida_) are of the mostinterest to us because the parasites that cause the malarial fevers andvarious other diseases belong here. These are dependent on two hosts fortheir existence, the sexual generation usually occuring in an insect orother invertebrate and the asexual generation in some vertebrate. 

CHAPTER III

TICKS AND MITES

The other group or Phylum of animals with which we will be particularlyconcerned is known as the Arthropoda, which means "jointed-feet" andincludes the crayfish, crabs, spiders, mites, ticks and insects. Ofthese only the last three are of interest to us now. It is customary tospeak of spiders, mites and ticks as insects, but as they have fourpairs of legs, instead of three pairs, in the adult stage, and as theirbodies are not divided into three distinct regions as in the insects, they are placed in a different class. 

GENERAL CHARACTERS OF TICKS

The ticks are all comparatively large, that is, they are all largeenough to be seen with the unaided eye even in their younger stages andsome grow to be half an inch long. When filled with blood the toughleathery skin becomes much distended often making the creature look morelike a large seed than anything else (Fig. 14). This resemblance isresponsible for some of the popular names, such as "castor-bean tick, "etc. 

The legs of most species are comparatively short, and the head is smallso that they are often hardly noticeable when the body is distended. Thesucking beak which is thrust into the host when the tick is feeding isfurnished with many strong recurved teeth which hold on so firmly thatwhen one attempts to pull the tick away the head is often torn from thebody and left in the skin. Unless care is taken to remove this, serioussores often result. 

Ticks are wholly parasitic in their habits. Some of them live on theirhost practically all their lives, dropping to the ground to deposittheir eggs when fully mature. Others leave their host twice to molt inor on the ground. The female lays her eggs, 1, 000 to 10, 000 of them, onthe ground or just beneath the surface. The young "seed-ticks" thathatch from these in a few days soon crawl up on some near-by blade ofgrass or on a bush or shrub and wait quietly and patiently until someanimal comes along. If the animal comes close enough they leave thegrass or other support and cling to their new-found host and are soontaking their first meal. Of course thousands of them are disappointedand starve before their host appears, but as they are able to live for aremarkably long time without taking food their patience is oftenrewarded and the long fast ended. 

Those species which drop to the ground to molt must again climb to somefavorable point and wait for another host on which they may feed for awhile. Then they drop to the ground for a second molt and if they aresuccessful in gaining a new host for the third time they feed anddevelop until fully mature and the female is ready to lay her eggs. TheTexas fever tick, and some others, as we shall see, do not drop to theground to molt but once having gained a host remain on it until ready todeposit their eggs. 

The young ticks have only six legs (Fig. 15) but after the first moltthey all have eight. 

TICKS AND DISEASE

_Texas Fever. _ Ever since stockmen began driving southern cattle intostates further north it has been noted that the roads over which theywere driven became a source of great danger to northern cattle. Often80% to 90% of the native cattle died after a herd of southern cattlepassed through their region and the losses became so great that bothstate and national laws were passed prohibiting the driving or shippingof southern cattle into northern states. 

[Illustration: FIG. 14--Castor Bean Tick (_Ixodes ricinus_) not fullygorged. ]

[Illustration: FIG. 15--Texas fever tick, just hatched; has only sixlegs. ]

[Illustration: FIG. 16--Texas fever tick (_Margaropus annulatus_) youngadult not fully gorged. ]

[Illustration: FIG. 17--_Amblyomma variegatum_ several ticks belongingto this genus transmit _Piroplasma_ which cause various diseases ofdomestic animals. ]

But for years the cause of this fever, which came to be known as theTexas fever, was not known. The southern cattle themselves seemedhealthy enough and it was difficult to understand how they could givethe disease to the others. It was early noticed, too, that it was notnecessary for the northern cattle to come in direct contact with theothers in order to contract the disease. Indeed the disease was notcontracted in this way at all. All that was necessary for them was topass along the same roads or feed in the same pastures or ranges. Stillmore puzzling was the fact that these places did not seem to become asource of danger until some weeks after the southern cattle had passedover them and then they might remain dangerous for months. 

In 1886 Dr. Theobald Smith of the Bureau of Animal Industry, UnitedStates Department of Agriculture, found that the fever was caused by thepresence in the infected cattle of a minute Sporozoan parasite(_Piroplasma bigeminum_). Further investigations and experiments provedconclusively that this parasite was transmitted from the infected to thewell animal only by the common cattle tick now known as the Texas fevertick (Fig. 16). 

The infection is not direct, that is, the tick does not feed on onehost then pass to another carrying the disease germs with it. Unlikemany other ticks the Texas fever tick does not leave its host until itis fully developed. When the female is full grown and gorged she dropsto the ground and lays from 2, 000 to 4, 000 eggs which soon hatch intothe minute "seed-ticks" which make their way to the nearest blade ofgrass or weed or shrub and patiently wait for the cattle to come along. 

If the mother tick had been feeding on an animal that was infected withthe Texas fever parasite, her body was filled with the minute organismsof which some found their way into the eggs so that the young tickshatching from them were already infected and ready to carry theinfection to the first animal they fed upon. 

It took many years of hard patient work to learn all this, but theknowledge thus obtained cleared up much of the mystery in connectionwith the occurrence of the fever in the north and, as we shall see, suggested the possibility of other diseases being communicated in thesame way. 

It was found that the southern cattle in the region where the ticksoccur normally, usually have a mild attack of the disease when they areyoung and although they may be infected with the parasite all the restof their lives it does not affect them seriously. These cattle arealmost always infected with ticks, and when taken north where the ticksdo not occur naturally and where the cattle are therefore non-immune, some of the mature ticks drop to the ground and lay their eggs which ina few weeks hatch out and are ready to infect any animal that passes by. The northern cattle not being used to the disease soon sicken and die. 

It is estimated that the annual loss due to this disease and the ravagesof the tick in the United States is over $100, 000, 000, so of course mostdetermined efforts are being made to stamp it out. Formerly variousdevices for dipping the tick-infested cattle into some solution thatwould kill the ticks were resorted to, but it was always expensive andnever very satisfactory. The immunizing of the cattle by inoculatingthem when they were young with infected blood has been practised. Veryrecent investigations have shown that it is possible and practicable torid pastures of ticks by a system of feed-lots and pasture rotation. Theaim is to have as many of the ticks as possible drop to the ground onland where they may be destroyed and to so regulate the use of thepasture that the ticks in all of them may eventually be left to starve. 

Several similar diseases of cattle, many of them probably identicalwith Texas fever, occur in other parts of the world where the losses aresometimes appalling. Horses, sheep, dogs, and other animals are alsoaffected with diseases caused by the same group of Protozoan parasites. Most of them have been shown to be transmitted by various species ofticks (Fig. 17) so that from an economical standpoint these little pestsare becoming of prime importance. Not only do they transmit the diseasegerms that infect domestic animals but they are known to be responsiblefor at least two diseases of men, Rocky Mountain spotted fever and therelapsing fevers. 

_Spotted Fever. _ The first of these is a disease that for some years hasbeen puzzling the physicians in Idaho and Montana and other mountainousstates. A few years ago certain observers recorded finding Protozoanparasites in the blood of those suffering from the disease, and althoughmore recent investigations have failed to confirm these particularobservations it is now quite generally believed that the disease iscaused by some such parasite and that the organism is transferred fromone host to another by certain species of ticks that live on wildmammals of the region where the disease exists. Dr. H. T. Ricketts, whohas made a special study of the disease, has shown:

 "1. That the period of activity of the disease is limited to the season during which the adult female and male ticks attack man. 

 "2. That in practically all cases of this disease it can be shown that the patient has been bitten by a tick. 

 "3. That the period between the tick bite and the onset of the disease in the many animals he has experimented with corresponds very closely to this period as observed in man. 

 "4. That infected ticks are to be found in the locality where the disease occurs. 

 "5. That the virus of spotted fever is very intimately associated with the tissues of the tick's body as is shown by the fact that the female passes the infection on to her young through her eggs, and further, by the observation that in either of the two earlier stages of the life cycle the disease may be contracted by biting a sick animal and communicated to other animals after molting or even after passing through an intermediate stage. "

Professor R. A. Cooley of Montana, from whose report the above quotationis taken, has also made studies of the habits of the tick and believesthere can be no doubt that it is the disseminator of the disease. 

_Relapsing Fever. _ The relapsing fever is an infectious disease orpossibly a group of closely related infectious diseases occurring invarious parts of the world. Occasionally it is introduced into America, but it does not seem to spread here. It has been shown that the diseaseis communicated from one person to another by means of blood-suckinginsects. In Central Africa where the disease is very prevalent a certaincommon tick (_Ornithodoros moubata_) (Fig. 18) is known to transmit thedisease. This tick lives in the resting places and around the huts ofthe natives and has habits very similar to the bedbug of other climes, feeding at night and hiding during the day. It attacks both man andbeast and is one of the most dreaded of all the African pests. 

Nathan Bank, our foremost authority on ticks, in summing up the evidenceagainst them says:

 "It is therefore evident that all ticks are potentially dangerous. Any tick now commonly infesting some wild animal, may, as its natural host becomes more uncommon, attach itself to some domestic animal. Since most of the hosts of ticks have some blood-parasites, the ticks by changing the host may transplant the blood-parasites into the new host producing, under suitable conditions, some disease. Numerous investigators throughout the world are studying this phase of tick-life, and many discoveries will doubtless signalize the coming years. "

MITES

The mites are closely related to the ticks, and although none of themhas yet been shown to be responsible for the spread of any disease theirhabits are such that it would be entirely possible for some to transmitcertain diseases from one host to another, from animal to animal, fromanimal to man, or from man to man. A number of these mites producecertain serious diseases among various domestic animals and a few areresponsible for certain diseases of men. 

_Face-mites. _ Living in the sweat-glands at the roots of hairs and indiseased follicles in the skin of man and some domestic animals arecurious little parasites that look as much like worms as mites (Fig. 19). Such diseased follicles become filled with fatty matter, the upperend becomes hard and black and in man are known as blackheads. If one ofthese blackheads is forced out and the fatty substance dissolved withether the mites may be found in all stages of development. The younghave six legs, the adult eight. The body is elongated and transverselywrinkled. In man they are usually found about the nose and chin and neckwhere they do no particular harm except to mar the appearance of thehost and to indicate that his skin has not had the care it should have. Very recently certain investigators have found that the lepræ bacilliare often closely associated with these face mites and believe that theymay possibly aid in the dissemination of leprosy. It is also thoughtthat they may sometimes be the cause of cancer, but as yet thesetheories have not been proven by any conclusive experiment. 

In dogs and cats these same or very similar parasites cause greatsuffering. In bad cases the hair falls out and the skin becomes scabby. Horses, cattle and sheep are also attacked. The disease caused by thesemites on domestic animals is not usually considered curable except inits very early stages when salves or ointments may help some. 

_Itch-mites. _ "As slow as the seven-years' itch" is an expression, themeaning of which many could appreciate from personal experience, for itcertainly seemed to take no end of time to get rid of the itch once itwas contracted. Just why seven years should have been set for the limitof the disease is not clear, for if the little roundish mites that causethe disease live for seven years on a host they are not going to moveout voluntarily even if their seven-year lease has expired. 

[Illustration: FIG. 18--_Ornithodorus moubata_, the Tick that TransmitsRelapsing Fever. From Boyce's "Mosquito or Man. "]

[Illustration: FIG. 19--The follicle mite (_Demodex folliculorum_). (After Murray. )]

[Illustration: FIG. 20--Itch-mite (_Sarcoptes scabiei_). (AfterMurray. )]

[Illustration: FIG. 21--Harvest-mites or "jiggers. " (_Leptus irritaus_and _L. Americanus_. ) (After Riley. )]

The minute whitish mites (Fig. 20) that cause this disgusting diseaseare barely visible to the naked eye. They are usually very sluggish butbecome more active when warmed. They live in burrows just beneath theouter layer of skin, sometimes extending deeper and causing most intenseitching. As the female burrows, she lays her eggs from which come theyoung mites that are to spread the infection. Various sulphur ointmentsand washes are used as remedies. Cleanliness will prevent infection. 

Closely related to the itch-mite of man (_Sarcoptes scabiei_) areseveral kinds attacking domestic animals, causing mange, scab, etc. Thevariety infesting horses burrows in the skin and produces sores andscabs, and is a source of very great annoyance. These mites may alsomigrate to man. Tobacco water and sulphur ointments are used asremedies. 

Horses and cattle are also infested by other mites (_Psoroptescommunis_) which cause the common mange. These do not burrow into theskin but live outside in colonies, feeding on the skin and causingcrusts or scabs. The inflammation causes the animal to scratch and rubconstantly and often causes the loss of much of the hair. 

_Harvest-mites. _ A score or more of different varieties of mites causemany other diseases of domestic animals, such as the scab of sheep andhogs and chickens, various other manges of the horses and cattle anddogs, etc. But we need to call attention to just one more example, thatof the harvest-mites or jiggers (Fig. 21). Professor Otto Lugger, fromwhose report on the _Parasites of Man and Domestic Animals_ most ofthese notes in regard to the mites are taken, thus feelingly refers tothis pest. 

 "About the very worst pests of man and domesticated animals are the Harvest-bugs, Red-bugs or Jiggers. . . . Men and animals passing through low herbage that harbors them are attacked by these pests, which, whenever they succeed in finding a host, burrow in and under the skin, causing intolerable itching and sores, the latter caused by the feverish activity of the finger-nails of the host, if that should be a man, whose energy in scratching, apparently, cannot be controlled and who is bound forcibly to remove the intruders. The writer has been there! Those who have ever passed through meadows infested with red-bugs will remember the occasion. "

Horses, cattle, dogs and cats and other animals suffer also. Againsulphur ointments are the best remedies. 

 "The normal food of these mites must, apparently, consist of the juices of plants, and the love of blood proves ruinous to those individuals which get a chance to indulge it. For, unlike the true chigoe, the female of which deposits eggs in the wound she makes, these harvest-mites have no object of the kind, and when not killed at the hands of those they torment they soon die victims to their sanguinary appetite. "

CHAPTER IV

HOW INSECTS CAUSE OR CARRY DISEASE

It has been estimated that there are about four thousand species orkinds of Protozoans, about twenty-five thousand species of Mollusks, about ten thousand species of birds, about three thousand five hundredspecies of mammals, and from two hundred thousand to one million speciesof insects, or from two to five times as many kinds of insects as allother animals combined. 

Not only do the insects preponderate in number of species, but thenumber of individuals belonging to many of the species is absolutelybeyond our comprehension. Try to count the number of little green aphison a single infested rose-bush, or on a cabbage plant; guess at thenumber of mosquitoes issuing each day from a good breeding-pond;estimate the number of scale insects on a single square inch of a treebadly infested with San José scale; then try to think how many morebushes or trees or ponds may be breeding their millions just as theseand you will only begin to comprehend the meaning of this statement. 

As long as these myriads of insects keep in what we are pleased to calltheir proper place we care not for their numbers and think little ofthem except as some student points out some wonderful thing about theirstructure, life-history or adaptations. But since the dawn of history wefind accounts to show that insects have not always kept to their propersphere but have insisted at various times and in various ways ininterfering with man's plans and wishes, and on account of theirexcessive numbers the results have often been most disastrous. 

Insects cause an annual loss to the people of the United States of over$1, 000, 000, 000. Grain fields are devastated; orchards and gardens aredestroyed or seriously affected; forests are made waste places and inscores of other ways these little pests which do not keep in theirproper places are exacting this tremendous tax from our people. 

These things have been known and recognized for centuries, and scores ofvolumes have been written about the insects and their ways and ofmethods of combating them. 

But it is only in recent years that we have begun to realize the reallyimportant part that insects play in relation to the health of the peoplewith whom they are associated. Dr. Howard estimates that the annualdeath rate in the United States from malaria is about twelve thousand, entailing an annual monetary loss of about $100, 000, 000, to say nothingof the suffering and misery endured by the afflicted. All this onaccount of two or three species of insects belonging to the mosquitogenus _Anopheles_. 

Yellow fever, while not so widespread, is more fatal and therefore moreterrorizing. Its presence and spread are due entirely to a singlespecies of mosquito. Flies, fleas, bedbugs, and many other insects havebeen shown to be intimately connected with the spread of several othermost dreaded diseases, so it is no wonder that physicians, entomologistsand biologists are studying with utmost zeal many of these forms thatbear such a close relation not only to our welfare and comfort but toour lives as well. 

It would be out of place to try to give here even a brief outline of theclassification of insects, such as may be found in almost any of themany books devoted to their study. 

The most generally accepted classification divides the insects intonineteen orders; as the Coleoptera, containing the beetles; theLepidoptera, containing the butterflies and moths; the Hymenopteracontaining the bees, ants and wasps, etc. Four or five of these orderswill be of more or less interest to us. 

The order Diptera, or two-winged flies, is the most important because tothis belong the mosquitoes which transmit malaria and yellow fever, andthe house-fly that has come into prominence since it has been found tobe such an important factor in the distribution of typhoid and otherdiseases. 

FLIES

The order Diptera is divided into sixty or more families, many of whichcontain species of considerable economic importance. For our presentconsideration the flies may be divided into two groups or sections:those with their mouth-parts fitted for piercing such as the mosquitoand horse-fly, and those with sucking mouth-parts such as the house-fly, blow-fly and others. 

Some of the species belonging to the first group are among the mosttroublesome pests not only of man but of our domestic animals as well. Next to the mosquitoes the horse-flies (Fig. 22) are perhaps the bestknown of these. There are several species known under various names, such as gad-fly, breeze-fly, etc. They are very serious pests of horsesand cattle, sometimes also attacking man. Their strong, sharp, piercingstylets enable them to pierce through the toughest skin of animals andthrough the thin clothing of man. The bite is very severe andirritating, and as the flies sometimes occur in great numbers theannoyance that they cause is often very great indeed. It has often beenclaimed that these flies as well as the stable-fly and others carry theanthrax bacillus on their proboscis from one animal to another, andalthough this may not have been definitely proven the evidence is strongenough to make a very good case against the accused. It is interestingto note in this connection that anthrax, a very common disease among thedomestic animals and one which may attack man also, was the firstdisease to be shown to be of bacterial origin. It was only aboutthirty-five years ago that the investigations of Koch and Pasteurdemonstrated that the presence of this particular germ (_Bacillusanthracis_) was the cause of the disease, and it was early recognizedthat such biting flies may be important factors in the spread of thedisease. 

[Illustration: FIG. 22--Horse-fly (_Tabanus punctifer_). ]

[Illustration: FIG. 23--Stable-fly (_Stomoxys calcitrans_). ]

[Illustration: FIG. 24--A Black-fly (_Simulium sp. _). (From Kellogg'sAmer. Insects. )]

[Illustration: FIG. 25--Screw-worm fly (_Chrysomyia macellaria_). ]

[Illustration: FIG. 26--Blow-fly (_Calliphora vomitoria_). ]

The stable-fly (Fig. 23) (_Stomoxys calcitrans_) which looks very muchlike the house-fly and, as will be noted later, frequently entershouses, is often an important pest of horses and cattle. Itsblood-sucking habit makes it quite possible that it too may be concernedin carrying anthrax and other diseases. 

In a later chapter it will be shown how the tsetse-fly, which issomewhat like the stable-fly, is responsible for the spread of thedisease known as the sleeping sickness. This disease is caused by aProtozoan parasite, a trypanosome, which is transmitted from one host toanother by the tsetse-fly. 

In Southern Asia and in parts of Africa there is a very serious diseaseof horses known as surra which is caused by a similar parasite(_Trypanosoma evansi_). This parasite attacks horses, mules, camels, elephants, buffaloes and dogs, and has been recently imported into thePhilippines. It is supposed that flies belonging to the same genus asthe horse-fly (_Tabanus_ and others), and the stable-fly (_Stomoxys_)and the horn-fly (_Hæmatobia_) are responsible for the spread of thedisease. 

Nagana is one of the most serious diseases of domestic animals inCentral and Southern Africa. In some sections it is almost impossible tokeep any kind of imported animals on account of this disease which iscaused by a parasite (_Trypanosoma brucei_) similar to the one causingsurra. This parasite is to be found in several different kinds ofnative animals which seem to be practically immune but are always asource of danger when other animals are introduced. Two or three speciesof tsetse-flies are responsible for the transmission of this disease. 

Another group of flies much smaller but more numerous and much moreinsistent are the black-flies or buffalo-gnats (Fig. 24). For more thana century these little flies have been recognized as among the mostserious pests of stock, particularly in the south where, besides theactual loss by death of many animals yearly, the annoyance is so greatas to sometimes make it impossible to work in the field. Human beingsare often attacked, and as the bite is poisonous and very painful greatsuffering may result and cases of deaths from such bites have beenreported. 

Belonging to another family, and smaller, but much like the buffalo-gnatin habits, are the minute little "punkies" or "no-see-ums" whichsometimes occur in great swarms in certain regions where they make lifea burden to man and beast. While it has not been shown that either thebuffalo-gnats or the punkies are responsible for the transmission of anydisease, their habits of feeding on so many different kinds of wild anddomestic animals as well as on man makes it possible for them to act ascarriers of parasites that might under proper conditions become ofserious importance. Then, too, the irritation caused by the bites ofthese insects usually causes scratching which may result in abrasions ofthe skin that open the way for various harmful germs, particularly thosecausing skin diseases. 

Coming now to the group containing the house-flies and related forms wefind a number that are of interest on account of the suffering that theymay cause, particularly in their larval stages. 

The screw-worm flies (_Chrysomyia macellaria_) are among the most commonand important of these (Fig. 25). These "gray flies, " as they aresometimes called, lay a mass of three or four hundred eggs on thesurface of wounds. The larvæ which in a few hours hatch from these maketheir way directly into the wound where they feed on the surroundingtissue until full grown when they wriggle out and drop to the groundwhere they transform to the pupa and later to the adult fly. Of coursetheir presence in the wounds is very distressing to the infected animal, and great suffering results. Slight scratches that might otherwisequickly heal often become serious sores because of the presence of theselarvæ. 

Many cases are recorded of these flies laying their eggs in the ears ornose of children or of persons sleeping out of doors during the day. Especially is this apt to occur if there are offensive discharges whichattract the fly. In such cases the larvæ burrow into the surroundingtissues, devouring the mucous membranes, the muscles and even the bones, causing terrible suffering and usually, death. The larvæ in suchsituations may be killed with chloroform and, if the case is attended tobefore they have destroyed too much of the tissues, recovery usuallyoccurs. 

The blow-flies (Fig. 26) (_Calliphora vomitoria_) and the blue-bottleflies (Fig. 27), (_Lucilia spp. _) and the flesh-flies (Fig. 28)(_Sarcophaga spp. _) all have habits somewhat like the screw-worm fly. Any of them may lay their eggs in wounds on man or animals with the sameserious results. 

The flesh-fly instead of laying eggs deposits the living larvæ upon meatwherever it is accessible, and as these develop with astonishingrapidity they are able to consume large quantities of flesh in aremarkably short time. In this way they may be of some importance asscavengers, but it is better to get rid of the waste in other ways thanto leave it for a breeding-place for flies that are capable of causingso much damage and suffering. 

Not infrequently the larvæ of certain flies are to be found in thealimentary canal where as a rule they do no particular damage. Altogether the larvæ of over twenty different species of flies have beenfound in or expelled from the human intestinal canal. In Europe, themajority of these larvæ belong to a fly which looks very much like thehouse-fly except that it is somewhat smaller and so is often known as"the little house-fly" (Fig. 29) (_Homalomyia canicularis_). The samespecies is very common in the United States, frequently occurring inhouses. Under certain conditions it may even be more abundant than thehouse-fly. It is believed that the larvæ in the intestinal canal comefrom eggs that have been deposited on the victim while using an outdoorprivy where the flies are often very abundant. Instances are also onrecord where these larvæ have been discharged from the urethra. 

Another fly (_Ochromyia anthropophaga_) occurring in the Congo regionhas a blood-sucking larvæ which is known as the Congo floor-maggot. Thefly which is itself not troublesome deposits its eggs in the cracks andcrevices of the mud floors of the huts. The larvæ which hatch from thesecrawl out at night and suck the blood of the victim that may be sleepingon the floor or on a low bed. 

BOT-FLIES

Another group of flies known as the bot-flies (Fig. 30) have theirmouth-parts rudimentary or entirely wanting so of course they themselvescannot bite or pierce an animal. Nevertheless they are the source of anendless amount of trouble to stockmen and sometimes even attack man. Although these flies cannot bite, the presence of even a singleindividual may be enough to annoy a horse almost to the end ofendurance. Horses seem to have an instinctive fear of them and will doall in their power to get rid of the annoying pests. 

The eggs of the house bot-fly are laid on the hair of the legs or someother part of the body. The horse licks them off and they hatch anddevelop in the alimentary canal of their host. Sometimes the walls ofthe stomach may be almost covered with them thus of course seriouslyinterfering with the functions of this organ. When full grown the larvæpass from the host and complete their transformation in the ground. 

[Illustration: FIG. 27--Blue-bottle fly (_Lucilia sericata_). ]

[Illustration: FIG. 28--Flesh-fly (_Sarcophaga sp_). ]

[Illustration: FIG. 29--"The little house-fly" (_Homalomyiacanicularis_). ]

[Illustration: FIG. 30--Horse bot-fly (_Gastrophilus equi_). ]

[Illustration: FIG. 31--Ox warble-fly (_Hypoderma lineata_). ]

[Illustration: FIG. 32--Sheep bot-fly (_Gastrophilus nasalis_). ]

The bot-flies of cattle or the oxwarbles (Fig. 31) gain an entranceinto the alimentary canal in the same way, that is, by the eggs beinglicked from the hairs on the body where they have been laid by the adultfly. But instead of passing on into the stomach they collect in theesophagus and later make their way through the walls of this organ andthrough the tissues of the body until they at last reach a place alongthe back just under the skin. Here as they are completing theirdevelopment they make more or less serious sores on the backs of theinfested animals. The hides on such animals are rendered nearlyvalueless by the holes made by the larvæ. When fully mature they drop tothe ground and complete their transformations. 

The sheep bot-flies (Fig. 32) lay their eggs in the nostrils of sheep. The larvæ pass up into the frontal sinuses where they feed on the mucus, causing great suffering and loss. Many other species of animals areinfested with their own particular species of bots. Several instancesare recorded where the oxwarble has occurred in man, always causing muchsuffering and sometimes death. 

One or more species of bot-flies occurring in the tropical parts ofAmerica frequently attack man. The early larval stage soon after it hasentered the skin is known as the _Ver macaque_. Later stages as _torcel_or _Berne_. The presence of the larvæ produces very painful andtroublesome sores. It is supposed that the adult flies (one species ofwhich is _Dermatobia cyaniventris_) lay their eggs on the skin whichthe larvæ penetrate as soon as they hatch. It has also been suggestedthat they might reach the subcutaneous tissue by migrating from thealimentary canal as do some of the other bot-flies. A very serious eyedisease, _Egyptian opthalmia_, is known to be spread by the house-fliesand others. These flies are often abundant about the eyes, especially ofchildren suffering from this disease. It is suspected that certain smallflies (Oscinidæ) in the southern part of the United States areresponsible for the spread of disease known as "sore eye. "

FLEAS

The fleas used to be considered as degenerate Diptera and were placedwith that group but they are now classed as a separate order(Siphonaptera). Within recent years these little pests have come intospecial prominence on account of their importance in connection with thespread of the plague. The fact that they are so abundant everywhere andthat they will so readily pass from one host to another makes thepossibility of their spreading infectious diseases very great. Besidesthe kinds that are concerned in the transmission of plague, which arediscussed in another chapter, there are many other kinds infestingvarious wild and domesticated animals and a few attacking birds. 

One of the most important of these is the jigger-flea or chigoe(_Dermatophilus penetrans_, Fig. 33). Various other names such aschigger-flea, sand-flea, jigger, chigger are also applied to this insectas well as to a minute red mite that burrows into the skin in much thesame way as the female of the flea. So although they are entirelydifferent creatures you can never tell from the common name, whether itis the flea or the mite that is being referred to. Both the male andfemale jigger-fleas feed on the host and hop on or off as do otherfleas, but when the female is ready to lay eggs (Fig. 34), she burrowsinto the skin. Her presence there causes a swelling and usually an ulcerwhich often becomes very serious, especially if the insect should becrushed and the contents of the body escape into the surrounding tissue. 

These little pests are found throughout tropical and subtropical Americaand have been introduced into Africa and from there have spread to Indiaand elsewhere. They attack almost all kinds of animals as well as manybirds, being of course a source of great annoyance and no inconsiderableloss. They are more apt to attack the feet of men, especially those whogo barefooted. Sometimes they occur in such numbers as to make greatmasses of sores. 

On account of being such general feeders they are difficult to control, but some relief may be obtained by keeping the houses and barns as freeas possible from dirt and rubbish and by sprinkling the breeding-placesof the pest with pyrethrum powder or carbolic water. Those that gain anentrance into the skin should be cut out, care being taken to remove theinsect entire. 

BEDBUGS

In the order Hemiptera, or the true "bugs" in an entomological sense, wefind a few forms that may carry disease. The bedbug (Fig. 35) (_Cimexlectularis_) has been accused of transmitting plague, relapsing feverand other diseases. Very recent investigations show that the commonbedbug of India (_Cimex rotundatus_) harbors the parasite that causesthe disease known as _kala azar_, and there is no doubt that ittransmits the disease. 

LICE

The sucking lice (Fig. 36) which also belong to this order are suspectedof carrying some of these same diseases. It is thought that the commonlouse on rats (_Hæmatopinus spinulosus_) is responsible for the spreadfrom rat to rat of a certain parasite. (_Trypanosoma lewisi_), which, however, does not produce any disease in the rats, but if they arecapable of acting as alternative hosts for such parasites, it is quitepossible that they may also carry disease-producing forms. 

[Illustration: FIG. 33--Chigo or jigger-flea, male (_Dermatophiluspenetrans_). (After Karsten. )]

[Illustration: FIG. 34--Chigo, female distended with eggs. (AfterKarsten. )]

[Illustration: FIG. 35--Bedbug (_Cimex lectularis_). ]

[Illustration: FIG. 36--Body-louse (_Pediculus vestimenti_). (Fromdrawing by J. H. Paine. )]

HOW INSECTS MAY CARRY DISEASE GERMS

Insects may carry the germs or parasites which cause disease in a purelymechanical or accidental way, that is, the insect may in the course ofits wanderings or its feeding get some of the germs on or in its bodyand may by chance carry these to the food, or water, or directly to someperson who may become infected. Thus the house-fly may carry the typhoidgerms on its feet or in its body and distribute them in places wherethey may enter the human body. 

Several other flies as well as fleas, bedbugs, ticks, etc. , may alsocarry disease germs in this mechanical way. While this method oftransmission is just as dangerous as any other, and possibly moredangerous because more common, another method in which the insect ismuch more intimately concerned is more interesting from a biologicalstandpoint at least and will be discussed more fully in the chapters onmalaria, yellow fever and elephantiasis. 

In these cases the insect is one of the necessary hosts of the parasite, which cannot go on with its development or pass from one patient toanother unless it first enters the insect at a certain stage of itslife-history. 

[Illustration: FIG. 37--One use for the house-fly. ]

BABY-BYE. 

 1. Baby-Bye, Here's a fly; We will watch him, you and I. How he crawls Up the walls, Yet he never falls! I believe with six such legs You and I could walk on eggs. There he goes On his toes, Tickling Baby's nose. 

CHAPTER V

HOUSE-FLIES OR TYPHOID-FLIES

The page shown in Fig. 37 was copied from one of our old second readersand shows something of the spirit in which we used to regard thehouse-fly. A few of them were nice things to have around to make thingsseem "homelike. " Of course they sometimes became too friendly during theearly morning hours when we were trying to take just one more little napor they were sometimes too insistent for their portion of the dinnerafter it had been placed on the table, but a screen over the bed wouldhelp us out a little in the morning and a long fly-brush cut from a treein the yard or made of strips of paper tacked to a stick or, still morefancy, made of long peacock plumes, would help to drive them from thetable. Those that were knocked into the coffee or the cream could befished out; those that went into the soup or the hash were never missed!

Not only were the flies regarded as splendid things with which to amusethe baby, but they were thought to be very useful as scavengers as theywere often seen feeding on all kinds of refuse in the yard. Then, too, they seemed to be cleanly little things, for almost any time some ofthem could be seen brushing their heads and bodies with their legs andevidently having a good clean-up. More than that it never occurred to usthat it would be possible to get rid of them even should it be thoughtadvisable, for they came from "out doors, " and who could kill all theflies "out doors"?

Fortunately, or otherwise, these halcyon days have gone by and thecommon, innocent, friendly little house-fly is now an outcast convictedof many crimes and accused of a long list of others (Fig. 38). 

Its former friends have become its sworn enemies. The foremostentomologist of the land has suggested that we even change its name andgive it one that would be more suggestive of the abhorence with which wenow look upon it. 

[Illustration: FIG. 38--The house-fly (_Musca domestica_). ]

And all these changes have come about because science has turned themicroscope on the house-fly and men have studied its habits. We know nowthat as the fly is "tickling baby's nose" it may be spreading therewhere they may be inhaled or where they may be taken into the baby'smouth thousands of germs some of which may cause some serious disease. We know that as they are buzzing about our faces while we are trying tosleep they may, unwittingly, be in the same nefarious business, and weknow that as they sip from our cups with us or bathe in our coffee orour soup or walk daintily over our beefsteak or frosted cake they areleaving behind a trail of filth and bacteria, and we know that some ofthese germs may be and often are the cause of some of our commondiseases. As the typhoid germs are very often distributed in this way, Dr. Howard has suggested that the house-fly shall be known in the futureas the typhoid-fly, not because it is solely responsible for the spreadof typhoid, but because it is such an important factor in it and is sodangerous from every point of view. The names "manure fly" and "privyfly" have also been suggested and would perhaps serve just as well, asthe only object in giving it another name would be to find a morerepulsive one to remind us constantly of the filthy and dangerous habitsof the fly. 

STRUCTURE

In order that we may better understand why it is that the house-fly iscapable of so much mischief, let us consider briefly a few points inregard to its structure, its methods of feeding and its life-history. 

The large compound eyes are the most conspicuous part of the head (Fig. 39). In front, between the eyes, are the three-jointed antennæ, the lastjoint bearing a short, feathery bristle. From the under side of the headarises the long, fleshy proboscis (Fig. 40). When this is fully extendedit is somewhat longer than the head; when not distended and in use it isdoubled back in the cavity on the under side of the head. About half-waybetween the base and the middle is a pair of unjointed mouth-feelers(maxillary palpi). At the tip are two membranous lobes (Fig. 41) closelyunited along their middle line. These are covered with many finecorrugated ridges, which under the microscope look like fine spirals andare known as pseudotracheæ. Thus it will be seen that the house-fly'smouth-parts are fitted for sucking and not for biting. Its food must bein a liquid or semi-liquid state before it can be sucked through thetube leading from the lobes at the tip up through the proboscis and oninto the stomach. If the fly wishes to feed on any substance such assugar, that is not liquid, it first pours out some saliva on it and thenbegins to rasp it with the rough terminal lobes of the proboscis, thusreducing the food to a consistency that will enable the fly to suck itup. Many people think that house-flies can bite and will tell you thatthey have been bitten by them. But a careful examination of theoffender, in such instances, will show that it was not a house-fly butprobably a stable-fly, which does have mouth-parts fitted for piercing. 

[Illustration: FIG. 39--Head of house-fly showing eyes, antennæ andmouth-parts. ]

[Illustration: FIG. 40--Proboscis of house-fly, side view. ]

[Illustration: FIG. 41--Lobes at end of proboscis of house-fly showingcorrugated ridges. ]

[Illustration: FIG. 42--Wing of house-fly. ]

The thorax bears the two rather broad, membranous wings (Fig. 42) whichhave characteristic venation. Three of these veins end rather closetogether just before the tip of the wing, the posterior one of the groupbeing bent forward rather sharply a short distance from the tip. Thestable-fly has this vein slightly curved forward but not nearly soconspicuously (Fig. 43). 

Nearly all the other flies that are apt to be mistaken for the house-flydo not have this vein curved forward. The wings, although apparentlybare, are covered with a fine microscopic pubescence. Among these finehairs on the wing as well as among similar fine ones and coarser onesall over the body, particles of dust and dirt or filth (Fig. 44) or, what interests us more just now, thousands of germs may find a temporarylodgment and later be scattered through the air as the insect flies. Orthey may get on our food as the fly feeds or while it rests and combsits body with the rows of coarse hairs on its legs. 

The legs are rather thickly covered with coarse hairs or bristles andwith a mat of fine, short hairs. On some of the segments the largerhairs are arranged in rows and are used as a sort of comb with which thefly combs the dirt from the rest of its body. The last segment (Fig. 45)of the leg bears at its tip a pair of large curved claws and a pair ofmembranous pads known as the pulvillæ. On the under side of the pulvillæare innumerable minute secreting hairs (Fig. 46) by means of which thefly is able to walk on the wall or ceiling or in any position onhighly-polished surfaces. 

HOW THEY CARRY BACTERIA

These same little pads, with their covering of secreting hairs, areperhaps the most dangerous part of the insect for they cannot help butcarry much of the filth over or through which the fly walks, and as thismay be well stocked with germs the danger is at once apparent. 

As the result of a series of carefully planned experiments it has beendemonstrated that the number of bacteria on a single fly may range allthe way from 550 to 6, 600, 000 with an average for the lot experimentedwith of about one and one-fourth million bacteria to each fly. Now wheredo all these bacteria come from? Necessarily from the place where thefly breeds or where it feeds. 

[Illustration: FIG. 43--Wing of Stable-fly (_Stomoxys calcitrans_). ]

[Illustration: FIG. 44--Wing of house-fly showing particles of dirtadhering to it. ]

[Illustration: FIG. 45--Last three segments of leg of house-fly showingthe claws, the pulvillæ and the hairs on the legs. ]

[Illustration: FIG. 46--Foot of house-fly showing claws, hairs, pulvillæ and the minute clinging hairs on the pulvillæ. ]

[Illustration: FIG. 47--Larva of house-fly. ]

LIFE-HISTORY AND HABITS

The eggs of the house-fly may be laid on almost any kind of decaying orfermenting material. If this is kept moist and a proper temperaturemaintained the larvæ or maggots (Fig. 47) that hatch from the eggs maydevelop. As a rule, however, these requirements are found only undercertain conditions and are ordinarily found only in manure heaps or inprivy vaults or latrines. All observers agree that the female flyprefers to deposit her eggs in horse manure when this can be found andwhen this is piled in heaps in the barn-yard (Fig. 48) or in the fieldthe heat caused by the decay and fermentation makes ideal conditions forthe development of the larvæ. Cow manure may serve as a breeding-placeto a limited extent. The flies are immediately attracted to humanexcrement and breed freely in it when opportunity offers. Decayingvegetables or fruit, fermenting kitchen refuse and other materialssometimes also serve as breeding-places. 

In suitable places in warm weather the eggs will hatch in from eight totwelve hours and the larvæ will become fully developed in from eight tofourteen days. They then change to pupæ (Fig. 50) in which stage theymay remain for another eight to twenty days when the adult flies willemerge. These figures must necessarily be indefinite because the weatherand other conditions always vary. Under the most favorable conditions ofmoisture and temperature it is probably never less than eight days fromegg to adult fly and under unfavorable conditions it may be as long assix weeks. 

The larvæ thrive best when the manure is kept quite wet. I have oftenfound them in almost incredible numbers in stables that had not beencleaned for some time. The horses standing there at night added freshmaterial and kept it just wet enough to make conditions almost ideal(Fig. 49). 

The pupæ are usually found where the manure is a little dryer, but itmust not be too dry. When the flies issue from the pupæ they push theirway up to the surface where they remain for a short time and allow thebody to harden and the wings to dry before they fly away to other manureor, as too often happens, to some near-by kitchen or restaurant ormarket place. 

[Illustration: FIG. 48--Barn-yard filled with manure. Millions of flieswere breeding here and infesting all the near-by houses. ]

[Illustration: FIG. 49--Dirty stalls; the manure had not been removedfor some days and the floor was covered with maggots. ]

Of course it is impossible for them to issue from this filth withoutmore or less of it clinging to their bodies. Now if these flies wouldbreed only in barn-yard manure and fly directly from the stable to thehouse there would be comparatively little reason to complain, at leastfrom a sanitary standpoint, for the amount of barn-yard filth that theycarried to our food would be of little consequence. But when they breedin privy vaults or similar places, or visit such places before cominginto the house or dairy or market place the results may be much moreserious. 

FLIES AND TYPHOID

It has been abundantly demonstrated that the excrement or the urine of atyphoid patient may contain virulent germs for some time before he isaware that he has the disease, and it has been shown that the germs maybe present for weeks or months, and in some cases even years after thepatient has recovered. If a fly breeds in such infected material, orfeeds or walks on it, it is very apt to get some of the germs on itsbody where they may retain their virulence for some time, and should itvisit our food while covered with these germs some of them wouldprobably be left there where they might produce serious results. Morethan that. If the fly should feed on such infected material the typhoidgerms would go on developing in the intestine of the fly and would bepassed out with the feces in which they retain their virulence for somedays. In other words, the too familiar "fly-specks" are not onlydisgusting, but may be a very grave source of danger. It will be seenthat in this way several members of a community might become infectedwith the typhoid germs before anyone was aware that there was a case oftyphoid or a "bacillus carrier" in the neighborhood. 

One more example out of the scores that might be cited to show how thefly may carry typhoid germs. They may enter the sick chamber in the homeor in the hospital and there gain access to the typhoid germs. Thesethey may carry to other parts of the house or to near-by houses, or theflies may light on passing carriages or cars and be carried perhaps formiles before they enter another house and contaminate the food there. 

These are hypothetical cases, but they illustrate what is taking placehundreds of times every season all over the world wherever typhoid feverand flies occur, and no country or race is known to be immune fromtyphoid, and the fly is found "wherever man is found. "

In the summer of 1898 a commission was appointed to investigate theprevalence of typhoid fever in the United States Army ConcentrationCamps. The following are some of the conclusions as reported by Dr. Vaughan:

 "FLIES UNDOUBTEDLY SERVED AS CARRIERS OF THE INFECTION

 "My reasons for believing that flies were active in the dissemination of typhoid may be stated as follows:

 "_a. _ Flies swarmed over infected fecal matter in the pits and then visited and fed upon the food prepared for the soldiers at the mess tents. In some instances where lime had recently been sprinkled over the contents of the pits, flies with their feet whitened with lime were seen walking over the food. 

 "_b. _ Officers whose mess tents were protected by means of screens suffered proportionately less from typhoid fever than did those whose tents were not so protected. 

 "_c. _ Typhoid fever gradually disappeared in the fall of 1898, with the approach of cold weather, and the consequent disabling of the fly. 

 "It is possible for the fly to carry the typhoid bacillus in two ways. In the first place, fecal matter containing the typhoid germ may adhere to the fly and be mechanically transported. In the second place, it is possible that the typhoid bacillus may be carried in the digestive organs of the fly and may be deposited with its excrement. "

In Dr. Daniel D. Jackson's report to the Merchants' Association of NewYork on the "Pollution of New York Harbor as a Menace to the Health bythe Dissemination of Intestinal Diseases Through the Agency of theCommon House-fly, " he shows graphically that the prevalence of typhoidand other intestinal diseases is coincident with the prevalence offlies, and that the greatest number of deaths from such diseases occursnear the river front where the open or poorly constructed sewers scatterthe filth where the flies can feed on it, or along the wharves withtheir inadequate accommodations and the resulting accumulation of filth. 

FLIES AND OTHER DISEASES

Not only is the house-fly an important factor in the dissemination oftyphoid fever, but it has been definitely shown that it is capable oftransmitting several other serious diseases. 

The evidence that flies carry and spread the deadly germs of cholera ismost conclusive. The germs may be carried on the body where they willlive but a short time, or they may be carried in the alimentary canalwhere they will live for a much longer period and are finally depositedin the fly-specks where they retain their virulence for some time. Fliesthat had been allowed to contaminate themselves with cholera germs wereallowed access to milk and meat. In both cases hundreds of colonies ofthe germs could later be recovered from the food. As with the typhoidgerms milk seems to be a particularly good medium for the development ofthe cholera germs. In several of the experiments that have been madealong this line the milk has been readily infected by the flies visitingit. 

Of course an outbreak of cholera is of rare occurrence in our country, but unfortunately this is not so in regard to some other intestinaldiseases such as diarrhea and enteritis which annually cause the deathof many children, especially bottle-fed babies. Those who have madeclose studies of the way in which these diseases are disseminated areconvinced that the flies are one of the most important factors in theirspread. 

It has long been observed that flies are particularly fond of sputum andwill feed on it on the sidewalk, in the gutter, the cuspidor or whereveropportunity offers. It is well known, too, that the sputum of aconsumptive contains myriads of virulent tubercular germs. A fly feedingand crawling over such material must necessarily get some of it on itsbody, and as it dries and the insect flies about the germs will bedistributed through the air, possibly over our food. It has been shownthat the excretion from a fly that has fed on tubercular sputum containstubercular bacilli that may remain virulent for at least fifteen days. Thus we see again the danger that may lurk in the too familiar"fly-specks. "

Although it is generally supposed that the flea is solely responsiblefor the spread of the bubonic plague and no doubt is the principaldistributing agent, the fact must not be overlooked that the house-flymay also be of considerable importance in this connection. Carefullyplanned experiments have shown that flies that have become infected bybeing fed on plague-infected material may carry the germs for severaldays and that they may die of the disease. During plague epidemics fliesmay become infected by visiting the sores on human or rat victims or byfeeding on dead rats or on the excreta of sick patients, and an infectedfly is always a menace should it visit our food or open wounds or sores. Anthrax bacilli are carried about and deposited by flies showing thepossibility of the disease being spread in this way. 

Some believe that leprosy, smallpox and many other diseases are carriedby the house-fly, so it is little wonder that it is fast losing itsstanding as a household companion and that we are beginning to regard itnot only as a nuisance but as a source of danger which should no longerbe tolerated in any community. 

Of course only a small per cent of the flies that visit our food in thedairies or market places or kitchens actually carry dangerous diseases, but they are all bred in filth and it is not possible without carefulexperiments or laboratory analysis to determine whether any of the germsamong the millions that are on their bodies are dangerous or not. Thechances that they may be are too great. The only safe way is to banishthem all or to see that all of our food is protected from them. 

FIGHTING FLIES

Screens and sticky fly-paper have their places and give some littlerelief in a well-kept house. But of what use is it to protect your foodafter it has entered your home if in the stores, in the market place, inthe dairy barn, or dairy wagon, in the grocers' and butchers' cart, ithas been exposed to contamination by hundreds of flies that have visitedit. 

The problem is a larger one than keeping the house free from flies;larger but not more difficult, for the remedy is simple, effective, practicable and inexpensive. Destroy their breeding-places and you willhave no flies. As the flies breed principally in manure the firstremedial measure is to see that all manure is removed from thebarn-yard at least once a week and spread over the fields to dry, forthe flies cannot breed in the dry manure. If it is not practicable toremove it this often the manure should be kept in a bin that is closedso tight that no flies can get into it to lay their eggs. Sometimes themanure may be treated with some substance such as kerosene, crude oil, chlorid of lime, tobacco water or mixture of two or more of these andthus rendered unsuitable for the flies to breed in, but in generalpractice none of them has been found very satisfactory for the treatmentis either not thorough enough or is too expensive of time and material. 

Outdoor privies and cesspools must be carefully attended to. The lattercan be easily covered so no flies can get in and if the filthy and inevery way dangerous pit under the privy be filled and the dry-earthcloset substituted one of the greatest sources of danger, especially inthe country and in towns with inadequate sewerage facilities, will bedone away with. After these things are done there remain only thegarbage cans and the rubbish heaps to look after. 

Of course your neighbor must keep his place clean too, for his flies arejust as apt to come into your house as his, so the problem becomes onefor the whole community. 

Almost all cities and many of the smaller towns have ordinances whichif enforced would afford adequate protection from flies, but they areseldom if ever rigidly enforced and it yet remains for some enterprisingtown to be able to advertise itself as a "speckless town" as well as a"spotless town. "

AN EXPERT'S OPINION

In a recent important bulletin issued by the Bureau of Entomology, Dr. L. O. Howard discusses the economic importance of several of the insectsthat carry disease. I wish to quote two or three paragraphs from thepages in which he discusses the house-fly or typhoid fly to show theopinion of this excellent authority in regard to this pest. 

 "Even if the typhoid or house fly were a creature difficult to destroy, the general failure on the part of communities to make any efforts whatever to reduce its numbers could properly be termed criminal neglect; but since, as will be shown, it is comparatively an easy matter to do away with the plague of flies, this neglect becomes an evidence of ignorance or of a carelessness in regard to disease-producing filth which to the informed mind constitutes a serious blot on civilized methods of life. "

On another page:

 "We have thus shown that the typhoid or house fly is a general and common carrier of pathogenic bacteria. It may carry typhoid fever, Asiatic cholera, dysentery, cholera morbus, and other intestinal diseases; it may carry the bacilli of tuberculosis and certain eye diseases. It is the duty of every individual to guard so far as possible against the occurrence of flies upon his premises. It is the duty of every community, through its board of health, to spend money in the warfare against this enemy of mankind. This duty is as pronounced as though the community were attacked by bands of ravenous wolves. "

Again:

 "A leading editorial in an afternoon paper of the city of Washington, of October 20, 1908, bears the heading, 'Typhoid a National Scourge, ' arguing that it is to-day as great a scourge as tuberculosis. The editorial writer might equally well have used the heading 'Typhoid a National Reproach, ' or perhaps even 'Typhoid a National Crime, ' since it is an absolutely preventable disease. And as for the typhoid fly, that a creature born in indescribable filth and absolutely swarming with disease germs should practically be invited to multiply unchecked, even in great centers of population, is surely nothing less than criminal. "

The whole bulletin (No. 78, Bureau of Entomology) should be read andstudied by all who are interested in this subject. 

OTHER FLIES

Occasionally other flies looking more or less like the house-fly areseen in houses. Some of these have the same type of sucking mouth-partsand have habits very similar to the house-fly, but as they are usuallymuch less common and as nearly all that has been said in regard to thehouse-fly would apply equally well to them and as the same measuresshould be adopted in fighting them they need not be discussed furtherhere. 

I have already called attention to the fact that a fly which looks verymuch like the house-fly is sometimes found in the house and will oftenbite severely. It has quite a different style of beak, one that isfitted for piercing so it may suck the blood of its victim (Fig. 51). Asthese flies often seem to be more persistent before a rain the weatherprophet will tell you that "It is surely going to rain for thehouse-flies are beginning to bite. "

These stable-flies, as they are called, are great pests of cattle andhorses in some sections. It is thought that they are important factorsin the spread of some of the diseases of domestic animals, and theirhabit of sometimes attacking human beings makes it possible for them tocarry certain disease germs from animals to man or from man to man. 

CHAPTER VI

MOSQUITOES

Mosquitoes are no more abundant now than they have been in the past, butwhen Linnæus in 1758 made his list of all the animals known to exist atthat time he catalogued only six species of mosquitoes. Only a few yearsago, 1901, Dr. Theobald of the British Museum published a book on themosquitoes of the world in which he listed three hundred and forty-threekinds. Soon other volumes appeared, adding more species, andsystematists everywhere have been describing new ones until now thetotal number of described species is probably over five hundred, morethan sixty of which occur in the United States. 

This shows only one phase of the great interest that has been taken inthe mosquitoes since the discovery of their importance as carriers ofdisease. Not only have they been studied from a systematic standpointbut an endless amount of work has been done and is being done instudying their development, habits, and structure until now, if onecould gather together all that has been written about mosquitoes in thelast ten or twelve years he would have a considerable library. 

[Illustration: FIG. 50--Pupa of house-fly with the end broken to allowthe fly to issue. ]

[Illustration: FIG. 51--Head of stable-fly showing sharp piercing beak. ]

[Illustration: FIG. 52--Mass of mosquito eggs (_Theobaldia incidens_). ]

[Illustration: FIG. 53--Mosquito eggs and larvæ (_Theobaldiaincidens_); two larvæ feeding on bottom, others at surface to breathe. ]

[Illustration: FIG. 54--Mosquito larvæ (_T. Incidens_), dorsal view. ]

Those who are particularly interested in the group will find some ofthese books and papers easily accessible, so there may be given hereonly a brief summary of the more important facts in regard to thestructure and habits of the mosquitoes in order that we may more readilyunderstand the part that they play in the transmission of diseases andsee the reasonableness of the recommendations in regard to fightingthem. 

THE EGGS

Mosquito eggs are laid in water or in places where water is apt toaccumulate, otherwise they will not hatch. Some species lay their eggsin little masses (Fig. 52) that float on the surface of the water, looking like small particles of soot. Others lay their eggs singly, somefloating about on the surface, others sinking to the bottom where theyremain until the young issue. Some of the eggs may remain over winter, but usually those laid in the summer hatch in thirty-six to forty-eighthours or longer according to the temperature. 

THE LARVÆ

When the larvæ are ready to issue they burst open the lower end of theeggs and the young wrigglers escape into the water. The larvæ are fittedfor aquatic life only, so mosquitoes cannot breed in moist or dampplaces unless there is at least a small amount of standing water there. A very little will do, but there must be enough to cover the larvæ orthey perish. 

The head of the larvæ of most species is wide and flattened. The eyesare situated at the sides, and just in front of them is a pair of shortantennæ which vary with the different species. 

The mouth-parts too vary greatly according to the feeding habits. Somemosquito larvæ are predaceous, feeding on the young of other species oron other insects. These of course have their mouth-parts fitted forseizing and holding their prey. Most of the wrigglers, however, feed onalgæ, diatoms, Protozoa and other minute plant or animal forms which areswept into the mouth by curious little brush-like organs whose movementskeep a stream of water flowing toward the mouth. 

Another group containing the _Anopheles_ are intermediate between thesetwo and have mouth-parts fitted for feeding on minute organisms as wellas for attacking and holding other larger things. 

[Illustration: FIG. 55--Eggs, larvæ and pupæ of mosquitoes (_T. Incidens_). ]

[Illustration: FIG. 56--Larva of mosquito (_T. Incidens_). ]

[Illustration: FIG. 57--Mosquito larvæ and pupæ (_T. Incidens_) withtheir breathing-tubes at the surface of the water. ]

[Illustration: FIG. 58--Anopheles larvæ (_A. Maculipennis_) resting atthe surface of the water. ]

A few kinds feed habitually some distance below the surface, others onthe bottom, while still others feed always at the surface. With one ortwo exceptions, the larvæ must all come to the surface to breathe (Figs. 53-57). Most species have on the eighth abdominal segment a rather longbreathing-tube the tip of which is thrust just above the surface of thewater when they come up for air. In this tube are two large vessels ortracheæ which open just below the tip of the tube and extend forwardthrough the whole length of the body, giving off branches here and therethat divide into still smaller branches until every part of the body isreached by some of the small divisions of this tracheal system thatcarries the oxygen to all the tissues. The length of the breathing-tubeis correlated with the feeding-habits of the larvæ. _Anopheles_ larvæwhich feed at the surface have very short tubes (Fig. 58), others thatfeed just below the surface have breathing-tubes as long or very muchlonger than the ninth abdominal segment. The last segment has at its tipfour thin flat plates, the tracheal gills. These too are larger orsmaller according to the habits of the larvæ. Those species that feedclose to the surface and have the tip of the breathing-tube above thesurface most of the time have very small tracheal gills, while thosethat feed mostly on the bottom have them well developed. 

When first hatched the larvæ are of course very small. If the weather iswarm and the food is abundant they grow very rapidly. In a few days theouter skin becomes rather firm and inelastic so it will not allowfurther growth. Then a new skin forms underneath and the old skin iscast off. This process of casting off the old skin is called molting, and is repeated four times during the one, two, three or more weeks oflarval life. 

PUPA

With the fourth molt the active feeding larva changes to the stillactive but non-feeding pupa (Fig. 59). The head and thorax are closelyunited and a close inspection will reveal the head, antennæ, wings andlegs of the adult mosquito folded away beneath the pupal skin. Insteadof the breathing-tube on the eighth segment of the abdomen as in thelarva, the pupa has two trumpet-shaped tubes on the back of the thoraxthrough which it now gets its air from above the surface. The pupalstage lasts from two to five or six days or more. When the adult isready to issue the pupal skin splits along the back and the mosquitogradually and slowly issues. It usually takes several minutes for theadult to issue and for its wings to become hard enough so it can fly. Inthe meantime, it is resting on the old pupal skin or on the surface ofthe water, where it is entirely at the mercy of any of its enemies thatmight happen along and is in constant danger of being tumbled overshould the water not be perfectly smooth. 

[Illustration: FIG. 59--Mosquito pupæ (_T. Incidens_) resting at thesurface of the water. ]

[Illustration: FIG. 60--Mosquito pupa (_T. Incidens_) with itsbreathing-tubes in an air bubble below the surface of the water. ]

[Illustration: FIG. 61--Mosquito larvæ and pupæ (_T. Incidens_) restingat the surface of the water. ]

[Illustration: FIG. 62--A female mosquito (_T. Incidens_); note thethread-like antennæ. ]

[Illustration: FIG. 63--A male mosquito (_T. Incidens_); note thefeathery antennæ. ]

THE ADULT

The adult mosquito is altogether too familiar an object to needdescription, but it is necessary that we keep in mind certain particularpoints in regard to its structure, in order that we may betterunderstand how it is that it is capable of transmitting disease. 

If we examine closely the antennæ of a number of mosquitoes that arebothering us with their too constant attentions we shall see that theyall look very much alike (Fig. 62), small cylindrical joints bearingwhorls of short fine hairs. But if we examine a number of mosquitoesthat have been bred from a jar or aquarium we will find two types ofantennæ, the one described above belonging to the female. The antennæ ofthe male (Fig. 63) are much more conspicuous on account of the whorl ofdense, fine, long hairs on each segment. Another interesting differencein the antennæ is to be noted in the size of the first joint. In bothsexes it is short and cup-shaped, but in the male it is somewhat larger. This basal segment contains a highly complex auditory organ whichresponds to the vibrations of the whorls of hairs on the other segments. Interesting experiments have shown that these hairs vibrate best to thepitch corresponding to middle C on the piano, the same pitch in whichthe female "sings. " Of course mosquitoes and other insects have no voiceas we ordinarily understand the word, but produce sound by the rapidvibration of the wings or by the passage of air through the openings ofthe tracheæ. The males and females are thus easily distinguished and, aswe shall see later, this is of some importance for only the females canbite. The males and females differ in another way. Just below theantennæ and at the sides of the proboscis or beak is a pair of three-tofive-jointed appendages, the maxillary palpi or mouth-feelers which inthe females of most species are very short (Fig. 64) while in the malesthey are usually as long as the proboscis (Fig. 65). The females of_Anopheles_ and related forms have palpi quite as long as the males, butthey are slender throughout while the male palpi are usually somewhatenlarged toward the tip and bear more or less conspicuous patches ofrather long hairs or scales. 

[Illustration: FIG. 64--Head and thorax of female mosquito(_Ochlerotatus lativittatus_); the short maxillary palpi are just abovethe proboscis and below the thread-like antennæ. ]

[Illustration: FIG. 65--Head and thorax of male mosquito (_O. Lativittatus_); the maxillary palpi are as long as the proboscis. ]

[Illustration: FIG. 66--Head of female mosquito (_Anopheles_), withmouth-parts separated to show the needle-like parts: _a_, _a_ antennæ;_b_, _b_, palpi; _c_, labrum; _d_, _d_, mandibles; _e_, hypopharynx;_f_, _f_, maxillæ; _g_, labium; _h_, labella. (After Manson. )]

[Illustration: FIG. 67--Cross-section of proboscis of female (_a_) andmale (_b_) mosquito. _lxe_, labrum-epipharynx; _mn_, mandibles; _mx_, maxillæ; _hp_, hypopharynx; _sal_, salivary duct; _li_, labium; _tr_, trachea; _mus_, muscles. (After Nuttall and Shipley. )]

THE MOUTH-PARTS

The mouth-parts of the mosquito are of course of particular interest tous. At first they appear to consist of a long slender beak or proboscis, but by dissecting and examining with a microscope we find this beak tobe made up of several parts (Fig. 66). The labium, which is the largestand most conspicuous, is apparently cylindrical but is grooved abovethroughout its length. At the tip of the labium are the labellæ, twolittle lobes which serve to guide the piercing organs. Lying in thisgroove along the upper side of the labium are six very fine, sharp-pointed needles. The uppermost of these, the labrum-epipharynx, orlabrum as we will call it, is the largest and is really a hollow tubevery slightly open on its under side. Just below this is thehypopharynx, the lateral margins of which are very thin. Down throughthe median line of the hypopharynx runs a minute duct (Fig. 67, sal)which, though exceedingly small, is of very great importance, forthrough it is poured the saliva which may carry the malaria germs intothe wound made when the mosquito bites. The other four needles consistof a pair of mandibles which are lance-shaped at the tip and a heavierpair of maxillæ, the tips of which are serrate on one edge. 

HOW THE MOSQUITO BITES

When the female mosquito is feeding on man or any other animal the tipof the labium is placed against the surface and the six needles arethrust into the skin, the labellæ serving as guides. As they are thrustdeeper and deeper the labium is bowed back to allow them to enter. Assoon as the wound is made the insect pours out through the tube of thehypopharynx some of the secretion from the salivary glands and thenbegins to suck up the blood through the hollow labrum into the pharynxand on into the stomach. 

The mouth-parts of the male differ in some important respects from thoseof the female. The hypopharynx is united to the labium, the mandiblesare wanting and the maxillæ are very much reduced so that the insect isunable to pierce the tough skin of animals. The male feeds on the juicesof plants as do the females when they cannot get blood. It is not at allnecessary for mosquitoes to have the warm blood of man or other animals. Comparatively few of them ever taste blood. They have been seen feedingon blossoms, ripe fruit, watermelons, plant juices, etc. They are veryfond of ripe bananas and are fed on them in the laboratory when we wishto keep mosquitoes for experimental purposes. 

THE THORAX

The middle part of the body, called the thorax, is really a strong boxwith heavy walls for the attachment of the powerful wing and legmuscles. The three pairs of legs are covered with hairs and scales, andtheir tips are provided with a pair of claws which vary somewhat in thedifferent species. The wings (Fig. 68) are long and narrow with acharacteristic venation. Along the veins and the margin of the wings arethe scales which readily enable one to distinguish mosquitoes from otherinsects that may look much like them. In some species these scales arelong and narrow, almost hair-like, in others they are quite broad andflat (Fig. 69). Just back of the wings is a pair of balancers, shortthread-like processes knobbed at the end. These probably represent thesecond pair of wings with which most insects are provided, and seem toserve as balancers or orienting organs when the insect is flying. On thesides of the thorax are two small slit-like openings, thebreathing-pores. These are the openings into the tracheal or respiratorysystem. 

THE ABDOMEN

The long cylindrical abdomen is composed of eight segments. These arerather strongly chitinized above and below, but a narrow strip along theside is unchitinized. In this strip are situated the abdominalbreathing-pores. The tip of the abdomen is furnished with a pair ofmovable organs, which in the male are variously modified and serve asclasping organs at mating time. 

THE DIGESTIVE SYSTEM

The mouth-parts of the mosquito have just been described. It will beremembered that the labrum is provided with a groove. Through this theblood or other food is sucked up by means of a strong-walled pumpingorgan, the pharynx, situated in the head (Fig. 70). Just back of thepharynx is the esophagus which leads to the beginning of the stomach. Close to its posterior end the esophagus gives off three foodreservoirs, two above and a single larger one below. In dissectionsthese will often be seen to be filled with minute bubbles. The stomachreaches from the middle of the thorax to beyond the middle of theabdomen. At its posterior end are given off five long slender processes, the Malpighian tubules which are organs of excretion, acting like thekidneys of higher animals. The hindgut is that portion of the intestinefrom the stomach to the end of the body. 

[Illustration: FIG. 68--Wing of Mosquito (_O. Lativittatus_). ]

[Illustration: FIG. 69--End of mosquito wing highly magnified to showthe scales on the veins. ]

[Illustration: FIG. 70--Diagram to show the alimentary canal andsalivary glands of a mosquito. ]

[Illustration: FIG. 71--Salivary glands of _Culex_ at right. _Anopheles_at left. (After Christophers. )]

THE SALIVARY GLANDS

Lying under the alimentary canal in the forward part of the thorax arethe salivary glands. There are two sets of these, each having threelobes with a common duct which joins the duct from the other set a shortdistance before they enter the base of the hypopharynx. Each of theselobes is made up of a layer of secreting cells (Fig. 71) which producesthe saliva that is poured into the wound as soon as the insect piercesthe skin of the victim, and we shall see, too, that the malarial germsalso collect in these glands to be carried by the saliva to the newhost. 

EFFECTS OF THE BITE

After a mosquito has bitten a person and withdrawn the stylets, a smallarea about the puncture whitens, then soon becomes pink and begins toswell, then to itch and burn. Some people suffer much more from thebites of mosquitoes than do others. For some such bites mean little orno inconvenience, indeed may pass wholly unnoticed, to others a singlebite may mean much annoyance, and several bites may cause muchsuffering. 

After an hour or so the itching usually ceases, but in some cases itcontinues longer. In some instances little or no irritation is feltuntil some hours, sometimes as much as a day, after the bite. In suchcases the effect of the bite is apt to be severe and to last for severaldays. Sometimes a more or less serious sore will follow a bite, probablydue to infection of the wound by scratching. It is doubtless the salivathat is poured into the wound that causes the irritation. It isfrequently asserted that if the mosquito is allowed to drink its filland withdraw its beak without being disturbed no evil results willfollow. Those who hold this theory say that the saliva that is pouredinto the wound is all withdrawn again with the blood if the mosquito isallowed to feed long enough. There may be some truth in this, but formost of us a bite means a hurt anyway and few will be content to sitperfectly still and watch the little pest gradually fill up on blood. 

It is not known just what the action of the saliva is, its compositionor reaction on the tissues. It is generally supposed to preventcoagulation of the blood that is to be drawn through the narrow tube ofthe labrum. Others think that its presence causes a greater flow ofblood to the wound. But the sad part of it is, for us at least, that ithurts and may cause malaria and possibly other diseases. 

HOW MOSQUITOES BREATHE

Mosquitoes and other insects do not have any nostrils nor do theybreathe through any openings on the head. Along the sides of the thoraxand abdomen is a series of very minute openings known as the spiracles. Through these the air passes into a system of air-tubes, the tracheæ. There are two main trunks or divisions of the tracheæ just inside thebody-wall and a number of shorter connecting trunks. From these largervessels arise a great number of smaller ones which branch and subdivideagain and again until all the tissues are supplied by these minutelittle air-tubes that carry the oxygen to all parts of the body andcarry off the waste carbon dioxid. These air-tubes are emptied andfilled by the contractions of the walls of the abdomen. When thebody-wall contracts the air is forced out of the thin-walled tracheathrough the spiracles; when the pressure is removed they are refilled bythe fresh air rushing in. 

THE BLOOD

After a mosquito has been feeding on a man or some other animal it isoften so distended that the blood shows rich and red through the thinsides of the walls of the abdomen. This, however, is the blood of thevictim and not of the mosquito. The blood of insects is not red but paleyellowish or greenish. It is not confined in definite vessels, but fillsall the space inside the body cavity that is not occupied by some of thetissues or organs. It bathes the walls of the alimentary canal andgathers there the nourishment which it carries to all parts of the body. It does not carry oxygen or collect the carbon dioxid as does the bloodof higher animals. That work, as we have just seen, is done by theair-tubes. Above the alimentary canal, extending almost the whole lengthof the abdomen and thorax, is a thin-walled pulsating vessel, the heart. This consists of a series of chambers each communicating with the one infront of it by an opening which is guarded by a valve. When one of thesechambers contracts it forces the blood that is in it forward into thenext chamber which, in its turn, sends it on. As the walls relax thevalves at the sides are opened and the blood that is in the body-cavityrushes in to fill the empty chamber. As these regular rythmicalpulsations recur the blood is forced forward through the heart into thehead where it bathes the organs there. We shall see in another chapterthat the malarial parasite escapes from the walls of the stomach of themosquito into the blood in the body-cavity and finally reaches thesalivary glands. As the heart is constantly driving blood to this partof the body the parasites readily reach the glands from which theyfinally escape into the new host. 

[Illustration: FIG. 72--Heads of Culicinæ mosquitoes; _a_, male; _b_, female. (After Manson. )]

[Illustration: FIG. 73--Heads of Anophelinæ mosquitoes; _c_, male; _d_, female. (After Manson. )]

[Illustration: FIG. 74--Wing of _Anopheles maculipennis_. ]

[Illustration: FIG. 75--Wing of _Theobaldia incidens_. ]

[Illustration: FIG. 76--A non-malarial mosquito (_T. Incidens_), male, standing on the wall. ]

[Illustration: FIG. 77--Female of same. ]

[Illustration: FIG. 78--A malarial mosquito (_A. Maculipennis_), male, standing on the wall. ]

[Illustration: FIG. 79--Female of same. ]

CLASSIFICATION

For our purpose it will not be necessary to try to give a system ofclassification of all the mosquitoes. Those interested in this phase ofthe subject will find several books and papers devoted wholly to it. Itis quite important, however, that we know something about a few of themore familiar groups and kinds, especially those concerned in thetransmission of diseases. 

THE ANOPHELES

In pointing out the differences between male and female mosquitoes wenoted that in one group, the genus _Anopheles_, both sexes have longmaxillary palpi (Figs. 72, 73). This is the most important characterseparating this genus from the other common forms and as the_Anopheles_ are the malaria carriers it is important that thisdifference be remembered. Most of the members of this group have spottedwings (Fig. 74), but as some other common kinds also have spotted wings(Fig. 75) this character will not always be reliable. When an_Anopheles_ mosquito is at rest the head and proboscis are held in oneline with the body and the body rests at a considerable angle to thesurface on which it is standing. Other kinds rest with the body almostor quite parallel to the surface on which they are standing. So if youfind a female mosquito with long mouth-palpi and spotted wings restingat an angle to the surface on which it stands you may be reasonably surethat it is an _Anopheles_ and therefore may be dangerous (Figs. 76, 77, 78, 79). 

In the United States there are three species of_Anopheles_--_maculipennis_, _punctipennis_ and _crucians_--which arecommon in various localities, and one or two other species that so faras known are local or rare. 

The _Anopheles_ eggs are not laid in masses as are the eggs of manyother mosquitoes, but are deposited singly on the surface of the waterwhere they may be found often floating close together. 

[Illustration: FIG. 80--Egg of Anopheles, side view. (After Nuttall andShipley. )]

[Illustration: FIG. 81--Egg of Anopheles, dorsal view. (After Nuttalland Shipley. )]

[Illustration: FIG. 82--Anopheles larvæ, the one to the right feeding. ]

[Illustration: FIG. 83--Anopheles larvæ, the one to the right feeding, the other just coming to the surface. ]

[Illustration: FIG. 84--Anopheles larva, dorsal view. ]

[Illustration: FIG. 85--Anopheles pupæ resting at surface of water. ]

The eggs (Figs. 80, 81) are elliptical in outline and are provided witha characteristic membranous expansion near the middle. 

The larvæ may be found at the proper season and in the localities wherethey are abundant in almost any kind of standing water, in clear littlepools beside running streams, in the overflow from springs, in swampsand marshy lands, in rain-barrels or any other places or vessels wherethe water is quiet. They do not breed in brackish water. As they feedlargely on the algæ or green scum on the surface of the water they areespecially apt to be found where this is present. We have already notedthat their positions in the water differ from that assumed by otherspecies (Fig. 82). 

As the breathing-tube is very short the larvæ must come close to thesurface to breathe, and when they are feeding we find them lying justunder and parallel to the surface of the water with their curious roundheads turned entirely upside down as they feed on the particles that arefloating on the surface (Figs. 83, 84). 

The pupæ do not differ very much from the pupæ of other species althoughthe breathing-tubes on the thorax are usually shorter and the creatureusually rests with its abdomen closer to the surface, that is, it doesnot hang down from the surface quite as straight as do other forms (Fig. 85). 

The adults may be found out of doors or in houses, barns or otheroutbuildings. They do not seem to like a draft and consequently will bemore apt to frequent rooms or places where there is little circulationof air. Although they are usually supposed to fly and bite only in theevening or at night, they may occasionally bite in the daytime. Onehungry female took two short meals from my arm while we were trying toget her to pose for a photograph one warm afternoon. 

The female passes the winter in the adult condition, hibernating in anyconvenient place about old trees or logs, in cracks or crevices in doorsor out of doors. In the house they hide in the closets, behind thebureau, behind the head of the bed, or underneath it, or in any placewhere they are not apt to be disturbed. During a warm spell in thewinter or if the room is kept warm they may come out for a meal almostany time. 

THE YELLOW FEVER MOSQUITO

Ranking next in importance to _Anopheles_ as a disseminator of diseaseand in fact solely responsible for a more dreaded scourge, is thespecies of mosquito now known as _Stegomyia calopus_. While this speciesis usually restricted to tropical or semi-tropical regions it sometimesmakes its appearance in places farther north, especially in summertime, where it may thrive for a time. The adult mosquito (Fig. 104) isblack, conspicuously marked with white. The legs and abdomen are bandedwith white and on the thorax is a series of white lines which inwell-preserved specimens distinctly resembles a lyre. These mosquitoesare essentially domestic insects, for they are very rarely found exceptin houses or in their immediate vicinity. Once they enter a room theywill scarcely leave it except to lay their eggs in a near-by cistern, water-pot, or some other convenient place. 

Their habit of biting in the daytime has gained for them the name of"day mosquitoes" to distinguish them from the night feeders. But theywill bite at night as well as by day and many other species are not atall adverse to a daylight meal, if the opportunity offers, so this habitis not distinctive. The recognition of these facts has a distinctbearing in the methods adopted to prevent the spread of yellow fever. There are no striking characters or habits in the larval or pupal stagesthat would enable us to distinguish without careful examination thisspecies from other similar forms with which it might be associated. Forsome time it was claimed that this species would breed only in cleanwater, but it has been found that it is not nearly so particular, someeven claiming that it prefers foul water. I have seen them breeding incountless thousands in company with _Stegomyia scutellaris_ and _Culexfatigans_ in the sewer drains in Tahiti in the streets of Papeete. Asthe larvæ feed largely on bacteria one would expect to find them inexactly such places where the bacteria are of course abundant. 

The fact that they are able to live in any kind of water and in a verysmall amount of it well adapts them to their habits of living aboutdwellings. 

So far as known the members of these two genera are the only two thatare concerned in the transmission of disease in the United States. Inother countries other species are suspected or proven disseminators ofcertain diseases, but these will be discussed in connection with theparticular diseases in later chapters. 

OTHER SPECIES

The many other species of mosquitoes that we have may be convenientlydivided as to their breeding-habits into the fresh-water and thebrackish-water forms. Among the fresh-water kinds some are foundprincipally associated with man and his dwelling places, others live inthe woods or other places and so are far less troublesome. Most ofthese do not fly far. Several of the species that breed in brackishwater are great travelers and may fly inland for several miles. Thus thetowns situated from one to three or four miles inland from the lowerreaches of San Francisco Bay are often annoyed more by the mosquitoesthat breed only in the brackish water on the salt marshes than they areby any of the fresh-water forms (Figs. 86, 87). The worst mosquito pestalong the coast of the eastern United States and for some distanceinland is a species that breeds in the salt marshes. 

NATURAL ENEMIES OF MOSQUITOES

In combating noxious insects we learned long ago that often the mostefficient, the easiest and cheapest way is to depend on their naturalenemies to hold them in check. Under normal or rather natural conditionswe find that they are usually kept within reasonable bounds by theirnatural enemies, but under the artificial conditions brought about bythe settling and developing of any district great changes come about. Itvery often happens that these changes are favorable to the developmentof the noxious insects and unfavorable to the development of theirenemies. 

A striking example and one to the point is afforded in the introductionof mosquitoes into Hawaii. Up to 1826 there were no mosquitoes on theseislands. It is supposed that they were introduced about that time bysome ships that were trading at the islands. Indeed it is claimed thatthe very ship is known that brought them over from Mexico. 

Once introduced they found conditions there very favorable to theirdevelopment, plenty of standing water and few natural enemies to prey onthem, so they increased very rapidly and gradually spread over all theislands of the group. This was the so-called night mosquito, _Culexpipiens_. Much later another species, _Stegomyia calopus_, just asannoying and much more dangerous was introduced and has also become verytroublesome. We have a few species of top-minnows (Fig. 88) occurring insluggish streams in the southern part of the United States that areimportant enemies of the mosquitoes of that region. A few years ago someof these were taken over to Hawaii and liberated in suitable places tosee if they would not help solve the mosquito problem there. The fishesseem to be doing well. Already they are destroying many mosquito larvæ, and there are indications that they are going to do an important work, but of course can be depended on only as an aid. 

[Illustration: FIG. 86--Salt-marsh mosquito (_Ochlerotatuslativittatus_); male. ]

[Illustration: FIG. 87--Salt-marsh mosquito (_O. Lativittatus_);female. ]

[Illustration: FIG. 88--Top-minnow (_Mollienisia latipinna_). (FromBull. , 47 U. S. Fish Com. )]

[Illustration: FIG. 89--Dragon-flies. (From Kellogg's Amer. Insects. )]

On account of the various habits of both the larvæ and adults it willnever be possible for any natural enemy or group of natural enemieseffectively to control the mosquitoes of any region, but as certain ofthem are important as helpers they deserve to be mentioned. 

ENEMIES OF THE ADULTS

Birds devour a few mosquitoes, the night-flying forms being particularlyserviceable, but the number thus destroyed is probably so small as to beof little practical importance. 

The dragon-flies (Figs. 89, 90, 91) or mosquito hawks have long beenknown as great enemies of mosquitoes, and they certainly do destroy manyof them as they are hawking about places where mosquitoes abound. Dr. J. B. Smith of New Jersey very much doubts their efficiency, butobservations made by other scientific men would seem to indicate thatthey often devour large numbers of mosquitoes during the course of theday and evening. 

Spiders and toads destroy a few mosquitoes each night. Certain externaland internal parasites destroy a few more, but the sum total of all ofthese agencies is probably not very considerable, for while the adultsmay have several natural enemies they are not of sufficient importanceto have any appreciable effect on the number of mosquitoes in a badlyinfested region. 

ENEMIES OF THE LARVÆ AND PUPÆ

The larvæ and pupæ on the other hand have many important enemies. Indeedunder favorable conditions these may keep small ponds or lakes quitefree from the pests. The predaceous aquatic larvæ of many insects feedfreely on wrigglers. The larvæ of the diving beetles which are known aswater-tigers are particularly ferocious and will soon destroy all thewrigglers in ponds where they are present (Fig. 92). Dragon-fly larvæalso feed freely on mosquito larvæ. Whirligig beetles are said to beparticularly destructive to _Anopheles_ larvæ and many other insectssuch as water-boatmen, back-swimmers, etc. , feed on the larvæ of variousspecies. A few of these introduced into a breeding-jar with _Anopheles_larvæ will soon destroy all of them, even the very young bugs attackinglarvæ much larger than themselves. 

It is interesting to note that the larvæ of some mosquitoes arethemselves predaceous and feed freely on the other wrigglers that maychance to be in the same locality. 

[Illustration: FIG. 90--The young (nymph) of a dragon-fly. (FromKellogg's Amer. Insects. )]

[Illustration: FIG. 91--The cast skin (exuvæ) of a dragon-fly nymph. ]

[Illustration: FIG. 92--Diving-beetles and back-swimmers. (FromKellogg's Amer. Insects. )]

Various species of fish are, however, the most important enemies of themosquitoes. Great schools of tide-water minnows (Fig. 93) are oftencarried over the low salt-marshes by the extreme high-tides and left inthe hundreds of tide pools as the tide recedes. No mosquitoes can breedin a pool thus stocked with these fish. In the fresh-water streams andlakes there are several species of the top-minnows, sticklebacks (Fig. 94), etc. , that feed voraciously on mosquito larvæ and unless the grassor reeds prevent the fish from getting to all parts of the ponds orlakes very few mosquitoes can breed in places where they are present. 

Minute red mites such as attack the house-flies and other insectssometimes attack adult mosquitoes, but they are rarely very abundant. Parasitic roundworms attack certain species. Others suffer more or lessfrom the attacks of various Sporozoan parasites. 

FIGHTING MOSQUITOES

When mosquitoes are bothering us we usually begin by trying to kill theindividual pests that are nearest to us. We try to crush them if theybite us; we screen the doors and windows to keep them from the house. Inwarmer countries the people are a little more hospitable and do notscreen the mosquitoes out of the house entirely, but screen the beds forprotection at night, and if the mosquitoes get too insistent during theday the bed makes a safe and comfortable retreat. All the mosquitoes ina room may be killed by fumigating with sulphur at the rate of twopounds to the thousand cubic feet of air-space. Pyrethrum is also usedlargely, but it only stupefies the mosquitoes temporarily instead ofkilling them. While in that condition they may be swept up anddestroyed. 

Various substances are sometimes used as repellants by those who must bein regions where the mosquitoes are abundant. With many of these, however, "the cure is worse than the disease. " Smudges are often builtto the windward of a house or barn-yard and the smoke from a goodsmoldering fire will keep a considerable area quite free frommosquitoes. The man who can keep himself enveloped in a cloud of tobaccosmoke will not be bothered by mosquitoes. Oil of pennyroyal, oil of taror a mixture of these with olive oil, and various other concoctions aresometimes smeared over the face and hands. These will furnish protectionas long as they last. Dr. Smith says that he has found oil of citronellaquite effective and of course less objectionable than the other thingsusually used. Care should be taken not to get it in the eyes. Anointment made of cedar oil, one ounce; oil of citronella, two ounces;spirits of camphor, two ounces, is said to make a good repellant and iseffective for a long time. 

[Illustration: FIG. 93--Killifish (_Fundulus heteroliatus_). (FromBull. 47, U. S. Fish Com. )]

[Illustration: FIG. 94--Stickleback (_Apeltes quadracus_). (From Bull. 47, U. S. Fish Com. )]

[Illustration: FIG. 95--An old watering trough, an excellentbreeding-place for mosquitoes. ]

FIGHTING THE LARVÆ

All of the efforts directed against the adult mosquitoes are usually oflittle avail in decreasing the number in any region. It is comparativelyeasy, however, to fight them successfully in the larval stage. We haveseen that standing water is absolutely necessary for mosquitoes to breedin. This makes the problem much simpler than if they could breed in anymoist places such as well-sprinkled lawns, a shady part of the garden, etc. The whole problem of successful campaigns against the mosquitoesresolves itself into the problem of finding and destroying or properlytreating their breeding-places. We have seen how certain kinds, such asthe yellow fever mosquito, are "domestic" species. They never go farfrom their breeding-places. If a house is infected by one of thesespecies the immediate premises should be searched for the source. Cisterns, rain-barrels, sewer-traps, cesspools, tubs or buckets of wateror old tin cans in out-of-the-way corners, are all suitable places forthem to breed in. Cisterns and rain-barrels should be thoroughlyscreened so that no mosquitoes can get in or out, or the surface shouldbe covered with a film of kerosene which will kill all the larvæ in thewater when they come to the surface to breathe, and will also kill thefemales when they come to deposit their eggs. The vent to open cesspoolsshould be thoroughly screened or the surface of the water kept wellcovered with oil. Water standing in any vessels in the yards should beemptied every week or ten days and the old tin cans destroyed or hauledaway. In fighting these domestic species you need be concerned only withyour own yard and that of your near-by neighbors. Other species, whilealso rather local in their distribution, fly much farther than thereally domestic ones. In fighting these the region for a considerabledistance around must be taken into consideration. Watering-troughs (Fig. 95) that are left filled from week to week, the overflow from suchplaces, and the tracks made in the mud round about them (Fig. 96), smallsluggish streams, irrigating ditches, and small ponds or lakes notsupplied with fish are excellent breeding-places for several species ofmosquitoes including _Anopheles_ and others. The remedy at once suggestsitself. The watering-trough can be emptied and renewed every week duringthe summer time, the overflow can be taken care of in a ditch that willlead it away from the trough to where it will sink into the ground, thebanks of the streams or ponds or lakes can be cleared in such a way thatfish can get to all parts of the water; most of the small ponds can bedrained or their surface may be covered over with a thin film ofkerosene. This is best applied as a spray; one ounce to fifteen squarefeet will suffice. If the oil is simply poured over the surface morewill be required. 

The fighting of the species that breed on the extensive salt-marshes inmany regions is a larger and more difficult problem, but as it is amatter that usually concerns large communities, sometimes whole states, it can be dealt with on a larger scale. The very excellent results thathave been accomplished in New Jersey and on the San Francisco peninsula, and in a smaller way in other places, show what may be done if thecommunity goes about the fight in an intelligent manner. In the fight inNew Jersey hundreds of acres of tide-lands have been drained so thatthey no longer have tide pools standing where the mosquitoes may breed. When it is impracticable to drain them the pools may be sprayedoccasionally with kerosene. 

The value of the land that is reclaimed by a good system of draining isoften enough to pay many times over the cost of draining, thus themosquitoes are gotten rid of and the land enhanced in value by a singleoperation. 

CHAPTER VII

MOSQUITOES AND MALARIA

Ever since the beginning of history we have records of certain feversthat have been called by different names according to the people thatwere affected. As we study these names and the various writingsconcerning the fevers we find that a great group of the most importantof them are what we to-day know as malarial fevers. Not only are theseills as old as history but they have been observed over almost theentire inhabited earth. There are certain regions in all countries wheremalaria does not occur, but almost always it will be found that otherregions near by are infected and it very often happens that theseinfected regions are the most profitable parts of the land, the placeswhere water is plentiful and vegetation is luxuriant. Indeed thecoincidence of these two things, low-lying lands with an abundance ofwater, particularly standing water, and malaria has always been notedand gave rise to the earliest theories in regard to the cause of thedisease. 

For instance, we find some of the very early writers emphasizing thepoint that swampy localities should be avoided for they produce animalsthat give rise to disease, or that the air is poisoned by the breath ofthe swamp-inhabiting animals. 

These views of the origin of the fever prevailed until about thebeginning of the eighteenth century when the recently discoveredmicroscope began to reveal the various kinds of animalculæ to be foundin decaying material. 

In 1718 Lancisi held that the myriads of insects, particularly gnats ormosquitoes, that arose from such swampy regions might carry some ofthese poisonous substances and by means of their proboscis introducethem into the bodies of the people, and although he had made noexperiments to test the assumption he did not consider it impossiblethat such insects might also introduce the smallest animalculæ into theblood. It took almost two centuries of study and investigation beforethis guess was proved to be right. 

One reason why the mosquitoes were not earlier associated with thesediseases was that all who investigated the matter at all turned theirattention to the bad condition of the air in these swampy regions. Malaria means bad air. We all know that we can see the mists arisingfrom such regions, particularly in the evening or at night, and asexposure to these mists very often meant an attack of malaria they werenaturally supposed to be the cause of the disease. So for a long timethe whole attention of investigators was turned toward studying andanalyzing these vapors, and various experiments were made which seemedto show conclusively that the malaria was caused only by theseemanations. The investigations even went so far that the exact germsthat were supposed to cause the fever were separated and experimentedwith. 

THE PARASITE THAT CAUSES MALARIA

The blood had been studied time and again and the characteristicappearance of the blood of a malarial patient was well known. In 1880Laveran, a French army surgeon in Algiers, began to study the blood ofsuch patients microscopically and soon was able to demonstrate theparasite that caused the disease. His discoveries were not readilyaccepted, but other investigations soon confirmed his observations andthe fact was gradually firmly established. Not until recently, however, did this distinguished physician receive a full recognition of his work. A few years ago he was awarded the Nobel prize for medicine, perhaps thehighest honor that can be bestowed on any physician. It is interesting, too, to note in this connection that it was another French surgeon whoin 1840 discovered that sulphate of quinine is a specific for malaria. 

[Illustration: FIG. 96--Horse and cattle tracks in mud filled withwater; good breeding-places for Anopheles. ]

[Illustration: FIG. 97--A malarial mosquito (_Anopheles maculipennis_);male. ]

[Illustration: FIG. 98--A malarial mosquito (_A. Maculipennis_);female. ]

The next important step was made in 1885 by Golgi, an Italian, whostudied the life-history of the parasite in the blood and distinguishedthe three forms which cause the three most familiar kinds of malarialfevers, the tertian, the quartan and the remittent types. From this timeon this parasite has been studied by physicians of many nationalitiesand the whole course of its life-history worked out. In order that wemay understand how it was that mosquitoes were determined to be themeans of disseminating this parasite we will discuss first itslife-history in the human blood. 

The parasites that cause the malarial fevers are Sporozoans and belongto the genus _Plasmodium_. Other names such as _Hæmamoeba_ and_Laverania_ have been used for them, but the term _Plasmodium_ is theone now most commonly employed. The three most common species are_vivax_, _malariæ_ and _falciparum_, causing respectively the tertian, quartan and remittent fevers. 

LIFE-HISTORY OF PARASITE

The life-history of all of these is very similar, the principaldifference being in the length of time it takes them to sporulate. Letus begin with the parasite after it has been introduced into the bloodand trace its development there. At first it is slender and rod-like inshape. It has some power of movement in the blood-plasm. Very soon itattacks one of the red blood-corpuscles and gradually pierces its waythrough the wall and into the corpuscle substance (Fig. 99); here itbecomes more amoeboid and continues to move about, feeding all thetime on the corpuscle substance, gradually destroying the whole cell. Asthe parasite feeds and grows there is deposited within its body ablackish or brownish pigment known as melanin. 

During the time that the parasite is feeding and growing it is alsogiving off waste products, as all living forms do in the process ofmetabolism, but as the parasite is completely inclosed in the corpusclewall these waste products cannot escape until the wall bursts open. After about forty hours if the parasite is _vivax_ or about sixty-fivehours if it is _malariæ_ it becomes immobile, the nucleus divides againand again and the protoplasm collects around these nuclei, forming anumber of small cells or spores, as they are called. In aboutforty-eight or seventy-two hours, depending on whether the parasite is_vivax_ or _malariæ_ the wall of the corpuscle bursts and all thesespores with the black pigment and the waste products that have beenstored away within the cell are liberated into the blood-plasm. 

[Illustration: FIG. 99--Diagram to illustrate the life-history of themalarial parasite. 1 is a red blood-corpuscle, 2 to 7 shows thedevelopment of the parasite in the corpuscle, _a_ _b_ _c_ _d_ and _aŽ__bŽ_ _cŽ_ and _e_ the development of the parasite in the stomach of themosquito, _f_ _g_ _h_ _i_ the development in the capsule on the outerwall of the stomach of the mosquito, _k_ in the salivary gland. ]

[Illustration: FIG. 100--Malarial mosquito (_A. Maculipennis_) on thewall. ]

[Illustration: FIG. 101--Malarial mosquito (_A. Maculipennis_) standingon a table. ]

These spores are round or somewhat amoeboid and are carried in theblood for a short time. Very soon, however, each one attacks a new redcorpuscle and the process of feeding, growth and spore-formationcontinues, taking exactly the same time for development as in the firstgeneration, so every forty-eight hours in the case of the _vivax_, andevery seventy-two hours in the case of the _malariæ_ a new lot of thesespores and the accompanying waste products are thrown out into theblood. Thus in a very short time many generations of this parasite occurand thousands or hundreds of thousands of the red-blood corpuscles aredestroyed, leaving the patient weak and anemic. It will be seen, too, that the recurrence of the chills and fevers is simultaneous with theescaping of the parasites from the blood-corpuscles, together with thewaste products of their metabolism. 

These waste products are poisonous, and it is believed that this greatamount of poison poured into the blood at one time causes the regularrecurring crisis. Zoölogists well know that this process of asexualreproduction, _i. E. _, reproduction without any conjugation of twodifferent cells, cannot go on indefinitely, and those who were studyingthe life-cycle of these parasites were at a loss to know where thesexual stage took place. In the meantime studies of other parasites moreor less closely related to _Plasmodium_ showed that the sexual stageoccurred outside the vertebrate host. The remarkable work of Dr. Smithon the life-history of the germ that causes the Texas fever of cattlehad a strong influence in directing the search for this other stage ofthe malarial parasite. Another thing that indicated that this sexualgeneration must take place outside the body of the vertebrate host wasthe fact that the investigators found that the parasites in certain ofthe cells did not sporulate as did the others. When these individualswere drawn from the circulation and placed on a slide for study it wasfound that they would swell up and free themselves from the inclosingcorpuscle and some of them would emit long filaments which would dartaway among the corpuscles. 

Many men have worked on this problem, but perhaps the most credit forits solution will always be given to Sir Patrick Manson, the foremostauthority on tropical diseases, and to Ronald Ross, a surgeon in theEnglish army. There is no more interesting and inspiring reading thanthat which deals with the development of the hypothesis by Manson andthe persistent faith of Ross in the correctness of this theory, and hiscontinuous indefatigable labors in trying to demonstrate it. It was animportant piece of scientific work, and shows what a man can do evenwhen the obstacles seem insurmountable. 

THE PARASITE IN THE MOSQUITO

Briefly stated again, the problem was this: We have here a parasite inthe blood which behaves as do many other forms of life. Some of theseparasites do not go on with their development until they are removedfrom the circulation. Now, how are they thus removed from thecirculation under normal conditions? This must first be solved beforethe still greater and more important problem of how the parasite getsfrom one human host to another can be taken up. In studying this overManson reasoned that certain suctorial insects were the agencies throughwhich blood was most commonly removed from the circulation and heventured the guess that this change in the parasite that may be seentaking place on the slide under the microscope, normally takes place inthe stomach of some insect that sucks man's blood. Ross was greatlyimpressed with the theory and began his long and apparently hopelesstask of finding these parasites in the stomach of some insect. When weremember that they are so minute that they can only be seen by the useof the highest power of the microscope we can realize something of themagnitude of the task. Ross, who was at that time stationed in India, selected the mosquito as the most likely of the insects to be the hostthat he was looking for. For over two and one-half years he worked withentirely negative results, for after examining thoroughly many thousandsof mosquitoes he found no trace of the parasite. 

Practically all his work was done on the most common mosquito of theregion, a species of _Culex_. But one day a friend sent him a differentmosquito, one with spotted wings, and in examining it he was interestedto note certain oval or round nodules on the outer walls of the stomach. On closer examinations he found that each of these nodules contained afew granules of the coal-black melanin of malarial fever. Furtherstudies and experiments showed that these particular cells could alwaysbe found in the walls of the stomach of this particular species ofmosquito a few days after it had bitten a malarial patient. Thisepoch-making discovery was made in 1898. Ross was detailed by theEnglish government to devote his whole time to the further solution ofthe problem, and after two years more of careful experimentation andstudy was able to give a complete life-history of this parasite. Hisexperiments have been repeated many times, and the conclusions hearrived at are as undeniable as any of the known facts of science. 

The whole life-history as we now know it can be summed up as follows:The parasites develop within the circulation but certain of them seem towander about and do not go on with their development there. When theseparticular parasites are taken into the stomach of most mosquitoes theyare digested with the rest of the blood. But when they are taken intothe stomach of a mosquito belonging to the genus _Anopheles_ or otherclosely related genera they are not digested but go on with theirdevelopment, conjugation and fertilization taking place, resulting in amore elongated form which makes its way through the walls of the stomachon the outside of which are formed the little nodules discovered by Rosson his mosquitoes. Within these nodules further division and developmenttakes place until finally the nodule is burst open and many thousandminute rod-like organisms, sporozoites, are turned loose into thebody-cavity of the mosquito. Owing to some unknown cause these littleorganisms are gathered together in the large vacuolated cells of thesalivary glands of the mosquito, and when the mosquito bites a man orany other animal they pour down through the ducts with the secretion andare thus again introduced in the circulation. 

The nodules or cysts on the walls of the stomach of the mosquito maycontain as many as ten thousand sporozoites, and as many as five hundredcysts may occur on a single stomach. 

It takes ten, twelve or more days from the time the parasites are takeninto the stomach of the mosquito before they can go through theirtransformations and reach the salivary gland, the time depending on thetemperature. So it is ten or twelve days or sometimes as much aseighteen or twenty days from the time an _Anopheles_ bites a malarialpatient before it is dangerous or can spread the disease. On the otherhand, the sporozoites may lie in the salivary gland alive and virulentfor several weeks. It does not give up all the parasites at one time, sothat three or four or more people may be affected by a single mosquito. 

It is well known that two parasites may often be seen in the samecorpuscle. This is often simply a case of multiple infection, but Dr. Craig has very recently shown that under certain conditions twoindividuals may enter the same corpuscle and conjugate and the resultingindividual will be resistant to quinine and may remain latent in thespleen or bone marrow for a long time. Under favorable conditions itmay again begin the process of multiplication and the patient willsuffer a relapse. 

SUMMARY

Now let us sum up some of the reasons why we believe that the malariafever can be transmitted only through the agency of mosquitoes. First, we know the life-history of the parasite, it has been studied in both ofits hosts. Attempts have been made to rear it in other hosts but withoutavail, and we know from the general relations of the parasite that itmust have this sexual as well as the asexual generations. Second, insome regions which would seem to be malarial, that is, where themiasmatic mists arise, no malaria occurs. Why? Usually it can bedefinitely shown that no _Anopheles_ occur there. Other mosquitoes maybe there in abundance, but if no _Anopheles_, there is no malaria. Incertain regions this is well demonstrated. The west coast of Africa isone of the worst pest-holes of malaria and _Anopheles_. The east coasthas no malaria and no _Anopheles_. In many islands the same conditionexists. On the other hand, the Fiji Islands have _Anopheles_ but nomalaria. No malaria has ever been introduced there to infect themosquitoes. In the same way _Stegomyia_ occurs in some of the South Seaislands and yet there is no yellow fever there. 

EXPERIMENTS

We may review, too, a few of the classic experiments that have served toshow that malaria can be contracted in no other way than through thebite of the mosquito. 

For many years Grassi, an Italian, devoted almost his whole time to thestudy of malaria. In 1900 he received permission from the government toexperiment on the employees of a piece of railroad that was being builtthrough a malarial region. This was divided for the purpose of theexperiment into three sections, a protected zone in the middle and anunprotected zone at each end. 

Those working in the protected zone had their houses completely screenedand no one was allowed out of doors after sunset except they wereprotected with veils and gloves. Early in the season they were all givendoses of quinine to prevent auto-infection. In the unprotected zone noscreens were used and every one was allowed to go without specialprotection. The result for the summer was that there were no new casesof fever in the protected zone. In the unprotected zones practically allhad the fever as usual. 

[Illustration: FIG. 102--Salt-marsh mosquito (_O. Lativittatus_)standing on a table. ]

[Illustration: FIG. 103--Anopheles hanging from the ceiling. ]

In the same year two English physicians, Sambon and Low, went to Italywhere they built a cabin in one of the marshes noted as being a malariapest-hole. The house was thoroughly screened so that no mosquitoes couldenter, but the windows were always open so as to admit the air freelyday and night. Here they lived for three months, out of doors as much asthey pleased during the day but inside where they were protected fromthe mosquitoes at night. No quinine was used and no fever developed, although all about them other people were having the fever as usual. 

Another English physician who had not been in malarial regions allowedhimself to be bitten by infected mosquitoes sent from a malariallocality. In due time he developed the fever. Many other experimentsmade in various places might be cited. The results have all beenpractically the same. To-day the soldiers of many civilized nations arerequired to protect themselves from mosquitoes because it has been foundthat it pays. Disease has always been a worse terror than bullets in anywar, and we are fast learning that the great loss from diseasesheretofore considered unavoidable may be very largely eliminated byproper sanitary arrangements and protection from noxious insects. 

CHAPTER VIII

MOSQUITOES AND YELLOW FEVER

Yellow fever is a disease, principally of seaport towns, from which theUnited States has suffered more than any other country. It is endemiconly in tropical regions but is often carried to subtropical, sometimeseven to temperate zones where, if the proper mosquitoes exist, it mayrage until frost. 

Vera Cruz, Havana, Rio de Janeiro, and the west coast of Africa werelong regarded as permanent endemic foci, the disease appearing there inepidemic form from time to time, often spreading to other ports in moreor less close communication with such places. In the United States theGulf states have been the greatest sufferers from the disease, althoughit has spread as far as Baltimore, Philadelphia and Washington, where atrare intervals it was most serious, abating its ravages only when frostcame. 

The last severe outbreak occurred in New Orleans in 1905 when eightthousand cases and nine hundred deaths occurred. At that time there waswaged one of the most remarkable warfares against death in its mostterrifying form that the world has ever known. And, thanks to theachievements of science, particularly to the investigations of threemen, one of whom gave his life to the cause, the fight was successfuland this dreadful outbreak was checked just at the time when accordingto all precedent it should have been at its height. 

This result which at other times and under other conditions would havebeen considered miraculous was achieved not by the usual custom ofisolation, quarantine, etc. , but by a direct, we may almost say hand tohand, conflict with mosquitoes: the mosquitoes belonging to a particulargenus and species, _Stegomyia calopus_ (_fasciata_). 

Before taking up a discussion of this achievement in New Orleans let usconsider first the work of the men that made such results possible. 

For many years the cause and methods of dissemination of this diseasehad been a puzzle to physicians and scientists. Very early it wasbelieved that it might be transmitted through the air, and the fact thatinfection usually occurred in the vicinity of the water and in thetropics or in midsummer led to the belief that the disease was due tofermentation. This theory received strong support in the fact thatserious outbreaks of the fever often followed the coming into port ofvessels from the tropics with the water in their holds in an offensivecondition. When it was discovered that bacteria were the cause offermentation and also of many diseases this theory was consideredabundantly proven. From time to time, announcements have been made thatthe particular species of bacteria that causes the disease has beenisolated, but there has always been something lacking in the finalproof. 

Yellow fever has always been regarded as a very highly contagious aswell as infectious disease, and the utmost precaution has been taken toisolate the patients when possible and in recent years strictquarantines have been established against infected localities and noperson or commerce or even the mails were allowed to come from suchplaces without thorough fumigations. But all these things provedunsatisfactory. The disease could not ordinarily be checked by simplyisolating the patients. Many people became sick without ever having beennear a yellow fever patient, while others worked in direct daily contactwith the disease and did not suffer from it. Those who had once had itand recovered became practically immune, rarely suffering from a secondattack. Negroes may suffer from the disease, but are usually regarded aspractically immune. 

[Illustration: FIG. 104--Yellow-fever mosquito (_Stegomyia calopus_). (R. Newstead, del. )]

It was early observed, too, that the danger zone might be quite welldefined and that outside this zone one would be safe. More than acentury ago the British troops and other inhabitants of Jamaica foundthat by retreating to the mountains during the warm weather thenon-immunes could escape the fever. It was also observed that those whoslept on the first floor were more apt to take the disease than those onthe second floor. 

THE YELLOW FEVER COMMISSION

In 1900, during the American occupation of Cuba, yellow fever becamevery prevalent there. A board of medical officers was ordered to meet inHavana for the purpose of studying the disease under the favorableopportunities thus afforded. This board, which came to be known as theYellow Fever Commission, was composed of Drs. Walter Reed, JamesCarroll, Jessie W. Lazear and Aristides Agramonte of the United StatesArmy. Agramonte was a Cuban and an immune, the others were non-immunes. Dr. Manson in his lectures on Tropical Medicines says of them:

 "I cannot pass on, however, to what I have to say in connection with this work without a word of admiration for the insight, the energy, the skill, the courage, and withal the modesty and simplicity of the leader of that remarkable band of workers. If any man deserved a monument to his memory, it was Reed. If any band of men deserve recognition at the hands of their countrymen, it is Reed's colleagues. "

Their first work was to determine whether any of the germs that had beenclaimed to be the cause of yellow fever were really responsible for thedisease. _Bacillus icteroides_ that for some time and by someinvestigators had been named as the offender was particularlyinvestigated, but was proved to be a secondary invader only. 

Dr. Charles Finlay of Havana had been claiming for some years that theyellow fever was transmitted by means of the mosquito and possibly byother insects also. He even claimed to have proved this theoryexperimentally. We know now, however, that there must have been errorsin his experiments and that his patients became infected from sourcesother than those he was dealing with. 

The Yellow Fever Commission decided to put this theory to the test andsecured a number of volunteers for the experiments. The first thing wasto let an infected mosquito bite some non-immune person. How this wasdone and the results, may be told in Dr. Carroll's own words. 

EXPERIMENTS

 "Two separate lines of work now presented: one, the study of the bacterial flora of the intestine and anaërobic cultures from the blood and various organs; the other, the theory of the transmission of the disease by the mosquito, which had been advanced by Dr. Carlos Finlay in 1881. After due consideration it was decided to investigate the latter first. Then arose the question of the tremendous responsibility involved in the use of human beings for experimental purposes. It was concluded that the results themselves, if positive, would be sufficient justification of the undertaking. It was suggested that we subject ourselves to the same risk and this suggestion was accepted by Dr. Reed and Dr. Lazear. It became necessary for Dr. Reed to return to the United States and the work was begun by Dr. Lazear, who applied infected mosquitoes to a number of persons, himself included, without result. On the afternoon of July 27, 1900, I submitted myself to the bite of an infected mosquito applied by Dr. Lazear. The insect had been reared and hatched in the laboratory, had been caused to feed upon four cases of yellow fever, two of them severe, and two mild. The first patient, a severe case, was bitten twelve days before; the second, third and fourth patients had been bitten six, four and two days previously, and were in character mild, severe and mild respectively. In writing to Dr. Reed that night of the incident, I remarked jokingly that if there was anything in the mosquito theory, I should have a good dose. And so it happened. After having slight premonitory symptoms for two days, I was taken sick on August 31, and on September 1, I was carried to the yellow fever camp. My life was in the balance for three days, and my chart shows that on the fifth, sixth and seventh days my urine contained eighth-tenths and nine-tenths of moist albumin. On the day I was taken sick, August 31, 1900, Dr. Lazear applied the same mosquito, with three others, to another individual who suffered a comparatively mild attack and was well before I had left my bed. It so happened that I was the first person in whom the mosquito was proved to convey the disease. 

 "On the eighteenth of September, five days after I was permitted to leave my bed, Dr. Lazear was stricken, and died in convulsions just one week later, after several days of delirium with black vomit. Such is yellow fever. 

 "He was bitten by a stray mosquito while applying the other insects to a patient in one of the city hospitals. He did not recognize it as a _Stegomyia_, and thought it was a _Culex_. It was permitted to take its fill and he attached no importance to the bite until after he was taken sick, when he related the incident to me. I shall never forget the expression of alarm in his eyes when I last saw him alive in the third or fourth day of his illness. The spasmodic contractions of his diaphragm indicated that black vomit was impending, and he fully appreciated their significance. The dreaded vomit soon appeared. I was too weak to see him again in that condition, and there was nothing that I could do to help him. 

 "Dr. Lazear left a wife and two young children, one of whom he had never seen. "

These experiments and many others like them conducted on soldiers andSpanish immigrants proved that this particular mosquito would transmitthe disease under certain conditions. 

1. The mosquito must bite the patient during the first three days of thefever; after that a yellow fever patient cannot infect a mosquito. 

2. A period of twelve days must elapse before the mosquito is able toinfect another person. After that she may infect anyone she may bite;that is, the germs remain virulent during the rest of the mosquito'slife. The French Yellow Fever Commission working in Rio de Janeiro claimthat the first generation of offspring from such an infected mosquito iscapable of causing the disease after they are fourteen days in the adultcondition. 

The next step was to ascertain whether the disease could be contractedin any other way than by the bites of infected mosquitoes. A camp namedCamp Lazear was established and the following tests made: Amosquito-proof building of one room was completely divided by a wirescreen from floor to ceiling. In one room fifteen mosquitoes that hadpreviously bitten yellow fever patients and had undergone the properperiod of incubation were liberated. In this room a non-immune exposedhimself so that he was bitten by several of the insects. A little laterthe same day and again the next day the mosquitoes were allowed to feedon him for a few minutes. Five days later, the usual incubation period, he developed yellow fever. 

At the same time that he entered the building two other non-immunesentered the other compartment where they slept for eighteen nightsseparated from the mosquitoes by the wire screen. They showed no signsof taking the fever. 

In another mosquito-proof house two soldiers and a surgeon, allnon-immunes, lived for twenty-one days. From time to time they weresupplied with soiled articles of bedding, clothing, etc. , direct fromthe yellow fever hospital in the city. These articles had been soiled bythe urine, fecal matter and black vomit obtained from fatal and othercases of yellow fever. These articles were handled and shaken daily, butno disease developed among the men and at the end of the twenty-onedays, two other non-immunes relieved them and handled a new supply ofclothing in the same way, sleeping between the same sheets that hadbeen used by a patient dying of yellow fever and exposing themselves inevery possible way to the soiled clothing. But no disease developed. That these men were susceptible was shown later by inoculating some ofthem, when they developed the disease. 

In another experiment certain men in a camp allowed themselves to bebitten by mosquitoes that had passed through the proper period ofincubation and every one of them and no others contracted the disease. It was also shown that a mosquito was capable of communicating thedisease as long as fifty-seven days after it had bitten a yellow feverpatient. Another set of experiments showed that a subcutaneous injectioninto a non-immune of a very small quantity of blood from the veins of ayellow fever patient in the first two or three days of the disease wouldproduce the fever. 

SUMMARY OF RESULTS

Since that time much other work has been done by independent workers aswell as by French and English Commissions both working at Rio deJaneiro. The results of their investigation are practically the same andmay be summed up as follows:

1. The virus of the yellow fever is in the blood-plasma, not in thecorpuscles, for these may be removed and the plasma still be infective. 

2. The virus is conveyed from one patient to another by the yellow fevermosquito, _Stegomyia calopus_, and in no other way except byexperimental injections. 

3. The patient is a source of infection only during the first three orfour days of the disease (this after the three to six days ofincubation). 

4. The virus must undergo an incubation period of twelve to fourteendays in the mosquito before she is capable of transmitting the disease. 

5. The parasite, whatever it is, has never been seen. It is probably toosmall to be seen by any of our present microscopes, even the recentlyinvented ultramicroscope. It is probably not a bacterial parasite butvery likely a Protozoan, and certain specialists have even shown by thestudy of all the available data that it almost certainly belongs to theSporozoan genus _Spirocheta_. 

Now what does all this mean? It means the saving of hundreds of humanlives annually. It means the banishing from many localities and possiblyvery soon from the face of the earth of a disease that since theearliest settlements on this continent has been a source of terror. Itmeans the making habitable of certain places which heretofore a whiteman has entered only at the risk of his life. It means that quarantinesneed no longer be established when yellow fever breaks out in adistrict; quarantines which have inevitably caused the loss of millionsof dollars to the world of commerce. 

RESULTS IN HAVANA

The first practical work based on these findings was done in Havana. TheYellow Fever Commission made their recommendations in 1900. In 1901 and1902 they were put into effect. The following table of the death ratethere during a period of ten years shows graphically the results:

DEATHS IN HAVANA FROM YELLOW FEVER

-----+------+------+------+------+------+------+------+------+------+------ | 1893 | 1894 | 1895 | 1896 | 1897 | 1898 | 1899 | 1900 | 1901 | 1902-----+------+------+------+------+------+------+------+------+------+------Jan. | 15 | 7 | 15 | 10 | 69 | 7 | 1 | 8 | 7 | 0Feb. | 6 | 4 | 4 | 7 | 24 | 1 | 0 | 9 | 5 | 0Mar. | 4 | 2 | 2 | 3 | 30 | 2 | 1 | 4 | 1 | 0Apr. | 8 | 4 | 6 | 14 | 71 | 1 | 2 | 0 | 0 | 0May | 23 | 16 | 10 | 27 | 88 | 4 | 0 | 2 | 0 | 0June | 69 | 31 | 16 | 46 | 174 | 3 | 1 | 8 | 0 | 0July | 118 | 77 | 88 | 116 | 168 | 16 | 2 | 30 | 1 | 0Aug. | 100 | 73 | 120 | 262 | 102 | 16 | 13 | 49 | 2 | 0Sep. | 68 | 76 | 135 | 166 | 56 | 34 | 18 | 52 | 2 | 0Oct. | 46 | 40 | 102 | 240 | 42 | 26 | 25 | 74 | 0 | 0Nov. | 28 | 23 | 35 | 244 | 26 | 13 | 18 | 54 | 0 | 0Dec. | 11 | 29 | 20 | 147 | 8 | 13 | 22 | 20 | 0 | 0-----+------+------+------+------+------+------+------+------+------+------

As long as the United States held control at Havana the yellow feverwas kept in check by fighting the mosquitoes, when this vigilance wasrelaxed the fever began to appear again and the Cubans found that it wasnecessary to keep up the fight against the mosquitoes if the island wasto be kept free from the disease. 

THE FIGHT IN NEW ORLEANS

In the summer of 1905 came another opportunity to put the knowledgegained during these experiments to a practical test. Samuel HopkinsAdams in his article in _McClure's Magazine_, June, 1906, says of thebeginning of this fight:

 "Eight years before, the mosquito-plague had infected the great, busy, joyous metropolis of the south. Ignorant of the real processes of the infection, New Orleans had fought it blindly, frantically, in an agony of panic, and when at last the frost put an end to the helpless city's plight, she lay spent and prostrate. The yellow fever of 1905 came with a more formidable and unexpected suddenness than that of 1897. It sprang into life like a secret and armed uprising in the midst of the city, full-fledged and terrible. But there arose against it the trained fighting line of scientific knowledge. Accepting, with a fine courage of faith that most important preventive discovery since vaccination, the mosquito dogma, the Crescent City marshaled her defenses. This time there was no panic, no mob-rule of terrified thousands, no mad rushing from stunned inertia to wildly impractical action; but instead the enlistment of the whole city in an army of sanitation. Every citizen became a soldier of the public health. And when, long before the plague-killing frost came, the battle was over, New Orleans had triumphed not only in the most brilliant hygienic victory ever achieved in America, but in a principle for which the whole nation owes her a debt of gratitude. "

For some time the authorities had been trying to keep secret the factthat the disease was prevalent, but the rapidity with which it spreadmade them realize that only united action on the part of all thecommunity would be of any avail. The Citizens Volunteer WardOrganizations were organized for the purpose of fighting the mosquitoeswhich were everywhere. To many the fight looked hopeless. The miles ofopen gutters, the thousands of cisterns and little pools of standingwater everywhere furnished abundant breeding-places for the mosquitoes. The ditches and ponds were drained or salted, the cisterns werescreened, infected houses were fumigated, yet the fever continued tospread. Rains refilled the ditches, winds tore the screens from thecisterns, the ignorant people of the French quarter refused tocoöperate. At last the city in desperation appealed to the President foraid. Surgeon J. H. White and a number of officers and men of the UnitedStates Public Health and Marine Hospital Service soon took charge of thework. This was continued along the same lines as before with the sameobject in view. But with the coming of the regulars the work was moresystematically and thoroughly done. Every case of fever was treated asthough it was yellow fever and every precaution taken to preventmosquitoes from biting such a patient. The houses in which the feveroccurred were thoroughly fumigated to kill any mosquitoes that might bethere, and the neighborhood was thoroughly searched to find any placeswhere the mosquitoes might be breeding. So confident were theauthorities that the mosquito was the sole cause of the diseasespreading, that besides fighting it no other work was undertaken save tomake the sick as comfortable as possible. 

Finally the results began to be apparent. The number of cases graduallydiminished, until long before frost came the city was free from thegreat pest. Yellow fever will doubtless appear from time to time in NewOrleans and other cities, but there is, at least there should be, smalldanger of another great epidemic, for the people now know how thedisease is caused and the remedy. 

Not long since I had occasion to write to a prominent entomologist inLouisiana for some specimens of the yellow fever mosquito for laboratorywork. The following extract from his reply will show something of thework that is still being done there. 

 "I am afraid we cannot furnish specimens of _Stegomyia_, in spite of the fact that Louisiana is _supposed_ to be the most favorable home of this species in the South. Since the light occurrence of yellow fever in this State in 1905, a very vigorous war has been kept up against _Stegomyia_, and the ordinances of all Louisiana cities and principal towns require the draining of all breeding places of this mosquito and the constant oiling or screening of all cisterns or other water containers. The result is this species is very rare. Here in Baton Rouge I only see one once in a great while, and it would require perhaps a good many days' work at the present season to get as good specimens and as many of them as you require. "

IN THE PANAMA CANAL ZONE

Yellow fever was one of the worst obstacles that confronted the Frenchwhen they were attempting to build the Panama Canal. The story of thesuffering and death from this dread disease there is most pathetic. Ship-load after ship-load of laborers were sent over, as those who hadgone earlier succumbed to the fever. The contractors were responsiblefor their men while they were sick and in order to avoid having to payhospital expenses the men were often discharged as soon as they showedsigns of sickness. Many of them died along the roadside whileendeavoring to reach some place where they could obtain aid. Thehospitals were usually filled with yellow fever patients, a very largepercentage of whom died. 

Not only the day laborers suffered but many of the engineers, doctors, nurses and others sickened and died of the disease. It is reported thateighteen young French engineers came over on one vessel and in a monthafter their arrival all but one had died of the yellow fever. Out ofthirty-six nurses brought over at one time, twenty-four died of thefever, and during one month nine members of the medical staff of one ofthe hospitals succumbed. 

One of the first things that the United States Government did inbeginning work in the canal zone was to take up the fight against theyellow fever mosquito. In Panama where the water for domestic purposeswas kept in cisterns and water-barrels, inspectors were appointed to seethat all such receptacles and other possible breeding-places formosquitoes were kept covered. After the first inspection, 4, 000breeding-places were reported. About six months later there were lessthan 400. Similar work was done in all the towns and settlements alongthe route of the canal. In addition to this fight against the yellowfever mosquito considerable attention was paid to the breeding-places ofthe malarial mosquito. The results have been remarkable. Cases of yellowfever are now rare throughout this zone, and there has been a very greatreduction in the extent of the malarial districts. The last case ofyellow fever occurred in May, 1906. Before this work was done a man tookhis life in his hands when he went into this region. Now it is regardedas a perfectly safe place to live. Indeed it is a much safer place thanmany sections of our own country where proper sanitary measures have notbeen taken to protect the health of the community. 

IN RIO DE JANEIRO

In Rio de Janeiro they have as yet been unable to get rid of themosquitoes, although thousands of dollars are spent annually in fightingthem. But the non-immunes there protect themselves by doing theirbusiness in Rio during the day and going back at night to Petropolis, twenty-five miles inland and twenty-five hundred feet higher, wherethey are safe, for no _Stegomyia_ have ever been found there. 

They claim there that the yellow fever mosquito does not bite during thedaytime after she has laid her eggs, and that she will not lay her eggsuntil about three days after she has fed on blood, therefore a_Stegomyia_ that bites during the day will not carry the yellow feverbecause she is too young. This seems to explain why the fever cannot becontracted by being bitten by a mosquito in the daytime. Certain otherexperiments, however, have given different results so that as far as weknow it is not safe to be bitten at any time by such a mosquito in aregion where the disease is endemic or where it is epidemic. 

In the main the work of the French Yellow Fever Commission working inRio de Janeiro has confirmed the findings of the American Commission. One interesting special thing that the French Commission seems to haveestablished is that the female may transmit the infecting power to heroffspring, so that it would be possible for a mosquito that had neverbitten a yellow fever patient to be capable of infecting a non-immuneperson. While all this is very probable in the light of what we know ofthe disease and the way in which other diseases caused by similarorganisms may be transmitted by the parent to the offspring, yet themost conservative investigators are waiting for further proof. 

HABITS OF STEGOMYIA

The whole fight against yellow fever, then is directed, as we have seen, against the mosquito, _Stegomyia calopus_. The habits of this speciesare such as to make it easy in some respects to combat. It is seldomfound far away from human habitation. The adults will not fly far. Oncein a house they usually stay there except when they leave to deposittheir eggs. 

On the other hand, some of these same habits make it all the moredangerous. It will breed in almost any kind of water, no matter howfilthy, and a very small amount will suffice. Thus any leaks fromwater-pipes or drains, cisterns, small cans of water or any such placesmay become dangerous breeding-places. If conditions are unfavorablethere will often be developed small individuals which can easily maketheir way through ordinary mosquito-netting. 

Dr. Manson has pointed out an interesting possible result of the crusadethat is now being waged against the yellow fever mosquitoes. Theimmunity of the people native to the endemic regions is supposed to bedue to their having had mild attacks of the fever during childhood, forthe children in these regions are subject to certain fevers which areprobably very mild forms of yellow fever. 

Now if we kill practically all of the _Stegomyia_ so that these childrendo not have this fever there will be developed, in due time, apopulation most of whom are non-immune. 

This freedom from the disease for some time will allow us to growcareless in regard to fighting the mosquitoes. They will be allowed toincrease and by some chance the yellow fever will again be introducedand there will then be very grave danger of most extensive anddestructive epidemics. 

DANGER OF THE DISEASE IN THE PACIFIC ISLANDS

I have already referred once or twice to the conditions in many of thePacific tropical islands. In some of these various species of_Stegomyia_ are abundant, and in some _Stegomyia calopus_ is the mostabundant and troublesome form. All the natives of these islands arenon-immune because there has never been any yellow fever there. Unlessextraordinary care is taken the disease will be introduced there sooneror later and the results are sure to be most appalling. The climatic andsanitary conditions and the habits of the people are ideal for thedevelopment and spread of the disease, and what I have seen of theconditions on some of these islands convinces me that it would be almostimpossible to control the disease before it had a chance to kill a largepercentage of the population. 

With the opening of the Panama Canal these things become more possible. Heretofore, the shipping to these regions has not been from ports whereyellow fever was endemic or even likely to be epidemic. But unless theyellow fever is kept out of the canal zone, the danger will be many foldwhat it is now. 

The white man has already carried enough misery to these island peoplesin the way of loathsome diseases, and it is to be hoped that this, another great curse, will not be carried to them with our civilization, the beneficial results of which have been so often very justlyquestioned. 

What I have said in regard to these islands applies with equal force andin some instances with even greater force to parts of Asia, the EasternArchipelago and other places. 

CHAPTER IX

FLEAS AND PLAGUE

Plague has always been one of the most dreaded diseases, and when weread of its ravages in the old world and the utter helplessness of thepeople before it we do not wonder that the very word filled them withhorror. One of the greatest scourges ever known began in Egypt aboutA. D. 542, and spread along the shores of the Mediterranean to Europe andAsia. It lasted for sixty years, appearing again and again in the sameplace and decimating whole communities. 

Another great pandemic, beginning in 1364, spread over the whole of thethen known world and appeared in its most virulent form. On account ofdiffuse subcutaneous hemorrhages it came to be known as the "blackdeath" and of course spread terror in all the communities where itappeared. Whole villages and districts were depopulated. The death-ratewas very high, one authority placing the total mortality at twenty-fivemillion. 

During this time new centers of infection were established, and sincethen it has been carried by the commerce of the nations to all parts ofthe world. It is not restricted, as many other epidemic diseases, to thetropics or semi-tropics, although as a matter of fact we find it is moreprevalent in these regions on account of the sanitary conditions. 

HOW PLAGUE WAS CONTROLLED IN SAN FRANCISCO

Attention is called to these things in order that we may compare pastconditions with present. During the last few years San Francisco hasbeen fighting an outbreak of plague that in other days would have beennothing less than a national calamity. But with modern methods ofhandling it, based on knowing what it is, what causes it and how it isspread, the authorities there have been able not only to hold thedisease in check, but practically to stamp it out with the loss ofcomparatively few lives. 

Dr. Blue of the Public Health and Marine Hospital Service and hisco-workers directed their whole energy toward controlling the rats. Asmall army of men were employed, catching rats in every quarter of thecity. Dr. Rucker reports that fully a million rats were slain in thiscampaign. Their breeding-places were destroyed by making cellars, woodsheds, warehouses, etc. , rat-proof and removing all old rubbish. Garbage cans were installed in all parts of the city, as it was requiredthat all garbage be stored where rats could not feed upon it, andaltogether every effort was made to make it as uncomfortable as possiblefor the rats. 

The marked success attending this work abundantly confirms the soundnessof the theory upon which it was based, and serves as another example ofthe way in which science is teaching us how to prevent or control manyof our most serious diseases. 

THE INDIAN PLAGUE COMMISSION

In 1896, what proved to be a very serious outbreak of plague, occurredin Bombay and spread to other parts of India. In 1898, a commission wasappointed to inquire into the origin of the different outbreaks, themanner in which the disease is communicated, etc. This was known as theIndian Plague Commission, and its exhaustive report, together with theminutes of the evidence presented to the committee, represents astupendous amount of work on this subject and is the basis for much ofthe later investigation that has been undertaken. 

After the consideration of the evidence from various sources thecommission decided that the principal mode of infection both for man andrats was through some sort of an abrasion in the skin, although itrecognized also the possibility of infection through the nose andthroat, and possibly, very rarely, through the intestinal tract or otherplaces. 

Considerable time was spent in considering Dr. Simond's claim, made in1898, that fleas which have been parasitic on plague-infected ratsmigrate on the death of their hosts and convey the infection to healthymen and rats. Dr. Simond sought to establish the following:

 "Firstly, that plague rats are eminently infective when infected with fleas and that they cease to be infective when they have been deserted by their parasites: Secondly, that living plague bacilli are found in association with fleas which are taken from plague-infected rats: Thirdly, that plague can pass from infected rats to other animals which have not come directly in contact with them or with their infected excretions: Fourthly, that fleas which infest rats will transfer themselves as parasites to men. "

After reviewing the experiments which had been made to establish theseclaims the commission believed that sufficient precaution had not beentaken to prevent infection from other sources and that not enoughdefinite evidence was produced. Against this claim much negativeevidence was considered and the final conclusion was "that suctorialinsects do not come under consideration in connection with the spread ofplague. "

In 1905 another body of men known as the Advisory Committee wasappointed to arrange for further studies in India and other places, particularly in relation to the mode of dissemination of the disease. They at once appointed a new working commission who immediately begantheir studies and experiments. The preliminary reports of their work, which are still known as the Reports of the Indian Plague Commission, aswell as the reports of contributing investigations that are being madefrom time to time, have served to establish entirely Dr. Simond's claimsand have completely revolutionized the methods of fighting plague. 

There are several different types of plague, seeming to depend largelyon the manner of infection. The most common type is that known as thebubonic plague which is characterized by buboes or swellings in variousparts of the body. This form of infection is usually received throughthe skin in some manner or other. Only rarely does direct man-to-maninfection occur though there is always the possibility of it. Theinvestigations have shown that the flea is the most common agent intransferring the disease from rat to rat or from rat to man. This may beaccomplished by the flea transferring the bacilli directly from one hostto another on its proboscis, or they may be carried in the alimentarycanal of the flea and gain an entrance into the skin through an abrasionof some kind when the flea is crushed as it is biting, or when some ofthe bacilli are left on the skin in the excreta of the insect. 

RESULTS OF VERJBITSKI'S EXPERIMENTS

A very important series of experiments bearing directly on this subjectwas made in 1902 and 1903 by Dr. D. T. Verjbitski. The paper giving theresults of this work was not published in any scientific journal until1908 when the Advisory Committee published it in one of their reports. The experiments were so well planned and executed and the results sodefinite that I think it is worth while to give in full his summary ofresults. The bugs referred to are bedbugs. 

 "(1) All fleas and bugs which have sucked the blood of animals dying from plague contain plague microbes. 

 "(2) Fleas and bugs which have sucked the blood of animals which are suffering from plague only contain plague microbes when the bites have been inflicted from 12 to 26 hours before the death of the animals, that is, during that period of their illness when their blood contains plague bacilli. 

 "(3) The vitality and virulence of the plague microbes are preserved in these insects. 

 "(4) Plague bacilli may be found in fleas from four to six days after they have sucked the blood of an animal dying with plague. In bugs, not previously starved or starved only for a short time (one to seven days), the plague microbes disappear on the third day; in those that have been starved for four to four and one-half months, after eight or nine days. 

 "(5) The numbers of plague microbes in the infected fleas and bugs increase during the first few days. 

 "(6) The fæces of infected fleas and bugs contain virulent plague microbes as long as they persist in the alimentary canal of these insects. 

 "(7) Animals could not be infected by the bites of fleas and bugs which had been infected by animals whose own infection had been occasioned by a culture of small virulence, notwithstanding the fact that the insects may be found to contain abundant plague microbes. 

 "(8) Fleas and bugs that have fed upon animals which have been infected by cultures of high virulence convey infection by means of bites, and the more certainly so the more virulent the culture with which the first animal was inoculated. 

 "(9) The local inflammatory reaction in animals which have died from plague occasioned by the bites of infected insects is either very slight or absent. In the latter case it is only by the situation of the primary bubo that one can approximately identify the area through which the plague infection entered the organism. 

 "(10) Infected fleas communicate the disease to healthy animals for three days after infection. Infected bugs have the power of doing so for five days. 

 "(11) It was not found possible for more than two animals to be infected by the bites of the same bugs. 

 "(12) The crushing of infected bugs in situ during the process of biting, occasioned in the majority of cases the infection of the healthy animal with plague. 

 "(13) The injury to the skin occasioned by the bite of bugs or fleas offers a channel through which the plague microbes can easily enter the body and occasion death from plague. 

 "(14) Crushed infected bugs and fleas and their fæces, like other plague material, can infect through the small punctures of the skin caused by the bites of bugs and fleas, but only for a short time after the infliction of these bites. 

 "(15) In the case of linen and other fabrics soiled by crushing infected fleas and bugs on them, or by the fæces of these insects the plague microbes can under favorable conditions remain alive and virulent during more than five months. 

 "(16) Chemical disinfectants do not in the ordinary course of application kill plague microbes in infected fleas and bugs. 

 "(17) The rat flea _Typhlopsylla musculi_ does not bite human beings. 

 "(18) Human fleas do bite rats. 

 "(19) Fleas found on dogs and cats bite both human beings and rats. 

 "(20) Human fleas and fleas found on cats and dogs can live on rats as casual parasites, and therefore can under certain conditions play a part in the transmission of plague from rats to human beings, and vice versa. "

RESULTS OF VARIOUS INVESTIGATIONS

Various other plague commissions from other countries as well as manyindividuals have investigated the same subject, and the results allpoint conclusively to the fact that the rats and the fleas are at leastthe most important factors in the spread of the disease. The evidencefrom many sources and from many experiments may be briefly summed up asfollows: The disease is caused by the presence in the system of minutebacteria, _Bacillus pestis_. It is probable that plague is primarily adisease of rats and only secondarily and accidentally, as it were, adisease of man. 

Rats are subject to the plague and are often killed by it in greatnumbers. An outbreak of plague among men is often preceded by a verynoticeable outbreak among rats. 

Rats dying of the plague have their blood filled with the plaguebacillus. Fleas or other suctorial insects feeding on such rats takemyriads of these bacilli into their stomach and get many on theirproboscis. 

The fleas usually leave a rat as soon as it dies and of course seek someother source of food. When such infected fleas are permitted to biteother rats or guinea-pigs these animals often develop the disease. Several of the species of fleas that infest rats will bite man also, andin the cases of many plague patients it can be definitely shown thatthey had recently been bitten by fleas. 

STRUCTURE AND HABITS OF FLEAS

A study of the structure and habits of fleas shows that in many respectsthey are particularly adapted for spreading such a disease as bubonicplague. The piercing proboscis consists of three long needle-likeorgans, the epipharynx and mandibles, and a lower lip or labium. Themandibles have the sides serrate like a two-edged saw. The labium isdivided close to its base so that it really consists of two slenderfour-segmented organs which lie close together and form a groove inwhich the piercing organs lie. When the flea is feeding, the epipharynxand mandibles are thrust into the skin of the victim, the labium servingas a guide. As the sharp cutting organs are thrust deeper and deeper thelabium doubles back like a bow and does not enter the skin. Saliva isthen poured into the wound through minute grooves in the mandibles, andthe blood is sucked up into the mouth by the sucking organ which lies inthe head at the base of the mouth-parts. Just above this piercingproboscis is a pair of flat, obtuse, somewhat triangular pieces, themaxillary blades or maxillæ. When the proboscis is fully inserted intothe skin the tips of these maxillæ may also be embedded in the tissueand perhaps help to make the wound larger. Attached to these maxillæ isa pair of rather stout, four-jointed appendages, the palpi. Theyprobably act as feelers. 

If the flea chances to be feeding on a plague-infected rat or personmany of the plague bacilli will get on the mouth-parts and myriads ofthem are of course sucked up into the stomach with the blood. Those onthe proboscis may be transferred directly to the next victim that it isthrust into, and those in the stomach may be carried for some time andfinally liberated when the flea is feeding again or when it is crushedby the annoyed host. The latter is probably the most common method ofinfection, for the bacilli that are liberated when the flea is crushedmay readily be rubbed into the wound made by the flea bite or intoabrasions of the skin due to the scratching. Kill the flea, but don't"rub it in. "

[Illustration: FIG. 105--Rat-flea (_Læmopsylla cheopis_); male. ]

[Illustration: FIG. 106--Rat-flea (_L. Cheopis_); female. ]

[Illustration: FIG. 107--Head of rat-flea showing mouth-parts. ]

[Illustration: FIG. 108--Human-flea (_Pulex irritans_); male. ]

During the recent outbreak in San Francisco many thousand fleas thatwere infesting man, rats, mice, cats, and dogs, squirrels and otheranimals have been studied and it has been found that while each fleaspecies has its particular host upon which it is principally found, fewif any of them will hesitate to leave this host when it is dead andattack man or any other animal that may be convenient. 

COMMON SPECIES OF FLEAS

Throughout India and in all the warm climates where plague frequentlyoccurs the most common flea found on rats has come to be known as theplague flea (_Læmopsylla cheopus_) (Figs. 105, 106), and is doubtlessthe principal species that is concerned in carrying the disease in thoseclimates. It now occurs quite commonly on the rats in the San FranciscoBay region and is occasionally found there on man also. In the UnitedStates, Great Britain and other temperate regions another largerspecies, _Ceratophyllus fasciatus_ is by far the most common flea foundon rats, and is commonly known as the rat flea. It occurs on both thebrown and the black rats _Mus norvegicus_ and _M. Rattus_, on the housemouse and frequently on man. It has also been taken in California onpocket gophers and on a skunk. 

The common human flea (_Pulex irritans_) (Figs. 108, 109), is found inall parts of the inhabited world. Although we regard it primarily as apest of human beings it often occurs very abundantly on cats, dogs, miceand rats as well as on some wild mammals such as badgers, foxes andothers and has occasionally been found on birds. 

Most entomologists regard the fleas commonly found on cats and dogs asbelonging to one species _Ctenocephalus canis_. Others believe them tobe distinct species and call the cat flea _Ctenocephalus felis_. So faras our personal comfort and safety is concerned it makes but littledifference to us whether the flea that bites us is called _canis_ or_felis_ for they both look very much alike, and act alike and the biteof one hurts just as much as the bite of the other. Although cats anddogs are their normal hosts they are very often troublesome householdpests, sometimes making a house almost uninhabitable. They arefrequently found on rats, and therefore may carry the plague bacillusfrom rat to rat or from rat to man. 

GROUND-SQUIRRELS AND PLAGUE

As early as 1903 Dr. Blue, in charge of the plague suppressive measuresin San Francisco, became impressed with the possibility of the commonCalifornia ground-squirrels (_Otospermophilus beecheyi_), acting as anagent in the transmission of plague. It was rumored at that time thatsome epidemic disease was killing the squirrels in some of the countiessurrounding San Francisco Bay, notably in Contra Costa County. None ofthe squirrels were examined at that time, but since then many thousandhave been carefully studied and it has been definitely shown that manyof them are plague-infected. Just how the plague got started among themwill probably never be really known. There is little doubt, however, butthat it was transferred in some way from the rats to the squirrels. Thetrains and the bay and river steamers running out from San Franciscowould afford abundant opportunity for the rats to go from the city tothe warehouses all along the shore. Once there they would use the samerunways as the squirrels about the warehouses and in the near-by fields. In harvest time the rats migrate to the fields and make constant use ofthe squirrel holes. The farmers in some sections report that theyfrequently catch more rats than squirrels in traps set in squirrel holesat that season of the year. 

This close association of the rats and the squirrels affords a goodopportunity for the fleas infesting them to pass from one host to theother. 

So far only two species of fleas have been recorded from theground-squirrels. One, _Ceratophyllus acutus_, is very common, sometimesliterally swarming over the squirrels, particularly if a squirrel issick or weak from any cause. The other species, _Hoplopsyllus anomalus_, is less abundant but still quite common. Both of these species infestrats also, so the chain of evidence is practically complete. We haveonly to assume that at sometime one or more of the plague-infected ratsfound their way into the region where the squirrels were, and the fleaspassing from the rats to the squirrels would carry the plague with them. 

The fact that the plague already has such a start among the squirrelsopens a new and very serious phase of the problem of suppressing thedisease. All who have hunted the ground-squirrels will testify to thereadiness with which the fleas from them will bite those who arehandling them. As it is the sick or weak squirrels that are most oftentaken there is always a chance that plague may be transferred from themto human beings. The records of the plague cases in California show atleast three cases in which there seems to be very little doubt that thedisease resulted from handling plague-infected squirrels. 

[Illustration: FIG. 109--Human-flea (_P. Irritans_); female. ]

[Illustration: FIG. 110--Mouse-flea (_Ctenopsyllus musculi_); female. ]

A still more serious thing is the possibility of the disease remainingin a more or less virulent form among the squirrels for some time, possibly for years, and then breaking out again in some locality wherethe rats or men may become infected. As long as there is a trace of thedisease among the squirrels there is always the chance of it spreading, so that new areas may become infested. Those in charge of theplague-suppressive measures are fully aware of these dangers and aremaking a careful study of the situation and will doubtless be able tocope with it successfully. It may be that the squirrels will have to beexterminated in the infected regions. This would be a long and difficulttask, but the success attending the fight against the rats in a greatcity shows what can be done when the determination to do it is there. 

REMEDIES FOR FLEAS

We have seen how a great city set to work to rid itself of theplague-sick rats. As a matter of fact it was not the rats that theywere after primarily. If the rats had not harbored fleas the city wouldhave been glad to let the disease take its course and destroy as manyrats as possible. But it was found that the only way to get rid of thefleas that might possibly be infected with the plague was to kill theirrat hosts. 

General cleaning-up measures will of course very materially lessen thenumber of fleas about the private dwellings, but there often remains anumber of fleas in the house that are a source of great annoyance evenif the danger is eliminated. 

Particularly is this apt to be so in places where cats or dogs aremembers of the household. These animals almost always harbor at least afew fleas, and where there are a few there is always a possibility, evena great probability, that there will be many more unless an effort ismade to get rid of them. 

In some sections of the country it is the cat and dog flea that is themost troublesome to man. The minute white eggs of the fleas are usuallylaid about the sleeping-places of these animals and the slender activelarvæ that hatch from them feed upon any kind of organic matter thatthey can find in the dust or in the cracks and crevices. About eight orten days after hatching the larvæ spin delicate brownish cocoons inwhich they pass the pupal stage, issuing a few days later as the adultfleas. 

It will at once appear, then, that it is important to provide the catsand dogs with sleeping-places that can be kept clean. If they have a mator blanket to sleep on this can be taken up and shaken frequently andthe dust swept up and burned. In this way many of the eggs or larvæ maybe destroyed. Very often the dust under a carpet that has not been takenup and dusted for some time will be found to be harboring a multitude offleas or their larvæ. In such cases a thorough cleaning of the carpetand the floors will bring relief. Houses that are unused for some timeduring the summer months are often found to be overrun with fleas in thefall, for the fleas have had an unmolested opportunity to breed andmultiply. Such rooms of course require a thorough cleaning or it issometimes possible to kill the fleas by a liberal use of pyrethrumpowder or benzine or to fumigate. In this connection, Dr. Skinner's notein the _Journal of Economic Entomology_ is worth repeating. 

 "In the latter part of last May (1908) I moved into a house that had not been previously occupied. No carpet was used and being summer only a few rugs were placed on the floors. A part of the household consisted of a collie dog and three Persian cats. Very soon the fleas appeared, the dog and cat flea, _Ctenocephalus canis_. I did not count them and I can't say whether they numbered a million or only a hundred thousand. On arising in the morning and stepping on the floor one would find from three to a dozen on the ankles. The usual remedies for fleas are either drastic or somewhat unsatisfactory. The drastic one is to send the animals to the institutions, where they are asphyxiated, or take the other advice, 'Don't keep animals. '

 "I tried mopping the floors with rather a strong solution of creolin but it did little good. Previous experience with pyrethrum was not very satisfactory. Knowing the volatility of naphthalene in warm weather and the irritating character of its vapor led me to try it. I took one room at a time, scattered on the floor five pounds of flake naphthalene and closed it for twenty-four hours. On entering such a room the naphthalene vapor will instantly bring tears to the eyes and cause coughing and irritation of the air passages. I mention this to show how it acts on the fleas. It proved to be a perfect and effectual remedy and very inexpensive, as the naphthalene could be swept up and transferred to other rooms. So far as I am concerned the flea question is solved and if I have further trouble I know the remedy. I intend to keep the dog and the cats. "

CHAPTER X

OTHER DISEASES, MOSTLY TROPICAL, KNOWN OR THOUGHT TO BE TRANSMITTED BYINSECTS

SLEEPING SICKNESS

One of the worst scourges of Africa and one that is to-day attractingworld-wide attention is the disease known as trypanosomiasis, theterminal phase of which is sleeping sickness, one of the most ghastlydiseases that we know. 

Among the Protozoa referred to in one of the earlier chapters mentionwas made of certain trypanosomes which inhabit the blood of man andcertain animals. Very little was known concerning these parasitesprevious to the beginning of the present century, but since that timeseveral have been found to be of great economic importance. The group isbeing studied extensively and every day our knowledge of them isincreasing so that we now know quite definitely the life-history ofseveral. 

_Trypanosoma lewisi_, a parasite of rats, is perhaps the best known asit is always common where-ever rats are found. Sometimes as many as 30%or 40% of the rats of certain districts are infected. It is thought thatthese are transmitted from rat to rat by the common rat-louse whichserves as an intermediate host. Fleas may also act as disseminatingagents. 

A few other kinds cause serious disease of animals, but we are moreinterested just now in the particular one that is causing so muchtrouble in Africa. This parasite was discovered in 1902 and was named_Trypanosoma gambiensi_ (Fig. 111). Since then it has been found to bewidely distributed. Although the natives have doubtless long beensubject to the disease caused by this parasite, the recent influx ofwhites to these regions and the consequent movements of the natives havecaused a great spread of the disease so that whole regions are now madedesolate, the inhabitants dying or fleeing to escape the uncanny death. 

The disease may run its course in a few months or it may take years. Thesymptoms are various, but infection is usually soon followed by fevers, sometimes mild, sometimes severe, which recur at irregular intervals. Certain glands or other parts of the body may become swollen. More orless extensive skin eruptions occur on all parts of the body and thepatient gradually becomes anemic and physically and intellectuallyfeeble. The nervous system seems to be affected by the parasite, eitherdirectly or by the action of the toxins it produces. The patient becomesmore debilitated and morose with an increasing tendency to sleep, hencethe name sleeping sickness. As the stupor deepens the patient looses alldesire or power of exertion and as little food is taken he rapidlywastes away and finally succumbs for after this final stage is reachedthere is no relief. 

It is definitely known that a species of tsetse-fly, _Glossina palpalis_(Fig. 112), which somewhat resembles our stable-fly, is responsible forthe dissemination of the disease, and some recent investigators havesuggested that certain species of mosquitoes may also carry the parasitefrom one host to another. There still remains some doubt as to the exactmanner in which the fly transmits the disease, but it seems altogetherlikely that it is an alternative host and does not serve as a simplemechanical carrier. In this respect it is like the mosquito which is oneof the necessary hosts of the malaria parasites, and unlike thehouse-fly which carries the germs of various diseases in a purelymechanical way without serving as a definite necessary host for theparasite. 

The tsetse-fly is found only in tropical Africa and is limited in itsdistribution there to certain very definite, narrow, brushy areas alongthe water's edge. If these places can be avoided there seems to belittle danger. Those who are fighting the disease have found that if thebrush in the vicinity of watering-places and ferry-landings is clearedaway such places become comparatively safe. These flies do not lay eggsbut produce full-grown larvæ which soon pupate in the ground. 

ELEPHANTIASIS

In many tropical regions human blood as well as that of other animals isthe normal habitat of certain worm-like parasites (Nematodes). They arenot entirely confined to the tropics but may extend far up into thesubtropical regions. Five or six different species of these parasitesare known, only one of which, however, has been shown to be of anypathological importance, as far as human beings are concerned. 

[Illustration: FIG. 111--_Trypanosoma gambiense_; various forms fromblood and cerebrospinal fluid. (After Manson. )]

[Illustration: FIG. 112--Tsetse-fly. (After Manson. )]

This species, _Filaria bancrofti_, is not only very widely distributed, but in regions such as some of the South Sea Islands a very large percent of the natives have the filariæ present in their blood. When theseparasites are withdrawn from the circulation and placed on a slide forstudy they are seen to be minute transparent, colorless, snake-likeorganisms inclosed in a very delicate sack or sheath. They are but alittle more than one-hundredth of an inch long and about as big aroundas a red blood-corpuscle. These are the larval forms of the parasite andhave been called by Le Dantec the micro-filaria. 

If blood of the patient drawn from the skin, is examined during the dayfew if any of these parasites are found, but if it is examined betweenfive or six o'clock in the evening and eight or nine o'clock the nextmorning they may be found in numbers. During the daytime they haveretired from the peripheral circulation to the larger arteries and tothe lungs, where they may be found in great numbers. 

This night-swarming to the peripheral circulation has been found to be aremarkable adaptation in the life-history of the parasite, for it hasbeen demonstrated that in order to go on with its development theselarval forms must be taken into the alimentary canal of the mosquito. Most of the mosquitoes in which the development takes place arenight-feeders, so that the parasites are sucked up with the blood of thevictim. Once inside the stomach they soon free themselves from theinclosing sheath and make their way through the walls of the stomach andenter the muscular tissue, particularly the thoracic muscles. Here theyundergo a metamorphosis and increase enormously in size, some attainingone-sixteenth of an inch in length. 

After sixteen to twenty days they leave these muscles and make their wayto other parts of the body. A few may be found in different parts of theabdomen, but most of them make their way forward into the head of themosquito and coil themselves up close to the base of the proboscis, finally finding their way down into the proboscis inside the labium. Here they lie until an opportunity offers for them to escape to the warmblood of a vertebrate. They probably pass through the thin membraneconnecting the labella with the proboscis and there find their way intothe wound made by the puncture when the insect bites. Whether theseparasites can gain an entrance into the circulatory system in any otherway is not known. It has been suggested that the mosquitoes dying anddisintegrating on the surface of water may liberate the filariæ whichmay later find their way into the system of the vertebrate host when thewater is used for drinking, but most of the investigations made so farseem to indicate that they make their way directly from the proboscisinto the new host. 

Soon after entering the circulatory system of the human host theparasites make their way into the lymphatics where they attain sexualmaturity, and in due time new generations of the larval filariæ ormicrofilariæ are poured into the lymph, and finally into the definiteblood-vessels, ready to be sucked up by the next mosquito that feeds onthe patient. 

In most cases of infection the presence of these filariæ in the bloodseems to cause no inconvenience to the host. They are probably neverinjurious in the larval stage, that is, in the stage in which they arefound in the peripheral circulation. 

In many cases, however, the presence of the sexual forms in thelymphatics may cause serious complications. The most common of these isthat hideous and loathsome disease known as elephantiasis in whichcertain parts of the patient becomes greatly swollen and distorted. Anarm or a leg may become swollen to several times its natural size, orother parts of the body may be seriously affected. 

In some of the South Sea Islands 30% to 40% of the natives are afflictedin this way, some only slightly others seriously. There is little or nopain, but in severe cases the distorted parts often render the patiententirely helpless. 

The exact way in which the parasites cause such swelling is not verydefinitely known. Manson, who has done more work on these diseases thanany one else, believes that the trouble arises from the clogging of thelymphatic glands or trunks, thus cutting them off from the generalcirculation, in which case the affected parts may become distorted. Thisclogging of the passages is believed to be due to the presence of greatnumbers of immature eggs which have been liberated by parasites injuredin some way before their eggs were entirely developed. 

This interference with the lymphatic circulation brings about theanomalous condition of a patient with a serious filarial disease withfewer of the filarial parasites in his blood than one who is not soseriously affected. This is supposed to be due to the fact that thedisease-producing parasites have died and that the lymphatics havebecome so obstructed that any microfilariæ they may contain cannot maketheir way into the general circulation. Such a patient then would not beas likely to infect a mosquito as would one less seriously affected. 

It has always been thought that little or nothing could be done in theway of successfully treating this disease, but quite recently a Frenchphysician, who has been conducting a long series of experiments in theSociety Islands, announced that he is able to cure many cases by certainsurgical operations on the affected parts. 

DENGUE OR "BREAKBONE FEVER"

This is another disease of the tropics often occurring in widespreadepidemics. It is probably most frequently met with in the West Indies, but may occur in any of the tropical countries or islands. Occasionallyit spreads into subtropical or even temperate regions. Several extensiveepidemics have occurred in the United States. Once introduced into acommunity it spreads very rapidly and nothing seems to confer immunity. 

The various names by which it has been called well describe its effecton the patient; breakbone fever, dandy-fever, stiff-necked orgiraffe-fever, boquet (or "bucket") fever, _scarlatina rheumatica_, polka-fever, etc. While the suffering is intense as long as the diseaselasts it seldom terminates fatally. 

It has always been classed as a very contagious disease and it has notyet been definitely shown that it is not. Recent observations, however, have shown that it is probably caused by a certain Protozoan parasitethat is found in the blood of dengue patients and several experimentshave been conducted by Dr. Graham which seem to indicate that it istransmitted by mosquitoes. In these experiments, _Culex fatigans_, acommon tropical or subtropical mosquito, was used. The same parasitethat is found in the human blood may be found in the stomach and bloodof the mosquitoes up to the fifth day after it has fed on a denguepatient. 

Sick and healthy individuals were allowed to remain in close contact ina room from which the mosquitoes had been excluded, and the disease wasnot spread. Mosquitoes that had bitten dengue patients were taken to ahigher region where dengue had never occurred and allowed to bite twohealthy persons. Both developed the disease and as they were protectedfrom other mosquitoes until they had recovered, the disease did notspread to others of the community. These and other observations seem tomake a complete chain of evidence, and most medical men to-day acceptthe theory as well proved and in their practice take every precaution toprevent the spread of the disease by keeping the infected patient frombeing bitten by the mosquitoes. 

The yellow fever mosquito is also suspected of carrying this samedisease, and it is possible that other species are also concerned. Ifit is true that the parasite can be carried by several different speciesof mosquitoes this would account very largely for its rapid spreadwherever it is introduced into a community. Where it occurs outside thetropics it is only in the warm summer months when mosquitoes are alwaysabundant. 

MALTA OR MEDITERRANEAN FEVER

This is also a tropical and subtropical disease that occasionally getsup into the temperate region, sometimes occurring in the United States. The fever begins with a severe headache, and other symptoms follow. Itis usually of the remittent type and may continue for some months. 

It is caused by minute bacteria (_Micrococcus melitensis_) and is a veryinfectious but not usually contagious disease. The germ is readilyconveyed by inoculation, and several investigators have sought to showthat the mosquito often serves as the inoculating agent. The disease isespecially prevalent during the mosquito season, and has twice beenconveyed to monkeys by infected insects. 

LEPROSY

This loathsome disease has long been known to be caused by a particularbacillus (_Bacillus lepræ_), but the way in which this organism gainsan entrance into the system is still unknown. Many theories have beenpropounded, but none of them has been well established. Within recentyears the possibility of insects carrying the germ and in one way oranother transmitting it to healthy individuals has been suggested andmuch discussed. As the lepræ bacilli are present in the skin and ulcersof leprous patients, insects sucking the blood or feeding on the sorescould not help taking some of them into their body or becomingcontaminated. These bacilli have been found at various times in thestomach or intestine of mosquitoes, fleas and bedbugs. So it is believedby some that these and other insects, such as lice and flies, maysometimes transmit the disease. On a previous page we have referred tothe possibility of the face-mites acting as disseminators of leprosy. 

Leprosy occurs most commonly among people where little attention is paidto bodily cleanliness. Such people are usually freely infested withvarious parasites that thrive well in the filth, so if the germs can betransmitted in this way the carriers are there in abundance. 

The fact that the sores usually occur on exposed parts of the body hasbeen pointed to as evidence that inoculation is due to such insects asflies and mosquitoes. It has been noted that leprosy is frequently verycommon in regions where elephantiasis occurs, suggesting the possibilityof the same carrier, the mosquito, for both diseases. So while there isas yet very little evidence one way or the other, insects that are foundaround leprous patients are to be regarded with suspicion, for until weknow more definitely just how the disease is communicated the insectsmust be looked on as possible sources of contamination. 

KALA-AZAR OR DUM-DUM FEVER

This is a very fatal infectious disease of many tropical and subtropicalregions, spreading terror among the natives wherever it occurs. It iscaused by the presence in the system of Protozoan parasites, theso-called Leishman-Donovan bodies, that have recently been studied byseveral observers. 

Dr. W. S. Patton of the Indian Medical Service has been making someextensive experiments with the common bedbug of India (_Cimexrotundatus_) which seem to demonstrate fully that this insect isresponsible for the transmission of the parasite that causes thedisease. He has found the parasite in all stages of development in thebedbug. This, taken with a number of other observations in regard to thetendency of the disease to cling to particular houses, makes a strongcase against the bedbug. Manson, however, believes that the parasite maybe transmitted by other agents also, possibly by means of flies thatvisit the sores or in other ways. 

ORIENTAL SORE

This disease, once supposed to be confined to the Orient, is now foundto be rather widely distributed throughout the tropics, where it issometimes very prevalent. It is caused by the presence in the system ofa parasite very similar to or identical with the one causing _kala-azar_and is regarded by some as a modified form of that disease. The patientis affected with one or more serious sores or ulcers which usually occuron exposed parts of the body. 

The parasite that causes the disease is supposed to be carried byinsects either directly or indirectly. 

In the latter case the insect may act as an intermediate host. 

Dogs and camels are also attacked by this disease and may be sources ofinfection. 

BIBLIOGRAPHY

A complete list of books and articles dealing more or less directly withthe subjects discussed in this book would be too extended for use here. For the past ten or twelve years many of the medical and biologicaljournals have contained articles in almost every issue, discussing thesesubjects in some of their phases. I have selected only a few of the moreimportant of them, and these only the English ones, confining myselfmostly to those that I have personally consulted, and giving briefannotations. Many of these will be found to include very fullbibliographies of the particular subject treated. 

In order to avoid repetition, references are given under one head onlyalthough many might properly be included in other sections as well. 

PARASITES AND PARASITISM

 BRAUN, MAX. Animal Parasites of Man. Translated by Pauline Falcke and edited by L. W. Sambon and F. V. Theobald. Third edition, 1906. A chapter on the general subject of parasitism and a description of parasites of all classes. Bibliography. 

 LEUCKART, R. The Parasites of Man and the Diseases Induced by Them. Eng. Transl. , London, 1886. 

 NEUMAN, THEO. Entoparasites and Hygiene. _Trans. Vassar Bros. Institute_, VII, 1895. A general discussion of parasitism; life-history of some common parasites that infest man. 

 NEUMANN, L. G. Treatise on the Parasites and Parasitic Diseases of the Domesticated Animals. Eng. Transl. By Fleming, 1892. 

 RANSOM, B. H. How Parasites Are Transmitted. _Year Book U. S. Dept. Agric. _, 1905, pp. 139-166 (pub. 1906). Discusses the ways in which parasites of all classes are transmitted. 

 SAMBON, L. The Part Played by Metazoan Parasites in Tropical Pathology. _Jour. Trop. Med. & Hyg. _, Vol. XI, Jan. 15, 1908. A comprehensive discussion of this subject. 

 SHIPLEY, A. E. , AND FEARNSIDES, E. G. Effects of Metazoan Parasites on Their Hosts. _Jour. Econom. Biology_, Vol. I, 1906, pp. 41-62. Discusses injury due to mere presence of parasite in host; to the migration of the parasite; loss to host by feeding of parasites; injury by certain toxins. 

 STILES, C. W. Diseases Caused by Animal Parasites. _Osler's Mod. Med. _, Vol. I, 1907, p. 525. General discussion; Trematodes; Cestodes; Roundworms; Acariasis; Parasitic Insects; Myiasis. 

 VAN BENEDEN, P. J. Animal Parasites and Messmates. 1889. Contains much that is interesting. 

 WARD, HENRY B. Influence of Parasitism on the Host. _Proc. Amer. Assn. For Advancement of Science_, Vol. 56, 1907. A comprehensive statement of this subject. List of literature. 

PROTOZOA

 CALKINS, G. N. The Protozoa. _Osler's Mod. Med. _, Vol. I, 1907, p. 353. General notes on the Protozoa; classification; reproduction; life-cycle of various forms. Regards Protozoa as subkingdom and the four great divisions as phyla. 

 CALKINS, G. N. Protozoölogy. N. Y. , 1909. Chapters on parasitism, pathogenic Protozoa, etc. 

 CLARKE, J. J. Protozoa and Disease. London, 1903, Pt. I. Discusses the various protozoa that cause disease, and refers frequently to those that are transferred from host to host by insects. 

 CLARKE, J. J. Protozoa and Disease. London, 1908. Part II, comprising sections on the causation of smallpox, syphilis and cancer. Notes on parasitic Protozoa, tropical diseases, ticks, piroplasmosis, etc. 

 DANIELS, C. W. Persistence of the Tropical Diseases of Man Due to Protozoa. _Jour. Trop. Med. & Hyg. _, 12, Aug. 2, 1909, pp. 232-234. Same in _Lancet_, II, 1909, p. 460. Good summary of present knowledge of the subject. 

 MINCHIN, E. A. Protozoa. In Albutt and Rolleston's _System of Medicine_, II, 1907, pp. 9-122. A comprehensive chapter on Protozoa. Many parasitic forms are figured and described. Bibliography. 

 MINCHIN, E. A. The Sporozoa. In Lankester's _Treatise on Zoöl. _, Pt. I, pp. 150-360, 1903. Best account of this group, list of Sporozoan hosts. Bibliography. 

BACTERIA

 FLEXNER, SIMON. Relation of Bacteria and Sporozoa to Disease. _Science_, N. S. , Vol. 27, No. 682, pp. 133-136. On these pages discusses relation of bacteria and Protozoa to human diseases. 

 JORDAN, EDWIN O. General Bacteriology. Philad. , 1898. A good general treatment of the subject. 

 LEVY, ERNST, AND KLEMPERER, FELIX. Elements of Clinical Bacteriology for Physicians and Students (transl. By A. A. Eschner), Philad. , 1909. Morphology and biology of bacteria; infection; immunity; specific diseases of bacterial origin, etc. 

 MUIR, ROBT. , AND RITCHIE, JAS. Manual of Bacteriology. N. Y. , 1903. Contains chapter on the relation of bacteria to diseases and discussion of several bacterial diseases. 

 STERNBERG, G. M. A Manual of Bacteriology. N. Y. , 1893. Part III is devoted to pathogenic bacteria. 

INSECTS AND DISEASE

 HERMS, W. B. Medical Entomology, Its Scope and Methods. _Jour. Of Eco. Ento. _, Vol. 2, No. 4, 1909, pp. 265-268. 

 HOWARD, L. O. Insects as Carriers and Spreaders of Disease. _Year Book U. S. Dept. Agric. _, 1901, pp. 177-192. Good review of the subject. 

 HOWARD, L. O. How Insects Affect Health in Rural Districts. _U. S. Dept. Agric. , Farmers' Bulletin, No. 155_, 1902. Discussion of city and county conditions; protection from typhoid, malaria and yellow fever. 

 HOWARD, L. O. Economic Loss to the People of U. S. Through Insects That Cause Disease. _Bull. 78, U. S. Dept. Agric. Bur. Of Ent. _, 1909. A comprehensive discussion and summary of the subject. Discusses mosquitoes, flies, the Panama Canal, epidemic diseases and the progress of nations. 

 KELLOGG, V. L. Insects and Disease, Chap. XVIII, in _American Insects_, pp. 615-654, 1905. Discusses Mosquitoes and malaria; yellow fever and filariasis. 

 KING, H. H. Report on Economic Entomology of Khartoum, in _Third Rept. Of Wellcome Research Lab. _, 1908. Discusses insects injurious to man: mosquitoes, blood-sucking insects other than mosquitoes, etc. 

 MASON, C. F. The Spread of Diseases by Insects, with Suggestions Regarding Prophylaxis. _International Clinics_, Vol. II, 1904, pp. 1-21. A brief summary of the subject. 

 MCCRAE, JOHN. Recent Progress in Tropical Medicine. _International Clinics_, Vol. II, 1904, pp. 22-36. Discusses several diseases, some of which are transmitted by insects. 

 NUTTALL, G. H. F. On the Rôle of the Insects Arachnids and Myriapods as Carriers in the Spread of Bacterial and Parasitic Diseases of Man and Animals. A critical and historical study. _Johns Hopkins Hospital Reports_, Vol. 8, 1899, pp. 1-154. A review of all the literature up to this date. Important article. 

 NUTTALL, G. H. F. Insects as Carriers of Disease. Recent advances in our knowledge of the part played by blood-sucking arthropods (exclusive of mosquitoes and ticks) in the transmission of infectious diseases. Bericht über den XIV. Intern. Kongress für Hygiene und Dermogrophic. Berlin, 1907, pp. 195-206. Discusses protozoan and bacterial diseases. 

 STILES, C. W. Insects as Disseminators of Disease. _Virginia Medical Semi-monthly_, Vol. 6, No. 3, May 10, 1901, pp. 53-58. Good statement of subject with list of recent workers. 

 WHERRY, W. B. Insects and Infection. _Cal. State Jour. Of Med. _, Nov. , 1907. Discusses the rôle of insects, ticks, etc. , in the transmission of infectious diseases. 

 Symposium on Yellow Fever and Other Insect-borne Diseases. _Science_, N. S. , Vol. 23, Nos. 584-585, 1906. The Protozoan Life-cycle, G. N. Calkins. Filariasis and Trypanosome Diseases, H. B. Ward. The Practical Results of Reed's Findings on Yellow Fever Transmission, J. H. White. Difficulties of Recognition and Prevention of Yellow Fever, Q. Kohnke. The Practical Side of Mosquito Extermination, H. C. Weeks. Without Mosquitoes There Can Be No Yellow Fever, Jas. Carroll. Estivo-autumnal Fever, Cause, Diagnosis, Treatment and Destruction of Mosquitoes Which Spread the Disease, H. A. Veazie. 

MOSQUITOES--SYSTEMATIC AND GENERAL

 BALFOUR, ANDREW, AND STAFF. _Second Report of the Wellcome Research Laboratories at the Gordon Memorial College_, Khartoum, 1906. Includes reports on work on mosquitoes and other noxious insects. 

 BOYCE, SIR ROBERT W. Mosquitoes or Man? The Conquest of the Tropical World. N. Y. , 1909. Reviews medical and sanitary work in the tropics and discusses the relation of insects to various tropical diseases. 

 BUSCH, AUGUST. Report on a Trip for the Purpose of Studying the Mosquito Fauna of Panama. _Smith. Miscell. Coll. _, Vol. 5, Pt. I, 1908, p. 49. Work that is being done in Panama to control the mosquitoes. Annotated list of species. 

 FELT, E. P. Mosquitoes or Culicidæ of New York State. In _N. Y. State Museum Bull. 79_, Entomology 22, 1904. Discusses distribution, migration and life-history of various species of mosquitoes and mosquito diseases. Bibliography. 

 GILES, GEO. M. A Handbook of Gnats or Mosquitoes, Giving the Anatomy and Life-History of the Culicidæ. London, 1902. Whole subject treated very fully. 

 GRUBBS, S. B. Vessels as Carriers of Mosquitoes. _Pub. Health and Mar. Hospt. Ser. Bull. _ II, Mar. 3, 1903. Believes that mosquitoes may come aboard when the vessel is lying at anchor one-half mile from shore, and that under favorable conditions they may come aboard when the vessel is fifteen miles from shore. 

 HOWARD, L. O. Mosquitoes. _Osler's Mod. Med. _, Vol. I, p. 370, 1907. General notes on classification and habits particularly in relation to diseases. 

 HOWARD, L. O. Notes on Mosquitoes of the United States. _U. S. Dept. Agric. , 1900. Div. Of Ento. Bull. No. 25_, N. S. Account of the structure; biology; remarks on remedies. 

 HOWARD, L. O. Concerning the Geographic Distribution of the Yellow Fever Mosquito. _Public Health Rept. , Pub. Health and Mar. Hospt. Ser. _, Nov. 13, 1903. The same revised to Sept. 10, 1905. 

 HOWARD, L. O. Mosquitoes: How They Live; How They Carry Disease; How They Are Classified; How They May Be Destroyed. N. Y. , 1901. One of the best popular books on mosquitoes. 

 MCCRACKEN, I. _Anopheles_ in California, with a Description of a New Species. _Entomological News_, Vol. 15, Jan. , 1904. Records of three species, their breeding-places, habits, etc. 

 MITCHELL, EVELYN G. Mosquito Life. N. Y. , 1907. A good popular account of the mosquitoes and their relation to disease. The appendix treats of mosquitoes and their possible relation to leprosy. 

 SMITH, J. B. Mosquitoes Occurring Within the State of New Jersey. Report of the New Jersey State Agric. Exper. Station upon the mosquitoes occurring within the State. Trenton, N. J. , 1904. Habits, development, relation to disease, checks and remedies; systematic. 

 SMITH, J. B. The General Economic Importance of Mosquitoes. _Popular Science Monthly_, 70, 1907, pp. 325-329. Mosquitoes affect not only the health and comfort of the people, but hinder development of agriculture and thus affect land values. 

 SMITH, J. B. The New Jersey Salt-marsh and Its Improvement. _New Jersey Agricultural Experiment Station Bulletin_, 207, 1907. Shows that the increased value of the land drained in the antimosquito crusade more than pays for the cost of the drainage. 

 THEOBALD, F. V. Monograph of _Culicidæ_ of the World. Four Vols. And one Vol. Of plates. London, 1901 to 1907. Vol. I contains 96 pages on structure, life-history, habits, etc. Vol. II contains a bibliography. Vol. Ill contains a list of species that carry disease. 

 THEOBALD, F. V. Mosquitoes or _Culicidæ_. In Albutt and Rolleston's _System of Medicine_, II, 1907, pp. 122-168. Structure, life-history, habits, distribution and classification of mosquitoes. Bibliography. 

MOSQUITO ANATOMY

 BERKELEY, WM. M. Laboratory Work with Mosquitoes. N. Y. , 1902. Chapters on development, anatomy, dissection, malarial parasites, filarial disease, yellow fever. 

 DIMMOCK, GEO. Anatomy of the Mouth-parts and Suctorial Apparatus of _Culex_. _Psyche_, 3, pp. 231-241, Sept. , 1881. Good. 

 IMMS, A. D. On the Larval and Pupal Stages of _Anopheles maculipennis_. _Journal Hygiene_, Vol. 7, No. 2, April, 1907. Morphology. 

 IMMS, A. D. On the Larval and Pupal Stages of _Anopheles maculipennis_. _Parasitology_, Vol. I, No. 2, June, 1908. Continuation of article in _Jour. Hyg. _, Vol. 7, No. 2. Continues discussion of morphology. 

 NUTTALL, GEO. F. , CORBETT, LOUIS, AND STRANGEWAYS-PIG, T. Studies in Relation to Malaria. Pt. I, The Geographical Distribution of _Anopheles_ in Relation to the Former Distribution of Ague in England. _Jour. Hyg. _, Vol. I, No. 1, Jan. , 1901. 

 NUTTALL, GEO. F. , AND SHIPLEY, ARTHUR E. Studies in Relation to Malaria. Pt. II, Structure and Biology of _Anopheles_, _Jour Hyg. _, Vol. I, No. 1, Jan. , 1901: The Egg and Larva; Bibliography. Pt. II, cont, Vol. I, No. 2, April, 1901: The Pupa. Pt. II, cont. , Vol. I, No. 4, Oct. , 1901: Adult External Anatomy. Pt. II, cont. , Vol. 2, No. 1, Jan. , 1902: Ætiology of Adult. Pt. II, cont. , Vol. Ill, No. 2, April, 1903: Anatomy of Adult. 

 THOMPSON, MILLETT T. Alimentary Canal of the Mosquito. _Proc. Bost. Soc. Nat. Hist. _, Vol. 32, No. 6, 1905, pp. 145-202. Good summary of recent investigations. 

 WESCHE, W. The Mouth-parts of _Nemocera_ and Their Relation to the Other Families of _Diptera_. _Royal Microscopic Soc. Jour. _, 1904, pp. 28-47. Discussion with illustrations of the mouth-parts of various _Diptera_. 

MOSQUITOES--LIFE-HISTORY AND HABITS

 AYERS, E. A. The Secrets of the Mosquito. A guide to the extermination of the prolific pest. _World's Work_, 1907, Vol. 14, pp. 8902-8910. Notes on life-history and methods of control. 

 JORDAN, E. O. , AND HEFFERAN, MARY. Observations on the Bionomics of _Anopheles_. _Jour. Infec. Diseases_, II, 1905, pp. 56-69. Occurrence, breeding-places, habits, etc. 

 MORGAN, H. A. , AND DUPREE, J. W. Development and Hibernation of Mosquitoes. _Bull. 40_, N. S. , _Div. Of Ento. _, pp. 88-92, 1903. Results of observation on five genera of mosquitoes in the vicinity of Baton Rouge, La. 

 ROSS, E. H. The Influence of Certain Biological Factors on the Question of the Migration of Mosquitoes. _Jour. Trop. Med. & Hyg. _, 12, 1909, pp. 256-258, Sept. 1. Only fecundated females feed on blood, and must be fertilized after each batch of eggs. This determines largely the time and place of breeding. 

 SMITH, J. B. Concerning Migration of Mosquitoes. _Science_, 18, Dec. 11, 1903, pp. 761-764. Observations on the migrations of mosquitoes, particularly _C. Sollicitans_. 

MOSQUITO FIGHTING

 CELLI, ANGELO. The Campaign Against Malaria in Italy. Transl. By J. J. Eyre. _Jour. Trop. Med. & Hyg. _, XI, Apr. 1, 1908, pp. 101-108. Includes a good discussion of the effectiveness of destroying the mosquitoes in controlling malaria. 

 FELT, E. P. Mosquito Control. In _Report of the N. Y. State Entomologist for 1905_, pp. 109-116. Notes on importance and methods of control of various species. 

 GOLDBERGER, JOS. Prevention and Destruction of Mosquitoes. _Public Health Reports, Pub. Health and Mar. Hospt. Ser. _, July 17, 1908. Life-histories and methods of fighting larvæ, pupæ and adults. 

 LE PRINCE, J. A. Mosquito Destruction in the Tropics. _Jour. Amer. Med. Assn. _, LI, p. 26, Dec. 26, 1908. Occurrence and habits of _Anopheles_, methods of destruction. Results of anti-malarial work on the isthmus. Discussion by various doctors. 

 QUAYLE, H. J. Mosquito Control Work in California. _Bull. No. 178, Calif. Agric. Ex. Sta. _, pp. 1-55, 1906. Habits and life-history of California species, with an account of experiments to control the salt-marsh species. 

 ROSENAN, M. J. Disinfection Against Mosquitoes with Formaldehyde and Sulphur Dioxid. _Hyg. Lab. Pub. Health and Mar. Hospt. Ser. , Bull. 6_, 1901. 

 ROSS, RONALD. Mosquito Brigades and How to Organize Them. New York, 1902. 

 ROSS, RONALD. Logical Basis of the Sanitary Policy of Mosquito Reduction. _Science_, N. S. , Vol. 22, No. 750, Dec. 1, 1905, pp. 689-699. Important article dealing with the methods of control. 

 SMITH, J. B. Salt-marsh Mosquitoes. _New Jersey Agric. Exper. Stn. Special Bulletin T_, 1902. Breeding-places and methods of control of this species. 

 SMITH, J. B. Mosquitocides. _Bull. 40, New Series U. S. Dept. Agric. , Div. Of Ento. _, pp. 96-108, 1903. Results of experiments with a number of substances, several of which were found to be effective and some cheap enough to permit of their use to a limited extent. 

 SMITH, J. B. The New Jersey Salt-marsh and Its Improvement. _Bull. No. 207_, Nov. 14, 1907, _New Jersey Agric. Exper. Stn. _ Results of draining the marshes to get rid of mosquitoes. 

 SMITH, J. B. The House Mosquito: a City, Town and Village Problem. _N. J. Agric. Ex. Stn. Bull. 216_, 1908. Work done on salt-marshes since 1904 practically eliminated the migratory species, so that _C. Pipens_, the house mosquito, is now the problem. Life-history and methods of combating. 

 UNDERWOOD, W. L. Mosquitoes and Suggestions for Their Extermination. _Pop. Sci. Mo. _, Vol. 63, 1903, pp. 453-466. Life-history, habits and methods of control. 

 UNDERWOOD, W. L. The Mosquito Nuisance and How to Deal with It. Boston, 1903. 

 First Antimosquito Convention, 1903. Pub. , Brooklyn, 1904. Contains articles on what railroads, government and laws should do toward mosquito extermination; mosquito work in Havana; how state appropriations should be used, etc. 

 National Mosquito Extermination Society. Bulletin No. 1, 1904. Object of Society; brief sketches of Ross, Reed, and others. Reprints of a few articles on mosquito extermination. 

 American Mosquito Extermination Society. _Year Book for 1904-05. _ N. Y. , 1906. Containing reports of meetings and discussions of various problems. Several interesting papers, among them "Criminal Indictment of the Mosquito, " F. W. Moss. "Mosquito Work at Panama Canal, " W. C. Sorgas. "Diversities Among New York Mosquitoes, " E. P. Felt. "Mosquito Extermination in New Jersey, " J. B. Smith. "The Mosquito Question, " Quitman Kohnke. 

 Antimalarial Work in the Panama Canal Zone. Editorial in _Jour. Trop. Med. & Hyg. _, XI, Aug. 15, 1908, p. 251. Notes on the success of the measures adopted there. 

MOSQUITOES AND DISEASE

 DOTY, A. H. The Mosquito, Its Relation to Disease and Its Extermination. _New York State Journal of Medicine_, May, 1908. 

 FINLAY, CHAS. Mosquitoes Considered as Transmitters of Yellow Fever and Malaria. _Med. Record_, May 27, 1899, pp. 737-739. Review of his theory in regard to mosquitoes and disease and the probable necessary changes in view of recent discoveries. 

 HOWARD, L. O. Mosquitoes as Transmitters of Disease. _Review of Reviews_, XXIV, 1901, pp. 192-195. A review of the work of various investigators. 

 SMITH, J. B. Sanitary Aspect of the Mosquito Question. _Medical News_, Mar. 7, 1903. Note on mosquitoes and their relation to disease. 

 TAYLOR, J. B. Observations on the Mosquitoes of Havana, Cuba. Reprint from _La Revista de Medicina_, June, 1903, p. 27. 

MALARIA

 BANKS, C. S. Experiments in Malarial Transmission by Means of _Myzomyia ludlowii_. _Phil. Jour. Sci. _, B. 2, 1907, pp. 513-535. Breeding-places of mosquitoes, life-histories of the species; mosquitoes and malaria. 

 CRAIG, C. F. Malarial Fevers. _Osler's Mod. Med. _, Vol. I, p. 392, 1907. Historical; distribution; malarial parasites; classification; development; malarial mosquitoes; pathology; treatment, etc. 

 CRAIG, C. F. Studies in the Morphology of Malarial Plasmodia after the Administration of Quinine and in Intracorpuscular Conjugation. _Jour. Infec. Diseases_, VII, No. 2, 1910. See also same, IV, 1907, pp. 108-140. Gives the evidence upon which he bases his theory of the meaning of intracorpuscular conjunction. 

 CRAIG, C. F. The Malarial Fevers, Hemoglobinuric Fever and the Blood Protozoa of Man. N. Y. , 1909. A thorough consideration of the subject of malaria and good discussion of the other subjects noted in title. Bibliography. 

 DEADERICK, W. H. Malaria. Philad. , 1909. The chapter on ætiology treats of the transmission by mosquitoes. 

 HARRIS, S. Prevention of Malaria. _Jour. Amer. Med. Assn. _, 53, Oct. 9, 1909, pp. 1162-67. Effects of malaria, transmission by mosquitoes, etc. In the discussion of the paper J. H. White summarizes the fight against yellow fever in New Orleans. 

 HERRICK, G. W. Relation of Malaria to Agriculture and Other Industries of the South. Economic losses occasioned by malaria; malaria responsible for more sickness among the white population than any other disease; relation to mosquitoes. _Pop. Sci. Mo. _, Vol. 62, Apr. , 1903, pp. 521-525. 

 JONES, ROSS, ELLETT. Malaria. London, 1907. Small book, introduction by Ross. Malaria in Greece and Italy; shows how this disease contributed to the downfall of great nations. 

 MANNABERG, JULIUS. Malaria. In Nothnagel's _Encyclopedia of Practical Med. _, Amer. Ed. , 1905, pp. 17-494. A very comprehensive discussion of the disease and the relation of mosquitoes to the malarial parasite. 

 MANSON, PATRICK. The Mosquito and the Malaria Parasite. _Brit. Med. Jour. _, Vol. II for 1898, pp. 849-853. History of the parasite in the human and insect host; observations of Ross and others and their meaning. 

 MANSON, PATRICK. Experimental Demonstration of the Mosquito-malarial Theory. _Brit. Med. Jour. _, Vol. 2 for 1900, pp. 949-951, also _Lancet_, II, 1900, pp. 923-925. Infected mosquitoes sent from Rome allowed to bite men in England who had not been in malarial regions. Malarial fever followed. 

 MANSON, PATRICK. Malarial Fever. Appendix to Vol. IX of T. C. Albutt's _System of Med. _, 1900. Relation of the malarial parasite to the disease and to mosquitoes. 

 ROBERTSON, E. W. Renaming of Malaria--Anophelesis. _Va. Medical Semi-monthly_, Sept. 10, 1909. Considers malaria a misnomer and gives reasons for suggesting new name. 

 ROSS, RONALD. On Some Peculiar Pigmented Cells Found in Two Mosquitoes Fed on Malarial Blood. _Brit. Med. Jour. _, 1897, Dec. 18, p. 1786. Records in his experiments in feeding mosquitoes on blood of malarial patients. Records finding the parasites in some of them. Important article. 

 ROSS, RONALD. Pigmented Cells in Mosquitoes. _Brit. Med. Jour. _, 1898, Feb. 26, p. 550. Further notes on them. 

 ROSS, RONALD. The Mosquito Theory of Malaria. Report dated Calcutta, Feb. 16, 1899. Reprinted in _Pop. Sci. Monthly_, Vol. 56, Nov. , 1899, pp. 42-46. Tells of his investigations in India and their results. 

 ROSS, RONALD. The Relationship of Malaria and the Mosquito. _Lancet_, II, 1900, July 7, p. 4880. Observation on the transmission of malaria. 

 ROSS, RONALD. Malaria Fever, Its Cause, Prevention and Treatment. London, 1902. Chapters on malaria, mosquitoes, prevention and treatment. 

 ROSS, RONALD. Parasites of Mosquitoes. _Jour. Of Hyg. _, VI, No. 2, Apr. , 1906. Brief review of several of his earlier papers on this subject with additional notes. 

 SIMPSON, W. J. R. Recent Discoveries Which Have Rendered Antimalarial Sanitation More Precise and Less Costly. _Brit. Med. Jour. _, 1907, II, pp. 1044-46. Discussion of the various factors in mosquito control. 

 STEPHENS, J. W. W. , AND CHRISTOPHERS, S. R. The Practical Study of Malaria and Other Blood Parasites. London, 1908. Chapters on mosquitoes, flies and ticks and their relation to diseases. 

 STERNBERG, G. M. The Malarial Parasite and Other Pathogenic Protozoa. _Pop. Sci. Mo. _, Vol. 50, 1897, pp. 628-641. Account of the discovery of the malarial parasite and more recent studies on it. 

 STERNBERG, G. M. Malaria. _Smith. Rept. _, 1900, pp. 645-656. Review of the experimental evidence in support of the mosquito-malaria theory. 

 Malarial Fever. _Jour. Trop. Med. & Hyg. _, II, Mar. 16, 1908, pp. 96-98. A list of literature mostly for the years 1906 and 1907. 

YELLOW FEVER

 ADAMS, S. H. Yellow Fever, a Problem Solved. The battle of New Orleans against the mosquito. _McClure's Magazine_, Vol. 27, June, 1906, p. 178. An interesting popular article. 

 CARROLL, JAMES. Yellow Fever. _Osler's Mod. Med. _, Vol. II, 1907, p. 736. History, ætiology, treatment. A good review of the work of the Yellow Fever Com. And the results of their work. 

 CARROLL, JAMES. The Transmission of Yellow Fever. _Amer. Med. Assn. _, 40, 1905, pp. 1429-33. Shows the relation of the mosquito to the disease. 

 CARROLL, JAMES. Yellow Fever. Lessons to be learned from the present outbreak of yellow fever. _Jour. Of Amer. Med. Assn. _, Vol. 45, 1905, pp. 1079-81. Among other things recommends that mosquitoes be kept from patients. 

 CHAILLE, S. E. The _Stegomyia_ and Fomites. _Amer. Med. Assn. _, 40, 1903, pp. 1433-40. Concludes that the mosquito is the only proven disseminator of yellow fever. Extended discussion by various physicians. 

 DASTRE, A. The Fight Against Yellow Fever. _Smith. Rept. _, 1905, pp. 339-350. History of the yellow fever epidemics, its geographical distribution, and the work that is being done to control it. 

 DOTY, A. H. On the Mode of Transmission of the Infectious Agent in Yellow Fever and Its Bearing upon the Quarantine Regulations. _Med. Record_, Oct. 26, 1901, pp. 649-653. Review of older theories in regard to the spread of yellow fever. Believes that the quarantines are now unnecessary. 

 FINLEY, CHAS. The Mosquito Theory of the Transmission of Yellow Fever and Its New Development. _Med. Record_, Jan. 19, 1901. Refers to his early observations on the subject, giving extracts from some of his earlier papers to show that he had long held the mosquito responsible for the dissemination of yellow fever. 

 GOLDBERGER, JOS. Yellow Fever, Ætiology, Symptoms and Diagnosis. _Yellow Fever Inst. Bull. 16, Pub. Health and Mar. Hospt. Ser. _, 1907. Includes discussion of the relation of mosquitoes to the disease. 

 GUITERAS, JOHN. Experimental Yellow Fever at the Inoculation Station of the Sanitary Department of Havana. _Amer. Med. _, Vol. II, No. 21, 1901, pp. 809-817. Experiments show that all types of the yellow fever from mild to severe may be produced by the bite of the mosquito. 

 MCFARLAND, JOSEPH. Life and Work of James Carroll. Memoir read at the fifth annual meeting of the Soc. Of Tropical Med. , 1908. Early life of Carroll and his work with the Yellow Fever Com. 

 PARKER, H. B. , BEYER, G. E. , AND POTHIER, O. L. Rept. Of Working Party No. 1, Yellow Fever Institute. _Bull. 13, Pub. Health and Mar. Hospt. Ser. _, 1903. As a result of their studies they believe that the disease is caused by a protozoan parasite which they name and describe. Discuss the relation of mosquitoes to the disease. 

 REED, WALTER; CARROLL, JAMES; AND AGRAMONTE, A. Experimental Yellow Fever. _Amer. Med. _, July 6, 1901, pp. 15-23. Records of certain experiments and their results. 

 REED, WALTER; CARROLL, JAMES; AND AGRAMONTE, C. A. The Ætiology of Yellow Fever. A preliminary note presented at the Amer. Pub. Health Assn. _Philad. Med. Jour. _, Oct. 27, 1900, pp. 790-796. Also an additional note in _Jour. Amer. Med. Assn. _, 36, pp. 431-440, 1901. Records of their experiments and a summing up of the data in regard to yellow fever and the mosquito. 

 REED, WALTER, AND CARROLL, JAMES. The Prevention of Yellow Fever. _Med. Record_, Oct. 26, 1901, pp. 441-449. History of the disease, especially in U. S. , results of the work of Yellow Fever Com. Description, life-history and habits of the mosquito, its relation to yellow fever, methods of control. Important paper. 

 REED, WALTER. Recent Researches Concerning the Ætiology, Propagation and Prevention of Yellow Fever by U. S. Army Com. _Jour. Hyg. _, 2, 1902, pp. 101-119. Review of work of the Yellow Fever Com. And the importance of the results. Bibliography. 

 ROSENAN, M. J. , PARKER, H. B. , FRANCIS, E. , AND BEYER, G. E. Rept. Of Working Party No. 2, Yellow Fever Institute. Experimental studies in yellow fever and malaria at Vera Cruz, Mex. _U. S. Pub. Health and Mar. Hospt. Ser. _, May, 1904. Includes experiments and observations on mosquitoes. 

 ROSENAN, M. J. , AND GOLDBERGER, JOS. Report of Working Party No. 3, Yellow Fever Institute. _Yellow Fever Inst. Bull. 15, Pub. Health and Mar. Hospt. Ser. _, 1906. Unsuccessful attempts to grow the yellow fever parasite. Negative results in the experimental study of the hereditary transmission of the yellow fever in the mosquito. Appendix A gives a translation of Marchoux and Simonds' report in which they report positive results in their experiments along the same line. 

 STERNBERG, G. M. Transmission of Yellow Fever by Mosquitoes. _Smith. Rept. _, 1900, pp. 657-673. Review of the early theories in regard to yellow fever and the work and findings of the yellow fever commission. 

 WHITE, J. H. Yellow Fever and the Mosquito. _Jour. Amer. Med. Assn. _, LI, No. 26, Dec. 26, 1908. Considers both _S. Calopus_ and _C. Pungens_. Results of early mistakes. Necessity of destroying mosquito. Methods of destroying mosquito. Habits of mosquito. 

 Abstract of the Report of the French Yellow Fever Com. At Rio de Janeiro, 1903. _Pub. Health Report, Pub. Health and Mar. Hospt. Ser. _, Vol. 19, Pt. I, p. 1019. A summary of their findings and conclusions to the date of report. 

 DE YBARRA, A. M. F. Yellow Fever Again in Cuba. _Jour. Trop. Med. & Hyg. _, XI, Mar. 2, 1908, pp. 73-78. Cites a number of cases of yellow fever within the last few years and uses them as evidence to show that the disease may be transmitted in other ways than by the mosquito. A strong summing up of the arguments against the mosquito theory. Reprint of editorial in _Tex. Med. Jour. _, Oct. , 1907, also follows this article. 

 The Extinction of Yellow Fever at Rio de Janeiro. _Lancet_, II, 1909, p. 404. A review of a French publication giving the results of the work from 1903 to present time. In 1903 before work was begun there were 584 deaths from yellow fever. In 1908 only 4, and none so far in 1909. Success accredited to mosquito work and general sanitation. 

 A Pioneer in Research on Yellow Fever. Editorial in _Brit. Med. Jour. _, May 30, 1908, p. 1306. Refers to the work of L. D. Beauperthuy, who, in 1853, set forth the theory that yellow fever was transmitted by mosquitoes. 

DENGUE

 ASHBURN, P. M. , AND CRAIG, C. F. Experimental Investigations Regarding the Ætiology of Dengue Fever. _Jour. Infec. Diseases_, Vol. V, 1907, pp. 440-475. Conclude that the disease is spread only by mosquitoes. 

 COLEMAN, THOMAS D. Dengue. _Osler's Mod. Med. _, Vol. II, 1907, p. 489. Ætiology, pathology, etc. ; possibility of _Culex fatigans_ disseminating the disease. 

 GRAHAM, H. "The Dengue"; a Study of Its Pathology and Mode of Propagation. _Jour. Of Trop. Med. & Hyg. _, July 1, 1903, p. 209. Experiments which seem to show that dengue is transmitted by _Culex fatigans_. 

 LEICHTENSTERN, O. Dengue. In Nothnagel's _Encyclopedia of Practical Med. _, Amer. Ed. , 1905, pp. 720-743. Consideration of the disease and its transmission. 

 ROSS, E. H. The Prevention of Dengue Fever. _Amer. Trop. Med. & Parasit. _, Vol. II, No. 3, July 1, 1908, pp. 193-195. A successful campaign against the mosquitoes in Port Said in 1906 stopped the outbreaks of malaria and dengue. 

 Dengue and Sand-flies. _Jour. Trop. Med. & Hyg. _, 12, 1909, pp. 172-173. A note on these pages refers to the work of Dr. R. Doerr, who suspects that dengue may be carried by sand-flies, _Phlobotomus_, as well as by mosquitoes. 

FILARIAL DISEASES AND ELEPHANTIASIS

 CHRISTOPHERS, S. R. What Is Really Known of the Cause of Elephantiasis. _Ind. Med. Gaz. _, Nov. , 1907, p. 404. Questions Manson's theory in regard to the disease being caused by filaria. 

 MANSON, PATRICK. Tropical Diseases. London, 1908, pp. 594-648. A most comprehensive chapter on filariasis and elephantiasis. 

 PHALEN, J. M. , AND NICHOLS, H. J. Filariasis and Elephantiasis in Southern Luzon. _Phil. Jour. Sci. _, Sept. , 1908. _Culex microannulatus_ regarded as the carrier of the filaria. 

 PROUT, W. T. On the Rôle of Filaria in the Production of Disease. _Jour. Trop. Med. & Hyg. _, Apr. 1, 1908, p. 109. Discussion of same in same journal, June 1, 1908. 

 WHITE, DUNCAN. Filarial Periodicity and Its Association with Eosinophilia. _Jour. Trop. Med. & Hyg. _, 12, July 15, 1909, pp. 175-183. Among other things he discusses the relation of mosquitoes to filarial diseases. 

LEPROSY

 BRINCKERHOFF, W. R. A Note upon the Possibility of the Mosquito Acting in the Transmission of Leprosy. _Pub. Health and Mar. Hospt. Ser. _ (general publications), 1908. Suggests the possibilities of such transmission, but concludes that the probabilities are against it. 

 GOODHUE, E. S. The Bacillus Lepræ in the Gnat and Bedbug. _Ind. Med. Gaz. _, Vol. XLI, Aug. , 1906, p. 342. Has found this bacillus in mosquitoes and bedbugs, but believes the latter is more concerned in transmitting the disease. 

 GOODHUE, E. S. Mosquitoes and Their Relation to Leprosy in Hawaii. _Amer. Med. _, N. S. , 2, 1907, p. 593. Suggests that mosquitoes may carry the disease, also warns against danger from flies and bedbugs. 

 HUTCHINSON, J. Mosquitoes and Leprosy. _Brit. Med. Jour. _, Dec. 22, 1906, Vol. II, p. 1841. Evidence against the insect theory of transmission of leprosy. 

 MUGLISTON, T. C. On a Possible Mode of Communication of Leprosy. _Jour. Trop. Med. _, Vol. VIII, July 15, 1905, p. 209. Suggests that the itch-mite may be the carrier of leprosy. Studies on 77 lepers led him to this conclusion. 

 SMYTH, W. R. Leprosy. _Brit. Med. Jour. _, Dec. 8, 1906, Vol. II, p. 1670. Believes that bedbugs or some similar wingless parasite conveys the disease. 

PLAGUE

 BRANNERMAN, W. B. Spread of Plague in India. _Jour. Of Hyg. _, Vol. 6, No. 2, Apr. , 1906, pp. 179-211. A digest of experiments made in India. Discusses various ways in which the disease may be spread. Review of the evidence that insects may be concerned. Bibliography. 

 CALVERT, W. J. Plague. _Osler's Mod. Med. _, Vol. II, 1907, p. 760. History; bacteriology; pathology; plague among animals; transmission, etc. 

 HAM, B. BURNETT. Report on Plague in Queensland, 1900-1907. P. 153 discusses the rat-flea theory of dissemination of bubonic plague, summing up the evidence of various observers, including the Indian Advisory Com. And others. Considers the evidence conclusive that _P. Cheopis_ and possibly _C. Fasciatus_ transmit plague. Other pages discuss various rat fleas and their relation to plague in rats. 

 HANKIN, E. H. On the Epidemiology of Plague. _Jour. Hyg. _, 5, 1905, pp. 48-83. A comprehensive discussion of the disease and its spread, several pages devoted to rats and fleas; evidence for and against the theory that rats and fleas are the principal carriers of the disease. 

 HERZOG, MAX. The Plague, Bacteriology, Morbid Anatomy & Histopathology, Including the Consideration of Insects as Plague Carriers. Biological Laboratory Bureau of Govt. Laboratories, Manila, Oct. , 1904. Reviews the evidence regarding the possibility of fleas carrying plague; describes a new rat flea (_Pulex philippinensis_); records experiments with fleas and cites a case of bubonic plague in a child in which the infection was possibly carried by _Pediculi_. 

 MCCOY, G. W. Plague Bacilli in Ectoparasites of Squirrels. _Pub. Health Reports, Pub. Health and Mar. Hospt. Ser. _, Vol. XXIV, No. 16, Apr. 16, 1909. Experiments with fleas and lice from infected squirrels demonstrating presence of plague bacilli. 

 MCCOY, G. W. The Susceptibility of Gophers, Field-mice and Ground-squirrels to Plague Infection. _Jour. Of Infec. Diseases_, Vol. 6, 1909, No. 3, pp. 283-288. Gophers highly resistant, field-mice moderately susceptible and ground-squirrels very susceptible to plague. 

 MITZMAIN, M. B. Insect Transmission of Bubonic Plague: a Study of the San Francisco Epidemic. _Ento. News_, 19, No. 8, 1908, pp. 353-359. Fleas obtained in examination of 1, 800 rats. Attempt to locate source of rat and flea introduction. 

 MORTON, F. M. Eradicating Plague from San Francisco. Report of the Citizens' Health Com. And an account of its work. San Francisco, 1909. Discusses the epidemics, methods of transmission, methods of fighting, etc. 

 RUCKER, W. C. Plague Among Ground-squirrels in Contra Costa Co. , Cal. _Pub. Health Reports, Pub. Health and Mar. Hospt. Ser. _, Aug. 27, 1909. Reports of human cases supposed to be connected with plague among ground-squirrels. Plague among squirrels; habits, methods of fighting, etc. 

 RUCKER, W. C. Fighting an Unseen Foe. _Sunset Mag. _, XXII, No. 2, Feb. , 1909. Story of the fight against plague in San Francisco. 

 SHIPLEY, A. E. Rats and Their Animal Parasites. _Jour. Eco. Biology_, Vol. III, No. 3, Oct. 28, 1908. List of species of ecto- and endoparasites. 

 SIMPSON, W. J. A Treatise on Plague. Cambridge Univ. Press, London, 1906. Deals with historical, epidemiological, clinical, therapeutic and preventive aspect of the disease. 

 THOMPSON, J. A. The Mode of Spread and Prevention of Plague in Australia. _Lancet_, Oct. 19, 1907, p. 1104. Rat fleas the essential factor in transmitting plague, and preventive methods should be directed against the rats. 

 THOMPSON, J. A. On the Epidemiology of Plague. _Jour. Hyg. _, Vol. VI, No. 5, Oct. , 1906. Methods of infection, spread, relation of rats to the disease and a review of the rat-flea theory. Bibliography. 

 VERJBITSKI, D. T. The Part Played by Insects in the Epidemiology of Plague. _Jour. Hyg. _, 8, 1908, No. 2, pp. 162-208. Record of extensive experiments with fleas. Fleas communicated plague for three days, bedbugs for five days. Interrelation of fleas, rats, dogs, cats, and man. An important article translated from Russian. 

 WHERRY, W. B. Further Notes on the Rat Leprosy and on the Fate of the Human and Rat Leper Bacillus in Flies. _Jour. Infec. Diseases_, Vol. 5, No. 5, 1908. Discussion and references, experiments with flies, summary, etc. More than 1, 115 lepra-like bacilli were counted in a single fly-speck. 

 WHERRY, W. B. Plague Among the Ground-squirrels of California. _Jour. Infec. Diseases_, Vol. 5, No. 5, 1908, pp. 485-533. How the plague was first discovered among rats, records of cases and a discussion of the possible relation of this to human plague cases. 

 Eradicating Plague in San Francisco; Report of the Citizens' Health Committee, 1909. An account of the recent outbreaks and the methods of fighting them. 

 Report of the Indian Plague Commission, Vol. V, pp. 75-77, 1901. In these pages the Commission considers the question of the transference of plague by suctorial insects. It considers Simonds' claims and others and believes that "suctorial insects do not come under consideration with the spread of plague. "

 Reports on Plague Investigations in India Issued by the Advisory Committee Appointed by the Sec. Of State for India, the Royal Society and the Lister Institute. The reports include the reports of the Working Commission appointed by the Advisory Committee and reports on various contributory investigations. They are published in the _Jour. Of Hygiene_ as "Extra Plague Numbers. " All these reports deal very largely with the relation of the rat and flea to plague, and are commonly referred to as "Reports of Indian Plague Commission. " The first number, Vol. VI, Sept. , 1906, contains articles on "Experiments upon the Transmission of Plague by Fleas. " "Note on the Species of Fleas Found on Rats, _Mus rattus_ and _Mus decumanus_ in Different Parts of the World. " "The Physiological Anatomy of the Mouth-parts and Alimentary Canal of the Indian Rat Flea, _Pulex cheopis_, " and other papers on the relation of rats to plague. The second number, Vol. VII, July, 1907, contains articles on "On the Significance of the Locality of the Primary Bubo in Animals Infected with Plague in Nature, " "Further Observations on the Transmission of Plague by Fleas with Special Reference to the Fate of Plague Bacillus in the Body of the Rat Flea, " "Experimental Production of Plague Epidemics Among Animals, " "Experiments in Plague Houses in Bombay, " "On the External Anatomy of the Indian Rat Flea and Its Differentiation from Some Other Common Fleas, " "A Note on Man as a Host of the Indian Rat Flea, " and others on the relation of rats to plague. The third number, Vol. VII, Dec. , 1907, contains articles on "Digest of Recent Observations on the Epidemiology of Plague" (Bibliography), "Epidemiological Observations in Bombay City, " "Epidemiological Observations in the Villages of Wadhala, Parel, Worli in the Neighborhood of Bombay Village, " "General Considerations Regarding the Spread of Infection, Infectivity of Houses, etc. , in Bombay City and Island, " "Epidemiological Observations in the villages of Dhand and Kasel (Punjab). " The fourth number, Vol. VIII, May, 1908, contains articles on "The Part Played by Insects in the Epidemiology of Plague" (see also ref. Under D. T. Verjbitski), "Observations on the Bionomics of Fleas with Special Reference to _P. Cheopis_, " "The Mechanism by Means of Which the Flea Cleans Itself of Plague Bacilli, " "On the Seasonal Prevalence of Plague in India. "

 See also under Fleas. 

FLEAS

 BAKER, C. F. Fleas and Disease. _Science_, N. S. , Vol. 22, No. 559, Sept. 15, 1905, p. 340. Discusses the possibility of fleas transmitting leprosy. 

 DOANE, R. W. Notes on Fleas, Collected on Rat and Human Hosts in San Francisco and Elsewhere. _Can. Ento. _, 40, 1908, pp. 303-304. Shows that _Ceratophyllus fasciatus_ and _Pulex irritans_ are common on both man and rats. 

 FOX, CARROLL. The Flea in Its Relation to Plague, with a Synopsis of the Rat Fleas. _The Military Surgeon_, 24, June, 1909, pp. 528-537. Review of the work of the Indian Plague Commission and others. Key for identification of rat fleas. 

 GALLI-VALERIO. The Part Played by Fleas of Rats and Mice in the Transmission of Bubonic Plague. _Jour. Trop. Med. _, Feb. , 1902. Attacks the theory that plague can be conveyed from rats to men by fleas because rat fleas do not bite men. 

 MCCOY, G. W. _Siphonaptera_ Observed in the Plague Campaign in California with a Note upon Host Transference. _Pub. Health Report, Pub. Health and Mar. Hospt. Ser. _, Vol. XXIV, No. 29, July 16, 1909. Lists of species from various hosts. Report on experiments in transferring rat fleas to squirrels and squirrel fleas to rats. 

 MCCOY, G. W. , AND MITZMAIN, M. B. An Experimental Investigation of the Biting of Man by Fleas Taken from Rats and Squirrels. _Public Health Report_, XXIV, No. 8, Feb. 19, 1909, pp. 189-194. Rat and squirrel fleas will bite man. 

 MITZMAIN, M. B. Insect Transmission of Bubonic Plague. A Study of the San Francisco Epidemic. _Entomological News_, Oct. , 1908. Source and distribution of species of fleas and brief notes on work of Indian Plague Commission. 

 MITZMAIN, M. B. How a Hungry Flea Feeds. _Entomological News_, Dec. , 1908. 

 MITZMAIN, M. B. Some New Facts on the Bionomics of the California Rodent Fleas. _Annals Ento. Soc. Amer. _, III, pp. 61-82, 1910. 

 SHIPLEY, A. E. Rats and Their Animal Parasites. _Jour. Of Economic Biology_, Vol. 3, No. 3, Oct. 28, 1908. List of species ecto- and endoparasites. 

 See also reports of Advisory Commission under Plague. 

TYPHOID FEVER

 ANDERSON, J. F. The Differentiation of Outbreaks of Typhoid Fever Due to Water, Milk, Flies and Contact. _Amer. Jour. Pub. Health_, 19, pp. 251-259. Discusses flies and typhoid. 

 MCCRAE, THOMAS. Typhoid Fever. _Osler's Mod. Med. _, Vol. II, p. 70, 1907. A full discussion of this disease. 

 REED, WALTER; VAUGHAN, V. C. , AND SHAKESPEARE, E. O. Abstract of Report on the Origin and Spread of Typhoid Fever in the U. S. Military Camps During the Spanish War of 1898. Washington, Govt. Printing Office, 1900. Shows among other things that "flies undoubtedly served as carriers of infection. "

 ROSEMAN, M. J. , LUMSDEN, L. L. , AND KASTLE, J. H. Report on Origin and Prevalence of Typhoid Fever in D. C. Including reports by Stiles, Goldberger and Stimson. _Bull. 35 of Hygienic Laboratory of U. S. Public Health and Mar. Hospt. Ser. _, 1907. (Second report in _Bull. 44_, 1907, includes nothing about insects. )

 VEEDER, M. A. Typhoid Fever from Sources Other Than Water Supply. _Med. Record_, 62, pp. 121-124, July 26, 1902. Cites several instances where flies might act as the carriers of the disease. 

 WHIPPLE, GEO. C. Typhoid Fever, Its Causation, Transmission and Prevention. N. Y. , 1908. Considers that house-flies and probably fruit-flies carry typhoid bacilli. 

HOUSE-FLIES; ANATOMY, LIFE-HISTORY, HABITS

 FELT, E. P. Observations on the House-fly. _Jour. Eco. Ento. _, III, No. 1, Feb. , 1910, pp. 24-26. Shows that it does not breed freely in darkness. 

 GRIFFITH, A. The Life-history of House-flies. _Public Health_ (London), 21, No. 3, 1908, pp. 122-127. Study of life-history. Flies require water frequently, eggs hatch in twenty-four hours, larval stage four days. Each female may lay four batches of eggs. Destroy manure and rubbish. 

 HAMER, W. H. The Breeding of Flies Summarized. _Am. Med. _, 3, 1908, p. 431. Habits of flies and experiments to show that they may carry the germs of various diseases. 

 HEPWORTH, JOHN. On the Structure of the Foot of the Fly. _Quar. Jour. Micro. Sci. _, II, 1859, pp. 158-563. One plate showing feet of different flies. A review of the older theories of how a fly was able to walk on smooth surfaces. 

 HERMS, W. B. The Essentials of House-fly Control. _Bull. Of Berkeley Board of Health_, Berkeley, Cal. , 1909. Recommends removing manure as soon as possible and keeping it in tight bins until removed. No very satisfactory insecticides have been found for use in treating manure piles. 

 HERMS, W. B. The Berkeley House-fly Campaign. _Cal. Jour. Of Technology_, Vol. XIV, No. 2, 1909. Discusses the methods that have been used in fighting the fly in Berkeley, Cal. Removing manure regularly or keeping it in closed bins recommended. 

 HEWITT, C. G. A Preliminary Account of the Life-history of the Common House-fly. _Mem. And Proc. Manchester Lit. Phil. Soc. _, 1906, Vol. 51, pp. 1-4. 

 HEWITT, C. G. On the Bionomics of Certain Calyptrate Mucidæ and Their Economic Significance with Especial Reference to Flies Inhabiting Houses. _Jour. Econ. Biol. _, 1907, Vol. II, pp. 79-88. Character and importance of group and notes on many species. 

 HEWITT, C. G. Structure, Development and Bionomics of the House-fly, _Muca domestica_. Part I, _Quar. Jour. Micro. Sci. _, 1907, p. 395, on anatomy, external and internal, and bibliography. Part II, same; 1908, p. 495. Breeding-habits, development and anatomy of larvæ, bibliography. Part III, same; 1909, pp. 347-414. The bionomics, allies, parasites, and the relations to human disease. The best article on the house-fly. 

 HOWARD, L. O. Further Notes on the House-fly. _Bull. 10, U. S. Dept. , Agric. Div. Of Ento. _, p. 63, 1898. Experiments to kill larvæ in manure. 

 HOWARD, L. O. House-flies. _U. S. Dept. Of Agric. , Bureau of Ento. , Circular No. 71_, revised ed. , 1906. Methods of control of house-fly and related species. 

 HOWARD, L. O. , AND MARLATT, C. L. _Bull. 4, U. S. Dept. Agric. , Div. Of Ento. _, pp. 43-47, 1896. General account with methods of controlling. 

 JEPSON, F. P. The Breeding of the Common House-fly During the Winter Months. _Jour. Econ. Biol. _, 4, 1909, pp. 78-82. Records of certain experiments which show that the flies will breed in winter under favorable conditions. 

 NEWSTEAD, R. Preliminary Report on the Habits, Life-cycle and Breeding-places of the Common House-fly as Observed in the City of Liverpool, with Suggestions as to the Best Means of Checking Its Increase. Liverpool, Oct. 3, 1907. 

 NEWSTEAD, R. On the Habits, Life-cycle and Breeding-places of the Common House-fly. _Ann. Trap. Med. Para. _, Vol. I, No. 4, Feb. 29, 1908, pp. 507-520. Final report on this subject. Sums up notes on life-history, habits, breeding-places, etc. Important article. 

 PACKARD, A. S. On the Transformation of the Common House-fly with Notes on Allied Forms. _Proc. Boston Soc. Nat. Hist. _, Vol. XVI, 1874, pp. 136-140. Life-history and anatomy. 

 WILCOX, E. V. Fighting the House-fly. _Country Life in America_, May, 1908. Methods of controlling this pest. 

HOUSE-FLIES AND TYPHOID

 AUSTEN, E. E. The House-fly and Certain Allied Species as Disseminators of Enteric Fever Among the Troops in the Field. _Jour. Roy. Army Med. Corps_, June, 1904. Suggests that it may carry enteric fever and other diseases; method of control. 

 FELT, E. P. The Typhoid or House-fly and Disease. In 24th _Rept. Of State Ento_. In _N. Y. State Museum Bull. _, No. 455, 1909. A general discussion with complete bibliography. 

 FIRTH, R. H. , AND HORROCKS, W. H. An Inquiry Into the Influence of Soil, Fabrics, and Flies in the Dissemination of Enteric Infection. _Brit. Med. Jour. _, Vol. II, 1902, pp. 936-942. House-flies carry enteric bacilli. They may pass through digestive tract and remain virulent. 

 HAMILTON, ALICE. The Fly as a Carrier of Typhoid. _Jour. Amer. Med. Assn. _, 40, 1903, pp. 576-83. A study of a typhoid outbreak in Chicago gives good evidence that the flies were important factors in the spread of the disease. 

 HEWITT, C. G. The Biology of House-flies in Relation to Public Health. _Royal Inst. Pub. Health Jour. _, Oct. , 1908. 

 HOWARD, L. O. A contribution to the Study of the Insect Fauna of Human Excrement. _Proc. Wash. Acad. Sci. _, 2, 1900, pp. 541-600. Special reference to the house-fly and typhoid fever. 

 HOWARD, L. O. Flies and Typhoid. _Pop. Sci. Mo. _, Jan. , 1901, pp. 249-256. A popular account of several species of flies that may be concerned in carrying typhoid. 

 KLEIN, E. Flies as Carriers of _B. Typhus_. _Brit. Med. Jour. _, Oct. 17, 1908, pp. 1150-51. In cultures made from flies he found great numbers of _B. Coli communis_ and _B. Typhosus_, showing that flies may carry these germs. 

 MARTIN, A. Flies in Relation to Typhoid and Summer Diarrhea. _Public Health_, 15, 1903, pp. 652-653. Believes that the house-fly is largely responsible for these diseases. 

 REED, WALTER. _War Dept. An. Rept. _, 1899, pp. 627-633. Flies the cause of a typhoid outbreak in army in 1899. 

HOUSE-FLY AND VARIOUS DISEASES

 BUCHANAN, R. A. , GLASG, F. F. , AND M. B. The Carriage of Infection by Flies. _Lancet_, 173, 1907, pp. 216-218. Flies carry various germs on their feet and distribute them where they walk. Must protect food from contamination. 

 BREWSTER, E. T. The Fly. The Disease of the House. _McClure's Magazine_, XXXIII; No. 5, Sept. , 1909, pp. 564-568. Proposes to make use of tropisms for ridding the houses of flies. 

 CASTELLANI, ALDO. Experimental Investigation on _Framboesia tropica_ (Yaws). _Jour. Of Hyg. _, Vol. VII, 1907, pp. 558-599. On pages 566-568 he discusses the part played by insects in transmitting the disease. Gives detail of experiments conducted and concludes that under certain conditions yaws may be conveyed by flies and possibly other insects. 

 COBB, J. O. Is the Common House-fly a Factor in the Spread of Tuberculosis? _Amer. Med. _, 9, 1905, pp. 475-477. Believes that the bacilli may enter the system through the digestive tract and that flies carry them to our food. 

 DICKENSON, G. K. The House-fly and Its Connection with Disease Dissemination. _Med. Record_, 71, 1907, pp. 134-139. Summary; bibliography. 

 ESTEN, W. M. , AND MASON, C. J. Sources of Bacteria in Milk. Starr's _Agric. Ex. Stn. , Conn. Bull. _, 51, 1908. Shows how flies may carry bacteria to milk. Table showing number of bacteria on flies from various sources. 

 FELT, E. P. The Economic Status of the House-fly. _Jour. Eco. Ento. _, Vol. 2, No. 1, Feb. , 1909, pp. 39-45. A summary of the charges, possibilities, proofs, etc. Discussion. 

 GUDGER, E. W. Early Note on Flies as Transmitters of Disease. _Science_, N. S. Vol. 31, Jan. 7, 1910, pp. 31-32. 

 HAMER, W. H. Nuisance from Flies. _London County Council Rept. _ No. 1, 138, pp. 1-10, and No. 1, 207, pp. 1-6, 1908. Observations on various flies and their relation to diseases. 

 HAYWARD, E. H. The Fly as a Carrier of Tuberculosis Infection. _N. Y. Med. Jour. _, 80, 1904, pp. 643-644. Tubercular bacilli pass through the digestive tract of flies and remain virulent. 

 HOWARD, L. O. The Carriage of Disease by Flies. _Bull. 30_, N. S. , pp. 39-45, _U. S. Dept. Agric, Div. Of Ento. _, 1901. Discussion of flies as carriers of disease. 

 HOWARD, L. O. House-flies. _U. S. Dept. Of Agric. , Bureau of Ento. _, Cir. No. 71, revised ed. , Sept. 21, 1906. Notes on the various species visiting houses; habits; methods of control; regulations for controlling flies in cities. 

 HUTCHINSON, WOODS. The Story of the Fly That Does Not Wipe Its Feet. _Sat. Evening Post_, March 7, 1908. 

 JACKSON, DANIEL D. Conveyance of Disease by Flies Summarized. _Bost. Med. & Surg. Jour. _, 1908, p. 451. Disease and flies prevail at same time; records over 1, 000, 000 bacteria to each fly caught on swill-barrels. 

 JACKSON, DANIEL B. Pollution of New York Harbor as a Menace to Health by the Dissemination of Intestinal Diseases Through the Agency of the Common House-fly. Account of experiments and deductions. Pamphlet issued July, 1908, by Merchants' Assn. Of New York. 

 LEIDY, JOSEPH. Flies as a Means of Communicating Contagious Diseases. _Proc. Acad. Nat. Sci. Phil. _, 23, 1871, p. 297. Believes that flies may carry disease; refers to flies in connection with gangrene and wounds. 

 LORD, F. T. Flies and Tuberculosis. _Bost. Med. & Surg. Jour. _, 1904, pp. 651-654. Fly-specks may contain virulent tubercular bacilli for at least fifteen days. 

 MAYS, THOS. J. The Fly and Tuberculosis. _N. Y. Med. Jour. & Phila. Med. Jour. _, 82, 1905, pp. 437-438. Believes that J. O. Cobb's data as given in _Amer. Med. Jour. _ is not at all conclusive. 

 NASH, J. C. T. A Note on the Bacterial Contamination of Milk as Illustrating the Connection Between Flies and Epidemic Diarrhea. _Lancet_, II, 1908, pp. 1668-69. Experiments show that milk left exposed to flies soon contains many more germs than that protected from them. 

 NASH, J. C. T. The Ætiology of Summer Diarrhea. _Lancet_, 164, 1903, p. 330. Believes house-fly carries this disease because the two appear and disappear together. 

 ROBERTSON, A. Flies as Carriers of Contagion in Yaws. _Jour. Trop. Med. & Hyg. _, 11, 1908, No. 14, p. 213. As a result of examinations the author concludes that the house-fly is capable of carrying the virus of yaws. 

 SANDILANDS, J. E. Epidemic Diarrhea and the Bacterial Control of Food. _Jour. Hyg. _, 6, 1906, pp. 77-92. Believes that house-flies convey these diseases from the excrement of infected infants. 

 SIBTHORPE, E. H. Cholera and Flies. _Brit. Med. Jour. _, Sept. , 1896, p. 700. Flies considered scavengers, think they thus help abate the disease. 

 SMITH, T. The House-fly as an Agent in Dissemination of Infectious Diseases. _Amer. Jour. Pub. Hyg. _, Aug. , 1908, pp. 312-317. Points out that flies on account of their habits, are dangerous sources of contamination. 

 SMITH, THEOBALD. The House-fly at the Bar. Merchants' Assn. , New York, 1909, pp. 1-48. Letters from various authorities giving their opinion; quotations from various authors. Bibliography. 

 VEEDER, M. A. Flies as Spreaders of Sickness in Camps. _Med. Record_, 54, 1898, pp. 429-430. Flies feed on typhoid excreta and pass to food. Cultures made from fly tracks and excreta show many bacteria present. 

 VEEDER, M. A. The Relative Importance of Flies and Water Supply in Spreading Disease. _Med. Record_, 55, 1899, pp. 10-12. Reasons for believing that flies spread disease in many instances. Burial of infected typhoid material no protection but a menace. 

 Dangers from Flies. E. P. W. _Nature_, Vol. 29, pp. 482-483. Review of an article by Dr. B. Grassi in regard to flies and various diseases. Opthalmia is discussed. Flies may ingest and pass unharmed eggs of various human parasites including tapeworm. 

HUMAN MYIASIS

 ALLEN, CHAS. H. Demonstration of Locomotion in the Larvæ of the OEstridæ. _Proc. Amer. Assn. Adv. Set. _, Vol. 24, 1875, pp. 230-236. Larvæ taken from flesh of child, one had moved thirty-six inches and one six inches. 

 FRENCH, G. H. A Parasite the Supposed Cause of Some Cases of Epilepsy. _Canad. Ento. _, 32, 1900, pp. 263-264. Larvæ of _Gastrophilus_ or _Dermatobia_ in the alimentary canal supposed to have caused spasms in young boy. 

 GILBERT, N. C. Infection of Man by Dipterous Larvæ with Report of Four Cases. _Archives of Internal Med. _, Oct. , 1908. Historical; various kinds sometimes found in man; good summary of subject. Bibliography. 

 HARRISON, J. H. H. A Case of Myiasis. _Jour. Trop. Med. & Hyg. _, XI, Oct. 15, 1908, p. 305. Over 300 larvæ of _Lucilia macellaria_ removed from face of negro woman. 

 HUMBERT, FRED. _Lucilia macellaria_ Infesting Man. _Proc. U. S. Nat. Museum_, 6, 1883, pp. 103-104. Records several cases in which the screw-worm infested patients. 

 JENYUS, LEONARD. _Trans. Ento. Soc. _, London, Vol. II, 1839, pp. 152-159. Notice of a case in which the larvæ of a dipterous insect, supposed to be _Anthomyia canicularis_, Meig. , were expelled in large quantities from the human intestines. 

 KANE, E. R. A Grub Supposed to Have Traveled in the Human Body. _Insect Life_, II, 1890, pp. 238-239. Larva of bot-fly taken from face of boy. It had been traveling under the skin for about five months. 

 MCCAMPBELL, E. F. , AND COOPER, H. J. _Myiasis intestinalis_ Due to Infection with Three Species of Dipterous Larvæ. _Jour. Amer. Med. Assn. _, 53, Oct. 9, 1909, pp. 1160-62. General notes on this subject and a report on a case in which larvæ of three different species of flies were obtained from one patient. 

 MEINERT, FR. _Lucilia nobilis_ Parasitic on Man. _Insect Life_, II, 1892, pp. 36-37. Two larvæ from the ear of a man proved to be the above species. 

 MURTFELEDT, M. E. Hominivorous Habits of the Screw-worm in St. Louis. _Insect Life_, IV, 1891, p. 200. Many larvæ of this species removed from the nasal passages of a patient. 

 NELSON, J. B. Insects in the Human Ear. _Insect Life_, VI, 1893, p. 56. Two cases in which blow-fly larvæ are reported as coming from the human ear. 

 RILEY, W. A. A Case of Pseudoparasitism by Dipterous Larvæ. _Canad. Ento. _, 38, 1906, p. 413. Several larvæ, species undetermined, removed from back of patient. 

 SAY, THOMAS. On a South American Species of OEstrus Which Inhabits the Human Body. _Tr. Phil. Acad. Nat. Sci. _, Vol. 2, 1822, pp. 353-360. Extended notes on various dipterous larvæ infesting man. 

 SNOW, F. H. Hominivorous Habits of _Lucilia macellaria_ "The Screw-worm. " _Psyche_, 4, 1883, pp. 27-30. Cites observations made by himself and others. 

 WILLISTON, S. W. The Screw-worm Fly _Compsomyia macellaria_. _Psyche_, 4, 1883, pp. 112-114. Notes on this species with a translation of a Spanish article by Anibalzaga in which instances of this fly infesting human beings are recorded. 

 YOUNT, C. E. , AND SUDLER, M. T. Human Myiasis from the Screw-worm Fly. _Jour. Amer. Med. Assn. _, Vol. 49, No. 23, 1907, p. 1912. Several cases giving reference to literature, symptomatology, diagnosis. 

STOMOXYS AND OTHER FLIES

 AUSTEN, E. E. Blood-sucking and Other Flies Known or Likely to Be Concerned in the Spread of Disease. In Albutt's and Rolleston's _System of Med. _, 2, 1907, pp. 169-186. A descriptive list of these flies. Bibliography. 

 AUSTEN, E. E. Illustrations of African Blood-sucking Flies Other Than Mosquitoes and Tsetse-flies. London, 1909. 

 NEWSTEAD, R. On the Life-history of _Stomoxys calcitrans_. _Jour. Econom. Biology_, Vol. I, 1906, pp. 157-166. Describes habits and life-history of larvæ and adults. Important article. 

 STEPHENS, J. W. W. , AND NEWSTEAD, R. The Anatomy of the Proboscis of Biting Flies. Part II, _Stomoxys_. _Ann. Of Trop. Med. & Parasit. _, Vol. I, No. 2, June 15, 1907, pp. 171-182. Good anatomical paper. Part I (_Glossina_) was published in mem. XVIII, 1906, Liverpool School Trop. Med. 

 TULLOCK, F. Internal Anatomy of _Stomoxys_. _Proc. Roy. Soc. _, London, 77, Series B, 1906, pp. 523-531. Descriptions and drawings comparing with _Glossina_. 

TSETSE-FLIES

 AUSTEN, E. E. A Monograph of the Tsetse-flies. Published by order of the Trustees of the British Museum, 1903. 

 MANSON, P. Tsetse-flies. In _Trop. Diseases_, p. 174. Description of genus; table of species; distribution; reproduction, habits. 

 MINCHIN, E. A. Report of Anatomy of the Tsetse-fly (_Glossina palpalis_). _Proc. Roy. Soc. _, London, 76, Series B, 1905, pp. 531-547. Good account of internal anatomy of this fly, important because of its relation to trypanosomiasis. 

 MINCHIN, E. A. The Breeding-habits of the Tsetse-fly. _Nature_, Oct. 25, 1906, p. 636. 

 MINCHIN, E. A. , GRAY, A. C. H. , AND TULLOCK, F. M. G. (Sleeping Sickness Com. ) _Glossina palpalis_ in Its Relation to _Trypanosoma gambiense_ and Other Trypanosomes (Preliminary Report). _Proc. Roy. Soc. _, Vol. 78, 1906, pp. 242-258. Report on certain experiments in feeding these flies on infected animals and in allowing supposedly infected flies to feed on various animals. 

 NOVY, F. G. The Trypanosomes of Tsetse-flies. _Jour. Infec. Dis. _, III, 1906, pp. 394-411. Notes on the various species. 

TRYPANOSOMES AND TRYPANOSOMIASIS

 BRUCE, DAVID. Trypanosomiasis. _Osler's Mod. Med. _, Vol. I, 1907, p. 460. A discussion of _Trypanosoma lewisi_, _evansi_, _brucei_, _gambiensi_, and the diseases caused by them. 

 DUTTON, J. E. , TODD, J. L. , AND HARRINGTON, J. W. B. Trypanosome Transmission Experiments. _Am. Trop. Med. & Parasit. _, Vol. I, No. 2, June 15, 1907, pp. 201-229. Sections on attempts to transmit trypanosomes by tsetse-flies; by other blood-sucking Arthropods, etc. , conclude that trypanosomes may be mechanically transmitted by the bite of blood-sucking Arthropods. 

 HOOKER, W. A. Descriptions of Certain Trypanosomes, and Review of the Present Knowledge of the Rôle of Ticks in the Dissemination of Disease. _Jour. Econ. Ento. _, Vol. I, No. 1, 1908, pp. 65-76. Good review, tables and literature. 

 MINCHIN, E. A. Investigations on the Development of Trypanosomes in Tsetse-flies and Other _Diptera_. _Quart. Jour. Micro. Sci. _, 1908, pp. 159-260. 

 MUSGROVE, W. E. , AND CLEGG, M. T. Trypanosomes and Trypanosomiasis, with Special Reference to Surra in the Philippine Islands. _Biological Lab. , Bull. No. 5_, Manila, 1903. Discuss flies, fleas, mosquitoes, lice and ticks as possible disseminators of the disease. 

 NOVY, T. G. , MCNEAL, M. J. , AND TORRY, H. M. The Trypanosomes of Mosquitoes and Other Insects. _Jour. Infec. Diseases_, IV, 1907, pp. 223-276. These parasites are often found in mosquitoes and other insects. Bibliography. 

 NUTTALL, G. H. F. The Transmission of _Trypanosoma lewisi_ by Fleas and Lice. _Parasitology_, Vol. I, No. 4, Dec. , 1908, pp. 296-301. This rat trypanosome is transmitted by fleas and lice. 

 OLD, J. E. S. Contribution to the Study of Trypanosomiasis and to the Geographical Distribution of Some of the Blood-sucking Insects, etc. _Jour. Trop. Med. & Hyg. _, 12, Jan. 15, 1909, pp. 15-22. Notes on blood-sucking _Diptera_ and ticks. 

 ROGERS, LEONARD. The Transmission of the _Trypanosoma evansi_ by House-flies and Other Experiments Pointing to the Probable Identity of Surra of India and Nagana or Tsetse-fly Disease of Africa. _Proc. Roy. Soc. _, Vol. LXVIII, 1901, pp. 163-170. 

 THIMM, C. A. Bibliography of Trypanosomiasis; embracing original papers published prior to April 1909, and references to works and papers on tsetse-flies. London, 1909. 

 TODD, J. L. A Note on Recent Trypanosome Transmission Experiments. _Jour. Trop. Med. & Hyg. _, 12, Sept. , 1909, p. 260. Show that they develop in _G. Palpalis_ when taken from their mammal host at the proper stage of development. 

 WOODCOCK, H. M. The Hæmoflagellates: a Review of Present Knowledge Relating to the Trypanosomes and Allied Forms. _Quar. Jour. Micro. Sci. _, Vol. 50, 1906, pp. 151-331. Characteristics; mode of infection; effects on host; biological considerations; life-cycle, etc. _Spirochaetæ_; bibliography. Important article. 

 Trypanosomiasis and Sleeping Sickness. _Jour. Trop. Med. & Hyg. _, II, pp. 146-147, 162, 179-180, 196. List of recent literature. 

SLEEPING SICKNESS

 BAGSHAWE, A. G. Recent Advances in Our Knowledge of Sleeping Sickness. _Lancet_, II, 1909, pp. 1193-97. A summing up of the important discoveries of the preceding year. 

 HEARSEY, H. Sleeping Sickness. _Jour. Trop. Met. & Hyg. _, 12, Sept. 1, 1909, pp. 263-264. Report on work accomplished particularly in relation to the distribution of _Glossina_ and other biting flies. 

 JARVIS, C. Sleeping Sickness. _Internat. Clinics_, Vol. II, 1904, pp. 37-44. Shows the relation of the tsetse-fly to this disease. 

 LANKESTER, E. R. The Sleeping Sickness. _Quar. Review_, July, 1904, p. 113. Discovery and early history; the fly, the parasite; other related parasites. Relation of parasites to their hosts. 

 MINCHIN, E. A. The Ætiology of Sleeping Sickness. _Nature_, Nov. 15, 1906, pp. 56-59. 

 WOLLASTON, A. F. R. Amid the Snow Peaks of the Equator: a Naturalist's Explorations Around Ruwenzori, with an _Account of the Terrible Scourge of Sleeping Sickness_. _Nat. Geo. Mag. _, XX, No. 3, Mar. , 1909. Abstracted from "From Ruwenzori to the Congo" by above author. 

 Reports of the Sleeping Sickness Com. Of the Royal Society, I to IX, 1903 to 1908. Studies and experiments with the trypanosomes and flies concerned in this disease. Later articles by this commission are to be found in the _Pro. Royal Soc. _, Series B, LXXXI and LXXXII. 

 Sleeping Sickness Bureau Bulletins, 1 to 14, 1908-1910. Records of studies and experiments with trypanosomes and tsetse-flies, etc. 

 Transmission of Sleeping Sickness. Editorial in _Jour. Amer. Med. Assn. _, 53, Oct. 2, 1909, pp. 1104-05. Reviews recent experiments and studies. 

ROCKY MOUNTAIN FEVER AND TICKS

 ANDERSON, J. F. Spotted Fever (Tick Fever) of the Rocky Mountains. _Hyg. Lab. Pub. Health and Mar. Hospt. Ser. , Bull. 14_, 1903. Distribution, ætiology, etc. Believes that ticks are responsible for the transmission of the disease. 

 COOLEY, R. A. Preliminary Report on the Wood-tick. _Bull. 75, Mont. Ex. Stn. _, 1908. Sums up Ricketts' finding; notes on life-history in laboratory and field. 

 KING, W. W. Experimental Transmission of Rocky Mountain Fever by Means of the Tick. Preliminary note. _Pub. Health and Mar. Hospt. Ser. _, 21, July 27, 1906, pp. 863-864. Conveyed this fever from one guinea-pig to another by means of the tick. 

 RICKETTS, H. T. The Transmission of Rocky Mountain Fever by the Bite of the Wood-tick (_Dermacentor occidentalis_). _Jour. Amer. Med. Assn. _, Vol. 47, Aug. , 1906, p. 358. Guinea-pig successfully inoculated by means of tick. 

 RICKETTS, H. T. The Rôle of the Wood-tick (_Dermacentor occidentalis_) in Rocky Mountain Spotted Fever. _Jour. Amer. Med. Assn. _, Vol. 49, July 6, 1907, pp. 24-27. Notes on experiments conducted and studies made. Takes position that these experiments connect the tick with the transmission of the fever. 

 ROBINSON, A. A. Rocky Mountain Spotted Fever. _Med. Rec. _, Nov. 28, 1908. Occurrence and distribution of the disease; review of the various theories in regard to its transmission. P. E. Jones of Salt Lake believes it is transmitted by mosquitoes. 

 STILES, C. W. A Zoölogical Investigation Into the Cause, Transmission and Source of Rocky Mountain Spotted Fever. _Hyg. Lab. Pub. Health and Mar. Hospt. Ser. , Bull. 20_, 1905. Does not find the parasite that had been recorded by others, and finds no evidence to indicate that the ticks transmit the disease. 

 WILSON, L. B. , AND CHANNING, W. M. Studies in _Pyroplasmosis hominis_ (Spotted Fever or Tick Fever of the Rocky Mountains). _Jour. Infec. Diseases_, 1, 1904, pp. 31-57. Evidence that the disease is transmitted solely by means of the ticks. 

TICKS AND VARIOUS DISEASES

 BANKS, NATHAN. Tick-borne Diseases and Their Origin. _Jour. Eco. Ento. _, Vol. I, No. 3, 1908, pp. 213-215. Shows how ticks may become important disease-carriers by changing their hosts as the normal host is exterminated, or for other reasons. 

 BANKS, NATHAN. A Revision of the Ixodoidea or Ticks of the United States. _Tech. Series No. 15, Bull. Of Bureau of Ento. , U. S. Dept. Agric. _, 1908. Structure, life-history, classification, catalogue, bibliography. 

 BARBER, C. A. The Tick Pest in the Tropics. _Nature_, 52, 1895, pp. 197-200. Direct and indirect effects of ticks on their hosts. 

 CHRISTY, C. _Ornithodoros moubata_ and Tick Fever in Man. _Brit. Med. Jour. _, Vol. II, 1903, p. 652. Relation of the tick to _Filaria perstans_. 

 DUTTON, J. E. , AND TODD, J. L. The Nature of Human Tick Fever in the Eastern Part of the Congo Free State with Notes on the Distribution and Bionomics of the Tick. Liverpool School of Tropical Medicine. _Memoir_, 17, Nov. , 1905, pp. 1-18. 

 HOOKER, W. A. A Review of the Present Knowledge of the Rôle of Ticks in the Transmission of Disease. _Jour. Eco. Ento. _, Vol. I, No. 1, 1908, p. 65. Review of the subject; table showing zoölogical position of parasites transmitted by ticks. Table showing zoölogical position of ticks. 

 HOOKER, W. A. Life-history, Habits and Methods of Study of the Ixodoidea. _Jour. Eco. Ento. _, Vol. 1, No. 1, 1908, p. 34. Notes on several species, especially _M. Annulatus_. Host relationship; adaptations as factors in host relationship; mating; geographical distribution; methods of breeding, etc. 

 HOOKER, W. A. Some Host Relations of Ticks. _Jour. Eco. Ento. _, Vol. 2, No. 3, 1909, p. 251. Notes on ticks found on various hosts. 

 HUNTER, W. D. , AND HOOKER, W. A. Information Concerning the North American Fever Tick with Notes on Other Species. _Bull. 72, Bureau of Ento. _, 1907. Life-history, host relation, etc. , of fever tick; classification and notes on other species; bibliography divided into sections. 

 LOUNSBURY, C. P. Habits and Peculiarities of Some South African Ticks. _Rept. Of the Brit. Assn. For the Advancement of Sci. _, 1905 (South Africa), pp. 282-291. 

 MCCRAE, THOMAS. Relapsing Fever. _Osler's Mod. Med. _, Vol. II, p. 245, 1907. Ætiology, symptoms, treatment, etc. (Apparently communicated by blood-sucking insects. )

 NEWSTEAD, R. On the Pathogenic Ticks Concerned in the Distribution of Diseases in Man. _Brit. Med. Jour. _, II, 1905, pp. 1695-97. Classification and habits, particularly of _Ornithodoros moubata_. 

 NUTTALL, G. H. F. The Ixodoidea or Ticks. _Jour. Of Roy. Inst. Of Pub. Health_, 1908. List of disease-bearing ticks. Position of ticks, classification. Biology. Preventive measures. 

 NUTTALL, G. H. F. Piroplasmosis. _Jour. Roy. Inst. Of Pub. Health_, 1908. What piroplasma are; diseases produced by them. Biology. 

 NUTTALL, GEO. F. , and co-workers. _Canine Piroplasmosis_, Parts I to VI. _Jour. Hyg. _, Vol. 4, No. 2, Apr. , 1904, to Vol. 7, No. 2, Apr. , 1907. A thorough discussion of the disease, the parasite which causes it and the ticks which convey it. 

 POCOCK, R. I. Ticks. In Albutt and Rolleston's _System of Med. _, II, 1907, pp. 187-203. Classification; description of the best-known pathogenic species. Extended bibliography. 

 SKINNER, B. Preliminary Note on Ticks Infecting the Rats Suffering from the Plague. _Brit. Med. Jour. _, Vol. II, 1907, p. 457. Records taking tick on a plague-sick rat and finding bacilli similar to plague bacilli in connection with it. 

 SMITH, T. , AND KILBORNE, F. L. Texas Fever. _U. S. Dept. Agric. Bureau of Animal Industry, Bull. No. 1_, 1893. Records of the experiments showing disease to be transmitted by ticks. 

 WELLMAN, F. C. Preliminary Note on Some Bodies Found in Ticks--_Ornithodoros moubata_--Fed on Blood Containing Embryos of Filaria. _Brit. Med. Jour. _, July 20, 1907, p. 142. Believes that _F. Perstans_ is conveyed from man to tick and from tick to man. 

KALA-AZAR AND BEDBUGS

 GIRAULT, A. A. The Indian Bedbug and Kala-azar Disease. _Sci. _, N. S. , Vol. XXV, 1907, p. 1004. Indian bedbug is _C. Rotundatus_ Sig. Its distribution. Summary of Dr. Patton's paper on "Preliminary Report on the Development of the Leishman-Donovan Body in the Bedbug. "

 PATTON, W. S. The Development of the Leishman-Donovan Parasite in _Cimex rotundatus_. _Scientific Mem. Of Gov. Of India_, Nos. 27 and 31, 1907. Traces the development of this parasite; believes that the bedbug is concerned in transmitting this disease. 

 See also Manson's _Tropical Diseases_, pp. 178-190. 

TEXT OR REFERENCE BOOKS IN WHICH THE RELATION OF INSECTS TO VARIOUSDISEASES IS DISCUSSED

 ABBOTT, A. C. Hygiene of Transmissible Diseases. Phil. , 1899. Causes, modes of dissemination, prevention, treatment of infectious and contagious diseases. 

 ALLBUTT, T. C. , AND ROLLESTON, H. D. A System of Medicine. London, 1907. Vol. II, Pt. II, contains sections on tropical diseases; animal parasites and the diseases they carry and zoölogical articles dealing with Protozoa, mosquitoes, flies and ticks. All articles have bibliographies, some of them quite extensive. 

 BALFOUR, ANDREW. Review of Recent Advances in Tropical Medicine. Supplement to _Third Rept. Wellcome Research Lab. _, London, 1908. Notes, extracts and references in regard to important articles during the preceding few months. 

 DANIELS, C. W. Studies in Laboratory Work, 2d ed. , London, 1907. A good discussion of animal parasites in the blood and blood-plasma; development of malarial parasites in mosquitoes; flies, fleas, lice, bedbugs, ticks, etc. 

 JACKSON, C. W. Tropical Medicine. Phil. , 1907. Discusses diseases due to bacteria and the parasites and uncertain causes. Splendid recent summary of the various ways in which the different diseases are disseminated. 

 LANGFELD, MILLARD. Introduction to Infectious and Parasitic Diseases, Including Their Causes and Manner of Transmission. Phil. , 1907. Chapters on infection, animal parasites, avenues of exit and portals of entry of infectious agents and parasites into the body. 

 MANSON, PATRICK. Lectures on Tropical Diseases. London, 1905. Delivered at Cooper Medical College, 1905. Discusses several of these diseases. Last chapter on problems in tropical medicine. 

 MANSON, PATRICK. Tropical Diseases. London, 1907, Diseases of the tropics discussed in a very comprehensive manner. Considerable attention given to the part played by insects in the transmission of many of the diseases. 

 METCHNIKOFF, E. Immunity in Infectious Diseases. (Trans. From the French by F. G. Binnie. ) Cambridge, 1905. Splendid discussion of various kinds of immunity. Insects referred to occasionally. 

 OSLER'S _Modern Medicine_. Vol. I, 1907, Pt. VI, Diseases Caused by Protozoa. Part VII, Diseases Caused by Animal Parasites. Vol. II, 1907, Infectious Diseases. Vol. III, Infectious Diseases (cont. ). One of the best and most modern text-books; the volumes noted above contain many references to the relation of insects to the particular diseases under discussion. 

 PARK, W. H. Pathogenic Micro-organisms, Including Bacteria and Protozoa. N. Y. , 1908. These organisms comprehensively treated. 

 RICKETTS, H. T. Infection, Immunity and Serum Therapy. Chicago, 1906. Chapters on parasitism, infection, contagion, immunity, various diseases, etc. 

 SCHEUBE, B. The Diseases of Warm Countries: a Handbook for Medical Men. Trans. From Ger. By Pauline Falcke, London, 1903. Sections on general infectious diseases, diseases caused by animal parasites, etc. Good bibliography of each disease treated. 

 SIMPSON, W. J. R. The Principles of Hygiene as Applied to Tropical and Subtropical Climates. London, 1908. Occasional references to flies and mosquitoes as carriers of disease. Chapter XV deals with malaria and other diseases caused by mosquitoes. 

 WILSON, J. C. Modern Clinical Medicine; Infectious Diseases. New York and London, 1905. Chapters on yellow fever, malarial diseases and plague; contains references to the relation of insects to these diseases. 

MISCELLANEOUS ARTICLES

 BALFOUR, ANDREW. Further Observations on Fowl Spirochætosis. _Jour. Trop. Med. & Hyg. _, 12, Oct. 1, 1909, pp. 285-289. Ticks and lice may carry this disease. 

 CHITTENDEN, F. H. Harvest-mites or "Chiggers. " _Circular 77, U. S. Dept. Agric. Bur. Ento. _, 1906, pp. 1-16. Descriptions of these pests and their habits. Remedies. 

 DOTY, A. H. The Means by Which Infectious Diseases Are Transmitted. _Amer. Jour. Of Med. Sci. _, 138, July, 1909, pp. 30-39. Flies and mosquitoes as disseminators of disease briefly discussed. 

 DUNCAN, F. M. Industrial Entomology: the Economic Importance of a Study of Insect Life. _Jour. Roy. Soc. Arts_, May 22, 1908, pp. 688-696. A very interesting review of the subject of insects and disease. 

 FLEXNER, SIMON. _Science_, N. S. , Vol. 27, No. 682, Jan. 24, 1908, pp. 133-136. On these pages the author discusses relation of bacteria and Protozoa to human diseases. 

 GOLDBERGER, JOS. , AND SHAMBERG, J. F. Epidemic of an _Utricaroid dermatitis_ Due to a Small Mite (_Pediculoides ventricosus_) in the Straw of Mattresses. _Pub. Health Rept. , Pub. Health and Mar. Hospt. Ser. _, July 9, 1909, Vol. XXIV, No. 28. Experiments showed that a certain skin disease occurring during summer was due to this mite. 

 GORGAS, W. C. The Part Sanitation Is Playing in the Construction of the Panama Canal. _Jour. Amer. Med. Assn. _, 53, Aug. 21, 1909, pp. 597-599. Shows the changes that have been brought about by modern sanitation and the destroying of the mosquitoes' breeding-places. 

 HOWARD, L. O. Hydrocyanic-acid Gas Against Household Insects. _Circular 46, U. S. Dept. Agric. , Div. Of Ento. _, 1902. Directions for handling this dangerous gas. 

 KING, A. F. G. Insects and Disease; Mosquitoes and Malaria. _Pop. Sci. Mo. _, XXIII, 1883, pp. 644-658. Extended article in which the author sums up the observations which led him to believe that malaria and other diseases were transmitted by the mosquito. One of the earliest articles on this subject; refers to an article in _New Orleans Med. & Surg. Jour. _, Vol. IV, 1848, pp. 563-601, by Josiah Nott, who maintained that yellow fever was carried by mosquitoes. 

 MANSON, PATRICK. Recent Advances in Science and Their Bearing on Medicine and Surgery. _Jour. Trop. Med. & Hyg. _, XI, pp. 337-338, Sept. 16, 1908. Discussion of parasites and disease and their methods of dissemination. 

 NEWSTEAD, R. , DUTTON, J. E. , AND TODD, J. L. Insects and Other Arthropoda Collected in the Congo Free State. _Ann. Trop. Med. & Parasit. _, Vol. 1, No. 1, Feb. 1, 1907, pp. 3-100. An interesting paper giving notes on many insects that cause or carry disease. 

 NUTTALL, G. H. F. Spirochætosis in Man and Animals. _Jour. Of Roy. Inst. Of Pub. Health_, 1908. Why Spirochætes should be regarded as Protozoa. Classification; list of blood-inhabiting forms; relapsing fevers; transmission by ticks and other Arthropods. 

 O'CONNELL, M. D. The Oversea Transport of Insect-borne Disease. _Jour. Trop. Med. & Hyg. _, XI, 43, Feb. 1, 1908. Refers to article in same journal (Jan. 15) and points out that malaria is very likely to be transmitted by mosquitoes in this way. 

 OSBORN, HERBERT. Insects Affecting Domestic Animals. _U. S. Dept. Of Agric. , Div. Of Ento. , Bull. No. 5_, N. S. , 1896. Discusses the various insect pests of man and domestic animals Host lists. Bibliography. 

 RICKETS, H. T. , AND WILDER, R. M. The Typhus Fever of Mexico. _Jour. Amer. Med. Assn. _, LIV, No. 6, Feb. 5, 1910, p. 463. Believes this disease is transmitted by insects, probably lice. 

 RITCHIE, JAMES. A Review of Current Theories Regarding Immunity. _Jour. Hyg. _, 2, 1902, pp. 215-285, and pp. 452-464. Discussion of various theories. Bibliography. 

 SHIPLEY, A. E. On the Relation of Certain Cestode and Nematoda Parasites to Bacterial Disease. _Jour. Of Eco. Biol. _, 4, 1909, pp. 61-71. Shows that these parasites may often cause serious diseases by opening the way for malignant germs. 

 WARD, H. B. Spirochetes and Their Relationship to Other Organisms. _Amer. Nat. _, 42, 1908, No. 498, pp. 374-387. Still undecided as to whether they belong with bacteria or Protozoa, probably the latter. 

 WARD, H. B. The Relation of Animals to Disease. _Science_, N. S. , 22, 1905, pp. 193-203. An interesting, comprehensive review of the subject. 

 WARD, HENRY B. Relation of Animals to Disease. _Transactions of Amer. Micro. Soc. _, Vol. 27, 1907, pp. 5-20. The various ways in which animals may produce or carry disease. 

 The Oversea Transport of Insect-borne Diseases. Editorial in _Jour. Trop. Med. & Hyg. _, XI, Jan. 15, 1908, pp. 22-23. Points out the danger of yellow fever, plague and other diseases being borne overseas by infected insects. 

 The Society for the Destruction of Vermin. Editorial in _Jour. Trop. Med. & Hyg. _, XI, Apr. 15, 1908, p. 124. Tells of organization of such society and its purposes. 

INDEX

 Adams, S. H. , 132. 

 Advisory Committee, 146. 

 Agramonte, Dr. Aristides, 123. 

 Alimentary canal, fly larvæ in, 49. 

 Amoeba, 19. 

 Anopheles, adults, 91; eggs, 92; habits of adults, 94; larvæ, 78, 79, 93; pupæ, 93; resting position, 92; species in U. S. , 92. 

 Anthrax, 44; and flies, 70. 

 Arthropoda, 26. 

 Asexual reproduction, 111. 

 Bacillus, anthracis, 44; icteroides, 124; lepræ, 171; pestis, 150. 

 Bacillus carriers, 66. 

 Back-swimmers, 100. 

 Bacteria, 15; saprophytic and parasitic, 17; effect on host, 18; dissemination, 18. 

 Bedbugs, 54, 147. 

 Banks, Nathan, 34. 

 Bell-animalcule, 22. 

 Berne, 51. 

 Birds as enemies of mosquitoes, 99. 

 Black-flies, 46. 

 Blackheads, 35. 

 Blow-flies, 48. 

 Blue, Dr. Rupert, 143. 

 Blue-bottle flies, 48. 

 Bot-flies, 50. 

 Break-bone fever, 169. 

 Breeze-fly, 44. 

 Buffalo-gnats, 46. 

 Calliphora vomitoria, 48. 

 Camphor, for mosquitoes, 102. 

 Cancer, 36. 

 Carroll, Dr. James, 123. 

 Castor-bean tick, 27. 

 Cattle tick, 29. 

 Cedar oil, for mosquitoes, 102. 

 Ceratophyllus, faciatus, 153; acutus, 156. 

 Cesspools, 72. 

 Chigger, 53. 

 Chigger-flea, 53. 

 Chigo, 30, 39. 

 Chigoe, 53. 

 Cholera, 68. 

 Chrysomyia macellaria, 47. 

 Cimex, lectularis, 54; rotundatus, 173. 

 Contagious diseases, 8. 

 Conjugation, 20. 

 Cooley, Prof. R. A. , 33. 

 Craig, Dr. C. F. , 118. 

 Ctenocephalus, canis, 154; felis, 154. 

 Culex, fatigans, 96, 170; pipiens, 98. 

 Dengue, 169. 

 Dermatobia cyaniventris, 51. 

 Dermatophilus penetrans, 53. 

 Diarrhea, 69. 

 Diptera, 43. 

 Diving beetles, 100. 

 Dragon-flies, 99. 

 Dysentery, 20. 

 Eggs, of flies, 63; of mosquitoes, 77; of Anopheles, 92. 

 Egyptian opthalmia, 52. 

 Elephantiasis, 164. 

 Enemies of mosquitoes, 97. 

 Enteritis, 69. 

 Euglena, 21. 

 Eye-worm, 12. 

 Face-mite, 35. 

 Fighting mosquitoes, adults, 101; larvæ, 103. 

 Fiji Islands, Anopheles in, 117. 

 Filaria bancrofti, 164. 

 Finlay, Dr. Charles, 124. 

 Fish, 100. 

 Flagella, 20. 

 Fleas, 52; and plague, 142, 145, 147; structure and habits, 151; common species, 153; on ground squirrels, 156; remedies for, 157. 

 Flies, 43; and typhoid, 65; specks, 66; and various diseases, 68. 

 Flesh-flies, 48. 

 Fumigating for mosquitoes, 102. 

 Gad-fly, 43. 

 Glossina palpalis, 163. 

 Golgi, Camillo, 109. 

 Grassi, Prof. G. B. , 118. 

 Gray-flies, 47. 

 Ground squirrels and plague, 155. 

 Guinea-worm, 11. 

 Hæmamoeba, 109. 

 Hæmatobia, 45. 

 Hæmosporidiida, 24. 

 Hæmotopinus spinulosus, 55. 

 Harvest-mite, 37. 

 Havana, yellow fever in, 131. 

 Hawaii, mosquitoes in, 98. 

 Hemiptera, 54. 

 Homalomyia canicularis, 49. 

 Hoplopsyllus anomalus, 156. 

 Horse bot-flies, 50. 

 House-flies, 57; structure, 59; how they carry bacteria, 62; life-history and habits, 63; fighting, 71; and typhoid, 65. 

 Horse-flies, 43. 

 Howard, Dr. L. O. , 59, 73. 

 Hyperparasitism, 3. 

 Immunity, 5. 

 Indian Plague Commission, 144. 

 Infectious diseases, 8. 

 Infusoria, 22. 

 Insects, cause or carry disease, 40; numbers, 40; annual loss caused by, 41; how they carry disease germs, 55. 

 Irrigating ditches, 104. 

 Itch-mite, 36. 

 Jackson, Dr. D. D. , 67. 

 Jennings, 22. 

 Jiggers, 38, 53. 

 Jigger-flea, 53. 

 Kala-azar, 173. 

 Kerosene, 104. 

 Koch, 44. 

 Læmopsylla cheopus, 153. 

 Lamprey-eel, 2. 

 Lancisi, J. M. , 107. 

 Larvæ, of flies, 64; of mosquitoes, 78. 

 Laveran, A. , 108. 

 Laverania, 109. 

 Lazear, Dr. Jessie W. , 123. 

 Leeuwenhoek, Anton von, 22. 

 Lepra bacillus, 36. 

 Leprosy, 36, 70, 171. 

 Lice, 54. 

 Linnæus, 76. 

 Little house-fly, 49. 

 Lock-jaw, 18. 

 Low, Dr. A. , 118. 

 Lucilia spp. , 48. 

 Lugger, Prof. Otto, 38. 

 Malaria, early theories in regard to, 106; parasite that causes, 108; life history of parasite, 109; parasite in mosquito, 113; summary, 117; experiments, 118. 

 Maggots, 63. 

 Malta or Mediterranean fever, 171. 

 Mange, 37. 

 Manure-fly, 59. 

 Manson, Sir Patrick, 112, 123. 

 Mastigophora, 20. 

 Melanin, 110. 

 Micrococcus melitensis, 171. 

 Microbes, 10. 

 Mites, 26, 35. 

 Mosquito, 76; abdomen, 86; adults, 81; Anopheles, 91; how they bite, 84; effect of bite, 87; blood, 90; how they breathe, 89; classification, 91; and dengue, 169; eggs, 77; and elephantiasis, 164; enemies, 77; fighting, adults, 101; larvæ, 103; larvæ, 78; and malaria, 106; malarial parasite in, 113; mouth-parts, 83; other species, 96; pupæ, 80; salivary glands, 87; thorax, 85; and yellow fever, 94, 120. 

 Mouth-parts, of fly, 60; of mosquito, 83. 

 Mus, norvegicus, 154; rattus, 154. 

 Nanga, 45. 

 Nematodes, 164. 

 New Orleans, yellow fever in, 120, 132. 

 Noctiluca, 21. 

 No-see-ums, 46. 

 Ochromyia anthropophaga, 49. 

 Oil of citronella, 102. 

 Oil of pennyroyal, 102. 

 Oriental sore, 174. 

 Ornithodorus moubata, 34. 

 Oscinidæ, 52. 

 Otospermophilus beecheyi, 155. 

 Oxwarbles, 50. 

 Panama Canal zone, 135. 

 Paramoecium, 22. 

 Parasite, defined, 1; classes of, 4; in new regions, 5; diseases caused by, 7; effect on host, 9; relation to host, 14. 

 Parasitism, 3. 

 Pasteur, L. , 44. 

 Pearls, 13. 

 Piroplasma bigeminum, 29. 

 Plague, early history of, 142; fleas that transmit, 153; and flies, 70; and ground squirrels, 155; how combatted in San Francisco, 143; results of other investigations, 150; Verjbitski's experiments, 147; work of Indian Plague Commission, 146. 

 Plasmodium, 109. 

 Protozoa, 19; classes of, 20. 

 Proboscis, of fly, 60; of mosquito, 80. 

 Privies, 72. 

 Privy-fly, 59. 

 Pseudopodia, 20. 

 Psoroptes communis, 37. 

 Pulex irritans, 154. 

 Punkies, 46. 

 Pupæ, of house-flies, 64; of mosquitoes, 80. 

 Pyrethrum, 102. 

 Rats, and plague, 143, 145; species of, 154. 

 Red-bugs, 38. 

 Reed, Dr. Walter, 123. 

 Relapsing fever, 21, 33. 

 Rhizopoda, 20. 

 Ricketts, Dr. H. F. , 32. 

 Rio de Janeiro, yellow fever in, 137. 

 Rocky Mountain spotted fever, 32. 

 Ross, Ronald, 112. 

 Rucker, Dr. W. C. , 143. 

 Sacculina, 2. 

 Salivary glands, 84, 87. 

 Salt marshes, 97, 105. 

 Sambon, Dr. L. W. , 118. 

 Sand-fleas, 53. 

 Saprophytic bacteria, 17. 

 Sarcophaga spp. , 48. 

 Sarcoptes scabiei, 37. 

 Scab, 37. 

 Screw-worm, 47. 

 Seed-ticks, 27, 30. 

 Sheep bot-flies, 51. 

 Simmond, Dr. P. L. , 145. 

 Siphonaptera, 52. 

 Skinner, Dr. H. , 159. 

 Sleeping sickness, 21, 161. 

 Slipper animalcule, 22. 

 Small-pox, 70. 

 Smith, Dr. Theobald, 29. 

 Smudges, 102. 

 Sore-eye, 52. 

 Spiders, 26. 

 Spiracles, 89. 

 Spirochæta, 21, 130. 

 Spore formation, 24. 

 Spores, 24. 

 Sporozoa, 22. 

 Spotted fever, 32. 

 Stable-fly, 44, 75. 

 Stegomyia, calopus, 94, 98, 139; scutellaris, 96. 

 Sticklebacks, 101. 

 Stomoxys calcitrans, 44. 

 Sulphur, 102. 

 Surra, 45. 

 Tabanus, 45. 

 Tahiti, mosquitoes in, 96. 

 Tapeworms, 2. 

 Tetanus, 18. 

 Texas fever, 28. 

 Theobald, Dr. F. V. , 76. 

 Ticks, 26. 

 Tide-water minnows, 101. 

 Tobacco smoke, 102. 

 Top-minnows, 98, 101. 

 Torcel, 51. 

 Tracheæ, 89. 

 Tracheal gills, 79. 

 Trichina, 2. 

 Trypanosome, 45, 161. 

 Trypanosoma, evansi, 45; brucei, 45; lewisi, 162; gambiensi, 162. 

 Tsetse-fly, 45, 163. 

 Tubercular bacilli, 69; germs, 69. 

 Typhoid-fly, 57, 59. 

 Vaughan, Dr. W. C. , 67. 

 Ver macque, 51. 

 Verjbitski, D. T. , 147. 

 Vorticella, 22. 

 Water-boatmen, 100. 

 Water-troughs, 104. 

 Whip-bearers, 20. 

 Whirligig beetles, 100. 

 White, Surgeon J. H. , 134. 

 Wrigglers, 78. 

 Yellow fever, 120; Commission, 123; early observations on, 121; experiments, 125; danger of in Pacific Islands, 140; in Havana, results of work on, 131; history of in United States, 120; mosquito, 94; habits of, 95; in Panama Canal zone, 135; in Rio de Janeiro, 137; summary of results of work on, 129.