EX-LIBRIS WJLUCAS ! William C. Reeves THE LIBRARY OF THE UNIVERSITY OF CALIFORNIA GIFT OF Professor William C. Reeves HEALTH T CAMBRIDGE PUBLIC HEALTH SERIES UNDER THE EDITORSHIP OF G. S. Graham-Smith, M.D. and J. E. Purvis, M.A. University Lecturer in Hygiene and University Lecturer in Chemistry Secretary to the Sub-Syndicate for and Physics in their application Tropical Medicine to Hygiene and Preventive Medi- cine, and Secretary to the State Medicine Syndicate FLIES IN RELATION TO DISEASE BLOODSUCKING FLIES CAMBRIDGE UNIVERSITY PRESS C. F. CLAY, MANAGER ILontJOn: FETTER LANE, E.G. lElttnburgf) : 100 PRINCES STREET ILonUon: H. K. LEWIS, 136 GOWER STREET, W.C. ILonfcon: WILLIAM WESLEY AND SON, 28 ESSEX STREET, STRAND jjieto $ork: G. P. PUTNAM'S SONS ISombas anU Calcutta: MACMILLAN AND CO. LTD. Toronto: J. M. DENT AND SONS, LTD. Eofego: THE MARUZEN-KABUSHIKI-KAISHA All rights reserved FLIES IN RELATION TO DISEASE BLOODSUCKING FLIES by EDWARD jHINDLE, B.A., PH.D. Assistant to the Quick Professor of Biology, Cambridge Cambridge : at the University Press 1914 TO OTTO BEIT IN RECOGNITION OF HIS GENEROUS GIFTS TOWARD THE ADVANCEMENT OF SCIENTIFIC RESEARCH Add'l GIFT Ft PUBLIC HEALTH EDITORS' PREFACE IN view of the increasing importance of the study of public hygiene and the recognition by doctors, teachers, adminis- trators and members of Public Health and Hygiene Committees alike that the salus populi must rest, in part at least, upon a scientific basis, the Syndics of the Cambridge University Press have decided to publish a series of volumes dealing with the various subjects connected with Public Health^ The books included in the Series present in a useful and handy form the knowledge now available in many branches of the subject. They are written by experts, and the authors are occupied, or have been occupied, either in investigations connected with the various themes or in their application and administration. They include the latest scientific and practical information offered in a manner which is not too technical. The bibliographies contain references to the literature of each subject which will ensure their utility to the specialist. It has been the desire of the editors to arrange that the books should appeal to various classes of readers : and it is hoped that they will be useful to the medical profession at home and abroad, to bacteriologists and laboratory students, to munici- pal engineers and architects, to medical officers of health and sanitary inspectors and to teachers and administrators. Many of the volumes will contain material which will be suggestive and instructive to members of Public Health and Hygiene Committees ; and it is intended that they shall seek to influence the large body of educated and intelligent public opinion interested in the problems of public health. M8951G8 PREFACE A LTHOUGH it is now generally recognized that flies •**• are very important agencies in the dissemination of infectious diseases, few people are aware, of the remarkable advances which have resulted from modern research in this field. To the general public the practical application of these researches appeals with greater force than the detailed accounts of investigations, of absorbing interest though many of them are, in the varied subjects which have to be called to our aid in combating disease. Some of the results hitherto obtained may be illustrated by two examples, both of which have brought this subject into some prominence. In the first of these, Yellow Fever, owing to the factors involved being relatively simple, it is literally possible within a few months to remove this most deadly disease from the list of human ailments. All that is required is public appreciation of the remedies at our disposal, as demonstrated by the result of the admirable measures adopted by the Americans first in Cuba and afterwards in Panama, which alone rendered possible the completion of the Canal. Similar measures in other regions directed against the mosquito (Stegomyia fasciata), which is responsible for the transmission of the infection, would render the reappearance of Yellow Fever in the highest degree improbable in the future. Sleeping Sickness may be taken as our second example. The difficulties in this case are undoubtedly more formidable, owing to the extreme complexity of the modes of dissemination. Vlll PREFACE Nevertheless much has already been accomplished, though it is little to what might be done if more adequate funds were at the disposal of our Colonial Medical and Administrative Authorities. The enlightened policy of the Colonial Office contrasts sadly with the lack of interest displayed by the public as a whole, both at home and in the Colonies affected. Public and private funds could not be directed more profitably to the service of humanity than in the fields which the far- sighted enterprise of this Department has opened up of recent years. New and formidable developments in the problem of Sleeping Sickness, to confine ourselves to the second example we have chosen, render it imperative that immediate steps should be taken to combat the spread of a particularly deadly variety of this infection, which, although at present confined to small areas in Nyasaland and the adjoining provinces, threatens to extend over a large part of Africa. In addition to these two examples, Malaria in all its forms is gradually becoming subject to human control, though some countries are slow to realize that they cannot remain neutral in this war waged by science against their most deadly internal enemies, the mosquitoes. Verily the fly's proboscis is more successful in retarding the progress of civilization and the alleviation of human suffering than all the armaments of our most Christian Powers ! The author's main object in writing this book has been to collocate the more important observations concerning the part taken by biting flies in the transmission of disease. In doing this it seemed advisable to include notes on the classi- fication of the flies concerned and also descriptions of the infections transmitted, but no attempt has been made to give any account of the clinical symptoms of the various diseases, PREFACE ix whether of man or animals. Special attention has been devoted to the modes of life of the more important insects mentioned, to the manner in which the infection is transmitted from one host to another, and also to any preventive measures directed either against the flies or the infections themselves. Hitherto those interested in this subject have been obliged to refer to entomological treatises for a knowledge of the insects, while information concerning the infections trans- mitted was only likely to be contained in medical or zoological publications. Thus there is danger of the interdependence of the two subjects being overlooked. The entomologist work- ing in this field, without a more or less complete knowledge of the factors influencing the transmission of any particular malady, is liable to waste his efforts in unprofitable directions ; whilst the Medical Officer or Administrator who is ignorant of the main 'results of entomological research is equally handi- capped in his attempts to combat the group of diseases under discussion. It is hoped, therefore, that this book will appeal to both classes and at the same time that its significance for the prevention of disease will be apparent to that wider public already indicated. The present volume together with that published by Dr Graham-Smith in the same series1, covers the whole field marked out by their general title, Flies and Disease. It may be useful to give the reader some idea of the general arrangement of the subject matter that we have adopted. After a short introduction, follow chapters on the structure and classification of the Diptera, accompanied by a list of biting flies known to transmit any infection. Each family, including any such carriers of disease, is then dealt with 1 Graham-Smith. Flies and Disease — Non-bloodsucking Flies. Cambridge Public Health Series. X PREFACE separately and in most cases some important member of the family is described in greater detail. As far as possible the description of the infections immediately follows that of the family concerned in their transmission. Thus the account of the Psychodidae and Phlebotomus is succeeded by a chapter devoted to Pappataci Fever (Three Day Fever), whilst the account of Malaria follows that of the Anophelinae. Certain difficulties have arisen in the case of diseases (e.g. trypano- somiasis) transmitted by members of more than one family, but such infections have been described in connection with their more important carrier. At the end of each chapter are given a few references to the literature on the subject, but it should be emphasised that the bibliography is not in any way complete, but merely contains the titles of publications that will be of assistance to students requiring detailed in- formation in any particular branch. The present edition does not profess to deal with works published later than the beginning of 1913, although in isolated cases it has been found possible to include references to later work. The writer has great pleasure in acknowledging the extremely valuable assistance which he has received from Major S. R. Christophers, I. M.S., in the preparation of chapters VIII and IX, devoted respectively to the classification of the Culicidae, and an account of Malaria. These are almost entirely the work of that distinguished authority and con- sidering their importance in the present work, his name ought to have appeared as a joint author. However, Major Christo- phers would not consent to this arrangement and therefore the author can only express his great indebtedness for this generous help. For permission to reproduce illustrations, which had previously appeared in other publications, and also for the PREFACE XI loan of the original blocks, I am indebted to the following: the Publisher (G. Fischer) and Editors of the Archiv fur Protistenkunde, for permission to reproduce Fig. 87; the Editor of the Bulletin of Entomological Research for the loan of the blocks of Figs. ^18, 19, 59-61, 67, 73 and 74 ; the President and Fellows of the Cambridge Philosophical Society for the loan of the block of Fig. 57 ; the Editors of the Journals of Pamsitology and Hygiene for the block of Fig. 41 and permis- sion to reproduce Figs. 4, 8, 25, 26, 27, 29 and 31 ; the Director of the Tropical Diseases Bureau for the loan of the blocks of Figs. 42-45 and 65; Dr P. H. Bahr and Messrs Witherby and Co. for the loan of the blocks of Figs. 54 and 56 ; Maclure, Philips and Co. for permission to reproduce Figs. 46, 47 and 49. Dr E. Roubaud for the loan of the blocks of Figs. 62, 64, 66, 68, 70, 76-78 ; Dr G. S. Graham-Smith for the loan of the blocks of Figs. 1-3 and 82 and 83 ; Professor G. H. F. Nuttall for permission to reproduce Figs. 30, 32 and 55 ; Surgeon- General Sir David Bruce for permission to reproduce Figs. 79 and 80; and Miss Muriel Robertson for permission to reproduce the drawings from which Fig. 75 was constructed ; Mr Edwin Wilson, F.E.S., kindly prepared the drawing of the stridulating organ of Anopheles (Fig. 28). It is the author's pleasant duty to return thanks for the assistance afforded by these gentlemen. In conclusion, I should like to express the great debt I owe to Professor G. H. F. Nuttall, who by his friendly criticism and helpful suggestions has lightened the author's labours and also prevented many serious omissions. E. H. September, 1914. CONTENTS CHAP. PAGE I. Introduction .,"»;.. . . . . . i II. Diptera — General description and classification . 12 III. Biting-Flies as carriers of disease .... 25 IV. Orthorrhapha Nematocera ' . . . . . 32 V. Family Psychodidae (Moth-flies and Sand-flies) . . 35 VI. Diseases carried by Phlebotomus — Pappataci Fever . 44 VII. Family Culicidae (Gnats or Mosquitoes) ... 50 VIII. Culicidae (Mosquitoes) continued. Classification . 75 IX. Anopheline-transmitted diseases . "... . 119 X. Culicinae . . j - ' . t ;. ^ . . . 165 XI. Diseases transmitted by Culicinae. Yellow Fever, Dengue, Bird Malaria, etc. . :\«.r: $ »* . . 177 XII. Diseases transmitted by Anophelinae and Culicinae. Filariasis ... . . .. . . 202 XIII. Orthorrhapha Brachycera . ,* ..... . . 224 XIV. Family Tabanidae (Breeze-flies, Cleggs, Horse-flies, Gad-flies, Seroot-flies) " .* '. . . . 226 XV. Cyclorrhapha Schizophora . . ' . " ' '" ". . . 239 XVI. The Tsetse-flies — Genus Glossina Wied., 1830 . . 243 XVII. Glossina and Disease. The Trypanosomes "" . . 293 XVIII. Glossina and Disease (continued) \ . . . 300 XIX. Stomoxys . '. "' '' '. ' .' . .; . . . . 355 XX. Infections transmitted by Stomoxys .'""''". . . 361 XXI. Lyperosia . ' . ' . . . . . . '. " 369 XXII. Family Hippoboscidae (Tick-flies) '. . . .372 XXIII. Infections transmitted by Hippoboscidae . . . 379 INDEX . , . 387 LIST OF FIGURES I ' FIG. PAGE 1. An Anthomyid fly immediately after emerging from the puparium . * ; : . w' :,U . . • '-.. . 14 2. Ventral view of head of the same fly . •-,;•. >•,:-* , . 14 3. Side view of head of the same fly * ., v < • v , . . 14 4. Side view of a female Anopheles maculipennis Meigen (x about 20) ..... v . . 16 5. Wing of Tabanus sp. shewing the venation . .•*•,-. . 17 6. Acephalous larva of Stomoxys calcitrans ( x 7) . t „ . . 20 7. Eucephalous larva of Phlebo torn us papatasii .. «..." ,f 20 8. Obtectate pupa of Anopheles maculipennis lf. . ,. f , 22 9. Coarctate pupa of Stomoxys calcitrans . -.»..• ;•«•.. . 22 10. Wing of Kellogg ina, a blepharocerid i .<> ; ». ,. ; » ; 34 11. Thorax of Tipula . . . v^ -U . . . 34 12. Wing of Ryphus '••.'• . % ; *;...;• i.. , • / 41 25 . A nopheles maculipennis. A , enlarged view of male ; B, head . s j: of female . . ... . »• n ; n. ito'ij • 51 26. Transverse section through proboscis of a female Anopheles maculipennis, shewing the relative position of the parts when at rest . . ., . . , . . ..,. 52 27. Side view of the head of a female Anopheles maculipennis, with the various mouth parts separated, but in the relative position in which they lie when enclosed in the groove of the labium ..... 53 28. View of under-surface of the base of the wing of Anopheles maculipennis, shewing stridulating organ .... 55 29. Schematic longitudinal section of a female Anopheles macu- lipennis ......... 57 XIV LIST OF FIGURES FIG. PAGE 30. Diagram shewing the corresponding stages in the life-cycle of Anopheles and Culex ...... 63 31. Anopheles maculipennis. A, side view and B, dorsal view of egg ; C, young larva and D, fully-grown larva ; E flabellum, or flap overhanging base of certain thoracic hairs ; F, a palmate hair ; G, ventral view of head of fully-grown larva ....... 65 32. Anopheles maculipennis $, captured in Cambridge, shewing acarine parasites attached to the body . . . 73 33. Anopheles bifurcatus . . . . . . . 80 34. Anopheles (Patagiamyia] gigas . • v:-? . . . . 82 35. Anopheles (Myzorhynchus] barbirostris . . . . , 84 36. Anopheles (Myzomyia] listoni . . . r . . . 86 37. Anopheles (Pyretophorus) neavei ..... 88 38. Anopheles (Nyssorhynchus] maculatus . ' ''/ '': . . 91 39. Anopheles (Cellia) pulcherrimus ..... 93 40. Diagrammatic representation of the life-cycle of the parasite of pernicious malaria . . . . . 130 41. Photomicrograph of sporozoites of malaria from salivary glands of Anopheles (Pyretophorus) costalis . . . 135 42. Breeding places of Anophelines. Railway cutting at Kurunegala . . . . . " . . . 137 43. Breeding places of Anophelines. Flooded Paddy Fields in Ceylon . . . . . . . . . 139 44. Indian fish of utility as mosquito-destroyers. A (£} and B (?) , Lebias dispar ; C, Nuria danrica . . . 150 45 . Indian fish of utility as mosquito-destroyers. A , Haplochilus panchax; B, Ambassis ranga; C, Trichogaster fas- ciatus . . . . . . . . . 152 46. Stegomyia fasciata, adult female . . . . . 166 47. Stegomyia fasciata, adult male . . . . . 168 48. Distribution of Stegomyia fasciata . . . . 169 49. Larva and pupa of Stegomyia fasciata . . . . 174 50. Approximate distribution of Yellow Fever . . . 179 51. Distribution of Dengue . . . . . . . 191 52. Distribution of Culex fatigans . . . . . . 193 53. Stomach of Culex shewing large numbers of the sporocysts of Plasmodium prcecox on its walls . . . . 199 54. Microfilarise of F. bancrofti emerging from the uterus of the parent filaria ........ 207 55. Filaria bancrofti. Stages in development within mosquito 211 56. Head and proboscis of Stegomyia pseudoscutellaris, 15 days after feeding, shewing two filariae lying in the head and three in the proboscis . . . . . . 213 57. A , view of the heart of a dog infested with Filaria immitis ; B, a female worm removed from the heart to shew its length . . . . . . . . 220 LIST OF FIGURES XV FIG. PAGE 58. Part of the Malpighian tubule of an Anopheles claviger, infected with the embryos of Filaria immitis . . 221 59. Tabanus kingi $ ........ 227 60. A rock at Khor Arbat, Anglo-Egyptian Sudan, shewing sites selected bv, Tabanus kingi for ovipositing . . 228 61. Egg-mass and mature larva of Tabanus kingi . . . . 229 62. Comparative morphology of the proboscis of Glossina (I), Melophagus (II) and Stomoxys (III) . . . . 244 63. Wing of Glossina palpalis to shew the venation . . 245 64. Gravid uterus of G. palpalis, containing a larva at an ad- vanced stage of development . . .. . . 246 65. Glossina palpalis. Photographs shewing the flies in a position of rest . . . . . . . 257 66. Internal anatomy of Glossina palpalis . . . . 259 67. View on River Gambia to shew a typical haunt of Glossina palpalis , . . . . . . . . . ' 261 68. Glossina palpalis in the act of feeding , . . . 264 69. Glossina palpalis. Female in the act of parturition . . 266 70. Freshly laid larva of G. palpalis shewing the changes in the body form . . . • , . . . . 267 71. G. palpalis. Puparia before and after the escape of the imago . . . i . . . , .. „ 268 72. Glossina morsitans. Dorsal view of female . '."'„• 276 73. Path through thin deciduous bush, to shew a typical haunt of G. morsitans . . . ..... 279 74. Base of a tree in Nyasaland shewing one of the positions in which the pupae of G. morsitans may be found . . 284 75. Diagram of the life-cycle of Trypanosoma gambiense . . 312 76. Transverse section (semi-diagrammatic) of the proboscis of an infected Glossina . . . . . . 314 77. Culture of Trypanosoma pecaudi, from the intestine of G. palpalis . . . . ' . . . 334 78. Culture of Trypanosoma congolense from the intestine of G. palpalis . ... . » . . 351 79. Trypanosoma simice. Successive stages in the division . 354 80. Trypanosoma simice. Large multinucleate form . . 354 81. Wing venation of Stomoxys calcitrans . . . . 356 82. Side view of head of Stable-fly. A, proboscis in resting position ; B, proboscis extended .... 356 83. Stable-fly, Stomoxys calcitrans ;; . . . ',. ; < . 357 84. Stomoxys calcitrans. Eggs . . » , . . 359 85. Lynchia maura $ . . . . . . . 376 86. Hippobosca rufipes . . . . . . . . 378 87. Developmental cycle of H&moproteus columbce . . 381 88. Trypanosoma theileri. A, small crithidial form; B, large individual from blood of cow ..... 385 ERRATA p. 37. After Fig. 20 insert the words "After Newstead." p. 38. After Fig. 21 insert the words " After Newstead." p. 87. For A. agripi Patton read A. azriki Patton. CHAPTER I INTRODUCTION Although biting-flies had long been suspected of being responsible for the spread of various diseases, it was not until 1877 tnat anv direct proof was brought forward in support of this hypothesis. In that year Manson, working in China, discovered that the minute worm, Filaria bancrofti, present in the blood of a large percentage of the natives that he examined, underwent a development inside the body of the common grey-legged mosquito, Culex fatigans. Although these observations were incomplete and the exact mode of transmission remained undiscovered until more than twenty years later, yet they were of the highest importance, since Hanson's work laid the foundation for all subsequent inves- tigations on the part played by biting-flies as carriers of disease. With the exception of these few observations on the de- velopment of Filaria in the mosquito, practically the whole of our knowledge of the transmission of disease by insects, has been acquired within the last twenty years. Thus Bruce, in 1895, discovered the cause of Nagana, Trypanosoma brucei, and its transmission by the tsetse-fly, whilst two years later Ross, by his brilliant researches on the development of Proteo- soma and the manner in which it is spread by the mosquito, placed the methods of eradicating malaria on a scientific basis. The rapid progress in this subject may be appreciated by the fact that, with the exception of the specific descriptions of certain insects and the above-mentioned work on Filaria, the present volume is entirely concerned with discoveries of the last twenty years. Within this period biting-flies have been H. B. F. 2 DIRECT TRANSMISSION [CH. shewn to transmit in addition to numerous infections of animals the following human diseases : malaria, sleeping sickness, yellow fever, three-day fever ; and evidence has been brought forward also suggesting that dengue and epidemic polyomyelitis are spread by these insects. Before proceeding to a discussion of individual infections, however, and the part played by flies in their transmission, it will be convenient to give a short general account of some of the problems connected with this subject. It has never been proved that, under natural conditions, biting-flies normally transmit any other than animal parasites from one host to another. In those cases in which the patho- genic agent is unknown, e.g. yellow fever, three-day fever, the clinical symptoms seem to indicate that these diseases are also due to animal parasites and not to bacteria. There is no a priori reason why biting-flies should not transmit bacterial infections as well as animal, but certainly no bacterial disease is known to be normally transmitted by these insects. Since a biting-fly feeds on blood and can only become infected by ingesting the parasite, it necessarily follows that the latter, at least during some part of its life-cycle, must be present in the blood of the vertebrate host, and the manner in which the infection is conveyed by the insect may be either " direct " or " indirect." (a) Direct transmission. When the pathogenic agent does not develop in the body of the biting-fly, but is merely carried on the mouth-parts and directly inoculated into the next host which the insect feeds upon, the transmission is said to be direct or mechanical. This kind of transmission somewhat resembles the method of infecting a healthy animal by means of the prick of a needle that has been thrust previously into an infected animal and which is thereby soiled with the infective blood from the latter. The efficiency of any particular species to act as the direct carrier of a disease agent obviously depends on such mechanical details as the size and shape of the mouth-parts, the number of parasites in the blood, etc. It is possible that bacterial as I] DIRECT TRANSMISSION 3 well as animal infections may be occasionally carried in this manner, especially in those cases where the bacteria are present in the peripheral circulation in considerable numbers, e.g. anthrax, Mediterranean fever. Moreover, by feeding sufficient numbers of any species of biting-fly on an animal containing large numbers of some parasite in its blood, and subsequently, without any interval, on a normal susceptible animal, it is possible to obtain experimentally the direct transmission of practically any blood-inhabiting parasite. Employing such methods the transmission of sleeping sickness and relapsing fever may be effected by means of the bites of Stegomyia, and Mediterranean fever by the bites of Culex ; it is almost certain, however, that such transmission rarely, if ever, occurs in nature. Nevertheless, the possibility must not be ignored and all biting-flies should be regarded with suspicion from the point of view of preventive medicine. Although under experimental conditions it is comparatively easy to demonstrate the direct transmission of certain diseases it is becoming more and more evident that, compared with in- direct transmission, this mode of infection plays a relatively unimportant part in the spread of disease. The pathogenic agent of the disease, even under the most favourable conditions, can only survive for a very limited time (at most two to three days) on the mouth-parts of the biting-fly and unless the latter feeds on another host before the expiration of this period no infection is produced. As a rule a fly which has had a full meal of blood rarely desires to feed again for some days and it is only those flies which are interrupted during their feeding that are liable to bite another host within a short space of time. El Debab, a trypanosomiasis of camels occurring in North Africa, is one of the best examples of a disease which seems to be transmitted in this manner. Edmond and Etienne Sergent have shewn that the outbreaks of this disease can be explained on the supposition that it is directly transmitted from infected to healthy animals by various species of tabanids, and they note that in nature these insects frequently bite two or more animals in quick succession, being disturbed whilst feeding, through the efforts of their unwilling victims. 4 INDIRECT TRANSMISSION [CH. It is, of course, quite possible for a biting-fly to transmit any particular infection both directly and indirectly, as in the case of the transmission of Nagana (Trypanosoma bmcei) by Glossina pallidipes. Bruce shewed that if a tsetse fed on blood containing these trypanosomes, the fly remained infec- tive for about forty-eight hours, during which period, if it bit another animal, the latter became infected. It has since been proved, however, that in addition this trypanosome develops in the alimentary canal of the tsetse-fly and after a certain incubation period, during which the fly is non-infective, it again becomes infective. This infection, therefore, is trans- mitted both directly and indirectly, but the epidemiology of the disease is strongly against the view that transmission is usually effected by the direct method. (b) Indirect transmission. When the pathogenic agent causing the disease undergoes some developmental cycle in the biting-fly, resulting in the latter becoming more or less permanently infective after this development has taken place, the transmission is said to be indirect or cyclical. In these cases there is always a definite biological relationship between the biting-fly and the parasite which it conveys, and the latter is only capable of development within the members of certain species or families of insects. The best known example of this indirect method of transmission is that of the malarial parasite by the mosquito. When the parasite, at a suitable stage of its life-history, is taken into the stomach of a susceptible species of mosquito, it undergoes a complicated cycle of development in its new host, finally resulting in the salivary glands of the latter becoming invaded by a stage of the parasite adapted for entry into the blood of the next person that the mosquito bites. It will be noticed that in this, and all other cases of indirect transmission by biting-flies, the parasite develops in two hosts, vertebrate and invertebrate, respectively. The host in which the parasite undergoes its sexual life-cycle is called the definitive host. In the case of the majority, if not all, I] INTERMEDIATE HOST 5 protozoal parasites, the sexual part of their life-cycle takes place in the invertebrate carrier, and therefore the latter is the definitive host. On the other hand, the sexual cycle of Filaria bancrofti takes place in its vertebrate host, man, and in this case man is the definitive host. The host in which the parasite merely multiplies asexually is called the intermediate host, and in the case of protozoal infections is the vertebrate, but in Filaria is the invertebrate, host. The term " intermediate host " has given rise to much con- fusion, for many writers still persist in considering the expression synonymous with " invertebrate host." As a matter of fact, in the majority of cases the vertebrate is the intermediate host, and it is only obscuring the true relations of parasite and host to persist in the erroneous application of this term. In all cases the equilibrium between parasite and host is much better established in the definitive than in the inter- mediate host. As a general rule parasites do not have a very harmful action on their definitive hosts, whether inverte- brate or vertebrate, whilst on the other hand there are many examples of parasites seriously affecting the health of their intermediate hosts. Thus the malarial parasite does not seem to affect injuriously the health of its definitive host, the mos- quito, whilst in the intermediate host, man, it produces malaria; a serious and often fatal disease. Similarly, the presence of Filaria bancrofti in its definitive host, man, does not produce any obvious ill-effects, whilst a large proportion of the infected mosquitoes succumb to the infection. Although so many parasites have an injurious effect upon their hosts, sometimes causing death, it is obviously a short- sighted policy for a parasite to kill its host, as by so doing it also destroys itself. A parasite which invariably killed its host would eventually die out, owing to the extermination of the latter, and it is not inconceivable that, in this way, excessively fatal infections have disappeared from the world, together with the animals they affected. At the present time the great majority of blood parasites do not cause the death of their hosts. An equilibrium between 6 CONDITIONS AFFECTING TRANSMISSION [CH. the parasite and its host has become established and the former does not increase beyond a certain limit, with the result that the health of the animal from which it is deriving nourishment is not very seriously affected. This is the case with numerous parasites, such as the majority of trypanosomes in vertebrates, Hamoproteus in birds, Haemogregarines in reptiles, etc. It is only in rare cases that the parasites increase to such an extent that they markedly affect the health of their hosts, but since our attention is only called to diseased animals, the cases in which disease is caused by the parasites are more generally noticed. A pathogenic blood parasite cannot persist indefinitely unless one or more of the following conditions are fulfilled : ; (i) The disease which it produces may be of long duration so that the invertebrate host has numerous opportunities of becoming infected with the parasite and spreading the infec- tion to other hosts. Of course the parasite must be present in the blood in sufficient numbers and at a suitable stage of development to ensure the infection of the biting host which transmits the disease. If these conditions were fulfilled an excessively fatal, though chronic disease, possessed of efficient means of distribution would be able to persist until the exter- mination of its host had been accomplished, after which it would also cease to exist, unless it became adapted to some other host. (2) The infection may be hereditarily transmitted in the invertebrate host, so that the offspring of an infected parent also carries the infection. Fortunately, with the doubtful exception of yellow fever in Stegomyia, no biting-fly is known to transmit any disease agent to its offspring. One of the best examples of this mode of hereditary infection in other groups is that of Spirochceta duttoni in its invertebrate host the tick, Ornithodorus moubata. (3) The parasite may infest more than one species of vertebrate host, in one or more of which the equilibrium be- tween parasite and host has become established. This is by far the most important condition from an epidemiological point of view. If a parasite is able to live in several verte- brate hosts and is non-pathogenic towards any one of them, I] CONDITIONS AFFECTING TRANSMISSION 7 the latter serves as a reservoir for the infection and in the presence of an efficient transmitting agent the parasite may persist indefinitely. It is now known that the parasite of sleeping sickness (Trypanosoma gambiense) is maintained in this manner, since in addition to man it infests other vertebrate hosts, e.g. ante- lopes, which are practically unaffected by it. In the case of the malaria parasite an equilibrium is becom- ing established between it and its vertebrate host, man, but only in those races that have been exposed to infection for a considerable period. As a result the latter serve as reservoirs of infection for those races that have not become immunized, in whom the parasite produces malaria, a disease which is often fatal unless checked by suitable treatment. The relations between the parasites and their hosts are very complicated and are not yet thoroughly understood. From a biological point of view, it is probable that all protozoal blood parasites carried by biting-flies are primarily insect parasites and have only secondarily become adapted for living in the blood of vertebrates. Certainly in every case where the life- cycle of the parasite is known the insect is the definitive host, and the equilibrium between the parasite and its insect host seems to be well established, whilst this is not the case with regard to the mutual relations in the vertebrate host. The extreme pathogenicity of certain protozoal infections in vertebrates, e.g. yellow fever in man, the various trypano- somiases of man and animals, etc., strongly suggests that these diseases are of comparatively recent origin and there has not yet been time for any balance to become established between the parasites and their respective hosts. The trypanosomes constitute an excellent example of a group of flagellates which primitively inhabited the alimentary tracts of various invertebrates, and have recently become adapted to a parasitic mode of life in the blood of vertebrates. A large variety of insects, both biting and non-biting, contain parasitic flagellates, Crithidia, Leptomonas, etc., in their digestive tracts, and there are all stages between fla- gellates which are just capable of living in the blood of 8 CONDITIONS AFFECTING TRANSMISSION [CH. vertebrates, but are usually insect parasites (e.g. Trypanosoma boylei Lafont), and such forms as Trypanosoma gambiense, which have become well-adapted to a parasitic mode of life in many of the larger vertebrates. In the latter case the tsetse-fly, the insect host of T. gambiense, has apparently developed an immunity against infection with this flagellate, for only a com- paratively small proportion of the flies becomes infected after ingesting blood containing the parasites. When once a biting-fly becomes infected with the par- ticular species of blood parasite of which it is the definitive host, it generally remains infective for a very considerable period, often for the remainder of its life. It is obvious, therefore, that when a parasite is transmitted by a true defini- tive host, it is much more difficult to eradicate than when it is spread mechanically. In the latter case it is only necessary to protect all infected vertebrates from the bites of flies for a period of not more than three days and the insects cease to be infective. In the former case, however, the eradication of the parasite can only be accomplished effectively by the destruc- tion of the insect host. In fact the prevention of protozoal infections, which include many of the more important tropical diseases, is mainly an entomological problem, as it depends on the destruction of insects and to do this a knowledge of their habits and life-cycles is essential. In the case of yellow fever the destruction of the invertebrate host, Stegomyia fasciata, is comparatively simple, and as a result this disease is rapidly disappearing from the more civilized parts of the world. On the other hand, no effective means have yet been discovered of destroying Glossina mor- sitans, one of the most important disease carriers in Africa. Yet there is little doubt that when we have acquired a complete knowledge of the bionomics of this redoubtable insect, it will be possible to devise some means of considerably reducing its numbers. An infected invertebrate host may spread infection from one vertebrate to another in a variety of ways, but in the case of biting-flies, the infected insect whilst feeding generally inoculates the parasite directly into the body of the host. I] DEVELOPMENT OF PARASITE 9 The possibility of other modes of infection, however, should not be ignored, for they are known to occur in closely related groups, and therefore it is considered advisable to include a short account of some of the ways in which the infective agent may be spread by its invertebrate host. The simplest case is that in which the parasite, without undergoing any morphological or biological changes, merely multiplies in the alimentary canal of its invertebrate host. The parasite may then enter a vertebrate either by regurgi- tation of the contents of the alimentary canal when the inverte- brate host is feeding, or else by the faeces of the latter, containing the parasites, entering the open wound caused by its bite. The plague bacillus, which multiplies in the gut of the flea, is probably transmitted in this way. Usually, however, the parasite undergoes a cyclical develop- ment, passing through various stages that are generally incapa- ble of living in the blood of vertebrates, and therefore during this developmental period the host is non-infective. This negative interval is known as the incubation period and may vary from two or three days up to as long as 12 or 13 weeks, its duration depending mainly on the temperature, as develop- ment is accelerated by increased warmth and retarded, or even completely arrested, by cold. The development of various species of trypanosomes in the alimentary canal of the tsetse-fly includes some of the simplest examples of cyclical evolution. In the case of Trypanosoma cazalboui, when ingested by the tsetse some of the parasites remain in the fly's proboscis. In this region they develop, also undergoing certain biological changes, and for a period of about seven days they are incapable of living in the blood of vertebrates. At the expiration of this short incubation period, however, the trypanosomes recover their infectivity for vertebrates, and after this the tsetse is infective for a consider- able period. In other trypanosomes, e.g. T. gambiense and T. brucei, the evolution in the tsetse-fly is more complicated, the parasites developing in the digestive tract and passing through a crithidial stage before finally becoming infective, but in every case during this development they are restricted 10 DEVELOPMENT OF PARASITE [CH. to the lumen of the alimentary canal and its ducts. It is probable that the evolution of Hcemoproteus columbce is also restricted to the alimentary canal of its invertebrate host, Lynchia, but in this case the development is rather more complicated than that of the trypanosomes, as it includes a sexual phenomenon. The most complex type of evolution is that of the malaria parasite (Plasmodium) in its definitive host, the mosquito. In this case the development commences with the production of sexual forms which only become mature in the stomach of the mosquito, and the result of conjugation is a motile body which bores its way through the gut-wall and comes to rest in or near the outer lining of the gut. It then grows at the expense of the tissues of the mosquito and forms a large spherical cyst in which are developed minute sickle-shaped bodies, the sporozoites. Eventually the latter are set free into the body- cavity of the insect and make their way to the salivary glands, where they come to rest in the salivary ducts. These forms are capable of developing in the blood of the vertebrate host and are inoculated, together with the salivary fluid, when the mosquito feeds. The development of the Haemogregarines and Piroplasmidae in their respective invertebrate hosts seems to resemble that of Plasmodium. Between the simple evolu- tion of T. cazalboui and the highly complicated development of Plasmodium there are numerous gradations, but the majority of protozoal parasites probably pass through a life- cycle comparable with that of Plasmodium. The development of the ultra-microscopic virus of yellow fever is peculiar from the fact that it is possible to transmit the infection from one mosquito to another without the media- tion of the vertebrate host. The incubation period of the virus in the mosquito is about 12 days, but after the insect has become infective, if it. is crushed up and fed to another Stegomyia the latter becomes infective. The evolution of Filaria in the invertebrate host is very different from that of the Protozoa, as the sexual part of the life-cycle takes place in the vertebrate, in this case the defini- tive host, and the embryonic filariae, contained in the blood, I] MODES OF INFECTION II merely require to complete part of their larval development in the tissues of the mosquito. The manner in which the infective agent re-enters the vertebrate host is of considerable interest and varies in dif- ferent cases. As a rule the infective agent is directly inoculated into the body when the infected invertebrate feeds on some vertebrate host. The parasites may be present in the proboscis of the infected arthropod or leech, or contained in the salivary fluid, but in either case the result is the same and the infection is passed directly into the blood. In the case of Filaria, the parasite is contained in the proboscis of the infected insect and when it feeds escapes on to the surface of the skin. The parasite subsequently bores its way through the skin and thus reaches the general circula- tion of its vertebrate host. Sometimes the infective agent is merely deposited on the surface of the skin in the faeces of the invertebrate host. From this site the parasite may reach the blood circula- tion by means of the open wound caused by the bite of the invertebrate host (as in the case of Spirochceta duttoni), or through an excoriated part of the skin. Sometimes the same result is obtained by the host licking up the parasite from the surface of its body. This is one of the modes of infection of Trypanosoma lewisi, in which the infection reaches the circulation through the mucous membrane of the alimentary canal of the rat. The transmission of Spirochceta recurrentis by the louse is comparable with that of 5. duttoni by the human tick, for in the former case the parasites, set free only by crushing the insect, pass through the excoriations produced by scratching with the finger-nails. As lice are frequently crushed between the nails, it is easy to see how the infective agent can reach the circulation. Occasionally it is necessary for the vertebrate to swallow the parasite, which subsequently bores its way through the alimentary canal. The best known example of this method is that of Filaria medinensis, which develops in the body of 12 DIPTERA [CH. Cyclops. When an infected specimen of the latter is taken into the stomach, the filariae are set free and penetrate into the tissues of the vertebrate host. The transmission of the Leucocytozoon of the rat by Lalaps is of the same nature, for the rats can only become infected by swallowing Lcelaps containing the parasites. As mentioned above the transmission of Trypanosoma lewisi by the rat-flea is also of this nature, and Strickland has shewn that the surest way of infecting rats with this trypanosome is to feed them with fleas containing the parasite. REFERENCES. Brumpt, E. (1910). Precis de Parasitologie. Paris : Masson et Cie. Castellan! and Chalmers (1912). Manual of Tropical Medicine, 2nd edition. London : Baillidre, Tindall and Cox. Hindle, E. (1911). The Transmission of Spirochceta duttoni. Para- sitology, vol. iv. pp. 133-149. Manson, P. (1908). Tropical Diseases, 5th edition. London : Cassell and Co. Ltd. Mesnil, F. (1912). Modes de propagation des Trypanosomiases. Les Trypanosomes chez 1'hote invert6bre. Bull. Inst. Pasteur, vol. x. pp. 1-17 and 49-63. Minchin, E. A. (1912). An Introduction to the Study of the Protozoa. London : Edward Arnold. Strickland, C. (1911). Mechanism of Transmission of T. lewisi by the Rat-flea. Brit. Med. Journ. 1911, p. 1049. CHAPTER II DIPTERA. — GENERAL DESCRIPTION AND CLASSIFICATION Definition. The large Order of Diptera includes all those insects provided with two well-developed wings and, in addi- tion, a hinder pair of rudimentary wings known as halteres, or balancers. The mouth-parts are usually adapted for piercing and sucking, and are more or less modified according to the habits of the insect. The various stages of development, larva, pupa, and adult, or imago, are quite distinct, metamorphosis being complete. In addition, all the members of the Order II] GENERAL MORPHOLOGY 13 possess a distinctly segmented abdomen with the exception of the Pupipara, a very aberrant group which has become modified for an exclusively parasitic mode of existence. General Morphology. The head is connected with the thorax by an extremely slender neck and in consequence is very mobile, being capable of undergoing semi-rotation. The majority of the exposed surface is occupied by the large faceted eyes, which are usually much larger in the male than in the female, probably owing to the fact that the former has to seek out its mate. The eyes may actually meet in the middle line, in which case they are termed holoptic, in contradistinction to when they are separate, or dichoptic. The holoptic condition is especially characteristic of the male but occasionally is found in both sexes. In certain families, e.g. Muscidae, the head shews anteriorly a small depression, the lunula, which is bounded by an arched suture passing over the bases of the antennae. This structure is the remnant of a peculiar organ, the ptilinum, which, in the fly emerging from the pupal case, appears as a bladder- like expansion of the front of the head. The ptilinum can be expanded and retracted and consequently it is of . great use in helping the fly to break through the pupal case, and also to force its way through any material in which the latter may be buried. It is only present during the first few hours after the fly has emerged and subsequently it becomes com- pletely introverted, forming the inconspicuous lunula of the mature fly (Figs. 1-3)'. The antennae are of great use to the systematist as they offer a simple means of classification, the number of segments being of considerable importance. In the more primitive families of the Order, e.g. Culicidae, there are a series of segments of approximately equal size, the number of which varies from eight to sixteen. In some cases the antennae of the male are larger and composed of more segments than those of the female. The majority of flies, DIPTERA — MOUTH-PARTS [CH. however, possess antennae of a totally distinct form, peculiar to the order, consisting of three segments, the outer one of which, at its distal extremity, bears a fine process known as the arista, which is occasionally segmented and often covered with hairs. It probably represents the remaining segments of the more primitive type of antennae. Fig. i. An Anthomyid fly immediately after emerging from the puparium, shewing the greatly distended ptilinum and unexpanded wings. Figs. 2 and 3. Ventral and side views of the head of the same fly. After Graham-Smith. The mouth -parts are composed typically of the following structures : labrum, epipharynx, maxillae, mandibles, hypo- pharynx and labium. These are liable to great variation, even within the same family, but all blood-sucking Diptera agree in the possession of a mouth that is adapted for piercing and cutting. The labrum, or upper lip, together with the epipharynx, is usually elongated ; the hypopharynx, or tongue, is also much prolonged and, together with the labrum, may form a tube for the ingestion of blood or other liquids ; the II] THORAX AND ABDOMEN 15 labium, or lower lip, is more or less membranous or fleshy, and usually functions as a shea'th for the protection of the other mouth-parts. The mandibles and maxillce are each represented by a pair of long pointed processes adapted for piercing. In addition, a pair of well-developed maxillary palps is always present, situated one on each side of the base of the labium. The palps are extraordinarily well developed in the Culicidae (Fig. 4), in the genus Megarhinus being nearly as long as the whole body of the insect. The thorax is composed almost entirely of mesothorax, the prothorax and metathorax being very small and fused with it. A small part of the metathorax projects backwards over the base of the abdomen and is known as the scutellum. The abdomen is composed of a variable number of segments, more or less closely fused together. The number of segments externally visible may vary from nine to five, or rarely four. In certain cases the first two segments are fused together and the first one is often very much shortened. In the male the terminal segments are curled under the body, forming what is termed the hypopygium, which serves to protect the copulatory appendages. The three pairs of legs are attached to the prothorax, mesothorax and metathorax, respectively. The legs are in- variably composed of five parts known as the coxa, trochanter, femur, tibia and tarsus. The tarsus is generally five-jointed ; its terminal joint bears a well-developed pair of claws, and underneath each of these is often a free pad or membrane, the pulvillus. This structure is often absent amongst the Orthorrhapha and is usually better developed in the male than in the female. Between each pair of claws is situated a median structure known as the empodium, which may have the form of a pad, or a bristle. Occasionally the pulvilli are absent and the empodium takes on their function. The wings are of very great importance from a classificatory point of view. As in all insects they consist of simple folds supported by veins or nervures, the arrangement of which is known as the venation. The wings are membranous but may be covered with hairs or scales, and the shape and disposition i6 DIPTERA [CH. II] WING VENATION of the latter is of great use in the identification of various species of mosquitoes. The venation, although comparatively simple, has been greatly complicated by the fact that entomologists are not agreed as to the terminology of the various parts and in consequence different writers use different names for the same structures. In the following description of the wing of Tabanus, which is taken as an example because the venation is rather compli- cated, we have adopted the system of nomenclature most generally used by descriptive entomologists. Auxiliary nerve .... . X Subcostal cell Anterior cross-vein v ' — * Cosl"al vein Humeral cross-vein Posterior cross-vein Anterior basal cross-vein Fig. 5. Wing of Tabanus sp. shewing the venation. The numbers I, II, III, etc. indicate respectively the first, second and third longitudinal veins, etc. The most easy way of recognizing the veins is to commence with the discal cell, which is a large cell situated about the middle of the wing. It is present in the great majority of flies, but is absent in the Culicidae. Anteriorly, the discal cell is bounded by the fourth longitudinal vein, and somewhere along its length will be seen a short connecting vein, the anterior cross-vein. The latter is constantly present in all flies. In front it is connected with the third longitudinal, and behind with that part of the fourth longitudinal that bounds the discal cell. H. B. F. 2 1 8 DIPTERA [CH. Counting forwards from the third longitudinal, which is forked, occur the second and first longitudinals, these three veins arising from a common stem and radiating to the costal vein, which runs round the edge of the wing. Between the costal vein and first longitudinal, is present an auxiliary, or subcostal vein, which runs parallel with the costal for a short distance and then curves into it. Near the base of the wing the two latter veins are connected by the short humeral cross- vein, which is very constant. The subcostal, and the first three longitudinals support the anterior half of the wing. The fourth andy£///z longitudinals arise together and diverge towards the margin ; each of them forks before reaching the edge of the wing. The sixth longitudinal arises more or less independently, and runs towards the hind margin of the wing. The three latter veins together support the posterior half of the wing. The fourth and fifth longitudinals are connected by two cross- veins, the anterior basal near the axil and the posterior cross- vein in the outer half of the wing. Between the fifth and sixth longitudinals is a posterior basal cross-vein. It will be seen that the wing is divided by its longitudinal nervures into two fields separated by an interval which is traversed only by the anterior cross-vein. The various spaces or cells included between the veins are distinguished by special names ; their arrangement may be understood by referring to the figure (Fig. 5). In addition to this system of nomenclature, that proposed by Schiner is used by a certain number of writers. One great source of confusion between this and the older system is the different meaning of the subcostal ; Schiner employs the term mediastinal for the subcostal, and subcostal for the first longi- tudinal ; moreover, the corresponding cells are similarly named. The surface of the body in flies differs considerably in the nature of its vestiture. Sometimes the integument is almost naked, but generally it is covered with hairs, or bristles, or sometimes scales. Those flies which are provided with an armature of bristles, or macrochatcz, may be termed chceto- phorous ; and where there is no definite arrangement of bristles, the fly is said to be eremochcztous. Osten Sacken II] INTERNAL ANATOMY 1 9 has drawn up an elaborate system of nomenclature for the arrangement of the bristles, which is of considerable value for purposes of classification. Internal Anatomy. The alimentary canal is provided with a muscular pharynx. The ceosphagus usually gives off a large diverti- culum known as the crop or sucking stomach, but in some insects, e.g. Culicidae, its place is taken by two or three long thin-walled sacs, the cesophageal diverticula. The stomach is large and consists of an anterior portion, the proventriculus, and a true stomach behind it ; the latter usually gives off caeca. The intestine is coiled and ends in a rectum ; at its junction with the stomach open the long Malpighian tubules, generally four in number. The salivary glands are large and their common duct opens at the top of the hypopharynx. The heart consists of a thin-walled tube running along beneath the dorsal surface of the insect. Usually it is divided into several chambers but in the more specialized families there are only two. The respiratory system consists of two main tracheae running longitudinally one on each side of the body and open- ing to the exterior by means of the spiracles. The latter are arranged on each side of the body, two large pairs in the thorax and one pair to each abdominal segment. The two main tracheal trunks expand at the base of the abdomen into con- spicuous air-sacs, which are probably of use when the insect is flying. The nervous system is very variable. In the elongate Nematocera there are five or six abdominal ganglia and three distinct thoracic ganglia, but in the more specialized forms, such as the Muscidae, all the thoracic and abdominal ganglia are fused into a single mass. Various gradations may be found between these two extremes and it is interesting to trace the gradual concentration of the nervous system side by side with the higher specialization of the insects. The reproductive organs present some interesting peculiarities. The ovaries consist of a very large number of 2 — 2 20 DIPTERA [CH. egg-tubes. The female, in addition, has three spermathecae, paired accessory organs, and no true bursa copulatrix. The male has two oval testes with short ducts, communicating with a well-developed penis, surrounded by accessory copulatory appendages. Reproduction. The great majority of flies lay eggs, which are generally deposited in such a position that the young larva will be in easy reach of its food-supply. A number of families, however, are more or less viviparous, the eggs hatching within the body of the parent and the resulting larvae nourished for varying periods before being liberated. In the majority of such cases the larvae are deposited whilst quite young, but in the Pupipara and Glossina the larvae are nourished within the oviduct of the mother until quite full-grown and when set free at once proceed to pupate. Fig. 7. Fig. 6. Fig. 6. Acephalous larva of Stomoxys calcitrans (xy). After Newstead. cst, compound thoracic stigmen ; ast, posterior stigmen. Fig. 7. Fucephalous larva of Phlebotomus papatasii. After Newstead. II] LARVA 21 The larvae are generally of the form known as maggots. They are without exception destitute of true thoracic legs, although in some groups stumpy pseudopods, resembling those of the caterpillar, may be present. These pseudopods vary greatly in their arrangement ; sometimes they are provided with recurved hairs. The larvae may be divided into two groups according to the size of the head. In the cruciform maggots the head is so small as to be almost invisible and these are termed acepha- lous larvae (e.g. Glossina). In the eucephalous larvae there is a well-marked head provided with mandibles, and usually there is a distinct thorax and abdomen (e.g. Anopheles). The tracheal system exhibits great variety and the larvae may be classified according to the arrangement of their spiracles. In the peripneustic forms, the spiracles are arranged along the sides of the body, one pair to each segment ; in the amphi- pneustic forms there are two pairs of spiracles, one at each end of the body ; whilst in the metapneustic forms there is only one pair of spiracles placed at the posterior extremity of the body. The great majority of aquatic larvae belong to the latter type and there are often very elaborate devices for keeping the tip of the body in communication with the atmosphere so that air can enter the spiracles. The habitat of the larvae is much more variable than their structure, and they display great diversity in their mode of life. The majority of the maggot-like forms live in decaying organic matter, whilst nearly all the eucephalous larvae are aquatic, occurring in both fresh- and salt-water and feeding either on vegetable matter, or preying on other small animals. A certain number of them are parasites, occurring in both plants and animals, and there is one form, the Congo floor-maggot, which sucks the blood of human beings and in its method of feeding somewhat resembles the bed-bug. The pupa may be either oblectate or coarctate. In the former case the pupa is merely protected by a thin chitinous pellicle and the outlines of the various appendages of the future insect can be clearly distinguished through this covering — as, for example, in the mosquito. In these obtectate forms the 22 DIPTERA — PUPA [CH. larva casts off its skin before pupating. This type of pupa is found, with few exceptions, throughout the members of the Brachycera and Nematocera. In the coarctate forms there are no external protuberances, with the possible exception of a pair of projections at one end of the body, but the whole pupa looks like a tiny barrel, with rounded ends. In this case the pupating larva does not escape from its skin at the last moult but merely shrinks within it, and the larval skin tr Fig. 9- Fig. 8. Fig. 8. Obtectate pupa of A nopheles maculipennis. tr, respiratory trumpet. After Nuttall and Shipley. Fig. 9. Coarctate pupa of Stomoxys calcitrans. After Newstead. is strengthened by the secretion of chitin so that it forms an adequate protection for the pupa. The external case is fre- quently known as the puparium. This type of pupa is found in the Cyclorrhapha, which includes the house-fly, Stomoxys, Glossina, etc. The adult fly escapes from the pupal case in one of two ways. In the obtectate forms the dorsal surface of the pupal sheath splits longitudinally or in a T-shaped fashion, and the insect draws itself out through the opening. In the coarctate pupae the anterior end of the pupal case is pushed off by means of the expanded ptilinum of the emerging fly (vide supra, p. 14). II] CLASSIFICATION 23 The obtectate pupae, as for example in the mosquito, are often actively motile, progressing almost as freely as the larvae. The coarctate pupae, however, are devoid of all movement and are usually to be found buried in the earth, in crannies, or in similar localities. The mature fly, after breaking out of the pupal case, is aided in forcing its way through any covering of earth, or similar material, by the alternate expansions and contractions of the ptilinum, which becomes completely- retracted soon after the fly has emerged. Classification. The most generally adopted classification is that of Brauer who divides the Diptera into two suborders, the Orthorrhapha and Cyclorrhapha, according to the manner in which the adult fly emerges from the pupal case, either by a T-shaped opening along the back (Orthorrhapha) or by a circular opening at the anterior extremity (Cyclorrhapha). Although this distinction is of great importance it is rather difficult of practical applica- tion when the immature stages are unknown, and the only method of distinguishing the adult fly is the presence or absence of a suture over the insertion of the antennae. The position of the Pupipara is somewhat doubtful, but from Roubaud's researches it seems probable that the Hippoboscidae, at any rate, are merely a highly specialized group of the Muscidae. For the present, however, they will be regarded as a separate division and accordingly, following Sharp's arrange- ment, the Diptera may be divided into five sections : Series i. Orthorrhapha Nematocera. Flies in which the antennae are composed of more than six segments of which all except the first two are equal in size. An arista is not present. The palpi are long and flexible, and usually four- or five-jointed. The second longitudinal vein is often forked and with the exception of the Tipulidae and Rhyphidae a discal cell is not present. This section includes the mosquitoes, sand-flies, Chironomus, etc., all of which are what may be termed gnat- like flies. Series 2. Orthorrhapha Brachycera. Flies in which the antennae are composed of three dissimilar segments, the last 24 CLASSIFICATION OF DIPTERA [CH. of which often carries an arista, usually terminal in position. When an arista is not present the flagellum ends in an append- age consisting of a number of indistinctly separated segments. The maxillary palps are composed of one or two segments and are not flexible. There is no definite arched suture above the insertion of the antennae. The second longitudinal vein is not forked, but frequently the third is forked ; the venation is often very complex. This section includes the important family of Tabanidae, in addition to a few other less well-known forms. These first two divisions together constitute Brauer's sub- order Orthorrhapha, which includes all those Diptera in which the imago escapes from its pupal case by means of a dorsal T-shaped opening or longitudinal slit ; accordingly ptilinum and lunula are absent in the adult insect. The larva possesses a distinct head and the pupa is usually obtectate. Series 3. Cyclorrhapha Aschiza. Flies without a frontal suture and with a somewhat indefinite lunula. The antennae are composed of not more than three segments of which the end one bears an arista, which is not terminal, but usually superior, in position. This group includes a large number of very minute flies and also the great family Syrphidae, but none of the members are known to suck blood and are therefore of no interest in the present connection. Series 4. Cyclorrhapha Schizophora or Eumyiid flies. Flies in which the antennae are composed of three segments and an arista. None of the veins of the wing are forked. In the Calyptratae the frontal suture is well-marked leaving a distinct lunula over the insertion of the antennae. In the Acalyptratae, the form of the head is less characteristic, but the members of this section can generally be distinguished from the Bra- chycera by their less complex wing venation. This group includes the important family Muscidae, of which the common house-fly, also Stomoxys, and Glossina are well-known examples. The latter two series together constitute the suborder Cyclorrhapha, which may be defined as Diptera in which the imago escapes from the pupal case by means of a circular aperture at the anterior extremity produced by the pressure II] BITING-FLIES AS CARRIERS OF DISEASE 25 of the expanded ptilinum. In consequence a frontal lunula is generally present. The larva is without a distinct head (maggot-like) and the pupa is coarctate. The antenna is composed of three segments, the terminal one of which bears an arista, usually dorsal in position. The maxillary palps are each composed of a single segment, the maxillae are rudimentary and the mandibles absent. The third longitudinal vein is not forked and there are not more than three complete posterior cells. The number of abdominal segments never exceeds seven and is usually less. Series 5. Pupipara. Abnormal Diptera of parasitic habit in which the wings are often rudimentary or absent. The head fits into a hollow of the thorax and the abdomen is not distinctly segmented. The larva, until it is mature, develops within the body of the female and when deposited at once pupates. This group consists of an assembly of diverse forms, pro- bably of varied affinities but all agreeing in their habit of depositing fully-grown larvae. The best-known family is the Hippoboscidae, including Hippobosca, and Melophagus, the sheep-ked. REFERENCES. Alcock, A. (1911). Entomology for Medical Officers. London: Gurney and Jackson. Brauer, F. (1880). Denk.Kais. Akad. Wissensch. Math.-Naturwissensch. Klasse, vol. 42, p. 105. Sharp, D. (1899). Insects, Part n in the Cambridge Natural History. London : Macmillan and Co. Williston, S. W. (1908). Manual of North American Diptera. New Haven, U.S.A. : G. T. Hathaway. CHAPTER III BITING-FLIES AS CARRIERS OF DISEASE The term " Biting-Flies " has been selected in order to include all those members of the Order of Diptera that either habitually, or occasionally, feed by sucking the blood of verte- brates. As a result of their feeding habits they are mainly any blood-sucking members; in addition agents are mentioned. ed Locality Authority Mediterranean Doerr, Franz and Taussig '. ) Region, India, etc. (?). Peru. Townsend. i « p" en en Ctf J-i nj VH TJ U •^o g+j ||5g 4 g^d |^| flfg fen I lliil lltlif^tii'P 1 11!-^ If I. fifl8 11 0 £o«tf ^ c^Pic^ OD o3 rt c^ l^s> • • 13." ndoo^grt rt « sIi|ST|li . . rfr1 ^'|,. ^ gJligJlS'll J c Idi i i ^ •«* •1 £• > 1 1 fi^i •§ II 0-. . V . ¥-3 11 o > •«s> ^ VH n* ^ « |9 £ bVrf g JS "^S : ,3 " bo rt .213 III * M^ : s-c d • ;*o rt •3s -Si ^^ SS ^ ^ 1 § > I *^ Q g V) <& g Q . i V •" • ^S 1 N *o» •S 1 3 en 8 g • I '' h—l ^ ^3 *£ hH 'i £ . "o • ' ^ JD ^ •^ • e • . . . et ^ en | 8 S S -i2w.^ r^^ S S ^ • f*K 52 ^ <* 2 •SP •2 X £H • " "^ '~" ^ ^"^ 3 *& f) : <+-! •^ " c 1 |£ i 11 1S| "S ^ rt :^ ^H S'i rt1"^ '•SgHfi,^ "^ "* '^^'s | s .1 3 If. IP 's £ w o ** ^ : "ii :-^rl rC >2 -2 55 itl 11 f?lll:: : ::: — ;li !•*! life? a ill .0^3C/5 ••§ ,| ^^ " " " :::;::: : ::; 3 Ill lo 1 c/5 '6-§^ ex ' ' ' '1 £ G "2 S QH 4J 1 • • • • • * * * f^ ^ • ' ' J 9 S *° • .il^.i 6 . •S ! v tee B *s Its? °.e§l rf' /Aa/». Patton turkhudi, Listo /«/«', Theob. . . hispaniola, The wyj'a) ludlowi, 1 is) costalis, Loew chaudoyei, Th< superpictus, G myzo my fades , lus) pseudopictus barbirostris, £ .cT *t* >es, Theob. 'oensis, Theob. . maculatus, Goel< tephensi, Liston villmori, James :hus) fuliginosus maculatus, willmori, J maculipalp w G a & | W 1 I !l ' A i 1! ^ rt |w G G G i S o ^ i_ Er ' aCtf T3 - vO ^ § «: ?i **-sli x 6 o s'i. ^«^^^'e««^5S^l Illln.1.!*!1!111 3f3!^^^;hi vipalp 3§:j ifiii " §•&•&«• £g2S • a s •fs -^ ' — S-'S .» Stomoxy 32 ORTHORRHAPHA NEMATOCERA [CH. responsible for the transmission of the large number of parasitic animals that occur in the blood of vertebrates, especially in the tropics. Their great economic importance as carriers of disease agents has become universally recognized during the past twenty years and at the present time it is unnecessary to dwell on this point. In fact there seems to be a tendency for authors to go to the other extreme and credit biting insects with the spread of almost every disease in which the mode of infection remains unknown. Nevertheless, a large number of species of biting-flies have been shewn to be respon- sible for the spread of various diseases as may be seen from the preceding table, in which are included all biting-flies that are known to carry infections, together with the infection, or infections, which they transmit (Table I). CHAPTER IV ORTHORRHAPHA NEMATOCERA Definition. As a rule a member of this series may be easily recognized by its long thin body, slender legs and long narrow wings. Moreover the antennae are long and filiform, being composed of 6 to 15 segments that often bear whorls of hairs, especially in the male. The larvae are aquatic, or live in decaying organic matter (e.g. Phlebotomus) . The Nematocera includes some of the most important biting-flies that carry disease, as the great family of mosquitoes belongs to this group. Classification. Williston divides them into 12 families, of which four are known to include members that either occasion- ally or habitually feed on blood. In the present work his method of classification has been adopted and the following table includes all the families of the Nematocera. Those which include any members that are known to carry disease are printed in capital letters and will be discussed more fully. IV] ORTHORRHAPHA NEMATOCERA 33 Synopsis of the Families of Orthorrhapha Nematocera1. Body and wings thickly covered with hairs; flies resembling moths (Fig. 20) =PSYCHODID;E. L Flies not resembling moths =2. f Wings with a network of fine vein-like creases besides the ordinary 2 -4 veins (Fig. 10) =Blepharocerida2. I Wings without any additional network of vein-like creases =3. r Scutum usually with a V-shaped transverse suture (Fig. n) ; wings 3 < usually with a discal cell = Tipulidce. L Scutum without a transverse suture = 4. f Wings with a discal cell (Fig. 12) =Rhyphides. X Wings without a discal cell =5. r Antennae abnormal, apparently consisting of two segments and a 5 ^ terminal arista (Fig. 14) =Orphnephilid(e. L Antennae normally nematocerous =6. r Posterior 'edge of wing fringed with scales (Fig 25) =CULICID^;. ' \ Posterior edge of wing not fringed with scales = 7. r Minute fragile midges ; wings commonly with only three longitudinal i veins (Fig. 13) =Cecidomyidce. ' J Not abnormally delicate and fragile ; wings- usually with numerous L veins. —8. g r Ocelli present (Fig. 16, oc) =9. \Ocelli absent =10. r Coxae elongate ; antennae usually elongate ; all the tibiae end in spurs 9 ^ (Fig. 15) =MycetophilidcB. L Coxae short; antennae usually shorter than thorax =Bibionidcn. /The costal vein extends all round the wing = Dixid&. 10 \The costal vein stops at or near the tip of the wing (Fig. 17) = LI. /-Gnat-like flies with long slender legs; antennae filiform, often with whorls of hairs =Chironomid&3. 11 -J Thick-set flies with stout legs ; antennae stout and stiff, hardly longer than the head, and never having whorls of hairs ; wings remarkably broad =Simuliid(Z3. 1 From Alcock's Entomology for Medical Officers, p. 46. - Some of the females belonging to Curupira have been suspected of blood- sucking habits. 3 Signifies that some of the members of these families are known to suck blood. H. B. F. 34 ORTHORRHAPHA NEMATOCERA [CH. 12 n 14 13 10 17 Fig. 10. Wing of Kelloggina, a blepharocerid, shewing the network of fine vein-like creases ( X 12). Fig. n. Thorax of Tipula, with V-shaped transverse suture on scutum ( X 8). Fig. 12. Wing of Ryphus (Xi2). The costal vein does not extend beyond the apex of the wing. Fig. 13. Wing of Cecidomyia (XI2). The costal vein extends completely round the wing. Fig. 14. Antenna of Orphnephila (x8o). Fig. 15. Right hind-leg of Mycetophilus, shewing the tibial spurs (X8). Fig. 16. Head of Bibio (Xi2); oc, ocelli. Fig. 17. Wing of Chironomus sp. ( X 8). V] FAMILY PSYCHODIDyE 35 CHAPTER V FAMILY PSYCHODID.E (MOTH-FLIES AND SAND-FLIES) Definition. The members of this family are small insects, generally not exceeding 5 mm. in length, which somewhat resemble moths, as the body and wings are thickly covered with hairs, amongst which patches of scales may occur. The wings are unlike those of any other Nematoceran, being oval or lanceloate in form (Fig. 19), and with a somewhat striking venation. The second longitudinal vein branches into three near the base of the wing, and as the transverse veins are very faint, the wing appears to contain nine or ten longitudinal veins without any connections. The antennae are long, being com- posed of 16 segments, which often carry whorls of hairs. The larvae, as a rule, live in decomposing vegetable matter. The Psychodidae are cosmopolitan, but are most abundant in tropical and subtropical regions. The species belonging to the genus Phlebotomus are the only ones which are known to suck blood habitually. Phlebotomus. General account. All the members of this genus are small inconspicuously coloured insects, the females of which feed by sucking the blood of vertebrates. In some species the male also sucks blood, and it often possesses mouth-parts resembling those of the female. The flies are commonly known as " Sand- Flies," or, in Southern Europe, " Pappataci Flies," and on account of their voracious habits and the fact that their small size enables them to creep through the meshes of an ordinary mosquito net, they are a source of much annoyance in those parts of the world in which they occur, especially as their bite causes great local irritation. Moreover, the well-known " Pappataci Fever," or " Three-Day Fever," is certainly carried by P. papatasii, and probably by other species of the 3—2 PHLEBOTOMUS [CH. genus, which is, therefore, of considerable importance from a medical point of view. pro. Fig. 18. Head of Phlebotomus papatasii ; ant, antenna ; e, eye ; cl, clypeus ; pal, palpus ; pro, proboscis. After Newstead. Definition. The genus Phlebotomus may easily be dis- tinguished by the following characters : Psychodidae in which the mouth is modified for piercing and sucking. The antennae are long and slender, composed of Fig. 19. Wing venation of Phlebotomus papatasii ; upper, ? ; lower, $ . After Newstead. 16 segments, and the joints are not markedly constricted. The wings are narrow, covered with hairs, and in repose are V] BIONOMICS 37 always carried uplifted so that the insect resembles a tiny moth. The second longitudinal vein branches twice, all three branches being distinct. The body is hairy. Sexual dimor- phism is distinct. The total length never exceeds 3 mm. and is usually much less. Phlebotomus papatasii is the most important member of the genus and the following remarks apply especially to this species. Bionomics. When P. papatasii is feeding it lifts its wings up to an angle of about 45°, this characteristic attitude being well shewn in Fig. 21. On the slightest disturbance the insect Fig. 20. Phlebotomus papatasii, Scop. Male. moves suddenly to either the right or left by short rapid flights, somewhat resembling the movements of a flea. If undisturbed the females rapidly gorge themselves with blood and then silently fly away to some dark corner. In rooms they usually hide behind pictures, underneath clothes or in similar places. In Malta, where they have been studied by Marett and New- stead, their favourite localities during the day seem to be the numerous small caves and catacombs, and also the interstices of stone walls. Atmospheric conditions have a marked effect 3$ PHLEBOTOMUS [CH. on the flies, for on still warm nights they are found in large numbers in houses. On the other hand, they rarely appear when cool fresh breezes are blowing, in this respect resembling the common midges of England. The chief breeding places seem to be the crevices between rocks, in loose stone walls, caves, also dark cellars, and especially on the sides of drains kept moist by the occasional splashing of water. Unfortu- nately, much work remains to be done on this subject, for the task of finding the minute larvae or pupae is very difficult, Fig. 21. Phlebotomus papatasii, Scop. Female. and little is known about their habits. The difficulty of find- ing the larvae is still further increased by their peculiar habit, when exposed to light, of flicking themselves off the surface of the object on which they are resting. The pupae are even more difficult to detect, for not only are they very minute, but closely resemble the colour of their surroundings. It is therefore not surprising that so little is known about their habits, in spite of the importance of this knowledge from a prophylactic point of view. The flies are very unequally distributed even in regions that seem to present the same conditions, such as an abundance of stone walls for breeding places. Moreover, some houses are visited much more frequently than others without any apparent V] LIFE-CYCLE 39 reason. In Malta, Newstead found that bedrooms on the first floor facing the sheltered side of the house were much more favoured than those of the opposite side ; and only a single example was ever found in rooms on the second floor. Some persons seem to be immune to the attacks of these insects, as for some reason they have their likes and dislikes with regard to hosts, as well as habitat. It is probable that reptiles constitute the main hosts of these insects, for in West Africa, Roubaud found a lizard covered with gorged females of P. minutus. More recently Hewlett has brought forward convincing evidence to shew that in India geckos are the chief hosts and are preferred to man. The flies are especially abundant in the hot season of the year but in tropical countries they may be found at all times. When kept in captivity on wet blotting-paper P. papatasii lives but a short time (3-9 days),, even though fed on human blood and kept under the most favourable conditions. The life of the adult therefore is probably of but short duration. The females readily oviposit in captivity but often die during the process. From an examination of the ovaries, the number of eggs is found to be from 40 to 50, so that the insect is comparatively little prolific. Life-cycle. After copulation, the female seems to require a feed of blood before being able to lay any eggs. This condition having been fulfilled, the insect then retires to some dark corner and deposits her eggs either singly or in clusters, the total number varying from 30 to 80, according to .the species. The act of oviposition is accompanied by very extraordinary move- ments on the part of the female. The whole process has been described by Newstead in the case of P. papatasii. A gravid female was placed into a glass-topped box and supplied with wet blotting-paper, when the insect at once settled on the paper and brought her proboscis into contact with it. After a few seconds she appeared to become intoxicated and collapsed, crossing the middle- and hind-legs behind the abdomen, whilst the front pair remained in their normal position. The abdomen was then raised and fully extended, after which three eggs were laid at short intervals. Each egg was ejected with 40 PHLEBOTOMUS [CH. considerable force to a distance at least three times the length of the abdomen. The whole process occupied about two minutes, after which the insect appeared very fatigued and rested for at least three hours before continuing the egg-laying. The eggs are almost transparent when first laid, and are covered with a thin coating of sticky substance which causes them to adhere to any surface. They are very elongate in form, dark brown, shining, with longitudinal black wavy lines, which are slightly raised and joined by very fine cross-lines. The length of the egg varies from 0*1 to 0*15 mm. (Fig. 22.) The incubation period is usually from six to nine days, but the eggs are very susceptible to external conditions and will only hatch if kept in a moist atmosphere. Fig. 22. Fig. 23. Fig. 22. Freshly extruded egg of P. papatasit. After Newstead Fig. 23. P. papatasii ; adult larva. After Newstead. The larva lives in damp earth and is very curious in form. It possesses a large well-marked head with big jaws, the latter being provided with four distinct teeth. The body is covered with toothed spines that may serve as a protection against enemies, and the posterior end bears two pairs of black caudal bristles. The bristles of one pair are almost as long as the body, whilst those of the other pair are short, but increase in length in the later stages (Figs, 7 and 23). The length of the full-grown larva is about 2 • 3 mm. In India the larval stage usually lasts from about three weeks to even as long as two months, but its duration depends mainly on the temperature, being much prolonged in cold weather. The larva closely resembles a caterpillar in its movements ; VJ BREEDING LOCALITIES 41 it progresses slowly and continually pecks at the stone on which it is placed. The caudal bristles are kept raised and extended in a fan-shaped manner, thus presenting a somewhat charac- teristic appearance. The larva feeds on semi-decaying vege- table matter and after undergoing a certain number of moults turns into the pupa. The pupa (Fig. 24), which is found on damp earth and under the surface of stones, is remarkable for the large ridges and excrescences on its thorax. The larval skin, with the bristles still attached, usually remains adhering at the caudal extremity. The fly generally emerges from the pupa after about six to ten days, but as in the other stages this period may be con- Fig. 24. Pupa of P. papatasii ; Is, larval skin with anal bristles attached. After Newstead. siderably prolonged by a low temperature. In India, accord- ing to Hewlett, the life-cycle of the sand-fly varies in duration from a month in the hot weather to six to eight weeks in the cold season, but in Malta Marett found the life-cycle occupied about three months. Breeding localities. Further information with regard to the breeding places of Phlebotomus is much to be desired. Captain Marett finds that in Malta the chief localities are the crevices in stone walls and the fissures between rocks in caves. In Italy Grassi found specimens in dirty cellars and similar dark places containing rubbish of various kinds. He states that the larvae live in dark and damp places amid all kinds of 42 SPECIES OF PHLEBOTOMUS [CH. rubbish ; they prefer underground situations such as cellars and more especially those parts of drains that can only be reached by splashes of dirty water. Although the adult fly is usually excessively abundant in those localities that it infests, no observer has yet succeeded in finding larvae in any con- siderable numbers. There are good reasons for believing that one of the breeding places ma}' be the dark and damp inner surfaces of the walls of latrines, and cesspools. The flies are notoriously common in latrines and in the case of a military camp in Herzegovina, Doerr brought forward evidence to shew that in summer the latrines were the only possible breeding places for the swarms of Phlebotomus that infested the camp. Phlebotomus and disease. The only disease1 which is known to be transmitted by members of this genus is the notorious Three-Day Fever, or Pappataci Fever. P. papatasii Scopoli is the only species that has been definitely proved to carry the infection, but it is almost certain that P. minutus and other members of the genus are equally capable in this respect ; therefore we append a short synopsis of the known species of Phlebotomus together with their distribution. Synopsis of known species of Phlebotomus. European species2. A . Abdominal hairs recumbent. (i) Integument black. Second segment of palpi slightly longer than third. Legs pale ochreous buff, with ochreous white refulgence. Length of female 2*5 mm. nigerrimus, Newstead. 1 Since the above account was written Townsend (Journ. Amer. Med. ASSGC. vol. 61, p. 1717) has brought forward evidence in support of the view that Verruga Peruviana is transmitted by Phlebotomus. These flies were found to be very abundant in the infected districts especially in the Verrugas Canyon. To prove this theory of transmission the author obtained two hairless Mexican dogs. After they had been kept under observation for nearly three months, one of them was inoculated subcutaneously with the ground-up bodies of 20 female Phlebotomus collected the night before in the Verrugas Canyon. On the fifth day this dog appeared ill and its blood was found to contain the peculiar endoglobular forms known as Barton's X-bodies, and also nucleated and broken down red cells. On the sixth day a typical nodular eruption was noticed on the right hind-foot and smears from one of the papules shewed bodies resembling Leishmania. On the eighth day the dog began to improve. The control dog remained in perfect health. 2 Modified from Alcock's Entomology for Medical Officers. V] SPECIES OF PHLEBOTOMUS 43 (2) Integument ochreous. Second segment of palpi one-half the length of the third. Length of female 2 mm., male considerably less. minutus, Rondani. B. Abdominal hairs erect. (3) Terminal segment of upper clasper of male hardly half the length of lower clasper. Legs relatively short ; average length of hind -leg 3 mm. Length of female, 1*9-2 '2 mm. perniciosus , Newstead (4) Terminal segment of upper clasper of male slightly longer than lower clasper. Legs relatively long ; length of hind-leg 4 mm. Thorax with a dull red-brown median stripe and a spot on each side. Length of female 2 '5-2 '65 mm. papatasii, Scopoli. (5) Resembling the preceding species in every respect except the form of the male claspers, the five spines of the terminal segment of the latter being long and falciform. mascittii, Grassi. African species. P. papatasii has been described from Algeria and Tunis and probably occurs throughout the whole of North Africa. General colour pale-yellow. Wing narrow, about three times as long as broad ; second marginal cell less than a third the length of the wing. Length of female 2 mm. ; male considerably less. duboscquii, Neveu-Lemaire. Pleurae clothed with large flat scales like those of mosquitoes. Third segment of palps with a compound group of minute modified spines, spathuliform with short pedicels. Khartoum. squamipleuris, Newstead. Resembling minutus but with shorter and stouter legs. Third to the thirteenth antennal segments bead-like. Gold Coast. antennatus, Newstead. Oriental species. P. papatasii is said to occur all over India and P. minutus (syn. babu Annandale) has also been recorded. In addition the following species have been described : Head and abdomen brown ; dorsum of thorax dark brown or blackish ; sides of thorax, coxae, and trochanters yellowish ; legs, antennae, and palpi grey ; the whole, especially the legs with a silvery sheen. Greatest breadth of wing about a third its length ; greatest length of second marginal cell (" first fork-cell ") about a third the length of the wing. argentipes, Annandale. Uniform grey with strong silvery lights, disk of wings with a bluish iridescence. Greatest breadth of wing not quite a third its length ; greatest length of second marginal cell a little more than a third the length of the wing. major, Annandale. Thorax, abdomen, and legs (except coxae and trochanters) brown with a tinge of purple and with silvery lights ; wings purplish, strongly iridescent. Greatest breadth of wing about a third its length ; greatest length of second marginal cell nearly half the length of the wing. South India. malabaricus, Annandale. Yellowish-grey with silvery lights. Greatest length of wing slightly over one-fourth its length ; greatest length of second marginal cell a little more than a third the length of the wing. Himalayas, between 4000 and 7000 feet. himalayensis, Annandale. 44 PAPPATACI FEVER [CH. Head and thorax yellowish-brown, abdomen brown with darker glistening hairs ; femora yellow with brown tip ; tibiae and tarsi brown with silver sheen. Greatest breadth of wing one-third its length ; greatest length of second marginal cell a little more than one-fourth the length of the wing. Batavia. perlurbans, Meijere. American species. Yellow, mesonotum brown ; legs appear brown in certain lights but are covered with white tomentum ; second marginal ceil slightly more than twice the length of its petiole. North America. vexator, Coquillet. Resembling vexator, except that the hairs are mostly yellow, and the second marginal cell is about thrice the length of its petiole. Guatemala. cruciatus, Coquillet . In female length of head with proboscis, half that of the rest of the body. Wing venation resembling that of malabaricus. In the male greatest length of wing 3^ times the greatest breadth. Wings bluntly pointed ; hind border not much more strongly arched than the front. Length of second marginal cell three-eighths that of the wing ; third marginal, six-elevenths the length, Halteres long and large. Brazil and Peru. rostrans, Summers. Dorsal surface of abdomen with numerous scales between the hairs. Palp index 4, 5, 3, 2. Length of body 2 mm. Para. squamiventris, Lutz and Neiva. Dorsal surface of abdomen without scales. Last segment of palps longer than the others ; palp index 4, 2, 3, 5. Length of body about 2 mm. St Paul and Minas. longipalpis, Lutz and Neiva. Dorsal surface of abdomen without scales. General colour brownish- yellow, the upperside darker. Palp index 5, 4, 3, 2. intermedius, Lutz and Neiva. CHAPTER VI DISEASES CARRIED BY PHLEBOTOMUS Pappataci Fever. Synonyms. Sand-Fly Fever ; Three-Day Fever ; Phle- botomus Fever ; Simple Continued Fever ; Pink Eye ; Som- merfieber ; Hundskrankheit ; Sommerinfluenza ; Soldaten- fieber ; Endemischer Magencatarrh ; Febbre dei tre Giorni ; Mai della secca; Febbre estiva; Chitral Fever; Fievre de Toga. History. This malady seems to have been known for many years in both Italy and India, but was first recognized as a definite disease by Pick in 1886. Taussig, in 1905, noticed that it was connected with the sand-fly and later, in 1908, the VI] DISTRIBUTION AND SYMPTOMS 45 researches of Doerr, Franz, and Taussig, clearly demonstrated the nature of this disease and its mode of transmission. Some authors, especially the French, regard Pappataci Fever as merely a form of dengue, but the febrile symptoms are rather different in the two cases and therefore, for the present, it seems advisable to consider them distinct. Distribution. Pappataci Fever occurs in various parts of Italy and is especially prevalent in Dalmatia, Istria, Herze- govina and various other parts of Austria-Hungary, and has also been recorded from Portugal. It is said to occur in Asia Minor, the Balkan Peninsula, North Africa and the Sudan. The majority of the islands in the Mediterranean seem to be liable to outbreaks, for the disease has been recorded from Corsica, Sicily, Malta, Crete and Cyprus, and probably occurs in most, if not all the islands of the Greek Archipelago. According to Robinson and Blackham the "Seven-Day Fever" of the Peshawur valley is also a variety of Sand-Fly Fever and is carried by Phlebotomus. In other parts of India, epidemics probably due to this infection have been observed, but the symptoms in many cases closely approximate those of dengue. The disease is said to occur in China. Symptomatology. In view of the fact that this disease has only recently been distinguished, a short account of the symp- toms is included. Different outbreaks shew considerable variations in the symptoms. The onset of the disease is usually sudden, with febrile symptoms, headache and pains, especially in the extremi- ties. The fever continues for one or two days and usually disappears on the third, fourth, or fifth day, but in some cases may persist as long as seven days. During the attack nervous symptoms are very pronounced ; headache, usually frontal, is constantly present and pains in the back, loins and lower extremities occur in the majority of cases. Muscle pains are frequently present, being chiefly located in the intercostal and lumbar muscles, and the muscles of the calves. On the other hand the joints are very seldom affected and this con- stitutes one of the means of distinguishing this disease from dengue. 46 PAPPATACI FEVER [CH. The eyes are injected, especially across the middle of the conjunctive, and the bulbi are painful on pressure. The distur- bances of the digestive system are very inconstant ; vomiting occurs in about one-third of the cases, usually as an initial symptom. Constipation is the rule when the temperature is high, but later on, diarrhoea often sets in and the liquid stools may contain blood. Epistaxis is a common phenomenon. Various cutaneous eruptions may occur, in the nature of erythema of a morbilliform or multiform character, and a few roseolae. The examination of the blood reveals no changes in the number or morphology of the red corpuscles. A pronounced leucopenia has been observed on the first day, and the numbers of leucocytes may fall as low as 1400 per c.mm. on the second day, after which the numbers slowly increase from the third day onwards. The percentage of polymorphonuclears varies between 80 and less than 50, and Gabbi finds a slight increase of the mono- nuclears. Eosinophile leucocytes are very scarce, their number being below the normal. The prognosis is invariably good and the patient's recovery is usually complete within two or three weeks after the begin- ning of the disease. In the absence of any knowledge of the causative agent of this disease, the diagnosis can only be based on clinical observa- tions and it is extremely difficult to distinguish between Pap- pataci Fever and various other febrile diseases. The presence of the transmitting agent may be of some help in establishing the diagnosis, but the discovery of the specific microbe is neces- sary before this disease can be distinguished with any certainty. Mode of infection. Pappataci Fever is transmitted by the agency of Phlebotomus papatasii, the sand-fly. Possibly P. per- niciosus, minutus, and other species of the genus are also capable of spreading the disease, but up to the present, with the possible exception of Aden1, no cases have been recorded from localities in which P. papatasii is not known to occur. 1 Sand-Fly Fever is said to occur in this region. The only species of Phlebotomus hitherto recorded from Aden is P. minutus. VI] MODE OF INFECTION, ETC. 47 Following the bite of an infected fly, there is an incubation period of from 3^ to 7 days, during which the blood of the patient is not infective. Then follows the first day of the attack during which the blood becomes virulent and is capable of infecting any Phlebotomus that may feed on it. The blood loses its infectivity within a very short period, probably not more than 24 hours, and after recovery the patient is immune against any further attacks of the disease. The flies become infected only if they feed on a patient during the short time that his blood is infective. After ingest- ing the virus, there is an incubation period of seven to ten days before the insects become infective and beyond this period they may again become non-infective, but experiments on this point are far from complete. Causal agent. Up to the present the causal agent of Pap- pataci Fever has not been discovered, but it belongs to the group of ultra-microscopic organisms which cause dengue, yellow fever, etc. Its presence in the blood is proved by the fact that the disease may be produced by the inoculation into a non-immune person of blood taken from an infected patient on the first day of the attack. Moreover, the injection of a small quantity of diluted serum filtered through a Cham- berland F filter is also followed by a typical attack of fever. The virus is sufficiently resistant to maintain its activity for a week in vitro. It is evident that the fly is a true host for the organism that causes the disease. If the Phlebotomus were only infec- tive up to the seventh day after an infective feed, there would be a strong suggestion that the virus was merely retained in the alimentary canal and regurgitated at subsequent meals. This supposition is disproved by the occurrence of a negative phase of about seven days, during which the infective agent of the disease undergoes some development, finally resulting in the fly becoming infective. Prophylactic measures. In view of the limited number of observations on the breeding habits of Phlebotomus it is some- what premature to advance any definite prophylactic measures. If crevices in stone walls and amongst rocks constitute the 48 PAPPATACI FEVER [CH. main breeding places, the task of destroying the immature stages is practically insurmountable. At present it is only possible to take precautions against being bitten by the insects and the simplest method is the use of repellents. Major Craw- ford recommends the following mixture which is said to be a very efficient deterrent : Ol. Anisi, 3 grs. ; Ol. Eucalypti, 3 grs. ; Ol. Terebenth, 3 grs. ; Ung. Acid Borac. The use of ordinary mosquito nets is of course impossible, as the flies are able to creep through the meshes, but spraying the net with a i per cent, solution of formol, or some other repellent, is said to be effective in keeping away these pests. By employing a screen of chiffon or some similar material, it is possible to exclude the flies altogether, but such a method is quite impracticable on warm nights, when the Phlebotomus are especially abundant. A brightly burning lamp appears to attract the flies more than a sleeping human being and is very useful in the absence of a net or punkah. As they are very sensitive to wind, the use of electric fans in rooms would pro- bably succeed in keeping them away and some such method might well be adopted in the case of patients suffering from Pappataci Fever, for by the careful isolation of all persons suffering from the complaint, the number of cases would be reduced. As the flies seem to avoid the upper stories of houses it might be advisable to keep patients suffering from the disease in upper bedrooms. By preventing the flies from feeding on the blood of infected persons it is even possible that the disease might be eradicated, and this is the only method that seems practicable at the pre- sent time. REFERENCES TO LITERATURE ON PHLEBOTOMUS AND PAPPATACI FEVER. Annandale, N. (1910). The Indian Species of Papataci Fly (Phle- botomus). Rec. Ind. Mus. vol. iv. pp. 35-52. With 3 plates. Birt, C. (1910). Phlebotomus fever in Malta and Crete. Journ. R.A.M.C. vol. xiv. pp. 142-159 and 236-258. - (1910). Sand-fly fever in India. Journ. R.A.M.C. vol. xv. pp. 140-147. VI] REFERENCES 49 Crawford, G. S. (1909). On the beneficial results of recent sanitary work in Malta. Brit. Med. Journ. vol. n. pp. 383-385. Doerr, Franz and Taussig (1909). Das Pappataci fieber. Leipzig and Wien : Franz Deuticke. Franca, C. (1913). Phlebotomus papatasii (Scopoli) et Fievre a Pap- pataci au Portugal. Bull. Soc. Path. Exot. vol. vi. pp. 123-124. Gabbi (1910) . Sulla febbre dei tre giorni o febbre da pappataci. Patho- logic-a, vol. ii. pp. 546—550. Grassi, B. (1907). Ricerche sui flebotomi. Mem. d. Soc. Hal. d. Scienze, Ser. 3 a, vol. xiv. pp. 353-394, with 4 plates. (1908). Intorno ad un nuovo flebotomo. Att. R. Accad. Line. Ser. 5 a, vol. xvn. pp. 681-682. Hewlett, F. M. (1909). Indian Sandflies. Trans. Bombay Med. Congr. Ser. 3, pp. 239-242. - (1913)- The Natural Host of Phlebotomus minutus. Ind. Journ. Med. Research, vol. i. pp. 34-38. Leger, M. and Seguinard, J. (1912). Fievre de Pappataci en Corse. Bull. Soc. Path. Exot. vol. v. pp. 710-713. Lutz and Neiva (1912). Contribuisao para o Conhecimento das Especies do Genero Phlebotomus existentes no Brazil. Mem. Inst. Oswaldo Cruz. vol. iv. pp. 84—95. Marett, P. J. (1910). Preliminary report on the investigation into the breeding-places of the sand-fly in Malta. Journ. R.A .M.C. vol. xv. pp. 286-291. - (1911). The life-history of Phlebotomus. Ibid. vol. xvii. pp. 13-29, with i plate. Newstead, R. (1911). The papataci flies (Phlebotomus} of the Maltese Islands. Bull. Entomol. Research, vol. 11. pp. 47-48. - (1912). Notes on Phlebotomus, with Descriptions of New Species. Part i. Ibid. vol. in. pp. 361-367. Robinson and Blackham (1912). Sand-flies and Sand-Fly Fever on the North- West Frontier of India. Journ. R.A. M.C. vol. xix. PP- 447-452. Seidelin, H. (1912). Pappataci Fever. Yellow Fever Bull. vol. n. pp. 74-84. Summers, Sophia L. M. (1913)- A Synopsis of the Genus Phlebotomus. Journ. Lond. School Trop. Med. vol. n. pp. 104-116. H. B. F. 50 CULICIDJE [CH. CHAPTER VII FAMILY CULICID^: (GNATS OR MOSQUITOES) General Account. Definition. The Culicidae are slender flies easily distin- guished from all other Nematocera by the presence of a row of scales on the posterior margin of the wings. In addition, the long projecting proboscis, and the plumose antennae of the males are characteristic features. External anatomy. The head is small and subspherical ; the occiput is always more or less covered with scales of various forms. The eyes are large and reniform and may, or may not, meet in the middle line ; in the living insect they are often brilliantly coloured, but in preserved specimens these colours usually fade. Ocelli are absent. The antennae are long and slender, composed of 14 or 15 segments ; the basal segment is large, round, and is sometimes provided with scales. The second segment fits into a depression at the apex of the first, and the remaining segments are all more or less elongated cylinders. Just above the base, or in the middle, of each segment arises a whorl of long thick hairs, which are some- what scanty in the female, but in the male are so thick-set as to give the antenna the appearance of a bottle-brush ; in addition, the last two segments of the male antenna are nearly always more elongated and nearly bare. The mouth-parts consist of the following appendages : (i) A pair of mandibles, each of which is an extremely delicate chitinous blade adapted for piercing the skin. In the male the mandibles are absent (Figs. 26 and 27). (ii) The first pair of maxillae, generally known simply as the maxillae, are extremely fine stylets usually longer than the mandibles. In the male the maxillae are sometimes rudi- mentary. From the outer side of the base of each maxilla, arises a maxillary palp, the form of which varies according to the sex. VII] EXTERNAL ANATOMY Fig. 25. Anopheles maculipennis. A, enlarged view of male; A', diagram of ditto to shew the natural size ; B, head of female. Modified from Nuttall and Shipley. 4—2 52 CULICIDyE [CH. In Anopheles the palps are five- jointed and as long as the proboscis in both male and female ; in the female Culex they are very short three- to four-jointed structures, whilst in the male Culex they are five- jointed and at least as long as in Anopheles ; in Aedes the palps are short in both sexes. (iii) The second maxillae are united together to form the labium, which ensheaths all the other mouth appendages with the exception of the palps, and the whole structure is generally known as the proboscis. It consists of a soft dor sally-grooved rod which bears a pair of small labellae at the distal extremity. lace. mn. U Fig. 26. Transverse section through about the middle of the proboscis of a female Anopheles maculipennis shewing the relative position of the parts when at rest. Two tracheae (tr) and two pairs of extensor and flexor muscles (mus) are seen in the labium. After Nuttall and Shipley. Lettering as in Fig. 27. Each of the latter represents the distal segment of the two- jointed second maxillae, the proximal segments of which are completely fused together. The labellae serve to guide the piercing organs of the mosquito. The cavity of the labium is hollow and it is within this space that the embryos of Filaria bancrofti and F. immitis come to rest after leaving the thoracic muscles or Malpighian tubules of an infected mosquito. The labium is covered by a thin cuticle and the filariae escape by rupturing this membrane when the insect feeds. In addition to the paired appendages mentioned above, there are two very important median structures. (iv) The labrum, or upper lip, which is united with the epipharynx, is an incomplete tube, in cross-section appearing VI l] EXTERNAL ANATOMY 53 something like an ft ; the slit-like opening is placed ventrally. At its distal extremity the labrum of the female narrows to a sharp point, whilst in the male the tip is truncated. (v) The hypopharynx arises just above the base of the labium and in the female is shaped " like a two-edged sword." When applied to the labrum it closes the ventral slit and the two structures together form a suctorial tube. In the male the hypopharynx is frequently fused with the labium and is Sw, Fig. 27. Side view of the head of a female Anopheles maculipennis, X about 26, with the various mouth-parts separated, but in the relative position in which they lie when enclosed in the groove of the labium. After Nuttall and Shipley. a, antennss ; cl, clypeus ; cs, cephalic scales ; hp, hypopharynx ; It, labium; Ixe, labrum + epipharynx; mn, mandibles ; mp, maxillary palps; mx, first maxillae. never adapted for piercing. In both male and female the thickened ventral part of the hypopharynx is traversed by the median salivary groove, ending at the distal extremity. The relative position of the mouth-parts is well shewn in the accompanying diagram (Fig. 27). The thorax is by far the largest of the three divisions of the body, being some 12-15 times as large as the head, and 54 CULICID^E [CH. 4-6 times as large as the abdomen. The major portion is taken up by the mesothorax, which forms the chief region of the mid-body. Its dorsal element, the scutum, is a large plate projecting slightly over the ' head ; posteriorly it is bounded by a curved narrow thickening of the integument known as the scutellum, which often bears conspicuous rows of hairs. Behind this comes the post-scutellum, or metathorax, a triangular plate which overlaps part of the first abdominal segment. The presence or absence of hairs and scales on the post-scutellum is of generic importance. At each side of the thorax are two large spiracles, respec- tively pro- and meso-thoracic in origin (Fig. 4). The six legs are each composed of the typical insect parts, viz. the coxa, trochanter, femur, tibia and tarsus, the last of which is five-jointed and ends in a pair of claws. The four proximal joints are often covered with scales. The first joint of the tarsus is long and hairy and its proportionate length with the tibia is of specific value. The shape of the claws varies accord- ing to the sex ; in the female they are equal and simple or may have a single tooth ; in the male those of the fore-legs are usually unequal and toothed. The wings are long and narrow and while at rest lie flat over the abdomen. The venation is very characteristic, there being six distinct longitudinal veins and two prominent fork- cells, and the costal vein extends completely round the edge of the wing (Fig. 28). The auxiliary vein is distinct, sometimes extending beyond the middle of the wing. The second, fourth, and fifth longi- tudinal veins are furcate. The hind margin of the wings is fringed with a row of hairs or scales and in addition all the veins are more or less covered with scales. The shape and arrangement of these scales varies in different groups and is the chief basis of Theobald's classi- fication. On the under surface, at the base of the wing, is a curious stridulating organ, consisting of a complex system of chitinous bars, by means of which two ridged surfaces are made to rub against each other when the wings vibrate (Fig. 28). It is VII] EXTERNAL ANATOMY 55 probable that this organ is responsible for some of the charac- teristic buzzing of the mosquito. Each halter consists of a short chitinous rod arising from a basal plate and ending in a rounded knob. The concave basal plate and a knob at the base of the halter are covered with small papillae, and Shipley and Wilson have suggested that by these two surfaces rubbing against each other when the halter vibrates, a faint note may be produced. scl Fig. 28. View of under surface of the base of the wing of Anopheles maculi- pennis, shewing stridulating organ. After Shipley and Wilson. A, right half of thorax with right wing. The shaded portion indicates the area which bears the stridulating organ. B, the stridulating organ, highly magnified, bl, ridged blade ; h, haltere ; kn, knob ; scl, sclerites ; tb, toothed bar. The abdomen consists of eight segments, each composed of a dorsal chitinous plate, the tergum, and a ventral chitinous plate, the sternum, between which is a soft membrane, the pleuron. On each side are six abdominal stigmata opening in segments two to seven inclusive. The surface of the abdo- men may be covered either with scales or hairs. The terminal segment is bilobed and in the male each lobe terminates in a long chitinous claw, the clasper. 56 CULICID.E [CH. VII Internal anatomy. . The internal anatomy of the Culicidae is very constant and the following description of Anopheles maculipennis will apply, with but slight modifications, to any other member of the family. This example has been selected since it has been minutely described by Nuttall and Shipley, from whose account the present description is largely taken. (a) Digestive organs. According to the above-mentioned authors the alimentary canal may be divided into eleven parts as follows : mouth ; buccal cavity ; pharynx or pumping organ ; oesophagus, with which are connected three diverticula, two dorsal and one ventral ; oesophageal valve ; mid-gut ; ileum ; colon ; rectum ; and anus. The mouth is that region where the various mouth-parts coalesce and is of no special interest. The buccal cavity extends from the mouth to a valvular arrangement situated at the com- mencement of the pharynx. It is lined with chit in throughout, that of the floor being much stouter than that of the roof, which forms a kind of soft palate capable of being raised or depressed by means of muscles. Accordingly the size of the buccal cavity can be increased by these means and it may at times assist in suction. At the junction of the buccal cavity and pharynx is situated a valvular apparatus, formed by a double row of chitinous hairs attached to the ventral surface. These hairs, in addition to acting as a valve, may also serve as a kind of filter and keep out large particles. The pharynx, or pumping organ, extends from this valve to the commencement of the oesophagus, and consists of a thick-walled tube composed of three longitudinal, chitinous plates, conjoined by a fold of chitin at their margins. The lumen of the tube is triangular in shape, and powerful muscles, arising from each of the three chitinous plates and attached to the exoskeleton, serve to separate the walls and increase the capacity of the pharynx. By means of the power- ful pharyngeal muscles, which almost fill the head of the mosquito, the insect is enabled to suck up liquids into its pharynx, and after the relaxation of the muscles the walls contract again, by virtue of the elasticity of the chitinous supporting plates. Any ingested liquid is thus forced out of xSocc^A. maculipennis. Meigen. A. annulimanus. Van der Wulp C. claviger. Fabricius \ =A. maculipennis. Meigen. A . grisescens. Stephens / or A . bifurcatus. Linn. A . atropos. Dyar and Knab "i A. occidental. Dyar and Knab/ = ? A' maculipennis. Meigen. C. trifurcatus. Fabricius ^j A. villosus. Desvoidy ^ = A. bifurcatus. Linnaeus. A. walkeri. Theobald J A. nigripes. Staeger=^4. plumbeus. Haliday. A. ferruginosus. Wied.=^4. crucians. Wied (?). Differentiation of species. V. Wings without pale spots on any of the veins. Dark spots at cross-veins and bifurcations . . A . maculipennis. Wings uniformly dark without any spots. (i) Palps unbanded. Petiole of first forked cell more than £ length of cell. Thorax with pale but not white streak anteriorly. Abdomen with yellow hairs . . . . A . bifurcatus. Abdomen with brown hairs . . . . A . algeriensis. Abdomen with black and white hairs . . A . barianensis. Thorax with white streak . . . . . . A . nigripes, Petiole of first forked cell £ length of cell . . A . barberi. (ii) Palps banded. Banding indistinct, light mosquito .. .. A. immaculatus. Banding narrow but distinct, dark mosquito A. smithii. H. B.F. 6 -> > j 82 SPECIES OF ANOPHELIN^E [CH. B. Wings with some pale areas. Hind tibiae with broad, white, apical band A. eiseni. Hind tibiae without broad band A. crucians. A". Costa shews at least one pale interruption. (a) No true scales on mesothorax. Group 3. Wing veins do not shew any conspicuous admixture of dark and light scales. (Patagiamyia. James. Type species A. gigas. Giles.) Fig. 34. Anopheles (Patagiamyia) gigas. (Group 3.) General characters of group. Appearance. Attitude Anopheles-like. Usually rather large Ano- phelines of brownish colour. Markings. Wings spotted. Dark costal spots may be distinct and well separated by pale areas but there are not four main dark spots. Palps. Unbanded or with four narrow bands including pale apex. Legs. Knee spots present. Tarsi unbanded or banded, but not conspicuously. Except for a white band on femur present in some species no other ornamentation of legs. • Scale structure. Head scales expanded. No prothoracic tuft. No true scales on mesothorax. Abdomen may or may not have scales on last few segments of abdomen, but some scales are usually present, especially in male. VIII] SPECIES OF ANOPHELIN^E 83 Species. A. gigas. Giles. A. simlensis. James and Listen. A. punctipennis. Say. A. formosus. Ludlow. *A. pallidopalpi. Theobald. **A. lindesayi. Giles. **A. lindesayi var. maculata. Theobald. **A. asiatica. Leicester. **A. wellingtonianus. Alcock. A. atratipes. Skuse. A. franciscanus. McCracken. A. perplexans. Ludlow. A. pseudopunctipennis* Theobald. *Feltinella. Theobald. Type species F. pallidopalpi. **Lophoscelomyia. Theobald. Type species L. asiatica. Leicester. Synonymy. A. (Culex) hyemalis. Filch=A. punctipennis. Say. Lophomyia. Giles=Lophoscelomyia. Theobald. Differentiation of species. Costa with large prominent dark spots. Palps not banded .. •• 1 •• •• ^- g^Sas- Palps banded. Tarsi banded. A. simlensis. A. formosus. Tarsi unbanded. Fringe spots present at all vein endings A. pseudopunctipennis. A. franciscanus. Fringe spots absent A. punctipennis. A. pallidopalpi. One fringe spot present .. .. A. perplexans. Costa with narrow interruptions only. Femur with broad white band. Ruff of scales on femur. White band apical . . . . . . A . asiatica. White band not apical . y ? •• A. wellingtonianus. No ruff of projecting scales -vrtu .. A. lindesayi. Femur without pale band . . . . A . atratipes. Group 4. Wing scales with conspicuous admixture of dark and light scales. (Myzorhynchus. Blanchard. Type species M. sinensis. Wied.) General characters of group. Appearance. Large species, black or nearly so. Anopheles -attitude strongly developed. Palps markedly shaggy. 6—2 84 SPECIES OF ANOPHELIN.E [CH. Markings. Wings dark with minute pale interruptions on costa usually only two in number, one at apex and one at junction of subcosta with costa. Sixth vein has two conspicuous dark spots, the scales forming which aggregated. Light spots on upper surface of wing not in all cases reproduced below. Palps. Unbanded or with four narrow pale bands including pale apex. Legs. Knee spots, banded tarsus, and in some cases further ornamentation. Scale structure. Head scales expanded. Prothoracic tuft present. No scales on mesothorax. May or may not be scales on terminal portion of abdomen. A tuft of scales usually present on ventral surface of penultimate abdominal segment. Wing scales very broad. Fig. 35. Anopheles (Myzorhynchus) barbirostris. (Group 4.) Species. A. barbirostris. Van der Wulp. A. pseudobarbirostris. Ludlow. A. bancroftii. Giles. A. umbrosus. Theobald. A. albotceniatus . Theobald. A. strachani. Theobald. A. sinensis. Wiedemann. A. sinensis var. indiensis. Theobald. A. pseudopictus. Grassi. A. paludis. Theobald. 'A. paludis var. similis. Theobald. A. mauritianus. Grandpre. *A. grabhamii. Theobald. * Cycloleppteron. Theobald. Type species C. grabhamii. Theobald. VIII SPECIES OF ANOPHELIN^E 85 Synonymy. A. vanus. Walker A . annular is. Van der Wulp A. jesoensis. Tsuzuki A. plumiger. Donitz A. minutus. Theobald A. uigerrimus. Giles =A. sinensis. Wied. A . nigerrimus. James and Listen Theobald. \ / =A. sinensis var. indiensis. A. B. A. separates. Leicester \ A. pedit&matus. Leicester J A. brachypus. Donitz = (?) A. sinensis. Wied. A. alboannulatus. James and Liston=^4. albotceniatus. Theobald. A. paludis var. similis. Theobald =A. mauritianus. Grandpre". A. mauritianus. Grandpre" = ( ? ) A . paludis. Theobald. A. coustani. Laveran | A. ziemani. Van Griinberg > —A. mauritianus. Grandpre. A. tenebrosus. Donitz A pictus. Loew \ A . pictus. Ficalbi J Differentiation of species. Wing scales not inflated (Myzorhynchus). Tip of hind tarsus not white. Palpi not banded. Hind tarsal points narrowly banded. No fringe spots . . . . . . One fringe spot . . . . . . Two fringe spots. Legs not mottled . . . . Legs mottled . . . . Several fringe spots .. .. Hind tarsi broadly banded .. .. Palpi banded. Wing fringe with one pale spot Wing fringe unspotted . . . . Wing scales inflated (Cycloleppteron] .. A . strachini. A. umbrosus. A . barbirostris. A . pseudobarbirostris. A. bancroftii. A. albotceniatus. A . sinensis. A . pseudopictus. A. grabhamii. (b) Mesonotum with true scales. Group 5. Costa with broad pale interruptions. (Arribalzagia. Theobald. Type species A. maculipes. Theobald.) General characters of group. Appearance. Large highly ornamented species. Markings. Wings prominently spotted, but with three main dark spots only. Small accessory spots present in addition to those at base of costa. Pale spots on upper surface of wing in many cases not represented beneath. Sixth vein with more than two spots. Palps. Four pale bands. Legs. Speckled and ornamented. 86 SPECIES OF ANOPHELIN^E [CH. Scale structure. Heavily scaled species. Head scales expanded. Prothorax with tufts. Mesothorax with broad scales. Abdomen with scales and lateral tufts. Species. A. maculipes. Theobald. A. pseudomaculipes. Chagas. A. malefactor. Dyar and Knab. *A. mediopunctatus. Theobald. *A. intermedium. Chagas. * Notonotricha. Coquillet. Type species N. mediopunctatus. B. Deuteroanopheles. Number of main dark costal spots, four. Not more than three dark spots on sixth vein. Junctions of cross-veins with longitudinals and bifurcations of second and fourth veins the seat of light interruptions (except Myzorhynchella) . B'. Female palps with terminal segment considerably less than half penultimate. Tarsi not broadly banded. Tips of hind- legs not white. Group 6. Mesothorax without true scales. (Myzomyia. Blanchard1.) Fig. 36. Anopheles (Myzomyia} listoni. (Group 6.) 1 The type species of Myzomyia is M. rossii Giles, but this species does not conform to the characters of Myzomyia as now usually understood. Group 6, therefore, though it contains most of the well-known Myzomyia (A . funesta, A. listoni, etc.) cannot correctly be described as Myzomyia, which name ought to be retained for whatever group M . rossii represents. Similarly, the name Pseudomyzomyia proposed by Theobald for M. rossii is incorrect. VIII] SPECIES OF ANOPHELIN.E 87 General characters of group. Markings. Small brownish species. Wings with four main dark costal spots. Middle spot not completely broken (i.e. shewing double interruption on first longitudinal as in A. maculatus. Theobald). Sixth vein with two or fewer dark spots (except A. albirostris Theobald, which has three). Fringe spots usually absent at sixth vein and often deficient at other vein endings. Palps. Three pale bands, the apical one including the whole of the apical segment1. Legs. Knee spots and sometimes narrow and incon- spicuous tarsal banding, but no other ornamentation. Scale structure. Head scales expanded. No pro thoracic scale tufts. Mesothorax without true scales. Abdomen without scales. Wing scales narrow. Species. A. funesta. Giles. A. funesta var. subumbrosa. Theobald. A. funesta var. umbrosa. Theobald. A. listoni. Listen. A. rhodesiensis. Theobald. A. culicifacies. Giles. A. nili. Theobald. A. turkhudi. Listen. A. hispaniola. Theobald. A. albirostris. Theobald. A. hebes. Donitz. A. ftavicosta. Edwards. A. impunctus. Donitz. A. longipalpis. Theobald. A. pyretophoroides. Theobald. A. agripi. Patton. A. d'thali. Patton. A. jehafi. Patton. Synonymy. A. listoni. Giles "^ A. turkhudi. Giles > =A. culicifacies. Giles. A. indica. Theobald J A. leptomeres. Theobald=(?) A. culicifacies. Giles. A. kumassii. Chalmers =A. funesta. Giles. A. umbrosa. Edwards (nom. preoc.)=v4. funesta var. umbrosa. Theobald. A. fluviatilis. Stephens and Christophers. MSS. "\ =A. listoni. A. Christopher si. Theobald jf Listen. A. Christopher si var. alboapicalis. Theo.=^4. albirostris. Theo. A. albirostris. Theo. = (?) A. aconita. Donitz. A. formosaensis. Tsuzuki=(?) A. aconita var. coh&sa. Donitz. A. impunctata. D6nitz-Blanchard = ^4. impunctus. Donitz. A. pictus. Macdonald = ^4. hispaniola. Theobald. A. cruzii. Dyar and Knab=^4. lutzi. Theobald. 1 In A. turkhudi and A. hispaniola the tip is dark. 88 SPECIES OF ANOPHELIN^E [CH. Differentiation of species. Proboscis unhanded. Apex of palps pale. Fringe spots present at all veins except sixth. Tarsal banding distinct though not conspicuous. Third longitudinal light Third longitudinal dark A. A. Tarsal banding absent or very narrow and indistinct A. Fringe spots absent or present only at two or three veins Palps with three pale bands. No fringe spots . . . . . . . . A . Two fringe spots . . '. . . : . . . . . . A . Palps with pale apex only .. .. .. A. Apex of palps dark. Black apex narrow . . . . . . . . A . Black apex broader . . . . • • • • • • A. Proboscis with apical half white . . . . ". . . . A . A. Group 7. Mesothorax with blue scales. (Pyretophorus1. Blanchard.) funesta. funesta var. umbrosa. listoni. rhodesiensis . culici fades, nili. turkhudi. hispaniola. albirostris. aconita. Fig. 37. Anopheles (Pyretophorus) neavei. (Group 7.) General characters of group. Appearance. Mostly rather light brown species with notably long and thin palps. Markings. Wings with four dark spots usually not completely broken. Wing fringe spots most frequently absent from sixth vein. Palps, With three bands or four. Sometimes with dark apex. Legs. Free from speckling or marked banding of tarsus. 1 Though most of the members of the genus Pyretophorus are included here, this generic name cannot be employed, as P. costalis Loew, the type species, clearly belongs to a separate group. VIII] SPECIES OF ANOPHELIN.E 89 Scale structure. Head scales expanded. No prothoracic tuft. Meso- thorax scaled. Abdomen completely devoid of scales. Species. A. superpictus. Grassi. A. nursei. Theobald. A. nigrifasciatus. Theobald. A. cleopatra. Willcocks. MSS. A. cardamitisi. Newstead and Carter. A. distinctus. Newstead and Carter. A . distinctus var. melanocosta. Newstead and Carter. A. palestinensis. Theobald. A. cinereus. Theobald. A. sergentii. Theobald. A. jeyporensis. James. A. my zomy fades. Theobald. A. chaudoyei. Theobald. A. transvaalensis. Carter. A. minimus. Theobald. A. pitchfordi. Power. A. arabiensis. Patton. A. austenii. Theobald. Synonymy. A. nursei. Theobald=(?) A. nigrifasciatus. Theobald variety A. chaudoyei. Billet =A. chaudoyei. Theobald. Differentiation of species. Palps with one broad pale band. Apex of palps light. Third costal spot not completely broken. Sixth vein with two dark spots . . . . A . sergentii. Sixth vein with three dark spots. Costal spots more or less confluent . . A . distinctus Costal spots distinct. Tarsi not banded. (A. nursei. A. cleopatra. A. palestinensis. A. minimus. Fore and hind tarsi banded ., ,. A. cinereus. (A. cardamatisi. All tarsi banded \ . ,. A • ,, (A. superpictus. Apex of palps dark. Tarsi not banded .. .. ""«;-. .. .. A. nigrifasciatus. Tarsi not banded. Three dark lines on mesonotum x. . .. A. my zomy fades. Two dark lines on mesonotum . . . . A . chaudoyei. Palps with two broad pale bands ' •-„» .. .. A. austenii.. 9° SPECIES OF ANOPHELIN.E [CH. B". Apical segment of female palps at least half length of penultimate. Tarsi broadly banded. (a) Mesothorax not completely clothed with true scales. Group 8. (Psendomyzomyia. Theobald1. Myzomyia. Blanchard. Type species, Ps. rossii. Giles.) General characters of group. Appearance. Light fawn to moderately dark species. Palps rather shaggy. Markings. Wings with light areas much developed. Costa with four main dark spots. Third spot completely broken. Sixth vein with two dark spots. Fringe spots at all veins. Palps. Three light bands, the apical one including whole of last segment. Legs. Tarsi banded. May be speckled. Tips of hind tarsi not white. Scale structure. Head scales expanded. No pro thoracic tufts. Mesothorax mostly with narrow hair-like scales. Abdomen with some scales on last segment, especially in male. Species. A. rossii. Giles. A. indefinata. Ludlow. A. ludlowi. Theobald. A. mangyana. Banks. Synonymy. A. mangyana. Banks = (?)^. ludlowi. Theobald. A. vagus. D6nitz = ^. rossii. Giles. A. rossii var. indefinata. Ludlow = ^4. indefinata. Ludlow. Differentiation of Species. Legs not speckled. Apical palpal band very broad . . . . A . indefinata. Apical band not so broad . . . . . . A . rossii. Legs speckled. Large species A . ludlowi. Smaller species . . . . . . . . A . mangyana. (b) Mesothorax completely clothed with true scales. Abdomen without lateral tufts. Group 9. Palps moderately shaggy only. Bifurcations of second and fourth veins both sites of pale interruptions. Head scales as in majority of Anophelines. (Nyssorhynchus. Blanchard2.) 1 Vide footnote to Group 6, on page 86. 2 Here again there is confusion in the nomenclature. The type species of Laverania Theobald ( = Nyssorhynchus Blanchard) is A. (Cellia) argyrotarsis. The well-known group of so-called Nyssorhynchus, therefore, is incorrectly so called. VIII] SPECIES OF ANOPHELIN^E QI General characters of group. Appearance. Highly ornamented species. Tips of hind tarsi always white. Markings. Wings clearly spotted. Fringe spots at all vein endings. Sixth vein with three spots. Palps. With three bands. Legs. With white hind tarsi often speckled. Scale structure. Head scales expanded. Mesothorax covered with scales. Abdomen with some scales. Fig. 38. Anopheles (Nyssorhynchus) maculatus. (Group 9.) Species. A. fuliginosus. Giles. A. nivipes. Theobald. A. freer CB. Banks. A. philippinensis. Ludlow. A. fowleri. Christophers. A. jamesii. Theobald. A. pretoriensis. Theobald. A. maculipalpis. Giles. A. maculatus. Theobald. A. theobaldi. Giles. *A. willmori. James. *A. stephensi. Theobald. A. costalis. Loew. A. costalis var. melas. Theobald. A. pseudocostalis. Theobald. A. merus. Donitz. A. marshallii. Theobald. \A. kochii. Donitz. A. karwari. James and Liston. A. ardensis. Theoba.ld. A. aureosquamiger. Theobald. * Meocellia. Theobald. Type species A. willmori. James, t Christopher sia. James, Type species A . kochii. Donitx. 92 SPECIES OF ANOPHELIN^E [CH. ff^4. lineata. Ludlow. A. flava. Ludlow. A. waponi. Edwards. A. tibani. Patton. ft Calvertina. Ludlow. Type species A. lineata. Ludlow. Synonymy. A. gambit. Giles 1 \>=A. costahs. Loew. A. gracihs. Domtz J A. jamesii. Listen 1 /•/•,•• /-,-, . J, y=A. fuhginosus. Giles. A. leucopus. Domtz / A. dudgeoni. Theobald =A. willmori. James. A. indica. Theobald = ^4. willmori var. James. A. pseudowillmori. Theobald.^ A. willmori. Leicester I =A. maculatus. Theobald. A. willmori. Watson J A. maculipalpis. James and Liston "\ =^4. maculipalpis var. A. indiensis. Theobald / indiensis. Theo. A. nigrans. Staunton=^4. karwari. James. A. halli. James=^. kochii. Donitz. A. intermedia. Rothwell "\ ., ~,, , }-=A. stephensi. Theobald. A. metaboles. Theobald / Differentiation of species. A. Tips of hind tarsi white. Palps with not more than one broad band. (a) Legs not speckled. White band at junction of first and second tarsal segment. C A . fuliginosus . Very closely related species ,.-hl .. < A' ™vipes' | A. freera. L A. philippinens,is. No white band at junction of first and second tarsal segments A. fowleri. (b) Legs speckled. Palpi with speckling in addition to bands .. A. maculipalpis. Palps without speckling. Three tarsal segments pure white . . . . A . jamesii. Two tarsal segments pure white .-. .. A. pretoriensis. Palps with two broad bands. Two tarsal segments altogether white . . . . A . theobaldi, One tarsal segment only altogether white. Scales on last few segments of abdomen .. A. maculatus. Scales on all segments .. .. .. •'. . A. willmori. Palp with more than two broad bands. Palps with five white bands .. .. .. A. kcchii. Palps with four white bands .. .. .. A. karwan. VIIl] SPECIES OF ANOPHELIN.E 93 B. Tips of hind tarsi not white. Apical band of palps only broad. First tarsus not spotted. Fringe spots narrow. Femur speckled Femur not speckled Fringe spots broad First tarsus spotted Two palpal bands broad. A few scales on abdomen Many scales on abdomen . . A. costalis. A. pseudocostalis. A. merus. A. ardensis. A. marshallii. A. stephensi. Group 10. Palps markedly shaggy. Bifurcations of second and fourth veins (one or both) dark scaled. Head scales flattened. (Myzorhynchella. Theobald. Type species M. nigra. Theobald.) General characters of group. Appearance. Black species. Palps shaggy. Markings. Costa with four main dark spots, the light interruptions in some cases bridged by dark on first longitudinal. Palps. Unbanded or with four bands. Legs. May be ornamented. Scale structure. Head scales flattish. Prothoracic tuft present. Mesothorax scaled. Abdomen free from scales. Species. A. nigrti. Theobald. A. lutzi1. Cruz. A. parva. Chagas. A. nigritarsis. Chagas. A. tibiomaculata. Neiva. A. gilesa. Neiva. (c) Abdomen with lateral scale tufts. Group ii. (Cellia. Theobald. Type species A. pharoensis. Theobald.) Fig. 39. Anopheles (Cellia) pulcherrimus. (Group n.) 1 There are three species of A . lutzi, of which A . (Myzomyia) lutzi Theobald was first so named. A. (Myzorhynchella) lutzi Cruz, therefore, requires renaming if generic distinctions between the Anophelinae are dropped. 94 SPECIES OF ANOPHELIN.E [CH. General characters of group. Markings. Costa with four main dark spots. Fringe spots at all veins. Palps. With four light bands. Legs. Ornamented. Scale structure. Head scales expanded. Prothorax may have a few scales or a tuft. Mesothorax covered with scales. Abdomen with scales and lateral scale tufts. Species, A. argyrotarsis. Desvoidy. A. pharoensis var. alba. Ventrillon. A. albimanus. Wied. A. bigotii. Theobald. A. jacobi. Hill and Haydon. A. gorgasi. Dyar and Knab. A. cincta. Newstead and Carter. A. squamosa. Theobald. A. pulcherrima. Theobald. A . squamosa var. arnoldi. Newstead A. pharoensis. Theobald. and Carter. Synonymy. A. albipes. Theobald ^ A . cubensis. Agramonte ' , „ . . ~r _ .,. y = A. albimanus. Wied. A. tarsi-maculatus. Goeldi f A. argyrotarsis. Theobald j A. albitarsis. Arribalzaga=vl. argyrotarsis. Desvoidy. A. albofimbriata. Giles = ^4. pharoensis. Theobald. A. bozasi. Neveu-Lemaire = ( ? ) A . pharoensis. Theobald. A. braziliensis. Chagas = ( ? ) ^4 . argyrotarsis. Desvoidy. A. punctipennis. Bigot. MSS.=^4. bigotii. Theobald. A. squamosa arnoldi. Stephens and Christophers = A. squamosa var. arnoldi. Stephens and Christophers. Differentiation of species. Tips of all legs pale. Metatarsus with distinct bands . . . . . . A . cincta. Metatarsus with flecks of white only . . . . . . A . jacobi. Tips of hind-legs only pale. (a) Three segments of hind tarsus altogether white. Apex of abdomen dark .. .. .. ..A. argyrotarsis. Apex of abdomen whitish grey .'. .. .. A. braziliensis. (b) Three segments of hind tarsus white except for small dark band on last segment .. .. A. albimanus. (c) One segment only of hind tarsus white. Femora and tibiae mottled .> • . . . . A . pharoensis. Femora and tibiae not mottled . . . . A . bigotii. Tips of hind-legs not pale . . . . . . . . ..A. squamosa. C. Neoanopheles. Costa with four main dark spots. Sixth vein with more than three dark spots. Junctions of cross-veins with longi- tudinal veins and bifurcations of second and fourth veins the seat of pale interruptions. VIII] SPECIES OF ANOPHELIN.E 95 Group 12. (Neomyzomyia. Theobald. Type species A . elegans. James.) General characters of group. Markings. Wings with a large number of spots on veins. Third longitudinal with several dark and light areas. Sixth vein may have five or six dark spots. Palps. With well-marked white bands. Legs. Speckled and ornamented. Scale structure. Prothorax usually with scale tuft. Species. A. elegans1. James. A. punctulata. Donitz. A. annulipes. Walker. A. tessellatus. Theobald. A. masteri. Skuse. A. natalensis. Hill and Haydon. A. deceptor. Donitz. A. watsoni. Leicester. Synonymy. A. ceylonica. Newstead and Carter=(?) A. tessellatus. Theobald. A. leucosphyrus. Donitz = (?) yl . elegans. James. A. muscivus. Skuse=^4. annulipes. Walker. A. ocellatus. Theobald = ^. punctatus. Donitz. A. punctulatus. Theobald = A. tessellatus. Theobald. A. punctulata. James=^. tessellatus. Theobald. A. thorntonii. Ludlow=(?) A. tessellatus. Theobald. Peculiar Anophelines not placed in Table. A. jajardoi. Lutz (Chagasia, Cruz). A. boliviensis. Theobald (Kerteszia, Theobald). A. lutzi. Cruz (Manguinhosia, Cruz). A. gracilis. Theobald (Bironella, Theobald). A. implexa. Theobald (Christy a, Theobald). A. lineata. Ludlow (Calvertina, Ludlow). A. brunnipes. (? Nyssorhynchus.) Theobald. A. christyi. (? Nyssorhynchus, Neocellia.) Newstead and Carter. A. lutzi. (? Myzomyia.} Theobald. A. wellcomei. (? Anopheles.} Theobald. A. pseudosquamosa. (? Cellia.) Newstead and Carter. Insufficiently described or doubtful Species. A. annulipalpis. Arrib. A. maculicosta. Becker. A. annulipes. Arrib. A. martini. Laveran. A. antennatus. Becker. A. multicolor. Camboulin. A. cohasus. Doune2. A. pursati. Laveran. A. error. Theobald = (no species). A. stigmaticus. Skuse. A. farauti. Laveran. A. subpictus. Grassi. A. formosaensis n. Tsuzuki2. A. vincenti. Laveran. A. neiriti. Ventrillon. 1 Neomyzomyia Theobald. 2 According to Kinoshita, A . cohcesus and A . formosaensis = A . listoni. TABLE II. The known species of Anophelines, with their their habitat and connection Present group tabulation Species and Synonyms and generic synonymy Distribution I 2 A . aconita Donitz [3] A. aconita var. cohtesa Donitz [4] . . 6. (Myzomyia) 6. (Myzomyia) Malay Malay 3 A. aitkeni James [ia] (1903) i. (Stethomyia) India, Malay 4 *A . albimana Wiedemann [i] ii. (Cellia) S. & C. America 5- A . albipes Theobald [2] ii. (Cellia) W. Indies, S. America 6. *A . albirostris Theobald [6] . . 6. (Myzomyia) Malay, etc. . . 7- A . albitarsis Arribalzaga [3] 8. A. alboannulatus James & Listen [4] 4. (Myzorhynchus) Malay 9- A. albofimbriata Giles (1904) n. (Cellia) Egypt 10. A . albotesniatus Leicester [2] 4. (Myzorhynchus) Malay ii. M. algeriensis Theobald [6] (1903) 2. (Anopheles) N. Africa 12. A . annularis Van der Wulp [4] 4. (Myzorhynchus) Malay 13- A . annulimanus Van der Wulp [2] . . 2. (Anopheles) — 14. A . annulipalpis Arrib. [i] . . — Argentine A . annulipes Walker [3] 12. (Nyssorhynchus) Australia 16. A . annulipes Arrib. [i] — Argentine ly. A . antennatus Becker — — 18. A. ardensis Theobald [ii] . . 10. (Pyretophorus) . . Natal 19- A . argyrotarsis Desvoidy [i] n. (Cellia) West Indies, S. America, etc. 20. A . arabiensis Patton ? 10. Aden 21. A. arnoldi Stephens & Christophers ii. (Cellia) Transvaal 22. A . asiatica Leicester [i] 3. (Lophoscelomyia) Malay 23. A . atratipes Skuse [i] 3. (Pyretophorus) . . Australia 24. A . atropos Dyar & Knab [2] 2. (Anopheles) N. America 25. A. aureosquamiger Theobald [14] 10. (Nyssorhynchus) Transvaal 26. A . aurirostris Watson — — 27. A. austenii Theobald [10] . . 7. (Pyretophorus) . . Angola A nwihi "Pa "f^oTi 6 (Mvzomyia) (^) Aden 29. A . bancroftii Giles [4?)] 4. (Myzorhynchus) Australia A. barberi Coquillet [4] (1903) 2. (Anopheles) — 31- A . barbirostris Van der Wulp [4] . . 4. (Myzorhynchus) India, Malay, China 32. A. barianensis James & Listen [4] (1911) .. 2. (Anopheles) India 33. A . bellator Dyar & Knab [2] 6. (Myzomyia) (?) 34. *A. bifurcatus Linnaeus [2] (1758) . 2. (Anopheles) Europe 35- 36. A . bifurcatus Meigen [i] A . bigotii Theobald [2] 2. (Anopheles) ii. (Cellia) Europe Chili 37- A . bisignata . . 6. (Myzomyia) — 38. A. boliviensis Theobald [12] (Kerteszia) S. America 39. A . bozasi Neveu-Lemaire [3] ii. (Cellia) N. Africa 40. A . brachypus Donitz 4. (Myzorhynchus) Malay Present classification and generic synonymy, and notes on viih malaria. Transmission experi- ments. Cycle observed of— l.T. Malignant tertian, S.T. Simple tertian, Q. Quartan ; of z, to /ygote stage, and s, to sporozoite stage Observations regarding transmission in nature, (z) Zygote and (s) Sporozoite stage observed Epidemiological evidence of transmission Darling, S.T. Darling, (T) (s), M.T. (s) •jtaunton.M.T. Staunton, (z) Ed.&Et.Sergent,(s) £inoshita, M.T. Daniels, ( + )? Christophers James, Staun- ton, ( + ) Remarks = A. albirostris Theobald (?). —A. formosaensis II Tsuzuki. Forest and j ungle species biting by day like a Stegomyia. Commonest carrier in Central and Tropi- cal S. America. 70 % of those fed by Darling became infected. =A. albimana Wied. Important carrier in Malay. =A. argyrotarsis. =A. albotaniatus. = A. pharoensis. Important carrier in Algeria (littoral). =A. sinensis Wied. —A. maculipennis Wied. Common Australian species. Darling, (F) Darling, M.T. (?), (z) Patton, (s) . ." Important carrier in Aden Hinterland. =A. squamosa var. arnoldi Newstead and Carter. ? A. albirostris Theobald. Stephens & Doubtful (Christo- Christophers phers) M.T. ^rassi, (T) . . Grassi, (T) Unlikely to Hill species. 8000 ft. carry in nature owing to distri- bution Common English Anopheles. = A. maculipennis Meigen. H. B. F. =A. sinensis (?). TABLE II (continued). The known species of Anophelines, notes on their habitat and Present group tabulation Species and Synonyms and generic synonymy Distribution 41. A . braziliensis Chagas II. (Cellia) S. America . . 42. A. brunnipes Theobald [17] p (Nyssorhynchus) Angola 43. A. cardamitisi Newst. & Carter [i] 7- (Pyretophorus) . . Greece 44. A . ceylonica Newst. & Carter [i] . . 12. Ceylon 45. A . chaudoyei Theobald [6] 7- (Pyretophorus) . . Algeria, etc. . . 46. A . chaudoyei Billet 47- A . christophersi Theobald [4] — — 48. A. christophersi var. alboapicales Theobald [17] — — 49- A . christyi Newst. & Carter [2] ii. (Neocellia) Uganda 50. A . cincta Newst. & Carter [i] ii. (Cellia) West Africa . . 5i. A . cinereus Theobald [2] . . 7- (Pyretophorus) . . Africa 52. A . claviger Fabricius — — 53- A . coh&sus Doune . . 54- A. corethroides Theobald [14] (1907) i. (Stethomyia) Australia 55- *A . costalis Loew [2] . . 10. (Pyretophorus) . . Africa 56. A . costalis var. melas Theobald [6] 10. (Pyretophorus) . . Africa 57- A . coustani Laveran [2] — — 58. A. crucians Wied. [2] (1828) 2. (Anopheles) N. America . . 59- A . cruzii Dyar and Knab [i] — — 60. A . cubensis Agramonte — — 61. A . culicifacies Giles [3] 6. (Myzomyia) India 62. A. culiciformis James & Listen [4] (1904) i. (Stethomyia) India 63- A . decepior Donitz [2] 12. ( ) Malay 64. A . distinctus Newst. & Carter [2] . . 7- (Pyretophorus) . . Rhodesia 65- A. distinctus var. melanocosta Newst. & Carter [2] 7- (Pyretophorus) . . Rhodesia 66. A . d'thali Patton 6. (Myzomyia) (?) Aden 67. A. dudgeoni Theobald [16] . . ii. (Neocellia) — 68. A. eiseni Coquillet [3] (1902) 2. (Anopheles) C. America . . 69. A . elegans James [ia] 12. ( Neomyzomyia) — 70. A . error Theobald [2] (Aldrichia) 7*« A . fajardoi Lutz [i] . . (Chagasia) Brazil 72. A . farauti Laveran [3] — — 73- A . ferruginosus Wied. [2] . . — — 74- A . flava Ludlow [5] . . IO. (Nyssorhynchus) — 75- A. flavicosta Edwards [i] . . ? Nigeria 76. A. fluviatilis Stephens & Christo- phers MSS — — 77- A . formosaensis I Tsuzuki 6. (Myzomyia) Formosa . «. 78. A . formosaensis II Tsuzuki ? Formosa 3- (Patagiamyia) . . Formosa 79- A . formosus Ludlow [66] 80. A. fowlen Christophers [i] . . 10. (Nyssorhynchus India or Neocellia) with their present classification and generic synonymy, and connection with malaria. Transmission experi- ments. Cycle observed of — .M.T. Malignant tertian, S.T. Simple tertian, Q. Quartan ; of z, to zygote stage, and s, to sporozoite stage Observations regarding transmission in nature, (z) Zygote and (s) Sporo/oite stage observed Epidemiological evidence of transmission Remarks = A. argyrotarsis (?). _ =A. tessellatus Theobald. Billet, ( + ) .. Common Anopheles in oases, breeding in saline waters. — —A . chaudoyei Theobald. =J. listoni Listen. — =A. albirostris. = fA. maculipennis Meigen. A. bifurcatus Linnaeus. Ross, Annett Ross, Stephens & & Austen Christophers, etc. S.T. Q. M.T. (s) Stephens & Christophers, S.T. Q. M.T. Stephens & Christo- phers, (s) Active and common transmitter in Tropical Africa. —A. mauritianus Grandpre. =A. (Myzomyia) lutzi Theobald. =A. albimana Wied. Commonest Indian carrier. Patton, ( + ?) — A. willmovi James. Forest species in Andamans (Christo- phers), ? any part in transmission. = no species. —A. crucians (?). Tsuzuki. M.T. Tsuzuki (s) (s) Tsuzuki, M.T. Tsuzuki (s) (s) — =A. listoni Listen. Tsuzuki, ( +) . . =A. aconita var. cohcesa Donitz (?). Tsuzuki, ( + ) . . 7—2 TABLE II (continued). The known species of Anophelines, notes on their habitat and Species and Synonyms 81. A.fragilis Theobald [8] 82. A . franciscanus McCracken [i] 83. A. freer a Banks [i] . . 84. *A . fuliginosus Giles [40] 85. *A. funesta Giles [2] . . Present group tabulation and generic synonymy Distribution ? (Anopheles) .. California, etc. 10. (Nyssorhynchus) Philippines . . 10. (Nyssorhynchus) India, etc. 6. (Myzomyia) Africa 86. A. funesta var. subumbrosa Theo- bald [6] 6 (Myzomyia) Africa 87. A. funesta var. umbrosa 6. (Myzomyia) Africa 88. A. funesta var. neiriti Blanchard . . 6. (Myzomyia) Africa 89. A. gambles Giles [46] — — 90. A. gigas Giles [3] 3- (Patagiamyia) India 91. A. gilesi Neiva 9- ( Myzorhynch etta ) Brazil 92- A. gorgasi Dyar and Knab n. (Cellia) C. America . . 93- 94- A. A. grabhamii Theobald gracilis Theobald [12] 4- ( Cycloleppteron) (Bironella) W. Indies, S. America 95- A. gracilis Donitz — 96. A. grisescens Stephens [2] . . — — 97- A. halli James [^a] — — 98. 99- A. *A. hebes Donitz [3] 6 (Myzomyia) (Myzomyia) East and S.W. Africa N. Africa, Spain hispaniola Theobald [6] . . 6. IOO. A. (C.) hyemalis Fitch 101. A. immaculatus James [i] (1902) . . 2. (Anopheles) India 102. A. implexa Theobald [7] (Christy a) Africa , 103. A. impunctus Donitz 6. (Myzomyia) Egypt . . I04. A. indefinata Ludlow [4] — 105. A. indica Theobald [14] 10. (Neocettia) India .. 106. A. indica Theobald [2] 6. (Myzomyia) India 107. A. indiensis Theobald [14] . . 10. ( Nyssorhynchus ) India 108. A. indiensis 4- ( Myzorhynchus ) India . . 109. A. intermedia Rothwell — India no. A. intermedium Chagas 5- ( Cycloleppteron, Brazil . . Notonotricha) III. A. jacobi Hill and Haj'don n. (Cellia) Natal 112. A. jamesii Theobald [2] 10. (Nyssorhynchus) India . . "3- A. jamesii Listen — — 114. A. jehafi Patton — — 115- A. jesoensis Tsuzuki ... — Formosa, etc. 116. A. jeyporensis James [i] 7- (Pyretophorus) . . India 4 . - 117. A. harwari James & Listen 10. (Nyssorhynchus) India, Malay •• 118. A. kochii Donitz [i] — — 119. A. kumassii Chalmers 120. A. leptomeres Theobald [6] . . — — 121. A. leucopus Donitz [i] — — with their present classification and generic synonymy, and connection with malaria. Transmission experi- ments. Cycle observed of— M.T. Malignant tertian, S.T. Simple tertian, Q. Quartan ; of z, to zygote stage, and s, to sporozoite stage Observations regarding transmission in nature, (z) Zygote and (s) Sporozoite stage observed Epidemiological evidence of transmission Remark.' Stephens & Adie, (s) Christophers, M.T.(Z) Q. (z). Ross, Annett & Austen, S.T. Q. Daniels, M.T. Stephens & Christo- phers, (s) ; some- times 50 % infected Not an active carrier as far as known. Adie found only i in 200 infected. Active and important common carrier in Tropical Africa. Improbable act- ing as carrier owing to dis- tribution vide A. neiriti Ventrillon fi]. =A . funesta Giles. Hill species. Ed. & Et. Sergent, (T) (s) =A. costalis Loew. =A. maculipennis or A. bifurcatus. = A. kochii Donitz. Common carrier, Algeria and S. Spairi. =A. punctipennis Say. Negative in Anda- mans (Christophers) Cruz, (T) =A. willmovi James var. = A. culicifacies Giles. =A. maculipalpis var. indiensis Theo. =A. sinensis var. indiensis Theobald. =A. stephensi Listen. Staunton (sus- pected) Daniels, ( + ) pro- bable —A. fuliginosus Giles. =A.'cinereus (?) (Theobald). =A. sinensis. = A. funesta Giles. = A. culicifacies Giles (?). = A . fuliginosus Giles. TABLE II (continued). The known species of Anophelines, notes on their habitat and Species and Synonyms 122. A. leucosphyrus Donitz [i] . . 123. A. lindesayi Giles [40] 124. A. lindesayi var. maculata Theo- bald [17] 125. A. lineata Ludlow . . 126. *A. listoni Listen [i] . . 127. A . listoni Giles 128. A. longipalpis Theobald [6] 129. *A. ludlowi Theobald [6] Present group tabulation and generic synonymy 12. (Neomyzomyia) 3. (Patagiamy'ia) Distribution Malay, etc. India 3. (Patagiamyia) India (Calvertia) . . Philippines 6. (Myzomyia) . . India 6. (Myzomyia) . . Central Africa 8. (Pseudomyzomyia) Malay 130. A. lutzi Cruz 131. A. lutzi Cruz . . 132. *A. lutzi Theobald . . 133. *A. maculatus Theobald [2] 9. (Myzorhynchella) Brazil (Manguinhosia) Brazil ? (Myzomyia'}) .. Brazil 10. (Nyssorhynchus) India 134- 135- 136. 137- A . maculicosta Becker A . maculipalpis Giles [4^] A . maculipalpis James & Liston . . *A. maculipalpis var. indiensis Theobald 10. (Nyssorhynchus} China 10. (Nyssorhynchus) India 1 38 . *A . maculipennis Meigen [2] ( 1 8 1 8 ) 139. A. maculipes Theobald [6] . . 140. \A . malefactor Dyar and Knab [ia] 141. A. mangy ana Banks [i] 142. A. marshallii Theobald [6] . . 143. A . martini Laveran [3] 144. A . mauritianus Grandpre .. 2. (Anopheles) 5. (Arribalzagia) 5. (Arribalzagia) 10. (Pyretophorus) . 4. (Myzorhynchus) Europe, America Brazil Brazil Mashonaland Cambodia Mauritius,Madagascar 145. A. masteri Skuse [i] . . 146. A. mediopunctatus Theobald [6] 147. A. merus Donitz 148. A. metdboles Theobald [4] . . 149. A . minimus Theobald [2] . . 150. A. minutus Theobald [6] 151. A . multicolor Cambouln 152. A. muscivus Skuse [i] 153. A. myzomyfacies Theobald [14] 154. A . natalensis Hill & Haydon 155. A. nigerrimus Giles [4id. XLIII. p. 215. *Dyar and Knab [ia] (1907). Journ. New York Entom. Soc. xv. p. 198. * [ife] (1909). Proc. of the U.S. Nat. Museum, xxxv. p. 53. * [2]. Proc. Biol. Soc. Washington, xix. p. 160. *Edwards [i] (1911). Bull. Entom. Research, n. part 2, p. 141. * _ _ [2] (1911). Ibid. n. part 3, p. 241. * [3] (1912). Ibid. in. part i, p. i. * [4] (1912). Ibid. in. part 3, p. 241. Fabricius [i] (1775). Sy sterna entomologica, etc. [2] (1777). Genera insectorum. [3] (1781). Species insectorum, etc. [4] (1877). Mantissa insectorum, etc. [5] (I794)- Entomologia systematica emendata et aucta. [6] (1805). Syst. Antliatorum, etc. 6, p. 35. Ficalbi [i] (1896). Bull. Soc. Entom. Ital. xxvm. * [2] (1899). Ibid. xxxi. Fischer [i] (1812). Mem. Soc. Impdriale Nat. Moscou, iv. p. 167. Fitch (1885). New York State Museum, 2nd Entom. Report. *Giles [i] (1899). Jour. Trop. Medicine, n. p. 62. * [2] (1900). Liverpool School of Trop. Med., Memoir n. * [3] (1901). Entom. Monthly Mag. xn. p. 196. * [4#] (1900) [46] (1902). Handbook of Gnats or Mosquitoes. London. [5] (I9°4)- A Revision of the Anophelince (supp. to handbook). *Goeldi (1905). Os mosquitos no Para. Para. *Grandpre [i] (1900). Planters' Gazette Press. Port Louis. [2] (1902). Zool. Anz. xxv. No. 677, 21 July. *Grassi [i] (1899). Atti Accad. d. Lincei, Ser. 5, Memor. HI. Griinberg (1905). Zool. Anz. xxix. p. 377. Haliday [i] (1828). Zool. Journal, xn. - [2] (1833). Entom. Magazine, i. [3] I1 839)- Annals of Natural History. *Hill and Hay don (1907). Annals of the Natal Gov. Museum. "Howard (1901). Mosquitoes ; how they live, etc. New York. * Dyar and Knab (1912). The mosquitoes of North and Central America and the West Indies. Publ. 159. Carnegie Inst. Washington. * James [i] (1902). Sci. Memoirs Med. and San. Departs, of Gov. of India, No. 2 VIII] PUBLICATIONS ON CULICID^ 117 * James [ia]. In Theobald, vol. m. * [2] (1910). Records of the Indian Museum, iv. No. 5. * [3] (1910). Paludism, No. i. * James and Liston [40] (1904) [46] (1911). The Anopheline Mosquitoes of India. Calcutta. Kert6sz (1904). Allattan Kozl. m. Laveran [ia] (1901). C. R. Soc. Biol. xxm. p. 993. — [16] (1901). Ibid. LIII. - [2] (1902). Archiv d. Parasit. vi. p. 359- [3] (1902). C. R. Soc. Biol. LIV. p. 907. "Leicester [i] (1904). The Entomologist, xxxvii. p. 13. * [2] (1908). Studies from the Instit. for Med. Research (Federated Malay States), vol. m. Linnaeus [i] (1746). Fauna Suecica. [2] (1735). Sy sterna Natures. *Liston [i] (1901). Indian Med. Gazette, xxxvi. pp. 361, 441. ... [2] (1901). Bombay Med. and Phys. Soc. v. No. 8. Loew [i] (1845). Dipterologische 'Beitrdge. [2] (1866). Entom. Zeitschr. *Ludlow [i] (1902). Jour. Amer. Med. Assoc. p. 426. * [2] (1902). Jour. New York Entom. Soc. x. p. 127. * [3] (1903). Ibid. xi. * [4] (1904). Canad. Entom. xxxvi. p. 297. * [5] (1908). Class. Geo. Dist. and Seas flight Mosq. (Philippine Islands). * [6] (1909). Canad. Entom. XLI. *Lutz [i] (1904). In Bourroul. McCracken [i] (1904). Entom. Mus. ix. Jan. 1904. Macquart [i] (1825). Mem. d. 1. Soc. R. des Sciences de I'Agric. et des Arts de Lille. [2] (1834). Histoire naturelle des Insectes Dipteres. Paris. - [3] (1854). Mdm. d. 1. Soc. R. des Sciences de I'Agric. et des Arts de Lille. Meigen [i] (1804). Klassifikation und Beschreibung der Europ. Zwe-if. Insekten, Bd. i. [2] (1818). Syst. Besch. der bekannt. Europ. Zweif. Insekten, vol. i. *Neiva (1908). In Peryassu. Neveu-Lemaire [i] (1902). M6m. d. 1. Soc. Zool. de France, xv. [2] (1902). C. R. Soc. Biol. LIV. * [3] (1905). Archiv d. Parasit. x. p. 238. *Newstead and Carter [i] (1910). Annals of Trop. Med. and Par. iv. No. 3. * - - [2] (1911). Ibid. v. No. 2. *Newstead, Button and Todd (1907). Ibid. i. No. i. Patton (1905). Jour. Bombay Nat. Hist. Soc. p. 623. Rothwell (1907). The Entomologist, XLV. p. 34. Il8 PUBLICATIONS ON CULICID^ [CH. *Skuse [i] (1889). Proc. Linnean Soc. N. S. Wales. 2nd Ser. in. [2]. Indian Museum Notes, in. Calcutta. Smith [i] (1901). Jour. Boston Soc. of Med. Sc. v. p. 34. [2] (1904). New Jersey Agric. Exp. Sta. pp. 1—40. Staeger [i] (1839). Syst. for. o. d. c. Denmark nid HI fundre Dipt. Stephens [2] (1828). Zoological Journal, xu. *Stephens and Christophers (1908). The Practical Study of Malaria, 3rd ed. *Theobald [i] (1900). Reports to the Malaria Comm. of Royal Society, i. * [2], [3] (1901). Monograph of the Culicidce of the World, vol. i and n. [4] (1902). Proc. Roy. Soc. LXIX. p. 367. [5] (I9°2)- Journ. Trop. Med. v. p. 181. [5a] (I9°3)- Ann. d. I'lnst. Pasteur, xvn. 2. [6] (1903). Monograph of the Culicidce, vol. in. [7] (I9°3)- Reports of the Sleeping Sickness Commission. [8] (1903). The Entomologist, xxxvi. p. 256. [9] (1904). First Report Gordon College, Welle. Labs. i. p. 62. [10] (1905). The Entomologist, xxxvin. p. 101. [n] (1905). Jour. Econ. Biology, i. No. i, p. 17. * [12] (1905). Ann. Mus. Nat. Hung. in. p. 65. * [13] (1905). Genera Insectorum Fam. Culicidce. Brussels. * [14] (1907). Monograph of the Culicidce, vol. iv. * [15] (1909). Records of the Indian Museum, in. No. 3. * [16] (1910). Ibid. iv. No. i. * [17] (1910). Monograph of the Culicidce, vol. v. * [18] (1901). Jour, of Trop. Med. iv. p. 229. *Theobald and Grantham (1905). Mosquitoes of Jamaica. Tsuzuki (1902). Cent. f. Bakt. xxxi. pp. 15, 763. Van der Wulp [i] (1839). Naturhist. Tijdschr. 11. p. 252. [2] (1869). Tijds. voor Entom. [4] (1884). Ley den Museum Notes. Ventrillon [i] (1906). Bull. d. Mus. d'Hist. Nat. xn. p. 100. [2] (1906). Ibid. xn. p. 198. Walker [3] (1850). Insecta Saundersonii, i. Watson (1910). Annals of Trop. Med. and Par. iv. No. 2. Wiedemann [2] (1828). Ausser Europ. Zweif. Insekten, i. IX] MALARIA IIQ CHAPTER IX ANOPHELINE-TRANSMITTED DISEASES MALARIA. Synonyms. Ague, Paludism, Intermittent fever, Remit- tent fever ; Marsh, Climatic, Jungle, Hill, Mountain and Coast fever, Plasmodiose, Fievre palustre, Wechselfieber, Kaltesfieber, Ylvperos, Bimbi ou Moustique (Galla), Mbou ou Moustique, and also many local names such as Roman fever, Sierra fever, etc., etc. Definition. Under the term malaria is grouped together a number of intermittent fevers caused by plasmodial parasites living in the red blood corpuscles At the present time only three distinct species of these parasites are usually recognized, viz. Plasmodium malaria, P. vivax, and P. falciparum ( = La- verania malaria) ; each gives rise to a distinct type of fever and is transmitted by various Anopheline mosquitoes. The common features of the disease, in addition to fever, are anaemia, hypertrophy of the spleen, and sometimes the liver, and the deposition of pigment (melanin) in the various organs and integument. Historical. The periodicity of the febrile attacks of malaria had attracted attention long before the parasitic nature of this disease was known, or its transmission by mos- quitoes suspected. Certain references have been taken as shewing that malaria was recognized even in the time of Homer (noo B.C.) and in the Hippocratic Books (500 B.C.) fevers having quotidian, tertian and quartan periodicity are described. This characteristic periodicity, which finds expression in the term intermittent fever, even now sometimes used, represented, however, practically everything that was known about the disease in these early times. A much more precise knowledge of malaria and a clear recognition of remittent and pernicious forms of the disease, where periodicity is not a feature, followed the introduction 120 MALARIA [CH. to Europe in the seventeenth century of Cinchona and its alkaloids, it being then possible to distinguish types of fever curable by quinine from those not affected by this drug. A third feature of malaria, namely its frequent association with paludic conditions, although it seems to some extent to have been known to the ancients (e.g. Varro, 116 B.C.), was first fully realized as a result of the work of Doni, Morton, Lancisi and others, from the seventeenth century onwards. This association was explained as shewing that malaria was due to exhalations from decaying vegetable matter, or to minute forms of life present in such exhalations. Hence there resulted the Miasm theory of malaria, a theory universally held by mankind up to a few years ago and responsible for the name "Malaria" (-bad air). In 1847 the occurrence of the characteristic pigment of malaria in the blood and organs was discovered by Meckel ; this pigment, it was thought, was the result of the chemical action of miasm on the blood. In 1881 Laveran discovered the organism containing this pigment now known as the malarial parasite. Within a few years Laveran's organism, the first discovered protozoon parasitic in man, was universally recognized as the cause of malaria. Thus in modern usage it has followed that no diag- nosis which has not been based upon the demonstration of this parasite, or its characteristic pigment in the blood, is accepted as of any value in a crucial case, malaria now being an example of a disease defined not on clinical but on parasitological grounds. In 1886 Golgi demonstrated the nature of the life-cycle of the parasite in man, and shewed that the periodicity of the febrile attacks was dependent on the length of the cycle of development of successive broods of the parasite, and that the attack of fever occurred at the time when such broods simul- taneously broke up into the spores which restarted the cycle. Golgi also differentiated two species of malarial parasite, the parasites of quartan and of tertian malaria, respectively. In 1891 Marchiafava and Bignami, after studying certain irregular fevers prevalent in Rome in the summer and autumn, IX] HISTORICAL 121 announced the existence of a third species of parasite, charac- terized by the occurrence of very minute forms, and now known as the cestivo-autumnal, malignant tertian or tropical parasite. It was shortly afterwards discovered that certain large and peculiar crescentic forms of the parasite, now very familiar as crescents, were a stage in the life-cycle of this third species. In addition these and other Italian workers by their collective researches made quite clear the real parasitic nature of Laveran's bodies and by elaborating methods by which they could be demonstrated, laid the foundation for the study of the malarial parasite by observers in other parts of the world. In the decade or so following upon these early observations a great many important facts in regard to malaria were elicited. It was shewn that infection could be conveyed to healthy persons by the subcutaneous or intravenous inoculation of the blood of malarial subjects. It was also proved that in such cases only that form of parasite appeared which had been present in the original infection, thus greatly strengthening the view of a plurality of species. Other species more or less resembling the malarial parasite, but shewn to be distinct, were also found to occur in birds, bats and other animals, and were closely studied. Special methods of staining were elaborated and much work was done with regard to the peculiar crescent bodies and the process of exflagellation exhibited by these and by certain other forms of the parasite. All efforts to discover how the parasites gained an entrance to the blood of man, however, failed. Experiments (Marchia- fava ; Celli, 1885 ; Marino, 1890, and Zeri, 1890, etc.), under- taken with a view to producing malaria in healthy persons by causing them to drink water from notoriously malarious places, were without result. When marsh water was injected into animals a condition thought at first to be malaria was produced, associated with tumefaction of the spleen and the appearance of pigment in the organs. But it is now obvious that this condition was one of septicaemia, and with the dis- covery of the malarial parasite any significance attaching to these experiments had to be abandoned. The possibility that mosquitoes might be concerned in the 122 MALARIA [CH. transmission of malaria had been put forward already by King (1883). That mosquitoes might convey malaria was also definitely suggested by Laveran on the analogy of the develop- ment of filarial embryos in the mosquito (1884). But it was Manson (1894) who more especially elaborated and emphasized the probability of mosquito transmission, and who by his remarkable deductions, based on the behaviour of the flagellate bodies, led directly to Ross's efforts to demonstrate this rela- tion experimentally. But none of these hypotheses, not even Hanson's carefully thought out deductions, anticipated the mosquito cycle as we now know it, as a result of Ross's brilliant research, in all its beautiful simplicity. According to Manson it was the flagella breaking away from the parasite that underwent development in the mosquito, and it was by the medium of water in which the mosquito eventually died that it was supposed re-infection of man took place. Ross's discovery of the cycle of develop- ment of Proteosoma shewed that it was the whole parasite which underwent development, and that re-infection did not take place through water, but that the parasites underwent growth and multiplication in the body of the mosquito, eventu- ally finding their way to the salivary glands, to be injected with the salivary secretion when the mosquito next fed. The significance of flagellation was almost coincidently shewn by MacCallum, who observed in Hcemoproteus ( = H alteridium) , another parasite of birds, the fertilization of the female form, or macrogamete, by the flagella, or microgametes, liberated from the microgametocyte, or male form, of the parasite. The discovery of the life-cycle of Proteosoma, and the fact that the protozoa, like the parasitic worms, might exhibit melaxeny, or the utilization of two or more hosts in their development, gave the clue to the method of transmission of human malaria, and the mosquito cycle of the malarial para- site, as worked out by Grassi and others, was found to follow almost exactly the development previously noted by Ross in the case of Proteosoma. But whereas the parasite of birds underwent development only in mosquitoes of the genus Culex (C. fatigans), that of man required those of the genus IX] HISTORICAL 123 Anopheles. (A. maculipennis and an Anopheles in which Ross had already seen zygote stages of the malarial parasite in India.) Observations and experiments in Rome shewed that the occurrence of Anopheline mosquitoes was especially charac- teristic of malarious localities, and still more important that patients contracted the disease when exposed to the bites of Anopheles brought from notoriously malarious districts, or those which had been previously fed on malarious subjects. A final proof was the classical experiment of Manson, in which Anopheles infected in Italy were allowed to feed upon two volunteers in England, both of whom as a result contracted malaria. This discovery, one of the most remarkable in the history of medicine, was so opposed to popular ideas of the way in which malaria was contracted, that for a time there were some who doubted whether the simple explanation given by Ross's experiments could explain all the facts regarding malaria transmission. Especially the idea that malaria was supposed to be contracted in remote and uninhabited swamps led to the frequently expressed suggestion that there might be channels of infection other than the mosquito, and a good deal was made of certain bodies found by Ross within the parasitic cysts, and called by him " black spores," as shewing that there might be a cycle of development over and above that already known. In order to explain the deadliness of tropical swamps and jungles, others suggested that Anopheles obtained infection by hereditary transmission from mosquito to mosquito, or from the blood of bats or other wild animals. " Black spores," however, are now known to be a species of Nosema attacking the mosquito independently of malarial infection, whilst it is now generally recognized that, contrary to current belief, remote jungles and swamps in themselves are harmless, in the absence of human inhabitants to yield infection. Neither hereditary infection of mosquitoes nor their infection from wild animals is now considered probable, and the view universally held at the present time is that malaria is an infectious disease passing from man to man, but requiring for this purpose the presence of an intermediary transmitting host, the mosquito. 124 HISTORY OF MALARIA [CH. This view, that malaria is a disease transmitted by Anopheles , but essentially of an infectious nature depending on pre-existing human infection for its origin, may be said to be that upon which all present day conceptions regarding the epidemiology and prevention of malaria are based. Such a conception of malaria is of course entirely opposed to the older notions of a " telluric " disease, and as a result the whole method of approaching malaria problems has so changed that writers sometimes refer to researches they may have conducted as being directed from the New Mtiological Standpoint. But though all the more modern work upon malaria has been based upon the discovery of the mosquito cycle, yet it would be a mistake to suppose that no considerable advance in the knowledge of malaria has been made since this great discovery. Not only has there been a vast accumulation of knowledge regarding the circumstances connected with malaria in almost all parts of the world, but even in some cases a distinct modification, or rather expansion, of original conceptions of the disease has resulted. Thus the idea of malaria as an infectious disease requiring some previous case of fever from which infec- tion was to be derived, has been modified, at least as far as tropical countries are concerned, and brought more into touch with the old telluric views by the discovery of the almost ubiquitous latent infection of native indigenous races and of the part played by native communities as " reservoirs of infection." Equally important have been the striking advances in the conception of the part played by economic influences in determining the degree of prevalence of malaria, for as stated by Celli it is not merely malaria parasite + Anopheles + man which determines the prevalence of malaria, especially the prevalence of this disease in epidemic form, but the formula malaria parasite + Anopheles 4- man + X. It is in fact the com- plicated factors involved in this unknown X with which the most recent investigations on malaria have been mainly con- cerned, and the complete elucidation of Celli's formula will constitute still another step of no mean importance in the history of malarial research. Again, with regard to advances in connection with IX] LIFE-CYCLE OF MALARIAL PARASITE 125 preventive measures directed against malaria, there has not only been a great increase of practical experience of such action under particular circumstances, but methods of combating the disease have sometimes become possible which at first sight were not self-evident. As examples may be mentioned the important method of dealing with malaria known as Segregation, now largely employed in Tropical Africa, and the no less remark- able development of prophylaxis as recently applied among British troops in India, where malaria has been combated not only by direct, but by a host of indirect and often extremely ingenious devices. Life-cycle of the Malaria Parasite in Man and in the Mosquito. Like many other parasitic Protozoa, the malarial parasite has two periods of multiplication in its life-cycle, one in which it multiplies and over-runs its mammalian host, the other in which, to ensure its eventual translation to a fresh host, it multiplies in the body of the mosquito. The first period of multiplication in the blood of man, since it occurs independently of any fusion of male and female elements (syngamy], is known as the asexual, or, from the fact that multiplication goes on by a process of schizogony, the schizogonous cycle. The period of multiplication, which starts with the entry of blood contain- ing suitable forms of the parasite into the stomach of the mosquito, is dependent on the fertilization of the female element (macro gamete] by a male element (microgamete) and is known as the sexual or sporogonous cycle, sporogony being the term applied to the analogous part of the life-cycle in other Sporozoa. The schizogonous cycle can be repeated, as far as is known, an indefinite number of times, and apparently without the inter- vention of any sexual process may keep up a condition of infection of the host lasting for several years. Sporogony, on the other hand, occurs but once, with the formation of a vast number of the forms known as sporozoites^ which, after accumu- lating in the salivary glands of the mosquito, remain without further development until introduced into the blood of man. 126 LIFE-CYCLE OF MALARIAL PARASITE [CH. Schizogony occurs only in man, and the schizont forms, if ingested by the mosquito, are simply digested. But whilst the greater part of the sporogonous cycle takes place in the mosquito, the early stages, as far as the formation of the sexual forms is concerned, takes place in the blood of man. Thus in the blood of a malarious patient both asexual and sexual forms may be seen ; the former are those concerned in the production of fever and the clinical effects of malaria generally, the latter are of importance only if they are taken up by a suitable mosquito. Although three species of Plasmodium occur in man and give rise each to a distinct type of fever, their methods of development and multiplication are essentially the same. Asexual cycle. — Schizogony. We will commence with a description of the parasite as it is introduced into the blood by the bite of an infected mosquito. At this stage it consists of a small sickle-shaped body, about IO-20//, in length by i-2fj, in diameter. It is known as the sporozoite, and large numbers of these are extruded with the salivary secretion of an infected mosquito, as may be seen by allowing the insect to feed on a drop of glycerine on a slide. The sporozoite consists of a central nucleus surrounded by a uniformly staining elongate mass of cytoplasm. It is pointed at both ends, and by means of flexion is capable of progressive movements in the blood plasma. After being introduced into the blood of a human being three possibilities are open to these sporozoites. They may be killed in the body and thus produce no infection ; they may remain latent in the spleen or some other internal organ until a favourable opportunity to develop presents itself ; and lastly, they may proceed at once to develop and give rise to the characteristic fever after a certain incubation period. The sporozoite begins to develop by first boring into a red blood corpuscle and thus becoming an intracellular parasite. Once it has entered the red cell it assumes a rounded amoeboid form, which is known as the trophozoite. The young trophozoite is actively amoeboid, giving off pseudopodia and absorbing nourishment from the contents of the red cell. At first it consists of a uniform mass of cytoplasm IX] LIFE-CYCLE OF MALARIAL PARASITE 127 containing a single nucleus, but soon a " vacuole " appears in the parasite, causing it to assume a ring form (Fig. 40, i). As the parasite grows it feeds on the substance of the red corpuscle, and gradually destroys the whole cell, but during this process certain waste products are formed, one of which is deposited within the cytoplasm of the growing trophozoite in the form of pigment granules. These granules are composed of a brown or black substance allied to melanin, to which the name " haemozoin " is sometimes applied. This substance is chiefly the result of the decomposition of the haemoglobin, and has very pronounced physiological properties, being mainly responsible for the febrile attacks that occur in patients suffer- ing from malaria. The trophozoite grows until it reaches a certain size — about three-quarters the diameter of the red cell — when it becomes rounded off and withdraws all pseudopodia. The full grown trophozoite is then known as the schizont, and consists of a rounded mass of cytoplasm containing numerous pigment granules and a nucleus situated to one side of the centre. This nucleus now begins to divide, according to the species of Plas- modium, into 6 to 20 smaller nuclei (Fig. 40, 5), which become arranged around the periphery of the parasite. Each of the nuclei then becomes surrounded by a mass of cytoplasm which separates off from the remainder, and thus a number of small parasites are formed. These are known as the merozoites and are usually ovoid bodies, about 2/4 by i/z, each containing a single nucleus. In the above-described process a certain amount of cytoplasm, containing all the pigment granules, is left unsegmented at the centre of the cell. After segmen- tation is complete the wall of the red cell bursts and the mero- zoites, together with the residual protoplasm and pigment granules, escape into the blood stream. Many of the merozoites are now ingested by the leucocytes, but a certain number escape and at once proceed to attack other red cells. Unlike the sporozoite, the merozoite does not directly bore its way into the red cell, but usually becomes attached to the surface of the cell. Very soon after the young parasite has attached itself, its 128 LIFE-CYCLE OF MALARIAL PARASITE [CH. cytoplasm becomes spread out and exhibits a characteristic, comparatively large, clear, central vacuole, the effect of which is to give the parasite the appearance of a ring, such ring forms occurring in the early stages of development of all three forms of the parasite. In fresh preparations these ring forms can be seen to possess on one part of their circumference a swelling like the stone of a signet ring which is the nucleus, and to extrude small pseudopodial processes, which in some forms are very long and slender, in others more lobose. In specimens stained by the Romanowsky method the nuclear portion is conspicuous as a bright red mass, whilst lying around the vacuole is a thin crescentic portion of delicate blue-staining cytoplasm. Many of the ring forms, especially in the case of the malig- nant tertian parasite, remain for some time attached to the surface of the red blood corpuscle, such forms being termed accole or attached parasites. Eventually in all species the parasite sinks into the substance of the cell. The subsequent development is identical with that pre- viously described, the termination of which is the formation of a schizont and the subsequent liberation of a number of merozoites into the blood stream. This cycle may be repeated any number of times until a large proportion of the red cells is infected. The asexual method of multiplication in the blood of the vertebrate host is characteristic of all species of Plasmodium. By this means the infection is carried from one cell to another within the vertebrate host, and very rapidly millions of the blood corpuscles become infected. The destruction of the blood cells thus entailed rapidly produces anaemia in the affected patient, but much more harm is done by the waste products of the parasites. These consist of the pigment granules and various other products of metabolism which are left behind in the residual protoplasm when schizogony occurs. As they can only escape into the blood stream when the red cell bursts, these various toxic waste products are liberated together with the merozoites, and as most of the infected corpuscles rupture about the same time, the effect of the accumulated IX] LIFE-CYCLE OF MALARIAL PARASITE I2Q products is so considerable as to produce an attack of fever in the patient. The febrile attacks only occur when schizogony is taking place and the merozoites are being liberated into the blood stream. The interval between the attacks indicates, therefore, the time taken by the parasite to develop from the merozoite through the trophozoite stages up to the schizont, and to subdivide into a number of merozoites, or, in other words, to pass through the complete asexual cycle. It has been found that the time taken for the completion of this cycle varies in different species of Plasmodium, being 72 hours in the case of P. malaria, 48 hours in P. vivax, and from 24 to 48 hours in P. falciparum. Hence the fevers caused by each of these parasites differ from one another by the intervals elapsing between the febrile attacks. The full description of these species, together with their distinguishing characteristics, is described below (vide p. 155). In these few words we have briefly described the asexual cycle of development that takes place in the vertebrate host, but, as will be obvious, the only method by which the merozoites could infect another host would be by the inoculation of blood containing them. This method of transmission is successful, for if blood containing malarial parasites is inoculated into a normal human being, the latter becomes infected with malaria. However, such a mode of transmission probably never occurs in nature, for the merozoites are incapable of withstanding desiccation, or any other of the vicissitudes to which they would be exposed on the proboscis of a biting arthropod, the only conceivable agent for such direct transmission. Con- sequently, in addition to its asexual multiplication, which merely serves to increase its numbers in the infected individual, it is necessary for the parasite to possess some means of being carried from one host to another. We shall see that provision is made for this transmission, but first it is necessary to describe another development that the young trophozoite may undergo in the red cell. Development of the sex^^al forms in the blood. About a week after a patient becomes infected with malaria certain large intracorpuscular forms may be observed that do not go through H. B. F. Q IN MOSQUITO ,02 Fig. 40. Diagrammatic representation of the life-cycle of the malarial parasite of pernicious malaria. 1-6. The schizogonous cycle shewing successive stages in growth from the young ring form (i) up to the fully-grown parasite (4) in which the nucleus has divided. 5 and 6. Division of the body of the parasite to form the merozoites. 7. A single merozoite, which CH. IX] LIFE-CYCLE OF MALARIAL PARASITE 131 is capable of entering another red cell and repeating the above-described cycle. 8-1 1. Formation of the gametocytes ; these arise by growth of merozoites and after reaching a certain size (10) develop into either male or female gametocytes (na and lib) ; in the male gametocyte (116) the nucleus is larger and more scattered than in the female (na). 1 2 -i 6. Stages of the sexual generation in the stomach of the mosquito. i2a, 130, and 140,. The formation of the female gamete. 126, 136 and 146. Stages in the formation of the male gametes. 15. Fertiliza- tion, resulting in the formation of a zygote (16), which then becomes motile and is known as the ookinete (17). 18-22. Stages in the sporogonous cycle in the mosquito. The ookinete (17) bores into the stomach wall and forms a cyst (18) ; it increases in size, its nucleus multiplies and eventually each nucleus becomes surrounded by a mass of cytoplasm, forming a number of sporo- blasts (19) ; each of these sporoblasts gives rise to numerous sporozoites (20-21). The ripe sporocyst is represented in 21, and the escaping sporozoites (22) enter the salivary gland of the mosquito and escaping with the salivary secretion, enter the blood and are capable of repeating the cycle. the process of schizogony. These are the sexual forms, and are of two kinds, male and female. It is probable that the merozoites differentiate sexually at an early stage of the disease, but what determines the sex is unknown. In its earliest stages the young sexual form is indistinguish- able from an ordinary trophozoite, but it grows extremely slowly and never assumes the ring form. As it grows its cytoplasm becomes filled with granules of pigment and soon certain differences can be noticed in the staining reactions of the protoplasm, resulting in the differentia- tion of what are known as the macrogametocytes and micro- gametocytes respectively. The former are destined to give rise to the female gametes, and are characterized by the pos- session of a small feebly-chromatic nucleus and a dense cyto- plasm containing numerous granules and much pigment. The microgametocytes, which give rise to the male gametes, have each a large densely chromatic nucleus extending across the middle of the cell, and the cytoplasm is clearer and contains less pigment. When full grown, the sexual forms are larger than the red cells which contain them ; consequently the latter are consider- ably distorted by the parasite and form conspicuous objects that were noticed long before their true nature was recognized. 9—2 132 LIFE-CYCLE OF MALARIAL PARASITE [CH. At this stage there are now three types of parasites, viz. the schizonts, macrogametocytes and microgametocytes, the two latter belonging to the sexual and the former to the asexual cycle. The sexual cycle cannot be completed in the blood but only in the internal organs of those species of mosquito which transmit the infection. In the absence of these the micro- gametocytes soon die off without any further development taking place. The macrogametocytes, on the other hand, are much more resistant, and can remain in the body for very considerable periods. These are the forms that are supposed to be respon- sible for the cases of latent malaria, in which a patient may remain in good health for some years and then suddenly develop typical malaria without having been exposed to the possibility of re-infection. In these cases it is the macrogametocytes that have remained dormant in the .body waiting for a convenient opportunity to develop, such as that afforded by a chill or any other diminution in the vitality of the patient. Under these circumstances the macrogametocyte develops parthenogeneti- cally. Its nucleus divides into two parts, one densely chromatic and the other poor in chromatin. The pigment granules and other waste products gather round the latter, and the whole is divided off from the remaining protoplasm and constitutes a sort of residuum similar to that left behind by the merozoites. The remaining part of the macrogametocyte, now much clearer by the loss of its pigment granules, divides up into a number of merozoites in exactly the same way as an ordinary schizont, and the merozoites escaping into the blood plasma penetrate other red cells and thus start another cycle of schizogony. Sexual cycle. — Sporogony. As mentioned above the macro- and microgametocytes only complete their development in the internal organs of the mosquito that is responsible for their transmission. When such a mosquito — in the case of malaria only Anophelines — feeds on the blood of a patient containing sexual forms, in addition to the latter, it ingests many parasites belonging to the schizogonous IX] LIFE-CYCLE OF MALARIAL PARASITE 133 cycle. All these are digested, the macro- and microgame- tocytes being the only forms that are capable of re- sisting the secretions in the stomach of the mosquito. Here they undergo further development, the stimulus for which is probably the reduction in temperature, combined with the dilution of the blood that takes place in the gut of the insect. The macrogametocyte escapes from its red cell and becomes spherical ; then its nucleus divides and one of the daughter- nuclei, together with a small amount of cytoplasm, is extruded as a polar body (Fig. 40, 14 a). After this maturation process is complete the parasite is now ready for fertilization, and is known as the female or macrogamete. The microgametocyte undergoes a different kind of develop- ment, for after becoming spherical and escaping from the red corpuscle, its nucleus breaks up into a number of fragments, sometimes known as chromidia, which travel outwards and become arranged round the periphery of the cell. Part of the nucleus remains behind at the centre as a residuum and is not used up in the subsequent development. The surface of the microgametocyte now grows out into a number of flagellum-like processes into each of which passes one of the nuclear fragments. These processes are highly motile, and by their lashing about cause the parasite to resemble a flagellate. In consequence the earlier observers referred these forms to the genus Polymitus, and they are still often referred to by this name. Each of the flagellum-like processes finally becomes free and swims away as an independent organism. These are the male or micro- gametes. The microgametocyte usually produces four to six of these microgametes which in their formation use up the protoplasm of the gametocyte, merely leaving a residuum com- posed of all the pigment granules, together with part of the original nucleus and a small amount of cytoplasm. The microgamete consists of an elongated filament with a slight thickening about the middle of its length, caused by the nuclear matter. It progresses by rapid wave-like movements and as it is only about 0*5 ^ in diameter, is extremely difficult to observe in the living state. 134 LIFE-CYCLE OF MALARIAL PARASITE [CH. Conjugation now takes place, one of the microgametes boring its way into a macrogamete. This is followed by union of the two nuclei, and the resulting structure is known as the zygote. At first the zygote is spherical, but it soon elongates into a small worm-like body which is actively motile, moving about in much the same way as a gregarine". The zygote is then known as the ookinete or, by some writers, the vermicule, because of the character of its movements. The whole of this process, including the formation of the gametes and their union to form the ookinete, takes place in the stomach (= hinder part of the mid-gut) of the mosquito, and is completed within a comparatively short time. All the above stages may be observed by placing a drop of blood con- taining the gametocytes on a slide and slightly breathing on it. If the preparation be now covered with a cover-glass and examined under an oil-immersion lens, all the stages in the evolution of the micro- and macrogametes, and their subse- quent union to form the ookinete, may be followed in the living state. The subsequent development of the ookinete can take place only in the mosquito, and we shall proceed with the description of the changes which it undergoes in this site. After moving about for some time, the ookinete bores through the epithelium of the gut-wall and comes to rest between this layer and the tissues immediately surrounding it. Here the parasite becomes rounded off and secretes a thin cyst-wall. This form is known as the oocyst and is parasitic upon the mosquito, for it grows considerably in size, absorbing nourishment from the surrounding tissues. During its growth, the gut-wall is bulged out towards the body-cavity, and conse- quently at this stage the stomach of the infected mosquito has a very characteristic appearance (Fig. 53). As many as 500 oocysts have been found in the stomach-wall of a single infected Anopheles. As the oocyst grows, its nucleus divides into a number of daughter-nuclei, each of which becomes surrounded by a mass of cytoplasm and gradually separated off from its neighbours. These are known as the sporoblasts ; they are irregular in form IX] LIFE-CYCLE OF MALARIAL PARASITE 135 and remain slightly connected together by means of cytoplasmic processes. After the formation of the sporoblasts a certain amount of protoplasm is left over, containing all the waste products and also some of the pigment granules originally present in the macrogamete. The nucleus of each sporoblast now divides into a large number of smaller ones which become arranged around the periphery. The surface of the sporoblast then exhibits a number of cytoplasmic projections, each of which increases in length and takes with it a daughter-nucleus. Eventually the spindle- shaped process, with its contained nucleus, becomes free from Fig. 41. Photomicrograph of sporozoites of malaria from the salivary glands of Anopheles (Pyretophnrus) costalis. X about 1000. After Hill and Hay don. the mother sporoblast, and is then known as the sporozoite. Each sporoblast produces large numbers of these bodies, but a certain amount of protoplasm containing waste products is always left unused in their formation. The oocyst, which con- tains the whole of the sporozoites derived from the many sporoblasts, and by this time has increased enormously in size, eventually bursts, and the sporozoites are set free in. the body- cavity of the mosquito. As the ccelomic fluid bathes all the organs of the mosquito, the sporozoites are brought in contact with all parts of the body. They appear to have a predilection for the salivary glands and the majority bore their way into 136 MOSQUITOES IN RELATION TO MALARIA [CH. these organs and may be seen filling the secretory cells and also becoming free^n the lumen. The sporbzoites are now incapable of further development in the mosquito, but if the latter feeds on a human being, large numbers of them are introduced into the wound together with the salivary secretion. They thus enter the blood and there penetrate into the red blood corpuscles and start the schizogonous cycle with which we commenced. The whole of this process, from the differentiation of the macro- and microgametocytes to the formation of the sporo- zoites, is known as the sexual or sporogonous cycle, and is completed in from ten to twelve days. Thus a mosquito that has ingested blood containing the gametocytes does not become infective until this incubation period has elapsed. Then its salivary glands contain the sporozoites, and the insect probably remains infective during the remainder of its life. Bionomics of Mosquitoes in Relation to Malaria. The habits of the particular species of mosquito concerned in the transmission of malaria in any particular locality are of the highest importance, and therefore, at the risk of repetition, some of the more important features may be briefly mentioned. The majority of Anophelines are more commonly associated with village life, and are especially prevalent in more or less uncultivated districts, and, unlike the Culicines, their breeding habits are usually unsuitable for their persistence in towns. With respect to this point, however, there are exceptions, and it will be necessary to refer to the connection between the habits of various species in relation to the spread of malaria. At the time of the discovery of the mosquito cycle, only some half-dozen species of Anopheles were known, most of which are European species. There are now more than 100 well defined and accurately described species, as well as many named varieties, and these taken collectively have a distribu- tion which extends almost all over the globe. These species differ not only in morphological details, but what is more important from our present point of view, they vary greatly in their habits and in their relation to malaria. IX] MOSQUITOES AND MALARIA 137 Among habits affecting the conditions of malarial dissemina- tion may be mentioned the predilection of particular species for particular kinds of breeding place. Some species are essentially stream breeders and are even adapted by their habits, and probably to some extent by structure, to prevent themselves being carried away by flood conditions. An example of a species Fig. 42. Breeding places of Anophelines. Railway cutting at Kurunegala. The water course flowing on each side of the permanent way supplying the engines with water. These channels are blocked with weeds, from amongst which larvae of A. culicifacies and A. rossii have been taken. After Bahr (from the Tropical Diseases Bulletin}. having this habit is A. (Myzomyia) listoni (M. Christopher si Theobald), which swarms in the streams of the sub-Himalayan terai, and is largely responsible for the high prevalence of malaria in these regions. Another example is A . (Nyssorhynchus) willmori, a species which is very difficult to eradicate, because of its power of breeding freely in the small streams of Malay 138 MOSQUITOES AND MALARIA [CH. Other species are pool- breeders, and some may even restrict themselves, or be able to flourish only in some particular kind of pool. Thus the numerical prevalence of the common Indian species A . (Myzomyia) rossii is dependent usually on the occur- rence of small freshly-filled shallow muddy rain-pools, such as are formed in countless thousands during the Indian monsoon. In the forests of South America a malaria-transmitting species, A. (Myzomyia) lutzi, breeds in various pitcher-plants, and especially in the cups of various epiphytic tree pines. An even more remarkable choice of breeding place is seen in the Malayan species A. (Lophoscelomyia) asiatica, which is found breeding only in bamboos that have been perforated by a borer. Over a large tract of the earth's surface, where mangrove swamps and salt marshes are a feature of the sea coasts, the species A . (Myzomyia) ludlowi breeds in brackish water, in pools that are entered by the sea at spring tides. In the case of the Andaman Islands, Christophers has recently shewn that this species is the chief carrier of malaria, and as it is not found at a greater distance than half-a-mile from the coast, is the cause of a littoral distribution of malaria in these islands. Another good example of the extent to which habits of particular species in regard to the choice of breeding place may affect the dissemination of malaria is seen in the case of the very interesting A nopheles, A. (Nyssorhynchus) stephensi. This species ordinarily is found in pools in large sandy river beds, and has a predilection for quite small collections of water, such as the hoof-marks made by cattle coming to drink, or shallow surface wells made in the sand at the river margin. It was found, however, by the Royal Societies Commission, to possess, like Culicines, the power of breeding in water pots and other domestic utensils, when these were filled with com- paratively clean water. More recently this species has been shewn by Liston and by Bentley to be the species concerned in the spread of malaria in Bombay City, where the population is as dense as in the heart of London, and under conditions where no other species of this genus has been able to survive. It is entirely due to the power of N. stephensi to breed in wells, covered cisterns, and such like places, that it has been able to IX] MOSQUITOES AND MALARIA establish itself in these novel and, to the genus as a whole, quite unsuitable surroundings. Apart from the differences in regard to the ability to flourish in particular kinds of breeding places, are other habits which sometimes influence very considerably the epidemiological conditions under which malaria is spread. Thus many species of Fig. 43. Flooded Paddy Fields in Ceylon. The picture shews in the fore- ground the pools formed by the hoof-marks of cattle ; in these Anophelines breed. After Bahr (from the Tropical Diseases Bulletin). Anopheles are naturally little addicted to entering or remaining in human habitations, and in nature are not found particu- larly associated with man. Other species readily take up a life of dependence on man and utilize his dwellings as shelter. It is to this latter class that the more important malaria carriers belong. Again, under ordinary circumstances, some species are entirely nocturnal in their habits, whilst others bite freely 140 MOSQUITOES AND MALARIA [OH. on cloudy moist days, and others again may have actively diurnal habits and feed by day like Stegomyia. An example of the latter habit is seen in the species A . (Myzorhynchus) barbirostris, which swarms in the forests of Malay and is most bloodthirsty throughout the daytime. Another diurnal species is Anopheles aitkeni. Even the boldness and persistence, or even the small size of particular species, may add greatly to their effect in transmitting malaria under particular circumstances. But in addition to these differences in habits which indirectly affect the transmission of malaria, there is the very important question of the relative suitability of different species of Ano- pheles for the development of the parasite. When it was shewn that certain species of Anopheles carried malaria and that Culex and other biting insects did not, it was assumed that the power to act as a suitable host to the malaria parasite was common to all Anophelines. The first instance of an Anopheles being shewn not to transmit malaria was in the case of the common Indian species A. (Myzomyia} rossii. This species is found quite commonly in very large numbers associated with every degree of prevalence of malaria, but it has not yet been shewn to act as a transmitting agent under natural conditions, though it can be infected experimentally. Not infrequently this species occurs along with others which are actively concerned in the spread of malaria, but though under these circumstances a considerable percentage of both A . (Myzo- myia) culicifacies and A. (Nyssorhynchus) stephensi have been found with sporozoites in the salivary glands, A. (Myzomyia) rossii has never been found infected. This peculiar fact, re- garding which the following independent figures have been given, is not easy to explain, but there seems little doubt that M. culicifacies N. stephensi Myzomyia rossii Stephens and Christophers Lahore ( Punjab) 4'6% o Ennur (Madras) 8-6% — o Bentley Bombay — 3'5% — IX] MOSQUITOES AND MALARIA 141 for some reason, A. rossii is not an active transmitter of malaria, if it transmits at all, under natural conditions. Another species not suitable as a carrier, and which in this case was refractory even to experimental infection, is the North American species Anopheles punctipennis. In this case A. maculipennis and A. punctipennis were fed together on an infected patient ; the former became infected whilst the latter remained free from infection. The development of the three species of malarial parasites does not take place with the same facility in any given species of mosquito. Thus Kinoshita found that in Formosa, Plasmodium falcipayum was incapable of development within A. (Myzo- rhynchus) sinensis, whilst this species of mosquito could easily be infected with Plasmodium viva% (seven times out of eleven) and less easily with Plasmodium malarice (one in seven). In the same region A. (Myzomyia) Christopher si almost invariably became infected when fed on a patient containing the gametes of P. falciparum in his blood. Other species have also been noted as probably not taking an active part in malaria transmission or to be actually refrac- tory to experimental infection with the malaria parasite. But though some species are possibly incapable of acting as hosts, and whilst some are more suitable hosts than others, there is reason to believe that very many of the species are at least potential transmitters. Thus in India, Stephens and Christo- phers succeeded in experimentally infecting all but one species out of a considerable variety of Anophelines. Similarly, Darling at Panama has produced infection in many of the Anophelines of that region. The most important point in regard to the transmitting power of a species is the extent to which it is found actively concerned in transmission under natural conditions. In this respect there are certain species which must be looked upon as the chief carriers in particular parts of the world. In Europe the common carrier is Anopheles maculipennis, but the common species, Anopheles bifurcatus, is also capable of transmitting malaria. A. maculipennis is the common carrier in the Mediterranean islands and is largely concerned 142 MOSQUITOES AND MALARIA [CH. in the spread of malaria in Algeria and Palestine. It is also the chief agent in North America. In Algeria, besides A . maculipennis, the species incriminated are : Anopheles algeriensis (Ed. and Et. Sergent, 1905), especi- ally occurring in the coast regions ; A. hispaniola (Sergents, 1905), found chiefly in the hilly broken country; A. (Pyreto- phorus) myzomyfacies (Ed. Sergent) ; A. (P.) superpictus and A. (P.) chaudoyei. A. chaudoyei is capable of breeding freely in saline waters and is the species chiefly concerned in malarial transmission in the Saharan oases. In Egypt, A. (Cellia) pharoensis is a proved and important carrier. Anopheles funesta and A. costalis have both been shewn by Ross to transmit the infection, and are the most important and widely distributed carriers of malaria in Tropical Africa. In India, Stephens and Christophers shewed that A. (My- zomyia) listoni is a very actively transmitting agent in the Duars or terai country at the foot of the Eastern Himalayas. A more general, and perhaps the commonest Indian transmitter is A. (Myzomyia) culicifacies. A. fuliginosus Giles has also been shewn to transmit the disease, but apparently is not a very important carrier. A. maculipalpis has been found infected in nature in various parts of India. Amongst the most impor- tant and active Indian carriers are A . (Nyssorhynchus) stephensi and A. (N.) willmori. In Malay, in addition to M. listoni, the proved carriers in nature are A. (Myzomyia) albirostris, A. (Myzomyia) ludlowi, and A. (Nyssorhynchus} willmori. In Central America a number of species are active carriers, the most important being A. (Cellia) argyrotarsis and A. (C.) albimana. In addition there are numbers of species very probably concerned in malaria transmission, perhaps even important carriers in particular parts of the world, e.g. A . formosaensis in the island of Formosa ; A . arabiensis in the Aden hinterland ; A . (Myzomyia) lutzi in the forests of Brazil ; and A . (Nys- sorhynchus) annulipes in Formosa, Australia, etc. IX] MOSQUITOES AND MALARIA 143 Influences affecting Malaria through the Transmitting Host. The most powerful influences affecting Anopheles are tem- perature, rainfall and humidity. Added to these must be considered the physical characters of the country under con- sideration, the nature of the soil, the prevalence of natural enemies, and even the races of mankind inhabiting the countries. With regard to physical conditions, generally hot moist climates are suitable, cold and also excessively dry climates unsuitable^ to the development of Anopheles. In this respect, however, the question of species and .even of special adaptive habits becomes important. Temperature plays a double role. If low it not only delays or prevents the propagation of Anopheles, but it even more actively interferes with the development of the parasite within the mosquito. A perennial low temperature may altogether prevent the propagation of the parasites, for it is found that the gametocytes cannot develop below a temperature of about 15° C. As a result, one can trace northern and southern limits to the occurrence of malaria, corresponding to the mean sum- mer isotherm of 15° to 16° C. Moreover, the different species of malaria require different degrees of warmth in order to ensure their development. Thus Plasmodium malaria develops best at comparatively low temperatures, and consequently is found in much colder regions than the other two species. On the other hand P. falciparum will only develop at comparatively high temperatures, and therefore in temperate regions it only occurs during the summer and autumn months, whilst throughout the tropics it is prevalent the whole year round. Plasmodium vivax occupies a somewhat intermediate position, for it is capable of development throughout a wide range of temperature and, as one would expect, this species is the most widely distributed, occurring in both tropical and tem- perate regions. A perennial low temperature within limits, however, does not prevent the propagation of certain species of Anopheles, e.g. A. bifurcatus reaches a particularly large size in the north of Scotland. Still less does a temporary or seasonal period of low temperature destroy or permanently 144 MOSQUITOES AND MALARIA [CH. affect the prevalence of Anopheles, such periods being tided over by " hibernation." It is thus easy to see how, as regards the northern and southern limits of malaria, we may have these fairly corresponding with the limits of the distribution of Anopheles, and to understand how, even apart from any other reason, a considerable altitude may be associated with a freedom from malaria, even though Anopheles are still found. Rainfall, up to a certain point, is very favourable to Ano- pheles, but if excessive it may have an adverse effect by washing away the larvae and destroying them. Humidity would seem to be entirely a favourable circumstance, and has been shewn to affect favourably the development of the malarial parasite within the mosquito. The nature of the soil may affect conditions as regards Anopheles, not only by its power to retain surface water or to allow of the formation of springs, but often by reason of its chemical nature ; surface waters in some soils readily develop a ferruginous scum or other conditions, unsuitable to the development of mosquitoes. The occurrence of natural enemies, especially circumstances which favour the general presence in surface waters of small fish, is a most powerful influence checking the multiplication of A nopheles . Under conditions of alternate rainfall and drought many pools utilized by Anopheles are of too temporary a nature for the presence of fish, or even of other natural enemies, such as various predaceous insect larvae. On the contrary, in very moist countries, even the smaller pools are usually stocked with fish and other predaceous animals. There may thus often be a very fortunate regulating mechanism which may com- pletely reverse the normal order of affairs and make Anopheles comparatively scarce under conditions that at first sight might appear wholly favourable. Besides being open to attack by fish and various predaceous aquatic insects, Anopheles are frequently the victims of parasites. Among such may be mentioned acarid ectoparasites, an encysted trematode, nematodes, gregarines, flagellates of the genus Leptomonas, and at least one species of Nosema. They are also liable to invasion by certain fungi. IX] MALARIA IN RELATION TO MAN 145 The part played by Anopheles in the transmission of malaria is often distinctly modified by the method of life and customs of man. Thus the type of dwelling may be such as to minimize the chances of Anopheles obtaining human blood or, on the other hand, to greatly favour such a chance. Thus, the introduction of glass windows into English houses may well have hastened the disappearance of malaria from this country. Again, communities, by housing cattle or other domestic animals, often favour the occurrence of Anopheles, whilst the amount of clothing worn and special modes of livelihood, may similarly affect the prevalence of malaria. Malaria in Relation to Man. So long as man was supposed to be the victim of animal- culae, that before entering his body lived a free life in marsh water, etc., the part man himself played in the continuance and preservation of the parasite was not considered. But as we now understand the rationale of malaria transmission, it is evident that man, no less than the mosquito, is essential to the continued life of the parasite, and the nature of man's influence as a host is at least equal in importance to those circumstances we have discussed in the previous section. It will be evident from what has already been said that it is man and not the mosquito which forms the chief reservoir of infection. A man once infected, even though no longer exposed to re-infection, may harbour the parasite for years. So long as he does so, and is liable to relapses with the formation of gametes, such a man is capable of infecting mos- quitoes and of restarting active transmission of the disease. The ability to maintain a prolonged state of infection in man is therefore a very valuable asset to the parasite, and all con- ditions which favour or are adverse to a maintenance of the parasite in the blood of man are of epidemiological importance. Similarly, the amount of infection passed on to the mosquito has been shewn to be an important matter, a mosquito which has taken in blood containing many gametes being capable of giving rise to a much more severe infection than one which H. B. F. I0 146 MALARIA IN RELATION TO MAN [CH. has taken in but a few parasites. Thus questions of suscepti- bility and immunity, whether natural or acquired, or due to the use of drugs, have to be considered. Also the condition of nutrition of the members of a community, and its effect on the natural resistance of the human organism against the parasite, and the extent to which influences favourable to relapses prevail, are all factors in the epidemiology of malaria. Susceptibility to malaria may be evidenced either by in- creased liability to infection, or by the degree to which toleration of the presence of the parasite exists. In the case of primitive and aboriginal races there is evidence to shew that apart from any possible lessened liability to infection, there is often a greater degree of toleration than is exhibited, for example, in Europeans. A real immunity with a lessened liability to infection is also undoubtedly developed in those persons long exposed to malarial infection. When in any race toleration and immunity are well marked, a considerable degree of malaria may occur in a latent form. In such cases susceptible strangers suffer far more than the native residents. The importance of the part played by susceptibility and immunity in malaria was demonstrated by Koch at Stephansort in New Guinea, where, at the time his observations were made, malaria was very prevalent. Koch was able to shew that after a batch of Chinese immigrant coolies, who formed a large portion of the population, had been resident for some years in the colony they suffered distinctly less from malaria than they did on their first arrival, and that in the absence of fresh immigration, malaria amongst the community, as a whole, shewed a steady decline, but with each successive large immigration of new coolies there was a marked recrudescence of the disease. These observations of Koch establish a principle in malarial epide- miology which may be termed the law of non-immune immi- gration (Christophers and Bentley), and which applies to all immigration of susceptible individuals into a malarial focus. Where the number of strangers is small, the effect is chiefly exhibited upon them, as in the case of Europeans residing in Africa. Here, as shewn by Stephens and Christophers, the whole epidemiological outlook as regards the European is IX] MALARIA IN RELATION TO MAN 147 dominated by the presence of a more or less latent native malaria. Where the influx of strangers is comparatively very large, the whole community is adversely affected, and under certain circumstances the prevalence of malaria through a whole tract of country may be greatly increased. Since the new-born child is, in a sense, an immigrant, in any community the young children are especially affected. Where malarial infection is intense, but the population is stable and possibly possesses a certain degree of racial tolerance, the amount of infection is highest in the young children and at a minimum in the adults. In this case the children go through life more or less permanently infected and with a certain amount of splenic enlargement. At about the age of puberty, they cease to shew parasites in their blood, or to exhibit enlarge- ment of the spleen. Where malaria is more or less seasonal in its occurrence, or where there is any serious degree of immigration or shifting of populations, the restriction of infection to children is less marked. All grades of difference in this respect may be en- countered, the usual rule being that strictly indigenous and primitive tribes shew the greatest amount of tolerance, and along with a high proportion of infection amongst children, exhibit the greatest adult immunity from infection. Recently much stress has been laid upon the influence of economic factors in determining a high or a low degree of malaria prevalence. Poverty stricken and squalidly living communities in malarious countries usually exhibit a far greater degree of malarial infection than do communities in a condition of prosperity. Besides the " social " distribution of malaria, very grave manifestations may be brought about at least partly by conditions of general stress, such as the occur- rence of famines or scarcity following failure of rainfall, especially when this is followed by floods still further adding to the distress and supplying all the requisites for an active transmission of the disease by Anopheline mosquitoes. Thus, in Denmark, epidemics of great severity have frequently followed great storms, which had led to extensive inundations associated 10 — 2 148 PREVENTION OF MALARIA {CH. with much hardship, and a similar condition has been described in India, where, during exceptional monsoons, many large rivers overflow their banks, causing extensive inundations. Under such conditions malaria may prevail with such intensity as to cause a mortality with which it is not usually associated, and may equal or exceed the ravages of even bubonic plague. Besides purely economic influences, the prevalence of malaria is often greatly enhanced in a community, or even in a population, by circumstances leading to unusual conditions of labour, increased physical fatigue, exposure to the sun and to rain. In such cases the mere production of relapses alone may lead to a greatly increased prevalence of malaria, but where Anopheles are present there is naturally associated with an increased output of parasites an increased transmission of the disease. Malaria may from such reasons be greatly increased during certain seasons, e.g. the rainy season in the Canal Zone, even though the number of Anopheles has not been increased. An increase of malaria during the harvests is another familiar example. Where unusual exposure and hardship are associated with inadequate food and general distress, the result is usually for malaria to assert itself in a very grave form, even though the conditions as regards Anopheles are not especially favourable. The Prevention of Malaria. Under present-day conceptions there can be no transmission of malaria under any of the following conditions : 1. Absence of Anophelines, by which infection would be conveyed. 2. Absence of infected persons in the community, from whom infection could be obtained by the mosquitoes, even if these were present. 3. The existence of adequate " protection " by means of which either (a) The healthy cannot be bitten. (b) The infected cannot be bitten. IX] OBLITERATION OF BREEDING PLACES 149 Preventive action therefore aims at bringing about more or less perfectly one or more of these conditions. Theoretically any one of the three, if completely realized, would suffice to prevent any fresh transmission of malaria, and finally to ex- terminate the disease. Unfortunately in practice it is usually possible only very imperfectly to achieve the desired end in any of these directions, and it becomes necessary to combine the effects of as many methods as possible. Circumstances alone can determine in any given case which line of action is most called for, or what combination of methods is likely to be most effective. Under the first head come all measures which have as .their object the reduction in the number of Anophelines present. Such action may be direct, as in the case of anti-mosquito campaigns, or indirect as by the extension of agriculture, or large drainage measures. Under the second head come various methods of quinine prophylaxis, all agreeing in the use of quinine as a destroyer of the parasite in the human host, but differing a good deal in the immediate object arrived at. Under this head also come certain measures applicable to mixed communities as the " Removal or prophylactic treatment of the reservoir of infection," " Segregation of the healthy," and the avoidance by the individual of sources of infection generally. Under the head of protection are included such measures as the screening of dwellings and barracks, the use of suitable protective clothing, and the use of the mosquito net. i. Many methods of attacking Anopheles are now known, the more important being : The obliteration of breeding places. By minor drainage measures, filling up pools or depressions with earth and, in some cases, subsoil drainage, pools utilized by Anopheles for breeding may be completely done away with. In cases where it is difficult or impossible to carry out such action, breeding places may be made less suitable by clearing out weeds, deepen- ing, and perhaps even lining with masonry, the edges of large sheets of water. Not infrequently the chief sources of Anopheles are to be found in connection with small streams, in which case training in some form or another should be performed. Where • B Fig. 44. Indian fish of utility as mosquito- destroyers. Chaudhuri (from the Tropical Diseases Bulletin). A ( rf ) and B ( $ ). Lebias dispar (nat. size). C. Nuria danrica (nat. size). After Seweli and CH. IX] LARVICIDES wells are an important source of Anopheles they often require special devices to prevent them being a source of danger whilst allowing water to be obtained from them, and other breeding places of a special nature may require special measures to deal with them. On the whole the most important consideration in such measures is that the action taken should be of as per- manent a nature as possible. The use of larvicides. Many substances have been experi- mented with in respect to their lethal effect upon the larvae of mosquitoes. The larvicide in most general use is some form of kerosene or mixture containing this substance. The oil floats on the surface of the water and thus interferes with the respiration of the larvae and pupae. Certain aniline dyes, and other chemical bodies which dissolve in the water, have very powerful larvicidal properties, and their use has been suggested. The chief difficulty with regard to all larvicides is the temporary nature of the effect they produce, and the necessity for regular and periodical treatment of the breeding places attacked in this way. Ordinarily such substances are now used only where more permanent measures are not possible. The introduction of natural enemies. So far the hope that by the introduction of some natural enemy, the number of Anopheles in a country could be at all affected, has not met with much encouragement. Nevertheless, under certain cir- cumstances, the use of suitable small fish has an application. The most effective larvae-eating fish for the most part belong to the family Cypriondontidcz, but species of Anabas, Ophio- cephalus and others are also of practical use in this respect. Measures directed against the adult mosquito. The fumigation of houses with burning sulphur, pyrethrum and other sub- stances, has been found of use. In Panama the catching of adult mosquitoes by children for a small reward is said to be very effective. Whitewashing and improvement in lighting during the daytime may be called for sometimes. The various measures briefly outlined above are but some of the tools in the hand of the sanitarian, to be used as circum- stances require them. Before they can be applied with success it is almost always necessary for the conditions relating to Fig. 45. Indian fish of utility as mosquito-destroyers. Chaudhuri (from the Tropical Diseases Bulletin}. A. Haplochilus panchax (nat. size). B. Ambassis ranga (nat. size). C. Trichogaster fasciatus (nat. size). After Sewell and CH. IX] QUININE PROPHYLAXIS 153 transmission to have been very thoroughly studied and the whole area accurately and thoroughly surveyed. Of measures indirectly affecting the prevalence of Anopheles, the most important are " drainage " and " agriculture." The drainage of marshes, lakes, etc. has long been known to have a favourable effect upon malaria. Agricultural operation, by which waste lands are reduced to the condition of tilled fields, is another general measure having a very definite influence upon malaria. Both these measures, though they do not aim directly at mosquito reduction, bring about this result indirectly by lowering the level of the subsoil water, lessening humidity and so forth. A measure of this general kind, which may assume importance under certain circumstances, is protection against flooding. It has recently been shewn that some of the worst manifestations of epidemic malaria follow in the wake of floods, arising from the overflowing of rivers and swollen mountain torrents. In such cases various engineering devices may be important anti-malarial measures of this general kind. 2. Where preventive action against malaria takes the form of attacking the parasite in the human host it usually consists of some method of quinine prophylaxis. In the method advocated by Koch an attempt is made to sterilize, as far as the malarial parasite is concerned, the blood of every member of the community by systematically searching out and treating every infected person. The method to which the term quinine prophylaxis is generally applied, is one in which as many of the community as possible are persuaded to take quinine regularly and systematically. Where large and at the same time poor and ignorant populations are concerned, it has generally been found impossible to apply either of the above measures sufficiently thoroughly to be effective, and it is now recognized that under these circumstances the greatest benefits are obtained by treating the sick and encouraging in every way the use of quinine in its curative rather than its prophylactic capacity. This method is usually designated as quinine treatment of the sick. Though directed especially to the saving of life, it has been found also to have a general influence upon malaria. 154 SEGREGATION [CH. In addition to this direct action of quinine upon the source of infection in man, there are a number of indirect methods of reducing the sources of infection. 3. (a) Very often where mixed communities are con- cerned, it may be desirable to protect especially the more susceptible class of individuals. When possible this is brought about by some form of segregation. Where the reservoir of virus is small in comparison with the community of susceptibles, as frequently happens in Algerian stations, segregation takes the form of removal of the indigenous community to a short distance from the station. Where the number of the suscep- tible persons is small in comparison with the reservoir, as is usual in the case of Europeans in Africa, it is advisable to build quarters for this community at some distance from the native settlement. In some cases it may be desirable to undertake measures against malaria in a small community acting as a " reservoir," not so much for the direct effect upon this com- munity, as for the indirect effect upon the larger susceptible community surrounding it. In this way, the actual application of segregation may vary, though the principle remains the same. Still another indirect method of diminishing the amount of human infection, and thus reducing the activity of malaria transmission, is the protection of a community from influences likely to bring about repeated relapses. For example, among labourers or convicts, or even among agricultural people, any amelioration of the conditions under which they are living may be looked upon as an anti-malarial measure coming under this head. (b) Protection against the bites of Anopheles by the screening of dwellings with wire gauze, etc. is a measure which has been found especially valuable in Panama and elsewhere. The protection brought about by the habitual and careful use of a mosquito net is perhaps the most effective measure of private prophylaxis known against malaria, and with some other minor precautions is quite sufficient to enable the educated individual to enter the most malarious tracts unharmed. The use of mosquito nets by the sick is a valuable prophylactic IX] PLASMODIUM VIVAX 155 measure in hospitals, where in the absence oi any such pre- caution the dissemination of malaria may result from the bringing together of many cases of the disease. DESCRIPTIONS OF THE THREE PLASMODIA CAUSING MALARIA. I. Plasmodium vivax (Grassi and Feletti, 1890) and Tertian Malaria. SYNONYMS : Oscillaria malaria Laveran, 1881, pro parte. Hcemosporidium tertianum Lewkowicz, 1887. Plasmodium var. tertiana Golgi, 1889. Hcemamceba vivax Grassi and Feletti, 1890. Plasmodium malarice var. tertiana Celli and San Felice, 1891. Hcemamceba laverani var. tertiana Labbe, 1894. Plas- modium malarice tertianum Labbe, 1899. Hcemamceba malarice var. magna Laveran, 1900. Hcemamceba malarice var. tertiance Laveran, 1901. Plasmodium tertiance Billet, 1904, pro parte. Description. The young trophozoite appears in the red blood corpuscles as a very actively amoeboid body about 1-2 /a in diameter. It is much more active than the other two species of malarial parasites and it was because of this feature that the specific name vivax was applied to it. The young trophozoite very . soon assumes the ring form, and by means of its pseudopodia and the large amount of exposed surface, it grows rapidly at the expense of the contents of the red cell. The latter becomes pale and swollen, and on staining with Giemsa its protoplasm presents certain degeneration phenomena, taking the form of scattered red granules, known as Schuffner's dots. The presence of these dots in the proto- plasm of the infected red cells generally serves to distinguish P. vivax from the other malarial parasites, but similar ap- pearances occur in the red cells of dogs infected with Babesia (Piroplasma] canis. As the trophozoite grows, melanin is formed and deposited in the form of fine rods scattered throughout the cytoplasm of the parasite. The period of growth occupies about 30 hours, by which time the trophozoite almost fills the corpuscle, the fully formed schizont being 8 -5-10^ in diameter. 156 PLASMODIUM VIVAX [CH. From the thirtieth to the forty-eighth hour the schizont divides up into from 15 to 20 merozoites, or rarely as many as 24. The stages in this process have been described above, but it may be well to repeat that all the melanin, together with a certain amount of waste protoplasm is left unused. The melanin granules are packed together in the form of one or two conspicuous brown masses, usually situated at the middle of the parasite. The merozoites are somewhat irregularly arranged, often in two concentric circles ; rosette forms, such as occur in P. malaria and P. falciparum, are absent. About the forty-eighth hour the wall of the red cell bursts open and the contained merozoites together with the melanin and other waste products are liberated in the serum. The cycle of schizogony therefore occupies 48 hours, and in conse- quence the febrile attacks recur after this interval. In P. vivax the gametocytes are common in the peri- pheral circulation as well as in the internal organs, and con- sequently their development can be followed without much difficulty. The macrogametocytes are large spherical bodies about i2-i6yu- in diameter, and in addition to their size may be distinguished from the schizonts by their denser protoplasm and larger and more numerous melanin granules. The nucleus is usually situated at the periphery and is an oval structure containing numerous chromatinic granules. The microgameto- cytes are similar in shape to the macrogametocytes, but are much smaller (9-11 /^), and in addition may be distinguished from the latter by their large densely staining nucleus. In addition, the cytoplasm is very much lighter and less granular. Both the kinds of gametocytes originate from ordinary merozoites, but during their development can be distinguished from the schizonts by their much slower growth and absence of active amoeboid and ring forms. The development of P. vivax in the mosquito was first worked out in Anopheles maculipennis, one of the common mosquitoes of Europe, but many other species are known to transmit the infection equally well. When ingested by the mosquito, the development of the gametes will not take place below 16° C., IX] LIFE-CYCLE 157 but the most favourable temperature is much higher (24- 30° c.). The microgametocyte gives rise to 4 to 8 microgametes, and the macrogametocyte undergoes division of the nucleus and extrusion of a polar body before becoming a macro- gamete ready for fertilization. After this process has taken place, the male and female pro-nuclei are said to remain apart for some time before uniting to form the single nucleus of the ookinete. At a temperature of 28° C. the latter has penetrated the gut -wall and become an oocyst by the end of about 40 hours after the mosquito's feed. At this stage the oocyst is an almost transparent spherical body containing thin brown strands of melanin, and is surrounded by a well- defined wall. The nucleus has already commenced to divide and several daughter-nuclei are scattered through the cyto- plasm. The following day the oocyst increases in size and the sporo- blasts begin to separate off from each other. The melanin is aggregated together into clumps lying between the sporoblasts. On the fourth day the oocyst is now seen to contain well-defined sporoblasts, each of which is covered by the growing sporo- zoites. During the fourth and fifth days the oocyst still continues to grow, attaining a diameter of about 50^ and projects outwards into the coelom of the insect. The sporo- zoites become completely formed and thus the oocyst is trans- formed into a hollow sphere containing innumerable sporozoites each about 14 ^ in diameter. About the seventh or eighth day the cyst ruptures and the numerous sporozoites are liberated into the ccelomic fluid. From here large numbers find their way to the salivary glands, but some of them bore into the developing eggs in the ovary. The fate of these latter is un- known, for up to the present, beyond this fact, there is nothing to support the view that the infection is transmitted to the offspring of an infected mosquito. The above cycle of sporogony is thus complete in about eight days, under these favourable conditions of temperature, and after the sporozoites have entered the salivary glands the mosquito becomes infective. At lower temperatures the 158 PLASMODIUM MALARLE [CH. development is very much prolonged and consequently the mosquito does not become infective until after a much longer incubation period. The length of time that a mosquito remains infected has never yet been proved, but it is probably for the remainder of its life! Distribution. ' This species is widely distributed throughout the world, occurring in most tropical and subtropical regions. It also occurs somewhat scantily in Northern Europe below 60° north latitude. As a result of successful mosquito campaigns and other prophylactic measures the distribution of the disease is being restricted, and it has been eradicated from some parts of the world. Tertian fever or ague was formerly prevalent in Britain and it is interesting to note that one or two isolated cases of malaria in patients that had never left England have been recorded within the present century. Consequently the con- ditions for the transmission of the disease have not yet entirely disappeared from this country. II. Plasmodium malaria (Laveran, 1881) and Quartan Fever. SYNONYMS : Oscillaria malaria Laveran, 1883. Plasmo- dium var. quartana Golgi, 1890. Plasmodium malaria var. quartana Celli and San Felice, 1891. Hamamceba malaria Grassi and Feletti, 1892. Hamamceba laverani var. quartana Labbe, 1894. Hamosporidium quartana Lewkowicz, 1897. Plasmodium malarice quartanum Labbe, 1899. Hamomonas malaria Ross, 1900. Hamamceba malaria var. magna Laveran, 1900. H. malaria var. quartana Laveran, 1901. Plasmodium golgii Sambon, 1902. Plasmodium quartana Billet, 1904. Laverania malaria Jancso, 1905. Description. The young trophozoite is somewhat smaller than that of P. vivax, and also much less active. The pseudo- podia are usually blunt, so that the parasite is rather com- pact in appearance. The pigment is deposited in the form of very coarse darkly-coloured granules, or rodlets, which are IX] LIFE-CYCLE 159 commonly gathered at the periphery of the parasite. In contra- distinction to the granules of the other species of malarial parasites, those of P. malarice are non-motile. A vacuole is formed, but is comparatively small and disappears during the growth of the trophozoite. The presence of the parasite in the red cell does not produce any evident changes in the cor- puscle beyond a slight decrease in size and a darker colour. The trophozoite takes about 60 hours to grow up into the mature schizont, which is a somewhat angular body 6-7 /x- in diameter. During the next 12 hours the nucleus of the schizont divides up into 6-12 smaller ones, which become arranged in a single circle at the periphery. Each becomes surrounded by a mass of cytoplasm which separates off from its neighbours and thus a regular circle of 6-12 merozoites is formed. The pigment granules form a dark clump at the centre and as the merozoites radiate from it, a very typical rosette appearance is produced. The merozoites (about i'75^ m diameter) are now set free by the rupture of the corpuscle and may enter another red cell and repeat the cycle. More often, however, they seem to be killed off by the phagocytes, and thus it is only rarely that this parasite produces fatal effects in its host. The whole of the above cycle takes place in the peripheral blood, and occupies 72 hours. Accordingly the fever which is caused by this parasite occurs every fourth day (hence the name Quartan Fever) after the schizogony takes place. In addition to the simple quartan fever in which the attacks recur every fourth day, cases of double and triple quartan are ^Iso met with. In double quartan fever the attacks recur on the first, second, fourth, fifth, seventh, eighth days, etc. This is merely a case of a double infection, and the parasites being the descendants of two separate lots of sporozoites, are at different stages of development. The first infection will undergo schizogony on the fourth, seventh, tenth days, etc. after the entry of the sporozoites, whilst if the second infection occurs on the day following any of these attacks the latter l6o PLASMODIUM FALCIPARUM [CH. parasites will complete their cycle of schizogony every 72 hours from this date onwards, i.e. on the fifth, eighth, eleventh days, etc. The result of such a double infection will be the occurrence of febrile attacks on two successive days followed by an interval of one day, and to this type of fever the term Double Quartan is applied. In the same way a patient may again become infected on the only day on which schizogony is not taking place, and after this last infection has developed will shew a rise in temperature every day. This type of fever is known as Triple Quartan Fever ; it may be distinguished from the other kinds of malaria by the shape of the parasites. III. Plasmodium falciparum (Welch, 1897) and Quotidian, Malignant Tertian, or ^stivo-Autumnal Malaria. SYNONYMS : Oscillaria malaria Laveran, 1881, pro parte. Hcemamceba pracox Grassi and Feletti, 1890. Hamamceba malaria pracox + H . malaria immaculatum Grassi and Feletti, 1890. Laverania malaria Grassi and Feletti, 1890. Plasmo- dium malaria var. quotidians Celli and San Felice, 1890. Hamosporidium undecimana Lewkowicz, 1892. H. sedeci- mana Lewkowicz, 1892. H. vigesimotertiana Lewkowicz, 1892. Hamamceba laverani Labbe, 1894. Hamatozoon falci- parum Welch, 1897. Hamamonas pracox Ross, 1899. Plasmo- dium malaria pracox Labbe, 1899. Plasmodium pracox R. Blanchard, 1900. Hamamce.ba malaria var. parva Laveran, 1900. Plasmodium immaculatum Schaudinn, 1902. Laverania pracox Nocard and Leclainche, 1903. Description. This is the smallest of the three species of Plasmodium affecting man, the fully developed schizont being not more, than about 5^ in diameter. The young sporozoite is very small and, after penetrating a red cell, as a rule at once assumes the ring form. The latter is characteristic in appear- ance as the nucleus is always peripheral and the contours of the ring are very dark and clear. The trophozoites have the peculiarity of frequently appearing at the surface of the red cell. They are distinguished from those of the other two species of IX] LIFE-CYCLE l6l malaria by their active amoeboid movements. The tropho- zoites grow rapidly and assume an oval form ; they contain a few pigment granules which are small, irregular and only feebly motile. During its growth the parasite causes an alteration in the substance of the red cell, which in stained preparations is seen to contain a number of granules known as Maurer's dots. Otherwise the erythrocyte remains unaltered in ap- pearance until the formation of the merozoites results in its destruction. The fully developed schizont is 4*5 to 5/u, in diameter, and is very rarely present in the peripheral circulation. It segments into 8-10 or sometimes 15 merozoites, which may either be arranged in the form of a rosette, or irregularly. The segmenta- tion almost invariably takes place in the capillaries of the internal organs, and when it is in process there is a tendency for the red cells to cling together and also adhere to the wall of the blood-vessel, thus causing obstruction of the circulation. The whole cycle of schizogony takes from 24 to 48 hours to be completed, and thus the febrile attacks are more or less irregular, but often occur each day. The gametocytes develop from the trophozoites in the usual manner, but are distinguished from those of the other two human species of Plasmodium by their crescentic form. The macrogametocyte may be distinguished by the arrangement of the pigment, which is usually concentrated in the neighbour- hood of the compact nucleus, leaving the remainder of the cytoplasm clear. In the microgametocyte the pigment is irregularly scattered through the cytoplasm and the nucleus is somewhat diffuse. Moreover the shape of the two kinds of gametocytes is different, being long and thin in the case of the former, and broad and somewhat rounded in the latter. The remains of the distorted red cell may be seen surrounding the " crescents," the haemoglobin often being concentrated in the form of a small clump attached to the side of the parasite. The dimensions of a fully grown macrogametocyte are about 12 / X 4... These gametocytes are very conspicuous in the circulation of patients suffering from P. falciparum, and under the name of H. B. F. II 1 62 MALARIA [CH. " crescents " were known for many years before their true nature was discovered. On being taken into the gut of a sus- ceptible species of mosquito, the gametocytes escape from the red cells and give rise to the gametes. The macrogamete is vermiform, whilst the microgametocyte becomes spherical before giving rise to the microgametes. The cycle of develop- ment in the mosquito at the most favourable temperature, 28-30° C., is complete within eight days. In this species development cannot take place below 18° C., and consequently it is only found in warm countries, the disease to which it gives rise being often known as " Malaria Tropica." The develop- ment of P. falciparum in the mosquito is more easily followed than that of the other species of malarial parasites, for when a mosquito is susceptible to this species, as in the case of A. (Myzomyia) Christopher si, practically all the insects become infected when fed on a patient suffering from this infection. In consequence of the comparatively high temperature required for the development of P. falciparum within the mosquito, the disease does not occur in temperate regions except during the summer. Usually associated with P. vivax, it is found throughout the whole of the tropics, except in regions like the Sahara, where mosquitoes are absent owing to the lack of water. LITERATURE. The more important and accessible general treatises upon malaria, and papers dealing with recent work upon epidemiology and preventive measures against malaria. fBahr, P. H. (1913). Malaria in Kurunegala. Report Colonial Office. April, 1913- fBentley (1910). Malaria in Bombay (Report). Govern. Central Press, Bombay. j-Celli (1901). Malaria according to the New Researches. Longmans, Green & Co. London, 1901. | Christophers. Malaria in the Punjab. Scientific Memoirs by Officers of the San. and Med. Depart, of the Gov. of India, No. 46. •j- Malaria in the Andamans. Ibid. No. 56. Christy. Mosquitoes and Malaria. Good elementary account. Craig (1909). The Malarial Fevers, Htsmoglobinuric Fever and the Blood Protozoa of Man. t Works representative of the more recent lines of investigation on malaria. 1 1 42 S g •j? 73 Tj 3 0 0 miit S cj O S ^0 3 Q • '5 •sl •flj-d 1 o'gjco g 73 J2 o CT1 "*•** * ,£ rt .23 w 1 d "1 III 1 ?2 ?- S .-= o 1 ft] S *o CD 6 _rt O 'PJ O O ^H Jj to '_p rt rt ti *-* 12 c • A M-t ZQ £4» Contou mover Round radius CO j^> II rt 1 of'i^ Q1 O 41 'In ^ M (j O H o S-g, o « o- a ^ CD Jo 3 ' d p 1^1 8 c _!_, "" bo C3 O -M cj d O ,3 co if ill 1 d •s indistinct ; nents active d oj 43 1 .n the form of y motile •4-> ^ 0) o rt F^ CO 0 g ||1 ||a 2 73 2 ,| 1 «O OH OO w OT •* 0 'En .§ 'to 3 CD «! 1-d a I •at; -*-> d ijn CD co : 3 2 w "" c" d S o S ^ rt CD O p> * 0 rt K ^^ H ; amoeboid w 1 /n 1 3 bo I "" ^J 13 >^^3 .-, lffl'3.| 'a^.s| 1*1 8 s ; present irculation • £ o •^ ••'" Q a C 4J bO So i-* CO &; Contours very sharj movements very s' Quadrilateral — sma normal red cell 1| i H "2? P Contracted, and i than the norma! staining one canno any protoplasmic Distinct rosette for in the peripheral C^ C3 VH HO 3 'C o ^ « ^H o ^ N "a. _g c I t •a I 2 6 S 3 cd fc O II IX] LITERATURE 163 Darling (1910). Factors in the Transmission and Prevention of Malaria in the Canal Zone. Annals Trop. Med. and Parasitology, iv. part 2. Droderick (1909). A Practical Study of Malaria. Saunders & Co. Philadelphia. Grail and Marchoux (1910). Traite de Pathologie Exotique. Bailliere et fils. Paris. Hirsh (1883). Handbook of Geographical and Historical Pathology. New Sydenham Society. Vol. i. *Laveran (1907). Traite du Paludisme. Masson & Co. Paris. Liihe (1906). Article on Blood Protozoa in Mense's Handbuch der Tropenkrankheiten. Mannaberg (1905). Malaria, in Nothnagel's Encyclopedia. English edition. fMathis and Leger (1911). Recherches de Parasitologie et de Pathologie humaines et animates au Tonkin. Masson & Co. Paris. fRoss, R. (1909). Report on the Prevention of Malaria in Mauritius. Waterlow and Sons. London. f (1911). The Prevention of Malaria. John Murray. London. Ruge, R. (1903). Introduction to the Study of Malarial Diseases- Rebman, London. f (1912). Malariaparasiten. In Kolle and Wassermann's Hand- buch (a comparatively short but very complete account). fSergent, Ed. and Et. Campagne antipaludique en Algerie, etc. Annals de I'lnstit. Pasteur. Jan. 1903, Feb. and Mar. 1904, April and May 1906, Jan. 1907, May 1908, and Campagne antipaludique (Gov. gen. de 1' Algerie), 1908-10. Stephens and Christophers (1907). The Practical Study of Malaria (deals with technique, Malaria Survey, etc.). t Watson (1910). Prevention of Malaria in the Federated Malay States. University Press, Liverpool. *Ziemann. In Mense's Handbuch, 1906. Vide also : \A tti delta Soc. per gli studi della Malaria. Annual volume. 1899-1908. ^Malaria. Vols. i and n, now discontinued. \Paludism. Nos. 1-5. t Various articles in Ross's Prevention of Malaria. The more important publications dealing with the question of transmission of malarial parasites by particular species of Anopheles. Adie (1903). A note on Anopheles fuliginosus and Sporozoites. Indian Med. Gazette, xxxvm. p. 246. Adie, Mrs (1911). Ne. Willmori, a proved carrier in nature. Paludism, No. 3. Banks (1907). Experiments in Malarial Transmission by means of M. ludlowi. Philippine Journal of Science, B. vol. n. No. o, p. 513. * Complete treatises dealing minutely with every side of the subject. f Works representative of the more recent lines of investigation on malaria. II — 2 164 MALARIA [CH. Bastianelli and Bignami (1899). Atti d. Soc. per gli studi d. Malaria, i. p. 28. Bastianelli, Bignami and Grassi (1898). Atti d. R. Accad. dei Lincei, vii. p. 313. Bentley (1911). Myzomyia rossi and Malaria. Paludism, No. 2. (1911). The Seasonal Malarial Infection of M. stephensi in Bombay. Paludism, No. 2. (1912). Malaria in Bombay. Gov. Central Press, Bombay. Billet (1903). Sur un Espece nouvelle &' Anopheles (A. chaudoyei) et sa relation avec le paludisme a Touggart. C. R. Soc. Biol. LV. p. 565. Christophers (1912). Malaria in the Andamans. Sci. Memoirs by Officers of the San. and Med. Departs, of Gov. of India, No. 56. Cruz (1910). Prophylaxis of Malaria in Central and Southern Brazil. In Ross's Prevention of Malaria. Daniels (1900). Development of Crescents in the small dark Anopheles prevalent in British Central Africa. Reports to Mai. Com. of R. S. Ser. v. (1909). Mosquitoes in the Federated Malay States. Studies from the Institute for Med. Research (Fed. Malay States], vol. in. Darling (1909). Transmission of Malarial Fever in the Canal Zone by Anopheles Mosquitoes. Jour. Amer. Med. Assoc. LIU. p. 2051. - (1910). Factors in the Transmission and Prevention of Malaria in the Canal Zone. Annals of Trop. Med. and Par. iv. part 2. Grassi (1902). Die Malaria, Studien eines Zoologen. 2. Aufl. Jena. Hill and Haydon. Annals of the Natal Government Museum. Hirshberg (1904). An Anopheles mosquito which does not transmit malaria. The Johns Hopkins Hosp. Bull. Feb. 1904. James (1902). Malaria in India. Sci. Memoirs by Officers of the San. and Med. Departs, of the Gov. of India, No. 2. James and Liston (1911). The Anopheline Mosquitoes of India. Cal- cutta. Jancso (1904). Zur Frage der Infektion der Anopheles claviger mit Malariaparasiten bei neiderer Temperatur. Cent. f. Bakt. xxxvi. p. 624. - (1905). Der Einfluss der Temperatur auf die geschlechtliche Generationsentwicklung der Malariaparasiten, etc. Cent. f. Bakt. xxxviu. p. 650. Kinoshita (1906). Uber die Verbreitung der Anophelen auf Formosa und deren Beziehung zu der Malariakrankheiten. Arch. f. Schijfs- u. Tropen-Hyg. x. p. 708. Koch (1899). X)ber die Entwicklung der Malariaparasiten. Zeit. f. Hygiene, xxxii. Liston (1908). The present Epidemic of Malaria in the Port of Bombay. Jour. Bombay Nat. Hist. Soc. 15 Nov. Lutz (1903). Waldmosquitos und Waldmalaria. Cent. f. Bakt. xxxm. p. 282. Macdonald (1910). Malaria in Spain. In Ross's Prevention of Malaria. IX] LITERATURE 165 Newstead, Button and Todd (1907). Insects and other Arthropoda collected in the Congo Free State. Annals of Trop. Med. and Par. i. p. 10. Patton (1905). The Culicid Fauna of the Aden Hinterland. Jour. Bombay Nat. Hist. Soc. p. 623. Ross (1908) . Report on the Prevention of Malaria in Mauritius. London. (1910). The Prevention of Malaria. London : John Murray. Ross, Annett and Austen (1900). Report of the Malaria Expedition of the Liverpool School of Tropical Medicine. Memoir u. Schaudinn (1904). Die Malaria in dem Dorfe " St Michele di Lerne " in Istria, etc. Arb. a. d. Kaiserl. Gesundh. xxi. p. 403. Schiiffner (1902). Die Beziehungen der Malariaparasiten zu Mensch und Miicke an der Ostkiiste Sumatras. Zeits. f. Hygiene, XLI. p. 89. Sergent, Ed. and Et. (1905). Anopheles algeriensis • et Myzomyia hispaniola convoient le Paludisme. C. R. Soc. Biol. LIX. p. 499. (1908-10). Campagne antipaludique en Alge"rie. Ann. Inst. Pasteur, vols. xxu. and xxiv. Staunton (1913). The Anopheles Mosquitoes of Malaya and their Larvae, with some notes on Malaria-carrying Species. Jour . of the London School of Trop. Medicine, vol. n. Stephens and Christophers (1899-1902). Reports to the Malaria Com- mittee of the Royal Society, i-vm. (1907) The Practical Study of Malaria. University Press, Liverpool. Tsuzuki (1902). Malaria und ihre Vermittler in Japan. Arch. f. Schiffs- u. Trop.-Hyg. vi. pp. 9, 285. Van der Scheer and V. Berlekom (1900). Malaria and Mosquitos in Zealand. Brit. Med. Jour. i. p. 202. 26 Jan. 1901. Vogel (1910). Myzomyia rossi as a Malaria Carrier. Philippine Jour, of Science, vol. v. No. 3, p. 277. Watson (1910). The Prevention of Malaria in the Fed. Malay States. University Press, Liverpool. CHAPTER X •CULICIN.E The main characters of the Culicinae have already been described in Chapter VIII and therefore we shall at once proceed to a description of by far the most important member of the group, namely, Stegomyia fasciata, notorious as one of the commonest domestic mosquitoes and also for the part it plays in the transmission of Yellow Fever. i66 STEGOMYIA FASCIATA [CH. Stegomyia fasciata (Fabricius, The Tiger Mosquito. Synonyms: Culex fasciatus Fabricius, 1805. C. calopus Meigen, 1818. C. frater Desvoidy, 1827. C. tceniatus Wiedemann, 1828. C. konoupi Brulle(?), 1832. C. viridifrons Walker, 1848. C. annulitarsis Macquart, 1848. C. excitans Walker, 1848. C. inexorabiHs Walker, 1848. C. formosus Walker 1848. C. exagitans Walker, 1856. C. impatibilis Walker, 1860. C. bancroftii Skuse, 1886. C. mosquito Arribalzaga, 1891. C. elegans Ficalbi, 1896. C. rossii Giles, 1899. Stegomyia fasciata Theobald, 1901. Description. In addition to possessing the characters of the genus (p. 109), according to Theobald this species may be distinguished by the following features : "Thorax dark-brown to reddish-brown, with two median parallel pale lines and a curved silvery one on each side, a small line in front between the two median ones. Abdomen black, with two white basal bands and lateral spots. Legs black, with basal white bands, last joint of hind-legs pure white." (Theobald.) The female has a head densely covered with broad flat scales, which are black and grey on each side. There is a white patch on each side and another Fig. 46. Stegomyia fasciata, adult female ; enlarged. (After Howard.) 1 According to Howard, Dyar and Knab (1913) the correct name of this species is Aedes calopus. X] DESCRIPTION 167 in the median line extending from in front back to the neck. The scales at the back of the head are in the form of long black bristles and project forward. The eyes are black surrounded by a white border and sometimes contain white patches. The antennae are brown, excepting the basal segment, which is black with a patch of white scales on its inner side. They are longer than the proboscis and have a banded appearance. The proboscis is brown, almost black towards the extremity, but lighter about the middle. The palps are black, and only about one-third the length of the proboscis ; each is composed of three seg- ments covered with large flat scales, those of the first two being brown, and silvery-white on the last segment. The dark-brown thorax is covered with reddish-brown, pale-golden and cream-coloured scales and is ornamented with various white spots and lines. In front, near the neck, there is a white spot on each side. The dorsal surface has a white, broad curved band on each side extending from the anterior edge of the thorax and curving inwards about the middle of the mesonotum, from which it is continued backwards as a thinner pale line to the scutellum. Between them are two parallel pale lines extending about half way across the mesonotum and on to the scutellum, and anteriorly is a short white line between these two. The scutellum has a thick row of white scales and also three tufts of bristles. The metanotum is brown. The pleurae are dark-brown with several patches of white scales. There is much variation in both the size and colour of the thoracic scales and many of the varieties have been described as distinct species. The arrangement of the ornamentation is however very constant and will serve to distinguish fasciata from any other species of the genus Stegomyia. The abdomen is brownish-black, circled with a white band at the base of each segment ; the posterior four bands before the last one are more or less tinged with yellow. There is a triangular white spot on the sides of each segment, and in addition the first segment is almost covered with cream- coloured scales and edged with pale hairs. The legs are brown, circled with white. The coxae are yellowish. The femurs are yellowish towards the base, brown towards the apex, but with white scales on the ventral surface, and finally the extreme tip is pure white. Those of the third pair are swollen at the extremity. The tibiae are black. The metatarsi have basal white bands. The fore tarsi have the first joint basally white and the rest black ; the mid tarsi are the same. The hind tarsi are all basally white except the last joint, which is white, and the penultimate segment, which is white with the exception of a black apex. The claws of the first two pairs of legs are toothed and those of the hinder pair without teeth. The wings are clear, unspotted, a little longer than the abdomen, with brown scales, those of the lateral nervures being very long and narrow, and of the median, short and broad. The first sub-marginal cell is longer and only slightly narrower than the second posterior cell, and the base of the former is a little nearer the base of the wing than the latter. The posterior cross-vein is about one and a half to twice its length distant from the mid cross-vein. The latter unites with the supernumerary forming a very obtuse angle, almost straight. The balancers are ochraceous and sometimes the knob is slightly fuscous. The length is 3-5 to 5-0 mm. i68 STEGOMYIA FASCIATA [CH. The male is darker than the female. The head is black with white scales in front and in the middle. The antennae are brown, marked with paler bands, sometimes almost white. The proboscis and palps are black, the latter possessing four white basal bands. The thorax is marked in the same way as the female, but the scales are more silvery and the markings more distinct. The first segment of the abdomen is covered with cream-coloured scales, the bases of the second to the fifth with white, and the fifth to the eighth have clear white lateral spots. The latter also occur on the sides of the anterior segments. The claws of the fore-legs are unequal, the larger one being toothed and the smaller, simple ; those of the mid-legs are simple, and unequal ; the hind claws are equal and simple. The genital armature is of the usual form. The length is 3*0 mm. to 4^5 mm. Fig. 47. Stegomyia fasciata, adult male; enlarged. (After Howard.) Habitat. This is one of the commonest species of mosquitoes and is widely distributed throughout almost all tropical and subtropical regions. Although sometimes occurring in tem- perate countries it is essentially a tropical species, for below a temperature of 23° C. the female refuses to feed and at 20° C. loses all activity and will not oviposit. The most favourable climatic condition for its development is a humid atmo- sphere, at a temperature of 25-30° C. all the year round. HABITAT 169 In the laboratory S.fasciata may be kept alive for some time at 7-8° C., if kept in a refrigerator and thereby protected from currents of air. When exposed to a similar temperature in the open air it soon dies. At o° C. the insect succumbs in a few seconds and, on the other hand, a temperature of 37° C. is also rapidly fatal. This susceptibility to variations in temperature causes this mosquito to be confined to certain degrees of latitude, from 40° N. to 40° S., or more exactly between the two isothermal lines of 20° C. Owing to the ease with which it may be carried from one country to another by means of ships, the species is now found in most of the regions between these limits. The accompanying map (Fig. 48) represents the distribution of Fig. 48. The distribution of Stegomyia fasciata. 5. fasciata, and it will be noticed that the insect especially occurs along the coast lines and the banks of large rivers, where the requisite conditions of humidity are fulfilled. It is absent from those regions in which the temperature during the night falls so low as to be harmful to reproduction. 170 STEGOMYIA FASCIATA [CH. In addition to its susceptibility to cold Stegomyia is even more affected by dryness, especially when accompanied by heat. The insect is somewhat protected from the vicissitudes of the climate by its domestic habits, as it is generally found inside houses. In fact its fondness for houses is so great that, according to Boyce, it is never found breeding at distances of more than 50 to 100 yards from buildings. On emerging from the pupa, the imago at once flies into a house or other shelter, and generally settles down in some dark corner and, like most other blood-sucking flies, it has a great preference for dark-coloured objects. If the mosquitoes are breeding close to ships they often enter them, and in consequence Stegomyia is the commonest species found on board ship. In the old sailing ships, not only could these insects live for weeks in the cabins, store- rooms, holds, etc., but actually breed in the water that was often left exposed in various receptacles. Although modern steamers do not afford such facilities for the persistence of this insect on board, yet recently there have been cases in which live Stegomyia fasciata were found on ships that had been at sea 13 to 20 days. Feeding habits. As in the majority of mosquitoes the female Stegomyia is the only one which feeds on blood and this food is necessary before the insect is able to lay its eggs. The male, which is fully developed on emergence, does not bite, in spite of statements to the contrary. It feeds on fruit juices and also settles on the skin, to which it is attracted by the secre- tions of the body. Although the male does not actually bite, the singing noise produced by its wings is very annoying ; its note is much higher than that of the female. The female does not feed on all persons indiscriminately, but seems to exercise some choice in the selection of its victims. Thus it prefers white people to black, in spite of its fondness for dark objects. Similarly blondes are preferred to brunettes, children to adults, and fresh arrivals from temperate regions suffer more than acclimatized persons. The factors which guide the insect in the selection of its host are not known, but scent is probably the most important, after the effect of the body-heat. X] BIONOMICS According to Marchoux, who has given one of the most complete accounts of 5. fasciata, the female is entirely nocturnal in its blood-sucking habits, except for a short time after it emerges from the pupal case. Under these latter conditions the insect is so hungry that as soon as it is able to fly it sets off to find a host. Once having succeeded in obtaining a meal, the female comes to rest in some dark corner, and in future only attempts to feed towards the evening, or at night. This statement, however, as to the nocturnal feeding habits of 5. fasciata has been denied by many subsequent investigators, who agree in the view that this mosquito is mainly diurnal in its feeding habits. Although in nature blood appears to be the only food of the females, Goeldi succeeded in keeping them alive for more than three months on a diet of honey. These insects, however, were unable to lay any eggs. Length of life. In a state of captivity, female S. fasciata have been kept alive for a period of more than four months, so that their duration of life is comparatively long, but in nature, it is doubtful whether an insect would often be able to live such a long time. The occurrence of isolated cases of yellow fever long after an epidemic has ceased may be due to the persistence of infected mosquitoes or, on the other hand, to the presence of mild and unrecognized cases of the disease. The male has a much shorter life than the female, for as it feeds on the nectar of flowers, and moreover is very active, it requires to feed much oftener. As a result of its continual search for nourishment, and also for females, the male is con- tinually exposed to accidents and soon loses his protective scales. From this moment the slightest drop of moisture is sufficient to cause the suffocation of the insect. The maximum period that female 5. fasciata have been kept alive when nourished on honey is 102 days, whilst under similar circumstances males only lived for periods varying from 28 to 72 days. Fertilization and egg-laying. Copulation is usually accom- plished in the open air, especially during the warm hours of the day. The union is made when the insects are flying, only 172 STEGOMYIA FASCIATA [CH. rarely when at rest, as the two ventral surfaces are brought in apposition. The spermatozoa are stored in the spermathecae, but although a fertilized female may thus remain fertile for a long time, eventually the sperm becomes used up and another copulation is necessary before more fertile eggs can be pro- duced. The female lays the first batch of eggs a few days after taking its first meal of blood, the exact period varying accord- ing to the conditions of temperature and humidity. When these are very favourable the period may be as short as two days, but at temperatures below 20° C. the interval may be prolonged indefinitely and two or three feeds may elapse before egg-laying commences. The average number of batches of eggs laid is usually two or three, but in individual cases as many as nine batches have been observed. The eggs are extruded singly and the number laid on the first occasion is generally 60 to 90. The number of eggs comprising the subsequent batches is always less than that of the first one, this being the most important. Goeldi has found that the females usually die immediately after the final act of parturition, though in two instances individuals survived 12 and 14 days respectively. The same author also states that fertilized eggs may remain latent in the body of the female for from 23 to 102 days. A meal of blood was capable of causing the female to lay her eggs after these two periods respectively. The eggs are generally laid at night, on the surface of almost any stagnant water. They may be found in the water collected in old tins, saucepans, rain-tubs, broken bottles, holes in trees, and practically in every accumulation of water, however slight, occurring in the vicinity of the houses the mos- quito inhabits. The nature of the water seems to be indifferent, for the eggs hatch out in the most stagnant and evil-smelling water, almost as readily as in pure water. The egg. The egg consists of an ovoid body, rather more pointed at one end than the other, and is blackish in colour, dotted over with small white hemispherical particles of X] LIFE-CYCLE 173 excretory matter. In addition the egg is surrounded by a series of small air-chambers which help to keep it afloat. As each egg is laid by the female a small drop of liquid is also extruded on the surface of the water and may help to keep the egg floating, as this secretion is of somewhat oily consistency. Certainly a slight agitation of the water is sufficient to cause the eggs to sink, but development proceeds almost as well beneath the water as at the surface. In the former case, however, the eggs are more liable to the attacks of bacteria, etc. Under favourable conditions the eggs hatch out in about two or three days. In the Amazons the normal incubation period is said to be from three to eight days, but its duration depends almost entirely on the temperature. If this falls below 20° C. the eggs are unable to develop, and if the ther- mometer falls to this temperature for a few hours each day the development is greatly prolonged. The eggs are very resistant and can withstand long exposures to cold and dryness. They may be exposed to a temperature of 37° C. for one hour, or kept at o° C. for many days, without their vitality being affected. Eggs have been maintained for several months between 10° C. and 20° C. and when the tem- perature was raised, about one-twentieth of them hatched out. The most striking results, however, are those obtained with eggs that have been dried. These may be kept for three months without more than 40 per cent, of them dying. Francis has also shewn that they may remain alive for six and a half months if kept dry. Newstead describes an experiment with eggs of S. fasciata that had been sent from Manaos on the Amazon. The eggs had been laid on moist white filter paper ; they were then dried in air and subsequently for 24 hours over calcium chloride. They were then packed in tubes and sent across to England. Forty-five to 47 days later, on their arrival at Liverpool, they were placed in water at 23° C. and several larvae hatched out within 12 hours. Moreover, these larvae developed very rapidly and the adult insects emerged within 12 days. From these results it is evident that the eggs of S. fasciata under certain conditions may remain alive for considerable periods without developing. 174 STEGOMYIA FASCIATA [CH. The larva. The egg gives birth to a small, colourless, and very active larva, which occasionally swims and wriggles along the surface of the water in the same manner as certain Ano- phelines. This larva under favourable conditions grows rapidly, and after a succession of moults attains the pupal stage. Fig. 49. Larva and Pupa of Stegomyia fasciata, with enlarged parts. (After Howard.) The larva of Stegomyia may generally be distinguished by two characters, viz. its comparatively colourless appearance and the short black respiratory syphon, one-quarter the total length of the abdomen. The larvae of Culex are darker coloured X] LARVA 175 and generally possess long respiratory syphons. In addition the larvae of S. fasciata possess the following characters : The antennae are smooth, the tuft being represented by a single short hair. At the apex there is a minute but distinct second joint and a few delicate hairs. The labial plate pos- sesses one large terminal tooth and n or 12 smaller ones on each side of it. The thorax is rather hairy and bears four large chitinous hooks, two on each side. Each of these hooks gives off one or two hairs. The abdomen is very broad, and is almost the same width all the way down. The two lateral combs, situated on the eighth segment, each consist of eight to ten serrated spines, varying in size and the number of serrations. The syphon is comparatively short and stumpy, being only one-quarter the total length of the abdomen, and about two and a half times as long as its width at the base. The syphon spines vary both in number and arrangement ; they are succeeded by a triple hair. The terminal segment of the abdomen is very short and almost rectangular and bears a number of blunt bifurcate hairs. The papillae are broad and rounded ; their length is about one and a half times that of the last segment. The larvae feed on decaying organic matter, especially on nitrogenous substances. They thrive best in neutral or slightly alkaline water, and soon die if free acids are present. Although still capable of development in very brackish water, 5. fasciata cannot live in sea-water, as at least one other species of the genus (S. pseudoscutellaris) has been shewn capable of doing. After a number of moults the larva gives rise to the pupa. The duration of the larval stage at fairly warm temperatures varies from seven to fifteen days, but a temperature of below 20° C. will prolong development almost indefinitely. The young larvae are remarkably tenacious of life under water and will stand submersion for three to five hours. The fully grown larvae can still endure a submergence of at least one and a half to two hours, a property which enables them to feed at the bottom of comparatively deep water. There is no record of the live larvae of Stegomyia ever having been found in ice, as in the case of those of the allied 176 STEGOMYIA FASCIATA [CH. genus Culex. Miss Mitchell has found them in water at i° C. and states that some pupated at 12° C., but in the labora- tory the larvae generally die if the temperature falls to 10° C. It is noteworthy that these low temperatures are more fatal to the fully grown larvae than to the earlier stages. If the temperature of the water in which the mosquitoes are developing falls daily below 20° C., the duration of the larval stage may exceed a month. The adults which eventually emerge, moreover, are generally so weak and unhealthy that they are unable to feed and soon die. The pupa. The duration of the pupal stage varies from one to five days, after which the adult insect emerges. The pupae are very sensitive to cold and a fall of temperature is almost invariably fatal to them, as their organization is not adapted to withstand the vicissitudes of climate. The pupae resemble those of Culex in their general appearance. The duration of the complete life-cycle from the new laid egg to the emergence of the imago maybe as short as n days, but is usually from 15 to 20 days. A prolonged exposure to cold, on the other hand, may increase this period to as much as five months, and as mentioned above, the dried eggs are capable of living for long periods without developing. Stegomyia fasciata and disease. In addition to being one of the commonest species of mosquito occurring in the tropics, Stegomyia fasciata is entirely responsible for the transmission of " Yellow Fever." It also has been shewn capable of trans- mitting Filaria bancrofti to man, but as this parasite is more commonly carried by members of the genus Culex, the infection will be described later. Ed. Sergent and Neumann have shewn that Plasmodium (Proteosoma) pracox or relicta, parasitic in birds, will develop in 5. fasciata. Finally, Fiilleborn and Mayer, by feeding this mosquito on the blood of animals swarming with trypanosomes and subsequently, after short intervals, on normal animals, have succeeded in the mechanical transmission of Trypanosoma gambiense. It is very doubtful, however, whether in nature S. fasciata ever carries sleeping sickness, and in any case such transmission can only be very exceptional. XI] YELLOW FEVER 177 REFERENCES. Boyce, R. (1911). Yellow Fever and its prevention. John Murray. London. Francis, S. W. (1907). Observations on the life-cycle of Stegomyia calopus. Publ. Health Reports, vol. xxn. pp. 381-3. Goeldi, E. A. (1904). Os Mosquitos no Para. Bol. Mus. Goeldi (Para), vol. iv. fasc. 2, pp. 129-197. Howard, L. O. (1901). Mosquitoes. McClure, Phillips and Co. New York. - Dyar and Knab (1912). The Mosquitoes of North and Central America and the West Indies. Publ. 159. Carnegie Inst. Wash- ington. Marchoux, E. (1910). Fievre Jaune, in Chantemesse and Mosny's Traite d 'Hygiene. Bailliere et fils. Paris. Theobald, F. V. (1901-10). A Monograph of the Culicidce or Mosquitoes. Vols. i to v. Brit. Museum, London. CHAPTER XI DISEASES TRANSMITTED BY CULICIN^E. YELLOW FEVER, DENGUE, BIRD MALARIA, ETC. I. YELLOW FEVER. Synonyms. Bilious remittent fever. Tropical toxaemic jaundice. Typhus Icteroides. Pestis Americana. Febris Flava. Yellow Jack. Magdalena fever. Fievre Jaune. Gelbfieber. Febbre Gialla. Fiebre Amarilla. Typhus Amaril. Matla- zahuatl. Coup de Barre. General account and history. Yellow fever is an acute non- contagious fever, usually characterized by the occurrence of two paroxysms of fever separated by an intermission, and accom- panied by albuminuria, haemorrhages and jaundice. The presence of the latter symptom has give.n rise to the name by which the disease is usually known, but it should be emphasized that this feature is often absent in mild cases. The disease is widely distributed in tropical and subtropical America, and also, according to most authorities, on the West Coast of Africa. It is endemic only in those regions where Stegomyia fasciata H. B. F. 12 178 YELLOW FEVER [CH. can exist all the year round, and in consequence only appears sporadically in subtropical and temperate regions. It is mainly a disease of seaport towns and practically all the great epidemics have occurred in such localities. About the early history of yellow fever very little is certain. It is said to have been known by the Aztecs under the title of " Matlazahuatl." Other authorities believe that the disease originally occurred in the Antilles and was carried by the Spaniards to the mainland of America. There is little doubt that the disease originated in America and was fully established by the time that the early explorers arrived from Europe. On the other hand certain authors have thought that it might have been introduced from West Africa by the slave- boats, but such a view is not in accordance with the fact that the disease seems to have been already known in America when Columbus discovered the continent. From Central America yellow fever has been carried by ships to various parts of the world, in some of which it has become endemic, and in others only occurred in epidemic form. Its distribution is shewn in Fig. 50, which represents the extreme range of all places in which yellow fever has been known to occur within recent times. At present many of these localities are quite free from the disease and, as a result of anti-mosquito campaigns, many more are likely to become so in the near future. At present the chief endemic foci of the disease are the States of Central and South America, with the exception of Panama, and the West Coast of Africa. In the United States, the Gulf States have frequently been the site of great epidemics, but the climatic conditions prevent the disease from becoming endemic. In West Africa yellow fever seems to have been known since 1778, when it was recorded from St Louis. The fact that the disease has existed in an unbroken line for more than a century, is strong evidence of its endemic character in West Africa, and although there have been no outstanding epidemics, yet the number of patients who annually succumb to " Bilious Remittent Fever " is considerable. One of the XI] HISTORY 179 greatest difficulties in the way of studying the disease is the fact that mild cases of yellow fever cannot be diagnosed with any certainty. As a result, although the natives of endemic regions must frequently harbour the virus in their blood, up to the present it has been impossible to discover any direct proofs of it. 140 120 100 20 20 140 120 Fig. 50. The approximate distribution of Yellow Fever at the present time. Infected regions are coloured black. • The cause and method of infection of yellow fever have been a puzzle ever since the disease became known, and although the latter of these two points has now been settled the causal agent is still a matter of discussion. In early times it was believed that the virus was in some way transmitted through the air, and the fact that it usually occurred in the vicinity of water led to the belief that it was produced by bacterial fermentation. Subsequently a number 12 2 180 YELLOW FEVER [CH. of bacteria were described as the cause of the disease, but all of them have been shewn to be merely secondary invasions. ; In addition to being regarded as a highly infectious disease, yellow fever was always considered to be contagious, and patients suffering from it were strictly isolated and their cloth- ing, etc. thoroughly sterilized. In spite of this isolation of patients, however, epidemics were not checked, and it was noticed that many persons became infected without ever having come in contact with infected cases, whilst frequently doctors and nurses, who worked in the same rooms as the patients, did not suffer from it. It was also observed that ships coming from infected ports frequently carried the infection and consequently quarantine ordinances were brought into force, which to some extent reduced the spread of the disease, but the wars at the end of the eighteenth century caused these measures to be relaxed, with the result that some very serious epidemics occurred about this time. These afforded some opportunities for the study of the disease and several American observers called attention to the large numbers of mosquitoes and other insects that occurred during yellow fever epidemics. In 1848, Nott, of Mobile, accused some insect or mosquito of being the possible carrier. It was not, however, till 1881 that Charles Finlay of Havana definitely attributed the transmission of the disease to a mosquito. He had noticed in Cuba the connection that seemed to exist between the prevalence of yellow fever and the presence of large numbers of the tiger mosquito, 5. fasciata. Accordingly, he attempted to transmit the infection experi- mentally by feeding mosquitoes on patients suffering from the disease and subsequently on normal persons. Although his experiments were open to many objections, there is no doubt that Finlay did succeed in transmitting the disease by means of the bites of mosquitoes and he energetically advanced his theory in a number of articles. Eventually his views began to attract the attention they deserved and finally, in 1899, an American Commission was sent to Cuba to study the disease. This commission was composed of four members, Reed, Carroll, Lazear, and Agramonte, and the way in which they XI] HISTORY l8l investigated the problem of the transmission of yellow fever will always remain famous. During their investigations Dr Lazear succumbed to the disease, but the research was carried on by his fellow workers, who succeeded in proving beyond all doubt that yellow fever is carried by the tiger mosquito, Stegomyia fasciata. The earlier work of the commission was devoted to an examination of the various bacteria that had been described as the cause of the disease. Of these the most notorious were Sanarelli's Bacillus icteroides, and Sternberg's Bacillus X, which had been found in a certain number of cases. Reed and Carroll found that both these bacteria played no part in the aetiology of the malady, but were merely the result of a secondary infection. Subsequently, in 1900, Reed, Carroll, Agramonte and Lazear shewed that the disease could be pro- duced in non-immune persons by the subcutaneous inoculation of blood from an infected patient. They also proved that the disease was not contagious but could only be spread by the bites of infected 5. fasciata. These results have been thoroughly confirmed by subsequent investigators. The work of the French Commission, composed of Marchoux, Salimbeni and Simond, is the most important of all subsequent researches on the disease, for these authors were able to elucidate some of the necessary conditions for the transmission of the malady. They also found that the first generation of the offspring from an infected mosquito is capable of infecting persons. Their results will be considered in detail in the section devoted to a description of the mode of transmission of yellow fever. The practical benefits that have resulted from the applica- tion of the discovery of the mode of transmission of yellow fever are only paralleled by those following Ross's work on the development of Plasmodium in the mosquito. In the Panama Canal zone, which used to be one of the worst endemic regions in Central America, as a result of anti- mosquito campaigns the number of cases of yellow fever was reduced so rapidly that within five years the disease had com- pletely disappeared from this region. l82 YELLOW FEVER [CH. Geographical distribution. In considering the distribution of yellow fever it is necessary to emphasize the fact that the disease is being rapidly eradicated from the more civilized regions of the world, and comparatively few endemic centres exist at the present time. The most important of these are the following : Guatemala, Nicaragua, Costa Rica, Ecuador, Spanish Honduras, Venezuela, French Guiana, certain parts of Mexico and the West Indies, and along the banks of the Amazon, Orinoco, and Magdalena Rivers. It will thus be seen that the States of Central and South America are the great centres of the disease, and from these regions it has spread into many other countries. It is probably endemic in West Africa for the continual recurrence of small epidemics cannot be explained on the supposition that these represent infections introduced by ships. The endemic centres of yellow fever do not extend beyond latitudes 40° N. and 40° S., where the mean isotherm is not below 26° C. The malady, however, often extends into colder regions during the summer months, and may produce great epidemics, which, however, always disappear on the return of cold weather. Great epidemics of yellow fever have occurred in many of the seaport towns of the Southern United States, especially in New Orleans where, in 1878, there was a record of 4046 deaths as the result of one epidemic. The Gulf ports were probably endemic centres during the eighteenth century and first half of the nineteenth, but as the result of improved hygienic conditions and better drainage the breeding places of the mosquitoes have been reduced until now the disease is almost extinct. The Atlantic ports, as far north as New York, were also frequently visited by more or less severe epidemics, as the disease was continually being introduced by ships coming from Cuba and other endemic centres. The infected Stegomyia carried from these places would be able to live on board for some weeks and thus be capable of spreading the infection at the ports at which the ship called. XI] GEOGRAPHICAL DISTRIBUTION 183 On the West Coast of America the general conditions are so unfavourable to the breeding of the mosquito, that the disease has not been able to establish itself and has only appeared sporadically in one or two localities, with the exception of the Isthmus of Panama, which until recently was one of the noted endemic centres. With this exception, therefore, the West Coast has never been the scene of any severe epidemics, for comparatively few ships sail up the coast and consequently there has been little chance of their spreading infected mosquitoes. Colon is practically the only port that has hitherto been liable to infection, but with the opening of the Panama Canal and the increase in trade which this is sure to effect, the question of the possibility of thus extending the range of yellow fever will have to be carefully considered. The recent outbreak at St Nazaire in 1908 has shewn clearly that even modern ships are capable of carrying infected Stegomyia for considerable distances. In Europe the appearances of the disease have been very similar to those in North America, and many epidemics occurred during the eighteenth and nineteenth centuries, when the growth of commercial intercourse resulted in an increase in the number of ships coming from endemic centres. In Southern Europe numerous epidemics of considerable severity have occurred, and the ports of France, and even Swansea and Southampton in England, have been the scenes of small outbreaks. In the south of Europe Stegomyia fasciata is capable of breeding, and therefore epidemics could easily become established during the summer months, but in the more northerly regions this is out of the question. In these cases the infection is strictly limited to persons who have been near a ship carrying infected mosquitoes on board. Thus in the case of the outbreak at St Nazaire in 1908, infected Stegomyia were taken on board a ship at Martinique. These were carried across the Atlantic and on arrival at St Nazaire, several of the mosquitoes escaped and fed on persons either on board or in the vicinity of the ship. Eleven individuals were known to be infected in this way, of whom seven died. 184 YELLOW FEVER [CH Unless greater care is taken to screen ships during their stay in infected ports, there is little doubt that occasional epidemics of this nature now and then will appear. In North Europe, where the absence of Stegomyia prevents any further spread of the infection, these slight outbreaks are of com- paratively slight danger, but in regions where the mosquito is abundant, e.g. Malay and India, the introduction of a few infected Stegomyia might lead to the production of terrible epidemics, such as those which raged in Barcelona during the eighteenth century. Mode of infection. The various theories as to the nature of this disease have been sufficiently discussed in the previous chapter, and we shall at once proceed to a description of the work of the American Commission of 1899, on the transmission of yellow fever. The first attempts of this commission to transmit the disease by mosquitoes were made with some Stegomyia fasciata that hatched in the laboratory from eggs supplied by Finlay. These insects were fed several times on patients suffering from yellow fever at various stages of the illness. Eleven persons having offered themselves for experiment, each day these infected mosquitoes were fed on a fresh human subject. Only two of these persons became infected, and both of them had been bitten by mosquitoes that had fed 12 days previously on the blood of a yellow fever patient in the first stage of the disease. In this preliminary experiment the possibility of these two patients having become infected by other means had not been definitely excluded. It was decided, therefore, to continue these experiments, after taking more rigorous precautions against any external contamination. A camp was established in the neighbourhood of Tuemados, on a plateau that was well .drained, and absolutely free from yellow fever. Twenty- eight non-immune subjects, mostly Americans and Spaniards, were shut up in this camp and carefully examined for several days in order to make sure that none of them were infected. Jf any of the patients shewed the slightest febrile symptoms they were at once removed from the camp, but none, of the XI] MODE OF INFECTION 185 others were allowed to go out of it. After these preliminary precautions, some Stegomyia that had fed 12 days previously on a yellow fever patient in the first stages of the disease, were allowed to bite twelve persons. Ten of them became infected after incubation periods varying from 41 hours to five days. Twelve other persons who remained in the camp never shewed the slightest signs of infection, although living in close proximity with these yellow fever patients. This experiment proved that not only is this mosquito the carrier of the infection, but that contact with patients is harmless. The latter is most important from an economic point of view, and therefore the commission carefully inves- tigated the question. A mosquito-proof house was constructed so as to present the worst possible hygienic conditions. It was badly venti- lated, and badly lighted, and the windows were kept shut all day. The air inside the house was very humid and the tem- perature often rose to 35° C. Into this house was introduced the soiled linen from beds that had been occupied by yellow fever patients. A certain number of persons occupied this house for 20 days, sleeping between bed-clothes that had been soiled by the excrement and black vomit of yellow fever patients. In spite of these conditions none of the persons occupying the house became infected and the experiment has been repeated several times with similar results. No matter under what conditions of sanitation, etc., in the absence of Stegomyia, nobody became infected with the disease. Finally, a house was constructed of the same dimensions as the preceding, but well lighted and ventilated, so as to present the best hygienic conditions. This house was rendered mosquito-proof by wire gauze, and also was divided into two halves by means of a partition of the same material. On one side the persons occupying the room were exposed to the same conditions as in the preceding experiment, namely, sleeping between the soiled bed linen from yellow fever patients, etc. In the other half only carefully sterilized material was allowed to enter but, in addition, there were introduced 15 mosquitoes that had fed, at least 12 days previously, on patients at the 1 86 YELLOW FEVER [CH. commencement of their infection. A young American doctor, Dr Moran, entered this half of the house and was bitten by a number of the mosquitoes. After a short incubation period, he developed a typical attack of yellow fever, whilst persons who occupied the other half of the house for at least 20 days remained healthy. In this manner was established the important truth that yellow fever is only carried by means of the- mosquito, and the above-mentioned results have been repeatedly confirmed by subsequent investigators. The causal agent. In spite of numerous researches the causal agent is still under discussion, for most of the organisms that have been described from yellow fever patients may be explained as the result of secondary infection, or in other cases, as artefacts. Because of the many points of resemblance be- tween relapsing fever and yellow fever, it has been suggested that the latter is also due to a spirochaete. Recently Seidelin has described the occurrence of a parasite, belonging to the Babesiidae, in the blood and organs of yellow fever patients. To this parasite Seidelin has given the name of Paraplasma flavigenum, and he considers it to be the causal agent of yellow fever. Whatever the causal agent may be, it is present in the circulation in large numbers, for the subcutaneous injection of minute quantities of infected blood into a non-immune person is followed by an attack of yellow fever. It is said to be present in the circulation only during the first three days of an attack, for blood taken from a patient on the fourth day, when his temperature was still high (40° C.) was found to be non-infective. However, as there has only been one attempt made to infect persons with the blood taken from patients after the third day, this statement is still open to question. On the whole it seems probable that yellow fever patients may remain infective even after all signs of the disease have dis- appeared, for it is difficult to explain its prevalence in certain cases except on the theory of latent infections. The organism must be excessively minute for it can easily pass through a Chamberland Filter F. When the infected serum is diluted XI] DEVELOPMENT IN MOSQUITO 187 with an equal quantity of water the virus is even capable of passing through a Chamberland Filter B, 0-033 c-c- of tne filtrate producing a typical attack when injected into a non- immune person. The virus is extremely fragile, for a drop of infected blood may be placed on an excoriated part of the skin with impunity, as the slightest desiccation destroys the disease agent. More- over, it is very susceptible to heat, for at a temperature of 55° C. it loses its virulence within five minutes. Development within the mosquito. Under ordinary cir- cumstances when a Stegomyia has fed on the blood of a yellow fever patient during the first three days of an attack, it becomes infective after an incubation period of about 12 days. The conditions of development within the mosquito are very uncertain, however, for it often happens that mosquitoes remain uninfective, even though fed on infected blood. The effect of temperature is very important and probably accounts to some extent for the restricted range of the disease. If a mosquito is kept at a temperature of about 22° C., instead of becoming infective 12 days after an infected feed, the incu- bation period is prolonged to three or four weeks. At 20° C. the virus is incapable of developing within the mosquito and thus the latter does not become infected. If an infected mosquito, capable of transmitting the disease, is exposed to a low temperature, it ceases to be infective, but recovers this power on again being warmed. It is possible that changes in temperature alter the virulence of the disease, for during the cool season the cases of yellow fever are often benign, the most severe ones occurring during the hot weather. Under certain conditions it seems that the infection may be transmitted to the offspring of an infected mosquito. Marchoux and Simond kept a female Stegomyia, which laid its eggs 1 6 days after an infective feed. These eggs were kept at a temperature of about 28° C. and developed in a com- paratively short length of time into the adult insects. The latter were found to be infected and produced a typical attack of yellow fever when fed on a non-immune subject. Although no one else has succeeded in repeating this experiment, the 188 YELLOW FEVER [CH French investigators were so careful to exclude all chance of error, that there is little doubt that under certain conditions, a Stegomyia infected with yellow fever is able to transmit the infection to its offspring. The reappearance of yellow fever in places where it had apparently become extinct may possibly t>e explained by this factor. Once a mosquito has become infected, it probably continues so for the remainder of its life, but there are not sufficient observations on this question. In nature the insects are certainly still infective after being nourished on sugar for two or three weeks, as shewn in the case of the St Nazaire epidemic. It is possible for the virus of yellow fever to be preserved indefinitely in the mosquito and thus the cycle of development must be quite different from that of Plasmodium. This was clearly shewn by an interesting experiment performed by Marchoux and Simond. Mosquitoes, that had fed on an infected patient more than 12 days previously, were ground up in thick syrup and some freshly hatched Stegomyia fed on this mixture. Fifteen days later these insects were found to be infected, although they had never fed on a yellow fever patient. Vaccination. Although no successful means of preventing infection by this means have yet been discovered, the results obtained by the use of various sera are of some interest. We have previously referred to the extreme susceptibility to temperature of the virus of yellow fever. Warming for five minutes at 55° C. destroys all its activity. If preserved at a temperature of 29° to 30° C. in an ordinary tube plugged with cotton, the serum loses its virulence within 48 hours. The same temperature acts much more slowly if the infected serum is covered with a layer of oil in order to protect it from the air. At the end of five days some serum kept in this manner was still infective, and produced an attack of yellow fever when injected into a non-immune person. It should be added that it only produced a very mild attack. After being thus preserved for eight days the serum lost its virulence entirely and could be injected into non-immunes without producing any infection. Xl] VACCINATION 189 The inoculation of serum that had either been warmed, or kept for eight days at 25° C., was found to confer a partial immunity against yellow fever. All the subjects that had received such injections, were subsequently inoculated with a virulent strain of yellow fever, and in every case the resulting attack was found to be extremely mild in character, shewing that the serum had had an immunizing effect. During the course of an attack of yellow fever the presence of antibodies in the blood of the patient may easily be demon- strated. The serum of a patient taken on the eighth day of an attack and injected into a non-immune person, completely protected the latter against infection when subsequently inocu- lated with virulent blood. The serum of a convalescent patient is even more effective, and if injected into non-immune persons will protect them against all attempts at infection for a period of about 20 days. By the twenty-sixth day the immunity begins to disappear but is still present, for the inoculation of virulent blood only produces a slight attack of fever. Such immune serum may also be applied therapeutically, and when injected into infected patients is said to diminish the severity of the symptoms and hasten the recovery. Unfortunately, all these methods are of little use, because they require the presence of infected patients and conva- lescents to furnish the necessary materials. REFERENCES. Boyce, R. (1911). Yellow Fever and its prevention. London : John Murray. Clarac, A. and Simond, P. L. (1912). Fievre Jaune, in Grail and Clarac's Traite Pratique de Pathologie Exotique. Paris. Vol. in. pp. 21-176. Finlay, C. (1883). Sur une nouvelle th£orie de la fievre jaune. Ref. Arch, de med. nav. January, 1883. Marchoux, E. (1910). Fievre Jaune, in Chantemesse and Mosny's Traitd d' Hygiene. Paris : Bailliere et fils. Marchoux, Salimbeni and Simond (1903). La fievre jaune. Ann. Inst. Pasteur, vol. xvn. pp. 665-731. Marchoux and Simond (1906). fitudes sur la fievre jaune. Ibid. vol. xx. pp. 16, 104 and 161. Reed, Carroll, Agramonte and Lazear (1900). Preliminary note on the Etiology of Yellow Fever. Phil. Med. Journ. Oct. 27. DENGUE [CH. Reed and Carroll (1902). Recent researches concerning the etiology, propagation, and prevention of Yellow Fever, by the U.S. Army Commission. Journ. of Hygiene, vol. n, pp. 101-119. Sanarelli, G. (1897). Etiologie et pathogenic de la fievre jaune. Ann. Inst. Pasteur, xi. p. 433. Seidelin, H. (1911). The Etiology of Yellow Fever. Yellow Fever Bulletin, vol. i. pp. 229—258. For a complete bibliography see the Yellow Fever Bulletin, and also Scheube's Die Krankheiten der warmen Lander. (Jena : G. Fischer.) II. DENGUE. Synonyms. The synonymy of this disease is very extensive, upwards of 100 names having been applied to it. The most important of these are as follows : Dandy Fever ; Breakbone Fever ; Febris Endemica cum Roseola ; Exanthesis Arthrosia ; Arthrodynie ; Knokkelkoorts ; Eruptive Rheumatic Fever ; Fievre rouge, etc. History. The first records of dengue do not appear before the end of the eighteenth century, though there is some possi- bility that an epidemic noted by Pazzio as occurring in Seville from 1764 to 1768 was caused by this disease. In 1779 dengue was noted in Cairo and Arabia, by Gaberti ; in India, by Persin ; and also in Batavia, by David Bylon. The following year Rush described an epidemic occurring in Philadelphia, and in 1784 the disease was introduced from the West Indies into Spain, where it caused severe epidemics in Cadiz and Seville, which were well described by Cristobal Cubillas. During the nineteenth century epidemics have been recorded from most tropical and subtropical regions. According to Manson there is a tendency for these epidemics to occur at intervals of about 20 years. The last epidemic to occur in Europe was in 1889, when the disease was especially prevalent in Turkey, Greece, and the Eastern Mediterranean region generally. Distraction and epidemiology. Dengue is essentially a tropical disease, but occasionally it extends into subtropical regions. It has occurred in practically every country between XI] DISTRIBUTION 32° 47' N. and 23° 23' S., and during the summer months it may extend up to as much as 42° N. The disease is usually more prevalent in low-lying lands well supplied with water, probably because such sites provide better opportunities for the breeding of Culex. There are exceptions to this rule, however, for during the epidemic in Syria in 1888-9 tne disease extended to villages having an altitude of nearly 4000 feet. Fig. 51. The distribution of Dengue. The countries from which cases have been recorded are coloured black. (Compare this chart with that on page 193, shewing the distribution of Culex fatigans.) The distribution of dengue, past and present, is represented in the accompanying map (Fig. 51). At the present time the chief endemic centres of the infection are India and the East Indies, and, in the New World, the West Indies and Central America. From these centres the disease, in warm summers, may even extend into temperate regions, but on the approach of winter it gradually disappears, as a certain amount of heat seems to be necessary for its transmission. DENGUE [CH. Neither age, sex, race, nor social conditions, seem to have any effect on this disease, which attacks rich and poor, old and young, black and white, with the utmost impartiality. The rapid spread of epidemics of dengue is another feature which was noticed even by the earliest observers. The rapidity with which it extends is probably unequalled by any other malady, and usually within a few days of its appearance in any particular locality a considerable proportion of the population will be found suffering from the disease. In 1884 an epidemic in Noumea broke out so suddenly that the majority of the public services were disorganized ; a regiment of marines was reduced to less than one section, and so many of the sailors were affected that the ships were temporarily put out of action. The disease is usually conveyed from one place to another by means of ships carrying infected passengers. Thus dengue was introduced into Tahiti by a steamer that carried a single infected passenger, who had contracted the disease in Noumea. This case was sufficient to start an epidemic in the island. When any particular maritime locality becomes the centre of an epidemic, all ships visiting the place are liable to become infected. Occasionally the disease is spread by means of trains as, for example, in India, where it was carried from Calcutta across Bengal by these means. Such a method of expansion, however, is somewhat unusual and seaports continue to be the localities most visited by epidemics, the infection being introduced by ships. An epidemic generally lasts for about five or six months, gradually diminishing in the number of cases until it finally disappears. It is interesting to note that the distribution of dengue shews a remarkable coincidence with that of Culex fatigans. (Figs. 51 and 52.) Causal agent. Our knowledge of dengue is still very im- perfect and in spite of numerous researches the cause of the disease remains unknown. McLaughlin, in 1886, found a micrococcus in the blood of infected patients and supposed that this was the causative agent, but his results have been disproved by subsequent investigators. In 1903, Graham believed that he had discovered the cause of the disease, in XI] CAUSAL AGENT 193 the form of small hyaline bodies, occurring in the red cells, which he considered to be related to Babesia. In addition, he fed Culex fatigans on infected patients and claimed to have found his parasites in the insects up to the fifth day after feeding, without, however, observing any signs of their develop- ment. Nevertheless the salivary glands were said to contain spores from two days up to a month after the mosquito had Fig. 52. The distribution of Culex fatigans. fed on infected blood. A typical attack of dengue was pro- duced in a healthy person by the injection of the salivary glands of a mosquito, that had fed on an infected patient 24 hours previously. Although Graham's work on the transmission of dengue by Culex fatigans has been confirmed, the organism which he described has never been observed by any subsequent investi- gators, but from the nature of the disease there seems little doubt that it is caused by some protozoal parasite living in the blood. Ashburn and Craig have studied the aetiology H. B. F. 13 IQ4 DENGUE [CH, and transmission of dengue in the Philippines, and were able to produce the disease in normal persons by the intravenous injection of 20 c.cs. of blood from an infected patient. The incubation period was two to three days, and was followed by typical attacks of dengue. These authors also found that the pathogenic agent was so small that it would pass through the pores of a filter which retained organisms 0^4 /z in diameter, filtered serum being equally as infective as non-filtered blood. The blood shews little alteration except in the leucocyte count, a slight or well-marked leucopenia being a fairly constant character. The number of polymorphonuclear leucocytes may be reduced to forty or fifty per cent., but at the same time there is an increase of the large mononuclears and lymphocytes, the latter predominating. Some authors maintain that the leucocyte formula remains essentially the same throughout the disease, whilst others are of the opinion that considerable variations occur. Dengue is not accompanied by any anaemia, the red cells remaining normal both in number and ap- pearance. Mode of infection. The transmission of this disease is still somewhat obscure in spite of the work of Graham, and Ashburn and Craig. For a long time it was considered to be a highly contagious infection and During recorded a case in which five families that received their washing from the same laund- ress all became infected about the same time and before the other inhabitants. Arnold, in 1846, was the first to support the idea that the disease is not contagious and based his theory on two facts noticed in Havana, namely, that the epidemic was localized in the town and did not spread into the surrounding country, and that among the first cases, not any of the patients had been in contact with one another, either directly or in- directly. The belief in the contagious nature of dengue has now been abandoned by the majority of investigators, but, in addition to the idea that it is carried by Culex, various other theories of animal transmission have been advanced. In America it is a common idea that the spread of the disease depends in some XI] MODE OF INFECTION way on the cattle. In India, Martialis has noticed that the cows and horses are sometimes attacked by dengue, often presenting a temporary paralysis of one or more legs, but usually recovering after three or four days. Also, Duchateau, during an epidemic in the Senegal, noticed that it coincided with a high mortality amongst the wild birds and fowls. None of these theories has received any support from experiments, for up to the present all attempts to infect animals have remained negative. Finally, in 1903, Graham propounded the theory that Culex fatigans is responsible for the transmission of this disease and supported his theory by experiments. Ashburn and Craig, however, are the only investigators who have actually succeeded in transmitting the disease by the bites of infected Culex fatigans. It should be noted, however, that they only succeeded on one occasion and their results have not been confirmed. The details of Ashburn and Craig's experiments are as follows : On September I2th, a non-immune soldier was placed under a mosquito net with about 20 Culex fatigans that had fed on a dengue patient the previous night. The man was bitten on the night of the I2th, approximately one day after the mosquitoes had fed. About three and a half days later he shewed a distinct rise of temperature and a day later developed a typical attack of dengue. It is evident that in this experiment the parasite causing the disease had no time to undergo any cycle of development in the mosquito, except a very short one. As all attempts to infect persons by the bites of mosquitoes after an interval of more than one day gave negative results, Ashburn and Craig are of the opinion that the parasite of dengue is merely capable of living in the stomach of the mosquito and does not need to undergo any cycle of development before becoming infective. It must be admitted that the experimental evidence in support of the mosquito transmission theory is very incomplete, but a consideration of its epidemiology leaves no doubt as to the usual mode of infection. 13—2 196 BIRD MALARIA [CH. In the first place the disease has been definitely proved to be non-contagious, but is infectious in the same way as yellow fever and malaria. Secondly, the distribution of dengue more or less coincides with that of Culex fatigans. Additional support, however, is that brought forward by E. H. Ross, who shewed that in Port Said, Egypt, dengue entirely dis- appeared after the destruction of mosquitoes. Previously the town had been subject to severe epidemics, but since the extermination of the mosquitoes, not a single case of dengue has been recorded, although the disease has been rife in other parts of Egypt. Of course, it is possible that other Culicines may be capable of transmitting the infection, and the observations of Legendre in Hanoi suggest that Stegomyia is probably a carrier of the virus. REFERENCES. Ashburn and Craig (1907). Experimental investigations regarding the etiology of Dengue Fever. Philippine Jour. Sci. Sect. B, Med. Sci. vol. ii. No. 2. Graham (1903). The Dengue ; a study of the pathology and mode of propagation. Journ. Trop. Med. 1903, p. 209. Legendre (1911). Bull. Soc. Path. Exot. vol. iv. p. 26. Seidelin, H. (1913). Dengue. A summary. Yellow Fever Bulletin, vol. n. pp. 335-358. (Contains a very good general account of the disease.) III. BIRD MALARIA (Plasmodium prcecox [Grassi and Feletti]). General account. A great variety of birds, such as finches, sparrows, crows, etc., have been found infected with a parasite closely resembling the Plasmodia of man. By some authors this bird parasite has been separated off into a distinct genus, Proteosoma, but the differences between it and Plasmodium are so slight that now the two are generally united. There is also some doubt as to whether all the Plasmodia occurring in birds should be regarded as one species, and some observers have preferred to give specific names to the Plasmodia from different XI] CAUSAL AGENT 1 97 species of birds, but there is no justification for this course, as hitherto all attempts to find any specific differences, apart from the kind of host, have failed. Therefore, for the present, all the plasmodial parasites occurring in birds may be regarded as belonging to one species, Plasmodium prczcox (Grassi and Feletti, 1890). The parasites have a decidedly pathogenic action upon the birds they infest. They grow at the expense of the red cor- puscles, which lose their haemoglobin, and gradually degenerate. As a result infected birds become anaemic and, in addition, the substances produced by the parasites seem to have a general toxic effect upon the organs of the body. As in the case of human malaria, the body temperature rises, but rarely more than i-i'5° C. Birds not infrequently succumb to the infection, especially during the early part of the year, when climatic conditions are somewhat severe. Causal agent. Plasmodium pracox in its general form somewhat resembles P. vivax. The small amoeboid sporozoites penetrate into the red cells and there generally assume a some- what triangular form, with a round vesicular nucleus containing a karyosome. This young trophozoite grows at the expense of the contents of the red cell and deposits waste materials in the form of pigment granules, which are scattered through its protoplasm. Danilewsky refers to these young forms as " pseudo-vacuolae." The protoplasm is finely granular and contains numerous vacuoles. According to Labbe there are two kinds of schizogony in the circulating blood. Sometimes the parasite divides up into six or seven merozoites arranged in the form of a rosette, whilst at other times the parasite divides up into very numerous merozoites scattered irregularly throughout the infected blood corpuscle. In both cases the pigment and waste materials are left behind in the form of a residual body. The merozoites escape and penetrate other blood corpuscles, where they either develop and repeat the schizogonic cycle, or give rise to the gametocytes. The development of the latter closely resembles that of the corresponding forms in other species of Plasmodia (e.g.' P. vivax}. 198 BIRD MALARIA CH. The Morphological Changes. Development in the mosquito. The experiments of Ross, Sergent, Ruge and Neumann have shewn that at least four species of Culicinae are capable of transmitting P. prcecox, viz. Culex pipiens, C. fatigans, C. nemorosus and Stegomyia fasciata. In all these species the development of the parasite is practically identical with that of P. vivax in Anopheles, and therefore it is unnecessary to describe it in detail. The development, however, does not take place with equal facility in all these species, even under the same conditions of temperature and humidity. Thus Neumann found, that out of 501 Stegomyia fasciata which fed on an infected canary, only 57 (= 11*4 per cent.) subsequently shewed the development of ripe cysts and the sporozoites of the parasite. On the other hand out of 104 Culex pipiens fed under similar conditions, 85 (= 817 per cent.) became infected. Moreover the time occupied in the develop- ment of the parasite, from the ingestion of the gametocytes to the appearance of sporozoites in the salivary gland of the mosquito, was longer in the case of Stegomyia than in Culex. At a temperature of 27° C., with a relatively high humidity of about 75 to 80 per cent., the times occupied by the various stages of development were as follows : Formation of microgametes Copulation Formation of ookinete, commencement of majority formed Disappearance of ookinetes from the stomach Formation of sporocyst Development of sporozoites in the cyst Total developmental period, from the ingestion of the infected blood to the appearance of sporozoites in the salivary glands of the infected mosquito In Culex 30 to 45 mins. 30 to 60 mins. About 10 to 12 hours 20 hours After 48 hours About 30 hours 6 to 7 days 9 to ii days In Stegomyia 30 to 60 mins. 39 to 90 mins. About 1 6 hours 26 hours After 72 hours Not before the 3rd or 4th day 8 to 10 days 13 to 15 days XI] DEVELOPMENT OF PARASITE I99 At a temperature of 20° to 22° C. the formation of the ookinete and its subsequent development is very greatly prolonged, but the liberation of the microgametes and the process of copulation does not seem to be delayed. If the humidity is lowered to about 40 per cent, the develop- ment of the cysts is prolonged for at least two days, so it seems that a dry atmosphere is relatively unfavourable to the infection of mosquitoes. Fig- 53- View of the stomach of a Culex shewing large numbers of the sporocysts of Plasmodium prcecox on its walls. (After Ross.) Neumann kept very large numbers of Culex and fed them entirely on the blood of an infected canary. Although the majority of these mosquitoes were heavily infected with the Plasmodium, none of them seemed to shew any ill-effects from the presence of these parasites. On the other hand Koch, who similarly fed a number of Culex nemorosus on birds infected with P. prcecox, found that many of the insects succumbed to the infection. REFERENCES. Grassi, B. (1901). Die Malaria- Studien eines Zoologen, Jena: Fischer. Koch, R. Ueber die Entwicklung der Malariaparasiten. Zeitschr. f. Hyg. u. Infektionskrankh. vol. xxxn. Neumann, R. O. (1909). Die Obertragung von Plasmodium prcecox auf Kanarienvogel. Arch. f. Protistenkunde, vol. xm. pp. 23-69. Ross, R. (1905). Nobel Prize Essay, 1905. Ruge, R. (1901). Untersuchungen iiber das deutsche Proteosoma. CentralbL f. Bakt. i. vol. xxix. pp. 187-191. Sergent, Ed. and Et. (1907). Etudes sur les H6matozoaires d'Oiseaux. Ann. Inst. Pasteur, vol. xxi. pp. 251-280. 200 SCHAUDINN'S RESEARCHES [CH. IV. APPENDIX. The Blood Parasites of Athene noctua. In addition to the above-mentioned infections, it is probable that most of the blood parasites of birds are trans- mitted by the agency of some species of mosquito. Schaudinn, in his famous memoir on the life-cycles of the parasites of the Little Owl (Athene noctua], described the development of these organisms in the alimentary canal of the common gnat, Culex pipiens. The Little Owl harbours in its blood at least six forms of avian parasites, namely, (i) a proteosoma ; (2) a halteridium ; (3) a small form of trypanosome ; (4) a large form of trypano- some ; (5) a leucocytozoon ; and (6) a spirochaete. According to Schaudinn all these forms belong to the life- cycle of only three species of parasites. The proteosoma is certainly a distinct form unrelated to any of the others. On the other hand the halteridium and the small trypanosome were said to be phases of the same parasite, whilst the large trypanosome, leucocytozoon and spirochaete were considered as stages in the development of another parasite. The halteridium was supposed to be the resting intra- corpuscular stage of the small trypanosome, which at night developed a locomotor apparatus, became free from the red cell and swam about as an ordinary trypanosome ; in the morning it penetrated another red cell, its locomotor apparatus disappeared, and it again became a halteridium. Three forms of the parasite were distinguished, known respectively as male, female and indifferent forms. The latter were the forms which multiplied in the blood, and from these small trypanosomes either indifferent, male, or female forms, might develop. The two latter developed slower than the indifferent forms, and as they grew larger were unable to change from the hal- teridium to the trypanosome form, but became exclusively intracorpuscular or halteridium forms. The further develop- ment of these sexual forms could only take place if they were ingested by a gnat, Culex pipiens. In the alimentary canal of this insect the male and female forms became free and copulated, forming typical ookinetes. The latter developed XI] HALTERIDIUM OF ATHENE NOCTUA 2OI into trypanosomes which again might be either female or indifferent, or divide up into a large number of male forms. Ultimately the indifferent and male trypanosomes were inocu- lated back again into an owl ; the female trypanosomes being too bulky could not pass through the proboscis of the gnat, and as the male forms soon died out in the blood the new infection was started by the indifferent trypanosomes. This extraordinary account of the life-cycle of the parasite of the Little Owl has been the subject of much discussion during the past few years. Mayer has brought forward evidence in support of one of Schaudinn's statements, for he found that when owl's blood containing only halteridia was kept in hanging drops under the microscope, eventually trypanosomes made their appearance and these could only have come there by the transformation of the halteridia. On the other hand no other confirmation of the life-cycle has hitherto been published, whilst there are many serious objections to it. In the first place the careful researches of Minchin and Woodcock, who worked at- Rovigno, the place where Schaudinn made his observations, have shewn that in the blood of Athene noctua there is every stage between the small trypanosomes and the large ones, and there is every reason to suppose that in this case, as in many other verte- brates, these are all merely forms of one polymorphic try- panosome. Further the development of Hcemoproteus columbce, the halteridium of the pigeon (v. Chapter XXIII), is of a totally different kind, as the transmitting host is not a mosquito and moreover the development does not include any trypanosome phases. Minchin suggests a solution of the difficulty by supposing that the trypanosome of the Little Owl, like other known species of trypanosomes, has intracorpuscular forms which have been confused with true halteridia. With regard to Schaudinn's account of the life-cycle of the Leucocytozoon there is not the slightest doubt that no relation exists between this parasite and the spirochaetes and 2O2 FILARIASIS [CH. trypanosomes, which are supposed to be stages in its develop- ment. The bacterial nature of the spirochaetes is now generally admitted, and the life-cycles of those species that have been investigated have been found to be of the simplest nature, not involving any sexual phenomena, or anything in the slightest degree comparable with Schaudinn's account. Up to the present, no observer has succeeded in working out the life-cycle of any Leucocytozoon , but it is unlikely that a gnat is responsible for its transmission. On the whole, therefore, it seems better to disregard Schaudinn's statements concerning this parasite, and to con- sider its life-cycle as still an open question. REFERENCES. Dobell, C. C. (1912). Researches on the Spirochsets and related organisms. Arch. f. Protistenkunde , vol. xxvi. pp. 117-240. Mayer, M. (1911). Ober ein Halteridium und Leucocytozoon des Waldkauzes und deren Weiterentwicklung in Stechmiicken. Ibid. vol. xx.i. pp. 232—254. Minchin, E. A. (1912). An Introduction to the Study of the Protozoa, PP- 389-394. London : Edward Arnold. Minchin and Woodcock, H. M. (1911). Observations on the Trypano- some of the Little Owl (Athene noctua). Quart. Journ. Micr. Sci. vol. LVII. pp. 141-185. Schaudinn, F. (1904). Generations- und Wirtswechsel bei Trypano- soma und Spirochaete. Arb. a. d. kais. Gesundheitsamt. vol. xx. P- 387. CHAPTER XII DISEASES TRANSMITTED BY ANOPHELIN^ AND CULICIN^E . FILARIASIS I. Filar ia bancrofti Cobbold, 1877. Synonyms. Trichina cystica Salisbury, 1868. F. sanguinis hominis Lewis, 1872. F. sanguinis hominis agyptiaca Sonsino, 1874. F. dermathemica da Silva Aranjo, 1855. F. wiicheresi da Silva Lima, 1877. F. sanguinis hominum Hall, 1885. F.- sanguinis hominum nocturna Manson, 1891. F. nocturna XII] HISTORY 203 Manson, 1891. Micro filar ia nocturna Hanson, 1891. F. phi- lippinensis Ashburn and Craig, 1906. History. The embryo of this species was discovered by Demarquay in 1863, in the chylous fluid from a case of dropsy of the tunica vaginalis, occurring in the West Indies. Wiicherer in 1866 noticed the parasites in the urine of several cases of tropical chyluria, and in the next few years these embryos were found in similar cases from various parts of the world. In 1872 Lewis found that the parasites occurred in the blood of man, and Manson, da Silva Lima and Crevaux established the identity of these blood filariae with those occurring in cases of chyluria and lymph scrotum. In 1876 the adult filaria was discovered by Bancroft in an abscess of a lymphatic gland of the arm and also in a hydrocele of the spermatic cord. Manson studied the disease in China, and was the first to notice the periodic increase and decrease in the number of parasites in the peripheral circulation. From these observations he deduced that some blood-sucking insect was responsible for the spread of the infection, and his discovery in 1878 that mosquitoes were the agents in the transmission of the disease constitutes one of the landmarks in the history of tropical medicine. In 1879 ne described the changes undergone by the filaria in the body of the mosquito, Culex pipiens, but the method in which the parasite again reached man remained undiscovered till 1900, when Low observed the worms in the proboscides of mosquitoes infected with Filaria bancrofti. Distribution. This species has been recorded from tropical and subtropical countries in most parts of the world. In Europe one case has been observed in Spain and another in Italy ; it is also probable that it occasionally occurs in Greece and Turkey. In Asia this filaria is widely spread throughout China, Japan, the Philippines, and India. It is rare in Indo- China. In Oceania it is extremely common in the majority of the islands, and in Samoa at least one half the inhabitants are said to be infected. In Australia it occurs as far south as Brisbane. In Africa it has been recorded from many localities in the north, east and west, and probably occurs throughout the whole continent north of latitude 20° S. It is also common 204 FILARIA BANCROFTI [CH. in Mauritius, Reunion and Madagascar. In America, it is common in many parts of the West Indies and Brazil, and cases occur in the southern United States up to lati- tude 40° N. Description. The adult filariae do not occur in the peripheral blood circulation, but are found in various parts of the lym- phatics. The males and females generally occur together, often coiled about each other. Sometimes several occur together in small cyst-like dilatations of the distal lymphatics ; they are also found in the larger lymphatic vessels and in the glands themselves, and, probably not infrequently, in the thoracic duct. The female is a long, hair-like, transparent, motile worm, 50-155 mm. in length, and O'i5-O'7i5 mm. in breadth. The two uterine tubes, easily seen through the transparent integument, occupy the greater length of the body, and are filled with ova and embryos at various stages of development. The body is plain, tapering rather abruptly towards the anterior end to form a distinct neck, beyond which is the slightly en- larged rounded oral extremity. The tail is also tapered, but ends rather abruptly. The cuticle is finely striated. At a short distance behind the head a luminous V-shaped spot is visible, that may represent the water- vascular system. The vulva is situated on the ventral surface at a distance of about 2-56 mm. from the anterior extremity. The anus opens immediately in front of the tail, o- 13-0*2 8 mm. from the posterior extremity. The worm is ovo- viviparous. The ova measure 25-38 ^ in length by 15 p in breadth. The male resembles the female in its general appearance but is somewhat smaller, usually about 70-80 mm. in length by 0*40 mm. in breadth. When living it may further be dis- tinguished from the female by its marked tendency to curl, and also by the shape of the tail, the extremity of which is sharply incur vat ed, often making one or two spirals. The anus is situated 0*11 mm. from the posterior extremity and from its aperture emerge two slender, unequal spicules, respectively 0-2 and 0-6 mm. in length. According to Looss there are three pairs of post-anal papillae ; pre-anal papillae seem to be XII] DESCRIPTION 2O5 absent. The anterior end is rounded and not marked off from the rest of the body by a distinct neck as in the case of the female. The embryos, or microfilariae as they are frequently termed, occur in the peripheral blood. Manson describes the move- ments of the living parasite in the following words : "In fresh blood, F. nocturna (= bancrofti) is seen to be a minute, trans- parent, colourless, snake-like organism which, without materi- ally changing its position on the slide, wriggles about in a state of great activity, constantly agitating and displacing the cor- puscles in its neighbourhood. At first the movements are so active that the anatomical features of the filaria cannot be made out. In the course of a few hours the movements slow down, and then one can see that the little worm is shaped like a snake or an eel — that is to say, it is a long, slender, cylindrical organism, having one extremity abruptly rounded off, the other for about one-fifth of its entire length gradually tapering to a fine point. When examined with a low power, it appears to be structureless ; with a high power, a certain amount of structure can, on close scrutiny, be made out. In the first place, it can be seen that the entire animal is en- closed in an exceedingly delicate, limp, structureless sack, in which it moves backwards and forwards. This sack or " sheath " as it is generally called, although closely applied to the body, is considerably longer than the worm it encloses, so that that part of the sack which for the time being is not occupied is collapsed, and trails after the head or tail or both, as the case may be. It can be seen also that about the posterior part of the middle third of the parasite there is what appears to be an irregular aggregation of granular matter which, by suitable staining, can be shown to be viscous of some sort. This organ runs for some distance along the axis of the worm. Further, if high power be used, a closely set, very delicate transverse striation can be detected in the musculo-cutaneous layer throughout the entire length of the animal. Besides this if carefully looked for at a point about one-fifth of the entire length of the organism backwards from the head end, a shining triangular V-shaped patch is always visible. This 206 FILARIA BANCROFTI [CH. V-spot is brought out by very light staining with dilute logwood. The dye brings out yet another spot, similar to the preceding, though very much smaller ; this second spot is situated a short distance from the end of the tail. The former I have designated the V-spot ; the latter the " tail spot." Staining with logwood also shows the body of the little animal is principally composed of a column of closely packed, exceedingly minute cells enclosed in the transversely striated musculo-cutaneous cylinder ; at all events, many nuclei are thereby rendered visible. Dr Low has recently pointed out to me that the break seen in all stained specimens in the central column of nuclei occurs at a point slightly posterior to the anterior V-spot. This break can only be recognized in stained specimens." According to Annett, Button and Elliott, if preparations of the living filaria are examined directly after being made from the patient, the embryos are seen to exhibit, for a short period, a rapidly progressive movement across the field of the microscope — at first so rapid that the parasites can only be traced with difficulty. This movement quickly ceases, as the sheath of the embryo soon becomes attached to the slide, as described above. The embryos vary from 270 to 340^ in length, by 7 to ii /^ in breadth. Life-cycle in the vertebrate host. We shall commence with the adult female in the lymphatics of the infected patient. The fertilization is internal and the fertilized female usually contains large numbers of embryos at various stages of development. As this animal is ovi-viviparous, the eggs are not liberated from the body of the parent until the embryonic filariae (= microfilariae) are well formed and capable of inde- pendent motion. The egg is surrounded by a transparent sheath, within which the embryos are enclosed the whole time they remain in the vertebrate host. The young filariae, each enclosed in its sheath, on being liberated make their way into the blood-vessels of the host and may be found in the peripheral circulation. Whilst remaining in the blood they are incapable of further development, but are enclosed XII PERIODICITY 207 within their sheaths, presenting an appearance similar to that shewn in Fig. 54. These are the filariae that one encounters on examining the blood of a filarious patient, and as will be seen they are merely immature forms and, consequently, it is very difficult to classify them, as the various species are distinguished mainly by the characters of the adults. These embryos are often termed " microfilariae " in order to distinguish them from the mature " filariae," but it should be remembered that such a term cannot be used in a generic sense. Fig. 54. Microfilariae of F. bancrofti emerging from the uterus of the parent filaria, uncoiling in their chorionic envelopes. {After Bahr, from Filariasis and Elephantiasis in Fiji.) Periodicity. The number of filariae in the peripheral cir- culation presents remarkable periodic variations, a pheno- menon which was first noticed by Manson. In the case of Filaria bancrofti, this author found that, in China, the parasites were present in the peripheral circulation during the night, but disappeared during the day ; and he proposed the specific name nocturna in order to express this habit. Under normal conditions of health and habit, during the day the parasite is 208 FILARIA BANCROFTI [CH. rarely seen in the blood of a patient, or, if present, only in very small numbers, but as evening approaches about five or six o'clock the filariae begin to enter the peripheral circulation in gradually increasing numbers. The maximum is usually attained about midnight, when it is no uncommon thing to find 300, or even 600, in every drop of blood. The numbers then begin to diminish, and by eight or nine o'clock in the morning the filariae have disappeared again for the day. This diurnal periodicity may be maintained with regularity for years. Manson was able to shew that during the daytime the parasites retire to the lungs, heart and larger arteries, where they may be found in enormous numbers. In the case of a filarious patient who had committed suicide during the daytime, the parasites were found to occur in the various organs in the following numbers, which indicate the average per slide : liver, § ; spleen, r ; brachial venae comites, 28 ; bone marrow, o ; muscle of heart, 122 ; carotid artery, 612 ; lung, 675. In the lungs the filariae were found lying outstretched or coiled in the blood-vessels, both small and large. In the carotid they occurred in enormous numbers on its inner surface, though how they managed to maintain their position in the blood current remains unexplained. Many authors have attempted to explain this remarkable periodicity in the occurrence of the parasites in the peripheral circulation. Mackenzie shewed that it was in some way con- nected with sleep, for by reversing the usual habits, and making a patient sleep during the day and work at night, it was found that, after a few days of hesitation, the filariae became diurnal instead of nocturnal. These results have also been confirmed by Annett, Button and Elliott working in Nigeria. Carter supposed that the embryos were carried into the circulation at the end of each day by the overflowing of chyle that follows alimentation. Myers suggested that the embryos are only laid at night and all die before the morning. Scheube supposed that the passage of the embryos from the lymphatics into the blood was prevented during the day by muscular work and digestion, and facilitated at night by the relaxation of the muscles. Von Linstow explained it on the XII] LIFE-CYCLE IN MOSQUITO 2CK) supposition that during the night the dilatation of the cutaneous capillaries facilitated the entrance of the filariae into the cir- culation. Against all these theories can be brought the objection that a closely related species, Filaria diurna, is normally diurnal, and yet presents a somewhat similar life-cycle to that of F. bancrofti. A still more serious difficulty in the way of any mechanical explanation is the occurrence, in some parts of the world, of varieties of F. bancrofti that are diurnal in habit, and yet others which exhibit no periodicity. The researches of Bahr have shewn that in Fiji and Oceania generally, the filariae occur in the blood of patients in no regular manner, and yet the parasites are morphologically identical with F. bancrofti. Similarly, Ashburn and Craig, because it exhibited no perio- dicity, considered the human filaria of the Philippines to be a distinct species, and gave it the name of -F. philippinensis, but Low has shewn that it is identical with F. bancrofti. Bahr's observations are of great interest, for they suggest that in Fiji the absence of periodicity in the filaria is a partial adaptation to the habits of its usual invertebrate host in this locality, Stegomyia pseudoscutellaris, a mosquito which only feeds during the day. At present, however, there is no hypothesis that will satis- factorily account for the phenomenon of filarial periodicity. Life-cycle in the mosquito — the intermediate host. As men- tioned above, the filarial embryos are incapable of further development within the body of their host, but require to be ingested by a mosquito belonging to one of the species that serve as the invertebrate hosts for F. bancrofti. Then the parasites undergo further evolution in the body of the mosquito. The various stages in the metamorphosis of this species in the body of Culex pipiens have been worked out by Manson. The development may be conveniently divided into seven stages. First Stage. Shortly after being ingested by the mosquito the transverse striation of the embryo becomes well marked, as if from longitudinal shrinking. Within about one hour the embryo breaks out of its sheath and then shews active move- ments. The parasite bores its way through the walls of the H. B. F. I4 210 FILARIA BANCROFTI CH. stomach and eventually comes to rest in the thoracic muscles of the mosquito. This process is usually complete in about 12 to 18 hours, but some of the worms die in the stomach. In the thorax all movement ceases, the striation disappears and various changes take place in the interior of the filaria. Second Stage. This generally occupies about two to three days, during which the body thickens, and a mouth begins to appear. The posterior V-spot appears as a large vacuole and the anterior V-spot becomes very distinct. Third Stage. The mouth becomes open and four large fleshy lips are formed. The posterior V-spot enlarges and definitely becomes the anus, appearing in front of the tail as a break in the cuticle, from which granular matter exudes. A row of cells appears in the previously apparently homogeneous body and terminates in front of the anus in some large cells. This row of cells later gives rise to the alimentary canal and a tegumentary layer with a cavity between. The larva is now 0-03-0-3 mm. in length by 0*029-0-05 mm. in diameter. At this stage the tail becomes large and sickle-shaped and the cells of the body usually dip into it. The alimentary canal extends from the mouth to the anus. Motion is entirely sus- pended. Fourth Stage. Rapid growth takes place and the body retracts from the tail, which becomes a mere appendage. The length of the worm varies from 0*35-0-5 mm. Fifth Stage. When the body has attained its maximum thickness the anterior end commences to elongate and become thinner, and the mouth begins to close. The anterior and posterior ends may elongate simultaneously, but more often this process occurs along the whole length of the larva. The mouth eventually closes and all, or nearly all, traces of the viscera disappear. About the seventh day of development the body of the worm assumes a fibrous and very transparent appearance, but before this stage is reached a well developed alimentary canal with pharynx and oesophagus may be distinguished. Slight movements now commence at the neck of the animal and extend downwards, and about this stage a general ecdysis takes place and the sickle-shaped tail is cast off, a new skin XII] DEVELOPMENT IN MOSQUITO 211 being developed within the old one. Large cells appear at the end of the tail and form three or four papillae which characterise the larva at the end of this and during the next stage. Fig. 55. Filaria bancroftiX2oo. Stages in the development within the mosquito. (After Nuttall.) a, young filaria immediately after escaping from the sheath ; b, 5 days, c, 10 days, and d, 16 days after ingestion by the mosquito. The worm is now about 1-5 mm. in length, and its breadth has diminished to about one-half. The anterior end tapers but is abruptly rounded off ; the posterior end also tapers 14—2 212 FILARIA BANCROFTI [CH. slightly from the anus backwards, and bears the above-men- tioned papillae. Sixth Stage. The movements now become more active. The lips of the mouth are closely pressed together in the form of a cone and minute horny papillae are present. The worm now measures about 1*5 mm. by 0*03 mm. Until 1900 it was supposed that this was the final stage in the development, and that the worm now required to escape into some water, in which it swam about until it was taken up by man in drinking water. In that year Low shewed that there was yet another stage. Seventh Stage. When the filariae have reached their highest development in the thoracic muscles they leave that tissue and begin to travel forwards, probably as a result of some chemiotactic attraction. They pass into the loose cellular tissue in the prothorax near the salivary glands, then force their way through the neck and coil themselves up in the loose connective tissue just below the cephalic ganglion and salivary sac. Finally, they pass into the proboscis of the mosquito by making an independent passage through Button's membrane at the base of the labrum, and pushing forward between the labrum and hypopharynx amongst the stylets. Here the worms are found stretched along the length of the proboscis, head foremost Two worms, probably male and female, are nearly always found together. In this stage the worm is usually about i mm. in length and 0*025 mm- m breadth. It tapers slightly towards each extremity, and at the anterior end the cuticle is thickened in places to form a few small papillae arranged round the terminal mouth. The posterior end, which is rounded off, is provided with three papillae almost at right angles to the axis of the body of the worm. The alimentary canal is straight and shews no marked differentiation into oesophagus and intestine. Towards the anterior end, 0*14 mm. from the extremity, there is an indication of the presence of an orifice, towards which the genital duct is seen to bend. These young filariae remain in the proboscis of the mosquito until it feeds on some host. The worms then escape and may be XII] DEVELOPMENT IN MOSQUITO 213 214 FILARIA BANCROFTI [CH. found on the skin in the neighbourhood of the wound caused by the bite of the insect. If the skin is sufficiently moist the filariae then bore their way through the epidermis into the subcutaneous tissues. In some cases they may select the wound caused by the mosquito as the point of entrance into the body of their vertebrate host, but in most cases it is pro- bable that they make an independent entrance through the undamaged skin, as Looss has shewn to be the case for the larvae of Agchylostoma duodenale. Moreover, Bahr has actually observed the larvae of Filaria bancrofti bore into the pores of the skin. The filariae were dissected out of infected mosquitoes and placed in a drop of saline on the back of a man's hand. The larvae could easily be seen wriggling about in the water, but when placed on the skin, after a few convulsive move- ments, they suddenly disappeared, apparently through the orifices of the gland ducts. Six filariae were observed to disappear in this manner, "with almost lightning-like rapidity." When the skin is very dry the young filariae often die before they are able to effect an entrance, and therefore a person may be bitten by an infected mosquito without developing filariasis. If, however, the young worms effect an entrance, they make their way to the lymphatics of their host and there develop into the adult filariae. After fertilization the females then develop embryos, which, on being liberated, make their way to the blood circulation, and thus the life-cycle may be repeated. Conditions affecting the development of the filaria within the body of the mosquito. One of the most important factors in- fluencing development is the species of mosquito in which this process takes place. In some species development occurs much more readily and occupies a shorter period than in others. For example, in Fiji, Bahr found that F. bancrofti developed very readily in Stegomyia pseudoscutellaris, under favourable conditions, the young worms appearing in the proboscis within ten days. On the other hand, in Culex fatigans the develop- ment proceeded much less regularly and occupied a longer period, whilst in C. jepsoni and S. fasciata the worms developed very slowly, and eventually degenerated in the thoracic muscles without arriving at maturity. The effect of different species XII] INVERTEBRATE HOSTS 215 on the development is well shewn by the number of filariae that developed in each species. Stegomyia pseudoscutellaris and Culex fatigans are both efficient intermediate hosts for F. ban- crofti ; but in the former practically all the embryos develop in the insect and come to maturity, whereas in the latter only two or three ever complete their development. The effect of temperature on the rate of development is very marked ; at a high temperature the worms may be found in the proboscis after six days, but during cold weather the same evolution is not complete for at least 20 days, or may even be totally arrested. The following species of mosquitoes are capable of acting as the intermediate hosts for F. bancrofti, and with further re- searches there is little doubt that the list will have to be considerably extended. In many cases the development in the mosquito has not been followed completely : Species Locality Observer ANOPHELINES : A. (Myzomyia) rossii1 .. .. India „ (Pyretophorus) costalis1 . . West Africa (Myzorhynchus) sinensis2 . . Malay ,, barbirostris2 ,, ,, pedit&niatus2 ,, (Cellia) argyrotarsis2 . . West Indies albipes James Annett, Button and Elliott Leicester Low Vincent CULICINES : Culex pipiens1 . . . . . . China . . . . Manson [Australia . . . . Bancroft St Lucia . . . . LOW ] West Indies .. „ (Philippines .. Ashburn and Craig „ gelidus*\ (Malay, Sumatra, the Leicester „ sitiens* } ' \ Celebes and Malacca Stegomyia fasciata3 . . St Lucia, W. Indies, Low etc. „ gracilis2 j ,, perplex a2 I .. Malay .. .. Leicester ,, scutellaris2 } ,, pseudoscutellaris1 . . Fiji . . . . Bahr Mansonia uniformis (? africana)2 Central Africa . . Daniels ,, annulipes2 j Scutomyia albolineata2 I . . Malay . . "' . . Leicester Tceniorhynchus domesticus2) 1 Species in which complete development has been observed. 2 Species in which in all probability complete development takes place, but forms have not been actually seen in proboscis. 3 Species in which an incomplete partial development occurs. Forms never reach stage suitable for proboscis. 2l6 FILARIA BANCROFTI [CH. Effect of filarice on the mosquito. The developing filariae have a very deleterious effect on the health of the mosquito, and heavily infected individuals can easily be recognized by their sluggish appearance. When a very large number of embryos are ingested by a favourable intermediate host, the resulting development usually causes the death of the mos- quito. In the case of 5. pseudoscutellaris, Bahr noticed that when mosquitoes were fed on a slightly infected patient nearly all of them were alive 21 days later, but out of a batch of 200 insects that fed on a patient shewing very numerous filariae in his blood, only 17 managed to survive an equal length of time. The period at which the infected mosquitoes died was dependent apparently upon the degree of development of the filariae. Thus, in warm weather most of the insects died on the sixth day after feeding, and in the cooler season on the tenth. The last stages of development, when the filaria is entering the proboscis, seem to be the most critical time for the mosquito, as in one batch 23 Siegomyia were alive on the i5th day after infection, but only three of them lived four days longer. Possibility of another "indirect" mode of transmission by the mosquito. The pathogenic effect of F. bancrofti upon its intermediate host is of considerable interest, for it suggests that the worm has only recently become adapted to its present mode of transmission. Moreover, it seems possible that Hanson's theory that the filariae first escape into water and subsequently enter man, has been discarded rather too hastily. When the mature larvae migrate from the thoracic muscles, although most of them come to rest in the proboscis, it is no uncommon occurrence to find them in the legs and other regions of the mosquito. These " mistakes " on the part of the larvae also afford support to the theory that this filaria has only re- cently adopted its present mode of entry into the body. When the young filaria escapes from the proboscis of the mosquito on to the skin, it is only capable of penetrating the surface in the presence of moisture. On the other hand the young filariae will live in water for several hours, and if a drop of water con- taining them is placed on the skin the parasites at once disappear down the openings of the gland-ducts. XII] ELEPHANTIASIS 217 It is evident, therefore, that if this filaria escapes into water, either by the death of its insect host, or some other cause, it is perfectly adapted for the penetration of any skin with which it may come in contact. This was probably the original manner in which the parasite was carried by mosquitoes, and the possibility of the occurrence of such an " indirect " mode of transmission, concurrently with the more recently acquired " direct " method, should not be ignored. Pathological effects. In most cases F. bancrofti does not seem to exercise any marked injurious effect on its host; patients often shew filariae in their blood for many years and all the time appear in perfect health. Under certain conditions, however, the adult filaria may give rise to various pathological symptoms, mainly as a result of obstructing lymphatics. Amongst these affections may be mentioned chyluria, lymph scrotum, vari- cose groin glands, etc. In some instances a living worm, or a bundle of worms, may plug the thoracic duct and act as an embolus, or originate a thrombus ; in others, they give rise to inflammatory thickening of the walls, as a result of irritation, and thus lead to obstruction from the consequent stenosis. In such cases the embryos may disappear from the blood, usually as a result of the death of the adults. Sometimes adult filariae occur in large numbers in the lym- phatic glands and also in the epididymis, testis and tunica vaginalis. In these situations the worms may die and become cretified, and whether alive or dead they cause fibrosis and blocking of the glands. Elephantiasis. Of all the affections that are supposed to be due to filariasis, elephantiasis is the most important, as it occurs in most tropical countries. The disease may be denned as a chronic inflammatory hypertrophy of the fibrous con- nective tissue in some region of the body, induced by lymph stasis and resulting in a considerable hypertrophy of the skin and subcutaneous tissues. It most commonly affects the legs, scrotum, vulva, arms and breast. The resulting growths may become of enormous size, especially in cases of elephantiasis of the scrotum, in which this organ may attain the weight of over 230 pounds. According to Manson the condition of lymph 2l8 ELEPHANTIASIS [CH. stasis, necessary for the production of elephantiasis, may be due to the blocking of the lymphatic ganglia by the unripe eggs of filariae, expelled from the parent before the embryos are able to uncoil. These eggs are five times as wide as the embryo, and being more or less rigid would be incapable of passing through any lymph glands. This theory accounts for the fact that the filaria embryos are rarely found in the cir- culation of patients affected with elephantiasis. The reasons for regarding elephantiasis as a filarial disease are given by Manson as follows : " (i) The geographical distribution of Filaria bancrofti and of elephantiasis correspond ; where elephantiasis is common there the filaria abounds and vice versa. (2) Filarial lym- phatic varix and elephantiasis occur in the same district and frequently concur in the same individual. (3) Lymph scrotum, an unquestionably filarial disease, often terminates in elephantiasis of the scrotum. (4) Elephantiasis of the leg sometimes supervenes on the surgical removal of a lymph scrotum. (5) Elephantiasis and lymphatic varix are essen- tially diseases of the lymphatics. (6) Filarial lymphatic varix and true elephantiasis are both accompanied by the same type of recurring lymphangitis. (7) As filarial lym- phatic varix is practically proved to be caused by the filaria, the inference that true elephantiasis — the disease with which the former is so often associated and has so many affinities — is attributable to the same cause, appears to be warranted." On the other hand the filarial nature of elephantiasis is strongly opposed by certain authors, who bring forward argu- ments in support of the view that the disease is caused by bacteria. Le Dantec considers it due to a symbiotic infection with a Streptococcus and a Dermococcus. Dubruel obtained Streptococci in pure culture from cases of elephantiasis, and lately favourable results in the treatment of the disease seem to have been obtained by employing a vaccine prepared from this streptococcus. This author remarks that in the Island of Moorea (Tahiti), where about one- twelfth of the inhabitants shew elephantiasis, he examined the blood of 200 persons XII] FILARIA IMMITIS 2IQ without finding a single filaria. Moreover, he cites examples in which the contagious nature of the disease seems to be admissible. REFERENCES. Annett, Dutton and Elliott (1901). Report on the Malaria Expedition to Nigeria. Part n, Filariasis. Liv. Sch. of Trop. Med. Liverpool. Ashburn and Craig (1907). Observations upon Filaria philippinensis and its development in the mosquito. Phil. Journ. Sci., Sect. B, vol. ii. pp. 1-14. Bahr, P. H. (1912). Filariasis and Elephantiasis in Fiji. Journ. of the School of Trop. Med., Supplement No. i. Bancroft, T. (1900). On the Morphology of the young form of Filaria bancrofti Cobb. in the body of Culex ciliaris. Proc. Roy. Soc. N.S. Wales, vol. xxm. p. 48. Cobbold (1879). The life-history of Filaria bancrofti. Journ. Linn. Soc. Zool. vol. xiv. p. 356. Demarquay (1863). Note sur une tumeur de bourse. Gaz. med. Paris (3), vol. xvm. p. 665. Le Dantec (1900). Precis de pathologie exotiqm. Paris. Lewis, T. R. (1872). On a Hcematozoon inhabiting Human Blood. Calcutta, 1872. Linstow, v. (1900). Ueb. d. Art. d. Blutfil. d. Mensch. Zool. Anz. vol. xxm. p. 26. Low, G. C. (1900). A recent observation on Filaria nocturna in Culex. Brit. Med. Journ. i. p. 1456. Manson, P. (1884). The metamorphosis of Filaria sanguinis hominis in the mosquito. Trans. Linn. Soc. Zool. vol. n. pp. 10 and 367. Tropical Diseases. London : Cassell and Co. Nuttall, G. H. F. Encycl. Medica, Edinburgh, vol. vm. Scheube (1883). Die Filar iakrankheit. Volkmann's Samml. kl. Vortr. No. 232. II. Filaria immitis (Leidy, 1856). Synonyms. F. canis cordis Leidy, 1850. F. papillosa, hcematica canis domestici Gruby and Delafond, 1852. General account. This parasite occurs in the dog, in which it was first seen by Panthot in 1679 anc^ afterwards by Pey- ronnie in 1778. It has also been found in the fox, and the wolf. Noe and Fiilleborn shewed that Anopheles maculipennis, and also Stegomyia fasciata, serve as the intermediate hosts of this species. 220 FILARIA IMMITIS [CH. Distribution. F. immitis is very common in China and Japan where most of the dogs are infected. It is also common in Italy, especially in the marshy districts round Pisa and Milan. It has also been recorded from England, France, Denmark, Germany, Australia, Fiji, the United States and Brazil. Fig. 57. A, view of the heart of a dog infested with Filaria immitis Leidy ( X £) ; the right ventricle and base of the pulmonary artery have been opened, a, aorta ; b, pulmonary artery ; c, vena cava ; d, right ventricle ; e, appendix of left auricle ; /, appendix of right auricle. B, a female F. immitis removed from the heart to show its length. Natural size. (After Shipley.) Description. The adult is a filiform whitish worm, tapering at both extremities, especially at the tail, and rounded ante- riorly. The mouth is terminal, and surrounded by six, small, indistinct papillae. The anus is near the end of the tail. The male is 12-18 cm. in length by 07-0*9 cm. in breadth, and possesses a spirally wound tail, bearing two small lateral ridges supported by papillae. According to Schneider there are n papillae, six of which are post-anal. From the anus XII] LIFE-CYCLE 221 arise two spicules of unequal length. The female is 25-30 cm. in length, by 1-1*3 mm. in breadth. The tail is short and blunt, and the vulva is situated near the origin of the intestine, a distance of about 7 mm. from the mouth. The eggs hatch in the uterus, liberating embryos about 285 to 295 /* in length, by 5 ft in breadth ; their anterior ends are somewhat tapered, whilst posteriorly the body tapers off into a long and delicate tail. Life-cycle. As in the case of F. bancrofti, the embryos of F. immitis are liberated into the blood and appear in the peripheral circulation. According to Manson the embryos of this species, as in bancrofti, are more common in the blood during the night, thus exhibiting a nocturnal periodicity, but this is denied by Fulleborn. If the embryos are injected into the blood of a healthy dog, they will persist in the circulation for several months. Fig. 58. Part of the Malpighian tubule of an Anopheles claviger, infected with the embryos of Filaria immitis. (After Noe.) 222 FILARIA IMMITIS [CH. The further development of the embryos takes place in certain species of mosquito and has been carefully investigated by Noe and Fulleborn. The most efficient intermediate host was found to be Anopheles maculipennis } which invariably became infected by feeding on blood containing the embryos. On the other hand, under similar conditions only about 20 per cent, of Stegomyia fasciata shewed any development of the filariae within their bodies. Noe found that development would also take place in a large number of Anophelines, including Anopheles bifurcatus, Myzorhynchus pseudopictus and Myzomyia superpicta, and also in the following Culicines : Culex penicil- laris, C. malaria and C. pipiens. When a mosquito has fed upon an infected dog, three or four times as many filariae are found in the stomach of the insect as in the blood of the dog. The reason for this apparent increase is the concentration of blood that takes place in the gut of the mosquito, most of the serum being excreted within an hour after a meal. Within 20 to 40 minutes after being ingested by an Anopheles, the filariae are found in the Malpighian tubules, in which site they undergo their further development. The worms are guided to the tubules by some chemiotactic influence, for they have been shewn to be attracted towards the mouth of an open capillary tube containing an emulsion of a Mal- pighian tubule in normal saline. The embryos, during their development in the mosquito, cause a marked alteration in the character of the epithelium of the Malpighian tubules, which may be the cause of the high mortality amongst infected insects. The rate of development of jp. immitis, as in the case of bancrofti, depends mainly upon the temperature, for at 26° C. the whole process is complete within ten days, whereas at 20° to 21° C., it is very much prolonged. When the development is complete, the young filariae bore through the walls of the Malpighian tubule into the body-cavity of their host, and migrate towards the head. They usually come to rest within the sheath of the proboscis, but isolated examples may be found in the palps and legs. XII] REFERENCES 223 When an infected Anopheles, containing filariae in its proboscis, feeds on a dog, the worms escape through the fine membrane (Button's membrane) uniting the labellae, and thus get on to the surface of the skin. If this is sufficiently moist they penetrate the epidermis, and may be found in the sub- cutaneous tissues. The young filariae then make their way towards the heart and great vessels of the dog, and there develop into the adults. The worms may also be found in other regions of the body, but in any case the embryos, on being liberated, make their way into the circulation. Accord- ing to Caleb and Pourquier the embryos may pass into the foetal circulation, and therefore the disease may be transmitted hereditarily. The pathogenic effects on the dog vary considerably ; weak- ness, anaemia, cough, icterus, ascites and -lameness may be observed and a fatal result is frequent. No effective treat- ment is known. Filaria recondita Grassi, 1890. This filaria, which also inhabits the dogs in many parts of the world, is closely related to F. immitis. Grassi and Calandruccio have shewn that the embryos develop in the body of the dog- flea (Pulex serraticeps), the cat-flea (Pulex irritans), and also in a tick (Rhipi- cephalus siculus Koch). Although infection experiments with fleas gave no positive results, it seems probable that these insects may serve as the inter- mediate hosts for this filaria. REFERENCES. Calandruccio (1892). Descrizione degli embrioni e delle larve della filaria recondita (Grassi). Atti dell' Accad. Giornia, vol. LXIX. Fiilleborn, F. (1908). Ueber Versuche an Hundefilarien und deren Uebertragung durch Miicken. Arch. f. Schiffs. u. Tropenhyg. vol. xii. Suppl. 8, 43 pp. 4 pis. (1912). Untersuchungen iiber die chemotaktische Wirkung der Malpighischen Gefasse von Stechmiicken auf Hundemikrofilarien. Centralbl. f. Bakter. vol. LXV. pp. 349-352. (1912). Zur Morphologic der Dirofilaria immitis Leidy, 1856. Ibid. vol. LXV. pp. 341-349. Grassi and Noe (1900). Uebertragung der Blutfilariae ganz auf- schliesslich durch den Stich von Stechmiicken. Centralbl. f. Bakt. Orig. vol. xxvin. No. 19. 224 ORTHORRHAPHA BRACHYCERA [CH. Noe, G. (1901). Sul circle evolutive della Filaria bancrofti (Cobbold) e della Filaria immitis (Leidy). Ric. f. n. laborot. d. anatomia normale d. R. Univ. di Roma, vol. vm. pp. 275-353. - (1903). Ulteriori studi sulla Filaria immitis. Rend. Ace. d. Lincei. vol. xn. pp. 476—483. Shipley, A. E. (1896). Nemathelminthes and Chaetognatha, in Cam- bridge Natural History. London : Macmillan and Co. CHAPTER XIII ORTHORRHAPHA BRACHYCERA The flies belonging to this series are characterised by the form of the antennae, which, although variable, are never truly Nematocerous, nor yet like those of the Cyclorrhapha. They are usually composed of three dissimilar segments, of which the third is sometimes elongate and subdivided into a number of indistinctly separated segments. When an arista is present it is always terminal in position, and never superior as in the Cyclorrhapha. Rarely, as in the Leptidae, the antennae may be divided into more than three segments. The palpi are one- or two- jointed. Around the base of the antennae there is no definite arched suture enclosing a small depressed space, as in the Cyclorrhapha Schizophora. The venation of the wings is usually more complex than that of any of the other divisions ; the second longitudinal vein is simple, but the third and fourth veins are often forked. The anal cell is closed before the border of the wing, or distinctly narrowed at the border. A discal cell is practically always present. This group includes 16 families of flies, of which only one — the Tabanidae — is of any interest from the present point of view. Two other families, the Leptidae and Asilidae, include 'a few blood-sucking species, but are of little importance. As, however, many of the species belonging to these and other families, are habitually predacious on insects, they have an economic interest, and therefore we append the following synopsis. The only one of these families that includes species known to carry disease is the Tabanidae. XIII] SYNOPSIS OF FAMILIES 225 Synopsis of the families of Orthorrhapha Brachycera1. I. Third antennal segment composed of a series of in- distinctly separated subsegments ; empodia pulvilliform ; third and fourth longitudinal veins forked. (a) Costal vein extending all round the wing ; squamae large ; the third antennal segment never has a style or arista . . . . Tabanida. (b) Costal vein extending all round the wing ; squamae small ; third antennal segment may have a style, or arista, or not, or the antenna may consist of a large number of segments . . . . . . . . Leptidts. (c) Costal vein not extending beyond tip of wing, longitudinal veins not crowded anteriorly ; two sub-marginal and five posterior cells always present, the fourth closed. Third antennal joint composed of seven annuli, with a terminal style or arista . . . . . . . . . . Acanthomeridcs. (d) Costal vein not extending beyond tip of wing ; longitudinal veins usually more or less crowded anteriorly, posterior ones often weak ; four or five posterior cells, the fourth rarely or never closed . . Stratiomyidcs . II. Third antennal segment simple, with or without a terminal style or arista ; empodia pulvilliform. (a) Head small, formed almost entirely by the eyes ; thorax large and humped ; squamae peculiarly large . . . . . . . . Acrocerida. (b) Squamae small or moderate ; venation of wings peculiarly intricate Nemestri nidcs . (c) Squamae small ; wing venation more or less resembling that of Tabanus . . . . . . . . . . . . . . . . Leptidce. III. Third antennal segment simple, with or without a terminal style or arista ; empodia, when present, bristle-like ; third longitudinal vein, and often the fourth, forked. (a) Crown of head concave between the eyes : (i) Proboscis a rigid chitinous dagger ; flies bristly and hairy AsilidcB. (ii) Proboscis with fleshy labella ; antennae composed of four segments ; flies without bristles . . . . . . . . .... * Mydaides. (b) Crown of head not excavated between the eyes : (i) Wing with five posterior cells ; third and fourth longitudinal veins curve forwards . . . . . . . . . . . . Apioceridce. (ii) Wing with five posterior cells ; fourth longitudinal vein does not curve forwards ; predaceous flies . . . . . . Thevevidce. (iii) Wing with three or four (rarely five) posterior cells and often with dark markings ; anal cell large ; usually hairy bee-like flies, often with a long slender proboscis used for sucking the nectar from flowers Bombyliidce. 1 Modified from Alcock, loc. cit. p. 132. H. B.F. 15 226 TABANID^: [CH. (iv) Wing with three or four posterior cells, anal cell often small ; femora and tibiae often with combs of spinules ; small dull-coloured pre- daceous flies usually with a stiff proboscis for impaling prey . . Empididce. (v) Wings with three posterior cells ; proboscis not projecting ; small flies often found on windows .. .. ,.. .. Scenopinida . IV. Third antennal segment simple, with or without an arista ; the empodia, when present, are bristle-like ; third longitudinal vein not forked. (a) Wings shaped like a lance-head, the venation somewhat as in the Psychodidae . . . . . . . . . . . . . . LonchoptevidcB . (b) Second basal cell confluent with discal cell ; anal cell, if present, small ; usually brilliantly coloured flies with metallic sheen . . Dolichopodidai . (c) Second basal and discal cells either confluent or distinct ; anal cell, if present, small ; not brilliantly coloured flies . . . . . . Empidida. (d) Antennas apparently two-jointed, with a three-jointed arista ; wings (rarely wanting) with several stout veins anteriorly and other, weaker ones apparently connected with them and running obliquely across the wing ; small hunchbacked, quick running, bristly flies.. .. .. Phorida, CHAPTER XIV FAMILY TABANIDJE (BREEZE-FLIES, CLEGGS, HORSE- FLIES, GAD-FLIES, SERUT-FLIES) Description. The members of this extensive and important family are usually large and strongly built flies, the females of which feed on blood. The head is large ; the antennae are projecting, and the third joint is composed of four to eight indistinct segments, or annuli. The eyes are very large and laterally extended ; in the male they meet along the middle line (holoptic), but in the female the eyes are smaller and a narrow streak is left between them (dichoptic). In the living insect the eyes are often iridescent and usually marked with green, purple, or brown bands, or spots. The proboscis is projecting, sometimes as long as, or longer than, the body, and the mouth parts are adapted for piercing and cutting. Generally the labium is coarse and fleshy and the labella are large ; the epipharynx and hypopharynx are strong dagger-shaped structures; the mandibles are XIV] DESCRIPTION 227 sharply pointed and the maxillae have serrate edges. The palpi are distinct and two-jointed ; the terminal joint is inflated and hangs in front on each side of the proboscis. The thorax and abdomen are clothed with fine hairs, never with bristles, and are often striped or marked with dull colours. The abdomen is broad, never constricted at the base, and com- posed of seven visible segments. The legs are stout and the tibiae sometimes dilated; the pulvilli and empodia are in the form of large membraneous plates. The venation of the wings is very constant ; the third and fourth longitudinals are forked, so that two marginal and five posterior cells are always present ; the basal cells are large and the anal cells usually closed. The marginal or costal vein encompasses the entire wing (Fig. 5) . The squamae are large. Fig. 59- Tabanus kingi Austen, ? ( X 3). (After Austen.) Habitat. The members of this family are widely distributed throughout the world and about 1800 different species have already been described. They are especially evident on clear warm days, as soon as the sun has warmed the air, and are usually most active towards midday, but near Sedbergh, York- shire, the writer has been badly bitten by Hcematopota in the early mornings. 15—2 228 TABANID.E [CH. The males live entirely on the juices of flowers, honeydew, etc., and, in the absence of other food, the female will also feed on these substances. By nature, however, the female feeds on blood, and is one of the most blood-thirsty of all insects. Its bite is painful, but usually is not followed by any marked inflammation, or swelling. Life-cycle. The eggs of the Tabanidse are commonly laid in large shapely masses on the leaves and -stems of plants growing in marshy ground, or overhanging water. In some species they are deposited on stones or rocks above the water of streams, and are very difficult to discover. Fig. 60. A rock at Khor Arbat, Anglo-Egyptian Sudan, showing sites selected by Tabanus kingi for ovipositing (indicated by crosses) ; the three lower crosses represent freshly laid egg-masses. (After King.) The eggs of Tabanus par were observed by King to be laid separately on the under surface of the leaves of water-plants. The colour of the eggs is usually brown gr black, and at ordinary summer temperatures they hatch out in from seven to nine days. XIV] LIFE-CYCLE 229 The larvae may be found in rotting logs and stumps, in the soil at the edges of pools and streams, under stones in ditches, or swimming free in the water. If kept supplied with a diet of angle- worms the larvae can easily be reared, either in jars of moist earth, or in jars containing sand and water. As a rule they are cannibalistic in habit and only one can be reared in each jar, but T. biguttalm is an exception to this rule, and in this species several can be reared together in the same receptacle. The larvae are cylindrical in form, pointed at both ends ; the body is composed of eleven segments, each of which is usually encircled by a prominent fleshy ring, or row of protuberances, Fig. 61. Egg-mass and mature larva of Tabanus kingi Austen, a, egg- mass, x 6 ; b, lateral view of larva, x 3 ; c, lateral view of 4th and 5th abdominal segments, x 6 ; d, posterior view of anal segment (inverted), X6 ; e, lateral view of anal pseudopod. (After King.) which are most pronounced on the ventral side, where they serve as prolegs. The head is small, but distinct, and the mouth parts are very peculiar ; the mandibles are attached so as to move antero-posteriorly ; when they are retracted the anterior ends point forwards, but when extended they point downwards and backwards, thus forming a pair of hooks that serve to hold prey. The duration of the larval stage depends upon the temperature. In temperate countries the larva usually lives through the 230 TABANID.E [CH. winter and only pupates the following spring, but in Egypt King was able to rear T. par, from the freshly hatched larvae to adults, in three and a half months. The pupal stage is usually completed in three to four weeks, and as the whole development generally takes about eleven months, the duration of the larval stage is very considerable. In some cases it probably takes more than one year for its development. When fully grown the larva buries itself in the sand, or earth, in its immediate neighbourhood, and then pupates. Classification. The following synopsis of the genera of Tabanidae is taken from Miss Ricardo's Revision of the Family ; the more important genera, which have a world-wide distribu- tion, are printed in capitals : Synopsis of Genera of Tabanidce. 1. TABANIN^E. Ocelli absent ; hind tibiae not spurred. f Third antennal segment composed of four subsegments or rings, and 1 •{ not angulated or spurred at base =2 I Third antennal segment composed of five subsegments or rings = 5 f Rings so distinct that the antenna appears to consist of six segments 2 ^ Hexatoma Meigen (Europe). L Rings not so distinct as to modify the appearance of the antenna = 3 f Wings with a profusion of ring-like and scroll-like markings 3 •{ H^EMATOPOTA. L Wings without circles and scrolls . . . . . . ... . . = 4 f First and second antennal segments pubescent in the male, third segment 4 •{ longer than the first ; eyes hairy Dasybasis Macquart (Chili and Australia), f First antennal segment globose, situated on a frontal protuberance 5 \ Bolbodimyia, Bigot (Venezuela). I First antennal segment not globose . . . . . . . . = 6 /Third antennal segment not angulated or toothed at base . . = 7 \Third antennal segment angulated or toothed at base . . . . =9 f Body covered with metallic scales Lepidoselasa Macquart (South America). 7 •{ Body metallic in colouring Selasoma Macquart (South America) I Body not in any way metallic ; first antennal segment longer than is L usual in Tabanus ; wings commonly with brown markings = 8 f Antennae long, the third segment cylindrical, and situated on a pro- 8 J jecting tubercle . . . . Udenocera Ricardo (Ceylon). I Antennas not as in Udenocera L Diachlorus Osten Sacken (America and Philippines). XI V] CLASSIFICATION 231 /Abdomen short, stout, very convex Stibasoma Schiner (America). \ Abdomen not as in Stibasoma . . . . . . . . = 10 f Antennae long and slender, first segment long 10 •( Acanthocera Macquart (South America). I Antennae not as in Acanthocera .. . . * .. .. .. =11 f Slenderer in build, usually with thorax and abdomen banded ; third IT J antennal segment slender, wings mostly with brown markings f Dichelacera Macquart (South America). I Stouter in build, third antennal segment stout . . TABANUS Linn. II. PANGONIINNE. Ocelli usually present ; hind tibiae spurred. f Third antennal segment composed of eight or seven subsegments or i •{ rings ; proboscis usually elongate . . . . . . . . = 2 I Third antennal segment composed of five rings ; proboscis short = 14 /Third antennal segment with a tooth Dicrania Macquart (Brazil). \ Third antennal segment not toothed . . . . . . = 3 /Wings short ; body flat, elliptical Apocampta Schiner (Australia). \ Wings not short . . . . . . . . . . . . . . = 4 f Third antennal segment with each subsegment branched 4 •{ Pityocera Tos (Central America). I Third antennal segment not branched .. .. .. = 5 f Upper corner of eye terminating in an acute angle 5 ~{ Goniops Aldrich (North America). I Upper corner of eye not terminating in an acute angle . . . . =6 f Antennae deep-seated, inclined downwards ; palpi very large 6 •{ Cadicera Macquart (South Africa) L Antennae and palpi not as in Cadicera . . . . . . = 7 f Antennae awl-shaped ; end of proboscis hatchet-shaped ; anal cell ! open and anal vein curved I Pelecorhynchus Macquart (Australia and S. America). I Antennae, proboscis, etc., not as in Pelecorhynchus = 8 f Proboscis scarcely extending beyond palpi 8 -{ Apotolestes Williston (California). L Proboscis extending beyond palpi = 9 /Wings with fourth posterior cell closed . . . . . . . . = 10 9 \Wingswithfourthposteriorcellopen .. .. .. .. =11 /Eyes bare . . . . . . Dorcalamus Austen (South Africa). \Eyes not bare Scione Walker (South America, Seychelles, Australia). /Wings with first posterior cell closed .. .. .. .. = 12 \Wings with first posterior cell open . . . . . . . . =13 /Eyes bare . . . . PANGONIA Latr. (subgenus Pangonid). \Eyeshairy . . ' .. PANGONIA Latr. (subgenus Erephrosis). /Eyes hairy . . DIATOMINEURA Rond. (subgenus Diatomineura). X3 \Eyes bare . . DIATOMINEURA Rond. (subgenus Corizoneura Rond.) /First and second segments of antennae short . . ,. . . =15 \First and second segments of antennae long . . CHRYSOPS Meigen. 232 TABANID^ AND DISEASE [CH. f Second segment of abdomen unusually large, spurs of tibiae small 15 ^ Pronopes Loew (Cape Colony). I Abdomen and tibiae not as in Pronopes .. .. .. .. =16 g /Face concave in the middle Rhinomyza Wied. (Cape Colony and Java). \ Face not concave *.. .. .. .. .. .. .. = 17 f Wings with first posterior cell open SILVIUS Meigen (subgenus Silvius). j Wings with first posterior cell closed I? ^ SILVIUS Meigen (subgenus Esenbeckia Rond., Brazil). Third segment of antennae with an acute spine L Gastroxides Saunders (India). Tabanidce and disease. It must be admitted that the evidence in support of the view that Tabanidae act as disease carriers is rather unsatisfactory. Their voracious blood-sucking habits and conspicuous size have given the flies a bad reputa- tion in many parts of the world, and natives frequently assign various ill-effects to their bites. Most of these accusations, however, have not yet been justified, although it seems probable that certain trypano- somiases of animals, especially Surra, may be carried by Tabanidae. There are many difficulties in the way of conducting experi- ments with these flies. They are always very impatient of captivity and spend most of their time attempting to escape. As a result it is difficult to make them feed on any particular animal, and the flies soon die. Up to the present time hardly a single experiment has been recorded in which the possibility of a cyclical mode of transmission of trypanosomes by Tabanidae has been investigated, for in no case hav^e the flies lived a. sufficient length of time to decide the point1. Possibly the best way of testing whether Tabanids act as the true inver- tebrate hosts for any disease, would be to capture large numbers of wild flies and feed them on susceptible animals. In this manner, the presence of any naturally infected insects might be detected. The occurrence of flagellates in the alimentary canal of a large proportion of Tabanids is certainly rather suspicious, for in many cases it is difficult to distinguish 1 Mitzmain has recently conducted experiments on the transmission of Surra by Tabanus stviatus and has definitely excluded the possibility of a cyclical development, but has succeeded in obtaining direct transmission. XIV] TRYPANOSOMIASIS 233 between developmental forms of ingested trypanosomes and the various insect flagellates. It has been shown repeatedly that when Tabanidae, inter- rupted in a feed on an infected animal, are at once transferred to a healthy one, the latter may become infected as a result of their bites. In these cases the parasites, present in the blood, are simply mechanically transferred from the first animal to the second by means of the proboscis of the insect. Almost any blood-sucking insect is capable of such transference of in- fection, but the importance of this mechanical transmission should not be under-estimated. With the exception of El Debab (T. soudanense), there now seems little doubt that the pathogenic trypanosomiases of Africa are all transmitted by various species of Glossina, which serve as the true invertebrate hosts and, once infected, remain so for considerable periods. On the other hand, there is evidence to shew that these diseases, once started, may continue to spread in the absence of tsetse-flies. In this connection the outbreak of Trypanosoma pecorum infection in a herd of cattle belonging to the Uganda Sleeping Sickness Commission is of some interest, for there seems to be little doubt that in this case Tabanus secedens Walk, was responsible for spreading the infection. The herd contained a few animals that had been experimentally infected with T. pecorum. Shortly after the appearance of swarms of Tabanus, large numbers of the cattle, that had remained healthy for a year, shewed signs of infection with T. pecorum. It should be noted, however, that Glossina palpalis were also found in small numbers after the Tabanids had disappeared, and their presence might have been overlooked previously. Jowett made some experiments near Cape Town with a cattle trypanosome of the Dimorphon type, obtained near Beira, Portuguese East Africa. As this infection seems to spread in the absence of tsetse-flies, transmission experiments were made with Hczmatopota and Stomoxys. " Numbers of Hcematopota and Stomoxys were collected at frequent intervals and placed in large glass lamp chimneys, the ends of which had been closed with mosquito netting. After 234 TABANID^E AND DISEASE [CH. having shaved and damped a patch of skin on the trypanosome infected subject, one end of such a tube was then applied to the latter. As soon as it was seen that a number of flies had commenced to feed on this animal, the tube was removed and without delay applied to the skin of a healthy animal, the flies being allowed to finish their meal on the latter. At the con- clusion of the experiment the flies in most instances were killed. Occasionally they were dissected. Only on two or three occasions were they kept and used for feeding a second time during the following days. The experiment therefore, permitted only of mechanical transmission." Only one positive result was obtained out of five experiments. In this case 122 Stomoxys were fed in the course of 14 days on an infected sheep and afterwards on a healthy sheep. After an interval of six days three Hcematopota, of which one was seen to bite, fed similarly. Trypanosomes were found in the blood of the sheep 13 days later, and it died after another 10 days. The experiment shews that this trypanosome can be conveyed mechanically by one of these species, and Jowett thinks that the Hcematopota were responsible. Hart records an experiment in North-Eastern Rhodesia supporting the view that Pangonia and Stomoxys may transmit trypanosome infections. An outbreak of trypanosomiasis (T. dimorphon, or pecaudi) occurred on a farm fifty miles from Fort Jameson. The owner stated that tsetse-fly had never been seen, but Pangonia had been numerous. Two bullocks infected with trypanosomes were kept at the farm and the remainder sent away. Then three healthy cows were brought from Fort Jameson and kraaled with the two bullocks, and to eliminate the chance of their being bitten by a stray tsetse-fly, the animals were fed close to the house. The experiment began on April nth and the animals were at once bitten by Pangonia and Stomoxys nigra. On May 27th trypanosomes were seen in one of the cows, and the remaining two died of trypanosomiasis at the beginning of July. It is impossible to decide whether the infection was due to Pangonia or Stomoxys, or both, and the possibility of stray tsetse-flies having bitten the animals is also not excluded. XIV] EL DEBAB 235 Captain Hadow sent to the Wellcome Research Laboratories blood smears from two sick bulls at Kadugli, Kordofan. These were examined by Dr Balfour and found to contain numerous trypanosomes, the species probably being T. brucei (or pecaudi) . These bulls could not have been bitten by tsetse-flies, for the only tsetse area in Kordofan is at Kawalib, sixty miles from Kadugli. The infection was attributed by the Arabs to the serut fly (Tabanus or Pangonia). The circumstantial evidence in support of the view that El Debab, a disease affecting dromedaries in the North of Africa, is mainly carried by Tabanids, is much stronger than in the case of the other African trypanosomiases. The natives of North Africa from time immemorial have accused the serut flies of inoculating this disease into the dromedaries. When these animals remain during the summer in regions where Tabanids are numerous, the mortality from El Debab in the following months is very great. On the other hand, if Tabanids are few or absent, the disease seems to be unable to become established. In Algeria the majority of the Tabanids appear between the ist and i5th of June ; they last for about forty days and then disappear, as soon as their enemies the Asilids begin to hatch out. The Tabanids live in the damp valleys and often frequent the tufts of Thapsia, appearing as soon as this plant flowers, and disappearing after it has withered. Experimentally, Drs Edmond and Etienne Sergent, in Algeria, have been able to transmit T. soudanense, the patho- genic agent of El Debab, by the bites of Tabanus nemoralis, Mg. and T. tomentosus Macq. The flies were first allowed to bite heavily infected rats or mice and subsequently fed on healthy animals. When there was no interval between the two feeds, five successful trans- missions were obtained, and in one case after an interval of 22 hours the flies were still infective. Throughout these experiments only rats and mice were employed, never the natural host of the trypanosome. These results are in harmony with what is known about the history of the disease. 236 TABANIDAE AND DISEASE [CH. Generally the infection lasts at least one year in camels, and in the month of June practically every herd contains several individuals with numerous trypanosomes in the blood. These animals would act as centres from which the infection could be spread by the Tabanids. These latter feed during the sunny hours of the day and usually attack the herd in swarms. As a result of the active movements of the camels, the insects are continually flying from one animal to another, and the conditions are very favourable to the spread of any infection. Horses may also be infected by the agency of these same insects, but such cases are rare, as horses are not usually kept in the neighbourhood of herds of camels. Three other trypanosome diseases, viz. Nagana, Mai de la Zousfana and Dourine, have been transmitted experimentally by the bites of various species of Tabanidae in Algeria. Transmission was only effected when the insects fed on the healthy animals immediately after having bitten an animal containing a great many trypanosomes in its blood. In no case was any infection produced if there was an interval of more than a few minutes between the two bites. A single bite was sometimes sufficient to cause inoculation of the disease, and therefore, under suitable conditions, it is probable that this mode of transmission can assume great importance. According to Cazalbou, the disease of dromedaries at Timbuctoo known as Mbori, and also Souma (T. cazalboui) at Segou, a disease affecting horses and cattle, are both propagated by Tabanus tceniatus, Macq. and T. biguttatus, Wied. There is evidence showing that Tabanidae are agents for the transmission of Surra (T. evansi}. Thus Rogers, in the Fede- rated Malay States, invariably produced the infection in dogs and rabbits by the successive bites of many Tabanids. A dog bitten by 12 flies that had just previously sucked blood from another dog, heavily infected with T. evansi, shewed parasites after an incubation period of seven days. Fraser and Symonds repeated these experiments employing various species of Tabanus, Hczmatopota and Stomoxys. With four species of Tabanus — T. fumifer, T. partitus, T. vagus, and XIV] SURRA 237 T. minimus — they had four successes, three when there was no interval between the two feeds, and one after a five-minute interval. Ten experiments were performed and in each case only one or two flies were used. Five experiments with Stomoxys and two with Hczmatopota under similar conditions gave negative results. A number of Tabanidae were then fed on infected animals and, at varying intervals, emulsions of the body contents of the flies inoculated into susceptible animals. It was found that the trypanosomes in the alimentary canal of Tabanus remained infective for 24 hours, but after longer periods lost their virulence. Leese studied the natural transmission of Surra at Mohaud, India, and made experiments with mosquitoes, Stomoxys, Tabanus, Hczmatopota and sand-flies. Four Tabanus, which were fed on camels, in two of which trypanosomes were numerous, and transferred immediately to a white rat, produced infection in the latter, and under similar conditions ten Hczmatopota produced infection in a guinea-pig. Of three similar experi- ments, employing Stomoxys, only one gave positive results, so it seems that Tabanus is able to transmit Surra better than Stomoxys. On the other hand, Leese is strongly of the opinion that Tabanus and Hczmatopota are not specific transmitters, for outbreaks of the disease have occurred under circumstances that precluded the possibility of their being the carriers. Neverthe- less, in the Punjab the worst " Surra zones " seem to be in places where Tabanus is most numerous. Baldrey has also performed some experiments on the transmission of Surra by various Tabanids and found that the trypanosomes remained virulent in the gut for not longer than 24 hours. An attempt was made to test the possibility of a cyclical mode of trans- mission, but all the Tabanids died by the end of the nineteenth day. Up to this date the inoculation of their body contents into susceptible animals gave negative results. In America, Mohler and Thompson noted an outbreak of Surra following the importation of zebus from India. This herd consisted of 51 cattle that had been imported from Poona, where their blood was examined twice with negative results. On arrival in New York they appeared to be in good condition, 238 SURRA [CH. but 2 ccs. of blood from each animal were injected into rabbits. Three of these rabbits showed T. evansi in their blood, and after some delay the three cattle thus shewn to be infected were destroyed and the remainder screened. At this time there were many Tabanus atratus present, together with other Tabanidae and Stomoxys calcitrans. In subsequent series of inoculations, 13 more animals were found to be infected and removed ; finally, the remainder were put in fly-proof box-stalls in a fly-proof stable, and these cattle all remained healthy. The authors are of the opinion that Tabanus atratus was responsible for the spread of the infection amongst the herd, but the results are not very conclusive, as the cattle may have been infected before they arrived. In the Philippines, Mr M. B. Mitzmain informs me that he has succeeded in obtaining the direct transmission of Surra by means of Tabanus striatus. The flies were bred in captivity and transmission was successful from guinea-pig to monkey, and from horse to horse. In addition, this observer states that T. striatus is undoubtedly the carrier of Surra in extensive epidemics throughout the Philippines, and that there is a " very decided correlation between the predominance of this fly and outbreaks of Surra." On the whole, the available evidence supports the view that Surra may be directly transmitted by the bites of various Tabanidae, and that in nature they play a very important part in the spread of the infection. It is doubtful, however, whether the transmission is always mechanical, and further experiments on this point are much to be desired. Since the above account was written, Leiper, in West Africa, has discovered that two species of Chrysops serve as the inter- mediate hosts of Filaria loa. At present no details are available, but this discovery is especially interesting, as it is the first record of any Tabanid having been shewn to be responsible for the transmission of a human disease. XV] CYCLORRHAPHA SCHIZOPHORA 239 REFERENCES. Alcock, A. (1911). Entomology for Medical Officers. Austen, E. (1909). African Blood-sucking Flies. British Museum. Cazalbou (1904). Recueil de Med. Vetevinaire, vol. LXXXI. p. 615. - (1906). Rev. Generate de Med. Vet. Nos. 89-90. Fraser and Symonds (1908). Studies from the Institute for Medical Research. Federated Malay States, No. 9. Hart, R. (1911). Journ. Comp. Path, and Therap. Dec. 1911, p. 354. Jowett, W. (1911). Ibid. vol. xxiv. p. 21. King, H. H. (1908). Third Report Wellcome Research Laboratories, Khartoum. London : Bailliere, Tindall and Cox, p. 213. Leese, A. S. (1909). Journ. Trop. Vet. Sci. vol. iv. p. 107. Mohler, J. R. and Thompson, W. (1911). 26th Annual Report (for 1909), Bureau Animal Industry. Washington, p. 81. Montgomery and Kinghorn (1907). Ann. Trop. Med. and Parasit. vol. n. p. 130. Ricardo, G. (1901-1904). Ann. and Mag. Nat. Hist. Rogers, L. (1901). Proc. Roy. Soc. B. vol. LXVIII. p. 163. Sergent, Ed. and fit. (1905). Ann. Inst. Pasteur, vol. xix. p. 17. (1906). Ibid. vol. xx. p. 665. CHAPTER XV CYCLORRHAPHA SCHIZOPHORA General description. All the members of this series are distinguished by the presence of a distinct frontal lunula and frontal suture. The antennae are composed of three segments of which the terminal bears an arista, almost invariably dorsal in position, and never thickened into a terminal style. There are never more than three posterior cells present (Fig. 63) the first of which may be closed or narrowed in the margin, but the others remain open. None of the longitudinal veins are forked ; the marginal and sub-marginal cells are never closed ; and the anal cell very rarely extends towards the margin of the wing. The flies are all more or less bristly. This very large division, including several families, is termed by Williston, the Myodaria. It may be divided into two groups, the Acalyptratae and Calyptratae, which are distinguished as follows : 240 CYCLORRHAPHA SCHIZOPHORA [CH. (i) Acalyptratae. The squamae are always small, or vestigial, so that they do not conceal the halteres when viewed from above. The auxiliary vein is often indistinct or vestigial, or close to the first longitudinal, with which it may be fused. The basal cells are small, and the posterior ones indistinct or wanting. The males are never holoptic and the front is never markedly constricted. The thorax is without a complete transverse suture and the posterior callosity is usually absent. The members of this group are never large flies, but usually small, or very small. None of them are known to suck blood, but certain species, e.g. Sepsis, are probably concerned in the transmission of disease1. (2) Calyptratae. The squamae are well-developed, never vestigial, and generally conceal the halteres when viewed from above. The auxiliary vein is always distinct along its whole course and the first longitudinal is usually of considerable length, never very short. The males are often holoptic or the front markedly constricted. The thorax has a complete transverse suture in front of the wings and a posterior callosity is present. The members of this group are generally flies of moderate or con- siderable size and are never very small. The house-fly and tsetse-fly are two well-known examples of this large and im- portant group, which is of the highest economic importance. Williston divides them into six families, of which the only one that we shall consider is the Muscidae. Synopsis of Families of Calyptrata. f Mouth and mouth-parts small or vestigial; first posterior cell closed 1 •{ or narrowed (except in Gastrophilus). Bot-flies . . —Oestvidce I Mouth of usual size, mouth-parts not vestigial . . . . . . =2 rHypopleurae with a tuft of bristles; first posterior cell narrowed or closed . . . . . . . . . . • • • • = 3 Hypopleurae without a tuft of bristles ; first posterior cell narrowed or L fully open in the margin . . . . . . . . . . = 6 1 Vide Graham-Smith, G. S. (1913), Flies and Disease. Non-bloodsucking Flies (Cambridge University Press). XV] MUSCID.E 241 / Antennal arista bare or somewhat pubescent .. =Tachinid(S. 3 \Antennalaristaplumoseordistinctlypubescent .. .. .. =4 f Antennal arista bare on the distal half ; bristles rarely present on the 4 -4 dorsal surface of the anterior segments of abdomen = Sarcop h agida. L Antennal arista plumose or pubescent to the tip .. .. .. =5 C Dorsum of abdomen usually bristly on anterior part ; legs usually long J =Dexiidce. | Abdominal segments without bristles, except more or less near the tip ; L legs not markedly elongated .. .. .. =MusciD^. r First posterior cell narrowed or closed ; arista plumose to the tip 6 ) First posterior cell very slightly or not at all narrowed in the margin ; t arista plumose, pubescent or bare . . . . =Anthomyida. Family MUSCID.E. The various individuals of this family are distinguished by the absence of bristles on the abdomen, except at the tip, and by the narrowed first posterior cell. The antennal arista is usually plumose to the tip, sometimes only on the upper side, and rarely bare. The eyes of the male are approximated or contiguous, and the front of the female broad. The eyes may be either bare or hairy. With the exception of Glossina, the abdomen is composed of four visible segments. The members of this family are generally of moderate size, and are never elongate, very hairy, or bare flies. For the sake of convenience, we have followed Alcock in dividing the Muscidae into two artificial groups according to whether the adults suck blood or not. The importance of the latter group (including house-flies, blowflies, etc.) as carriers of disease, has been described by Graham-Smith (loc. cit.} and it is unnecessary to give any further description of them in the present account. On the other hand, the blood-sucking Muscidae include some of the most formidable biting-flies that carry disease. Blood-sucking Muscidae1. In the majority of blood-sucking Muscidae the proboscis is strongly chitinized and rigid, is slightly or not at aU retractile, and is more or less slender and tapering, and the labella are small, rigid and strongly chitinized, and serrated or spinose, so 1 After Alcock, loc. cit. H. B. F. 16 242 BLOOD-SUCKING MUSCID^ [CH. that the proboscis forms a very efficient apparatus for piercing the skin. Occasionally the proboscis is only partly chitinous and is retractile, and the labella are large and fleshy, but even in these cases strong teeth, capable of cutting through the skin, are present. In other respects the proboscis resembles that present in the non-biting Muscidae, being longitudinally grooved on its dorsal surface, so as to ensheathe the epipharynx and hypopharynx, which together form a tube, by apposition and basal interlocking. The blood-sucking habit is equally well developed in both males and females. Although Glossina and Stomoxys are the only two genera that have been proved to carry infection, there is every possi- bility that other members of the group may suddenly acquire unenviable notoriety from this point of view, and therefore we include the following table of the genera, taken from Alcock : Genera of Blood-sucking Muscidce. f Arista feathered only on the dorsal surface, individual hairs being also feathered. Proboscis with a bulbous base and very slender shaft. Maxillary palps long and slender, forming a sheath round the pro- boscis. Fourth longitudinal vein curved in its proximal portion so as to enlarge the anterior basal cell distally and to contract the discal cell basally ; and sharply bent forward in its distal portion in line with the posterior cross-vein so as to nearly close the first posterior cell at a point much anterior to the tip of the wing. Abdomen composed of seven visible segments . . . . =Glossina. Individual hairs of arista not feathered. Shaft of proboscis not remark- ably slender. Maxillary palps not forming an obvious sheath for the proboscis. Fourth longitudinal vein not markedly sinuous in its proximal portion and bending forwards in its distal portion at a point considerably beyond the posterior cross- vein. Abdomen composed of four visible segments . . . . . . = 2 {Maxillary palps slender, less than half the length of the proboscis. (Arista feathered dorsally only. Third longitudinal vein with some bristles on its proximal part.) .. .. .. .. = Stomoxys. Maxillary palps more or less spatulate, almost as long as the proboscis, always much more than half its length . . . . . . =3 C Proboscis chitinous in all its extent, the labella small . . . . =4 Proboscis with the distal part, and large labella, fleshy. Terminal fleshy part of proboscis reflexed beneath the chitinous part in repose. Arista feathered dorsally and ventrally ; third longitudinal vein not bristly ; fourth longitudinal vein abruptly bent so as nearly to close the first posterior cell =Phil(zmatomyia (including ? Pristorhynchomyia). XV] TSETSE-FLIES 243 / Arista feathered only on dorsal surface . , . . . . . . =5 \Arista feathered on both dorsal and ventral surface . . v, =6 C Proboscis long and tapering ; fourth longitudinal vein gently curved distally so as to leave the first posterior cell wide open ; third longi- tudinal vein without bristles . . . . . . =Lyperosia. Proboscis short and stumpy ; first posterior cell narrowly open ; third I longitudinal vein with some bristles proximally — Stygeromvia. f Fourth longitudinal vein strongly curved distally, so as to leave first posterior cell narrowly open. Third longitudinal vein without 6 •{ bristles . . . . . . . . . . . . =Hcematobosca. I Fourth longitudinal vein slightly curved distally. so as to leave first posterior cell widely open . . . . . . . . = 7 7 / Third longitudinal vein with some bristles proximally =Hamatobia. \Thirdlongitudinalveinwithoutbristles .. .. =Bdettolarynx. CHAPTER XVI THE TSETSE-FLIES — GENUS GLOSSINA, WIED., 1830 Diagnosis. The genus Glossina is sharply distinguished from all other members of the Muscidae by its viviparous mode of reproduction, which resembles that of the Pupipara, and also by certain peculiarities in the structure of the antennae and in the wing venation. Austen gives the following diagnosis of the genus : " Narrow-bodied, elongate, dark brown, blackish, yellowish-brown, or yellowish flies belonging to the Family Muscidae, ranging in size from about 6 or 8 mm. in the case of Glossina tachinoides, Westw., to as much as 13 or 13-5 mm. in that of a large female of G. brevipalpis, Newst., or longipennis, Corti ; recognisable when alive and at rest by the wings being closed flat one over the other above the abdomen (beyond which they project considerably), instead of divaricate (as in the case of Stomoxys) or tectiform (as in Hcemato- pota], and by the proboscis (i.e. proboscis ensheathed in the palpi), projecting horizontally in front of the head ; palpi, as seen in the natural position, extend- ing slightly beyond the proboscis, their inner sides grooved so as to form a sheath for the latter, to which in life they are applied so closely as entirely to conceal it ; base of proboscis suddenly expanded beneath into a large onion- shaped bulb." General description. In addition to the above-mentioned characters, there are certain others which aid in the differentia- tion of the genus. The antenna, in both sexes, contains in the 1 6 — 2 244 GLOSSINA [CH. second and third segments a curious sense-organ, consisting of a number * of sacs lined with sensory epithelium and opening to the exterior by a well-marked pore on the inner surface of the third segment. From the structure of this organ it is supposed to be auditory in function. The arista of the antenna is three jointed, the first two joints being very small, the terminal one broad and compressed, and feathered on its upper side with about 22 or 23 fine branching hairs. The eyes are large and in both sexes are well separated ; the anterior facets towards the inner margin are much larger than those behind. w Fig. 62. Comparative morphology of the proboscis of Glossina (I), Melo- phagus (II) and Stomoxys (III). B, proboscis bulb ; G.S., common salivary duct ; Hyp., hypopharynx ; L., labellae ; Lab., upper lip (labium) ; L. inf., lower lip. I, Glossina palpalis ; II, Melophagus ovinus ; III, Stomoxys calcitrans ; x 35. (After Roubaud.) The horizontally projecting proboscis is strongly chitinized and consists of a bulbous base contracting to a long and very slender shaft. The base of the proboscis, or proboscis bulb, is surrounded posteriorly by a fold of skin forming the hind-wall of the buccal cavity. The proboscis is grooved dorsally to XVI] DESCRIPTION 245 contain the stylet-like epipharynx and the tubular hypopharynx which, by apposition, form a suctorial tube. The maxillary palps are slender and as long as the proboscis, round which they form a loose sheath when the insect is resting. The wings possess a very striking venation which is quite sufficient in itself to distinguish the genus. The fourth longi- tudinal vein is strongly curved in its proximal portions. The anterior basal transverse vein, at the base of the discal cell, is very short, and this first curve of the fourth longitudinal vein reduces the basal half of the discal cell, whilst the anterior basal cell is correspondingly increased. The fourth vein then bends upwards to join the anterior transverse vein, after which Anterior cross-vein j Auxiliary vein Fig. 63. Wing of Glossina palpalis to shew the venation. it runs obliquely downwards almost at right angles to its former course. After joining the posterior transverse vein it again bends upwards and reaches the margin of the wing some distance before the apex. The second, third and fourth longitudinal veins all turn upwards at their tips and the anterior transverse vein is very oblique. The sexes of Glossina can be readily distinguished, as in the male the external genitalia form a large oval swelling, the hypopygium, lying beneath the ventral surface of the seventh abdominal segment. The anus forms a median slit in the front part of this hypopygium and anteriorly on the venter of the sixth abdominal segment is a pair of smaller swellings, termed 246 GLOSSINA [CH. hectors. When the hypopygium is turned back a system of complicated appendages is displayed, the arrangement and structure of which have been shewn by Newstead to be of great use in classification. These appendages are briefly as follows : the superior claspers, whose chief function is apparently to grip the abdomen of the female ; the editum ; the inferior claspers, which present very striking morphological differences Pr Fig. 64. Gravid uterus of G. palpalis containing a larva at an advanced stage of development. Dorsal view x 10. C.G.gl., common excretory duct ; CL.gl. principal lateral trunk of the uterine glands ; L, body of the larva ; O.O., ovary ; Pr., caudal protuberances of larva ; R.gl., ramifications of uterine gland ; Sp, spermatheca ; Ut, uterus ; V, vagina. (After Roubaud.) in the various groups ; the harpes, small bilateral appendages most highly developed in the fusca group and rudimentary or absent in the remaining groups ; the juxta, or penis sheath ; the penis ; the median process, present only in the fusca group, lying in the middle line between the inferior claspers ; and the connecting membrane, present in the palpalis and morsitans groups, but absent in the fusca group. XVI] REPRODUCTION 247 The method of reproduction, discovered by Bruce, is very remarkable, resembling that of the Pupipara, and is probably the result of their exclusively blood-sucking mode of life. The female lays a single larva at a time, which is retained and nourished in the oviduct until it is full grown. After the larva is born, it at once burrows into the ground and pupates. The larva is generally of a yellowish-white colour and bears at its posterior extremity a pair of large dark-coloured protu- berances and between them is a depression into which open the spiracles (Fig. 70). The pupa is dark brown in colour with a slight sheen. It is broadly ovoid in shape and the larval protuberances are equally conspicuous, forming, to- gether with the size and shape of the depression between them, a means of identifying the immature stages of different species. Distribution. The members of this genus are entirely re- stricted to Africa and the south-west corner of Arabia, together forming the Ethiopian region, and range between the latitudes of 18° N. and about 31° S. Within these limits the tsetse-flies are not found continuously but are generally confined to belts or patches of forests, bush, and warm and damp situations where shade can be obtained. The areas in which the tsetse- fly occurs are commonly known as " fly-belts " and are well exemplified in the case of G. morsitans. Tsetse-flies are said to be absent from dry open plains without shade. Determination of the species of GLOSSINA. It seems probable that most, if not all, of the species of the genus Glossina, are of importance as carriers of disease and therefore we include the following table for their determina- tion. In the classification, the important work of Austen has been followed throughout, and according to his scheme the species may be divided into four groups : 248 GLOSSINA [CH. Synopsis of species of GLOSSINA, after Austen*. Tarsi of hind-legs entirely) Glossina palpalis Group (I), also G. morsitans dark brown or black ) var. paradoxa (vide infra). ( Species of small size, length not exceeding 10-5 mm., usually much less ; wing ex- pansion not greater than 22-5 mm. Upper surface of abdomen distinctly banded, with conspicuous dark brown transverse marks on a pale ground colour. J Only the two last joints of hind tarsi are dark-coloured, thus forming a conspicuous -< contrast with the remaining joints which are pale. Species of large size, exceeding 10-5 mm. Wing expansion at least 25 mm. Upper surface of ab- domen not marked with distinct bands as in the previous group. Wings fairly dark. Palpi long and slender (except in tabaniformis). Glossina morsitans Group (II). Wings pale. short. Palpi Glossina fusca Group (III). Glossina brevipalpis Group (IV) I. GLOSSINA PALPALIS group. Dorsum of abdomen ochraceous-buff or buff ; third and following segments exhibiting sharply denned, dark brown or clove-brown interrupted transverse bands. Length not more than 8 mm. . . . . tachinoides, Westw. (p. 253). • Closely resembling tachinoides, but distinguished by its bright ochraceous colour and relatively narrow head. Length of ? (only specimen known) 7 mm. austeni, Newstead. Third joint of antennae pale, clothed with long and fine hairs, forming a conspicuous fringe on front and hind margins. Length 8 to 9 mm. pallicera, Bigot. Dorsal surface of abdomen dark sepia-brown ; median paler area on second segment broad and more or less quadrate or irregular in outline. Hypopygium of male buff or ochraceous-buff . . . . caliginea, Austen. Dorsal surface of abdomen blackish-brown ; median pale area triangular in outline. Hypopygium of male grey. Length of male always exceeding 8-5 mm. . . . . . . . . . . . . palpalis, Rob. Desv. (p. 256). 1 Handbook of the Tsetse-Flies, 1911. XVI] CLASSIFICATION 249 II. GLOSSINA MORSITANS group. 1. Last two joints of front and middle tarsi with sharply denned, clove- brown or black tips .. .. .. .. .. .. .. = 2. Last two joints of front and middle tarsi either entirely pale or, at most, faintly brownish at the tips, never so dark as to form a sharp contrast with the remaining joints .. .. .. .. =pallidipes, Austen (p. 271). 2. Third joint of antennae fringed with fine hairs on front margin. The dark brown transverse abdominal bands extending close to the hind margins of the segments . . . . . . . . . . =longipalpis, Wied. (p. 274) Third joint of antennae not fringed with fine hairs on front margin. Trans- verse abdominal bands not extending close to the hind margins of the segments. = morsitans, Westw. (p. 276). (a) Markedly paler than typical morsitans, but more or less agreeing in its general characters . . . . . . . . morsitans var. pallida, Shircore. (b) Resembling morsitans but distinguished by having all the joints of hind tarsi dark as in palpalis group . . morsitans var. paradoxa, Shircore. III. GLOSSINA FUSCA group. Third joint of antennae fringed with fine hairs on anterior and posterior margins. Fringe on anterior margin conspicuous under a hand lens ( x 15) when fly is examined in profile . . . . . . = 2 Third joint of antennae with fringe of hairs on anterior margin so short as to be scarcely noticeable under a hand lens, the longest hairs not exceed- ing one-sixth the width of the third j oint. Palpi long and slender = 3 f Length of longest hairs on anterior margin of third joint of antennae equal <( to from one-fourth to one-third of the width of joint. Palpi of moderate length. Number of hairs on arista 18 to 23 =tabaniformis, Westw. f Pleurae drab-grey or isabella-coloured ; hind coxae buff or greyish-buff •{ =fusca, Walk. ^ Pleurae dark grey ; hind coxae mouse-grey . . = fuscipleuris, Austen. IV. GLOSSINA BREVIPALPIS group. f Dorsum of thorax with four sharply defined, dark brown, more or less oval or elongate spots, arranged in a parallelogram, two in front of and two behind the transverse suture. Proboscis bulb with a sharply defined brown or dark brown tip . . . . =longipennis, Corti (p. 286). Dorsum of thorax without such spots. Proboscis bulb not dark or brown at tip . . .V?- . . . . . . . . . . . . =2 f Wings with upper, thickened portion of anterior transverse vein much darker in colour than adjacent veins and thus standing out conspicu- ously against the rest of the wing =brevipalpis, Newstead (p. 288). | Wings with the part in question not darker than the adjacent veins, the wings being practically unicolourous .. =medicorum, Austen. 250 GLOSSINA AND TRYPANOSOMIASES [CH. GLOSSINA and Disease. The more common members of this genus have all been proved to be capable of serving as the invertebrate hosts of various species of trypanosomes, and in addition may carry infection directly from one animal to another, when there is no long interval between the bites. Some species of trypanosomes seem to be mainly spread by only one species of Glossina, as in the case of sleeping sickness (T. gambiense), which seems to be restricted to regions where G. palpalis is present. Nevertheless, G. morsitans has been shewn experimentally to be capable of transmitting T. gambiense and it is difficult to see why such transmission does not take place in nature. Fortunately, this trypanosome seems to be unable to readily adapt itself to development in more than one species of Glossina, but some of the cattle trypanosomes, e.g. T. cazalboui and T. dimorphon, seem to be able to develop in any species of Glossina, though not with equal facility in all of them. Probably the most important factor restricting the spread of trypanosomiases is the difficulty with which the tsetse-flies become infected. When several Glossincz are fed on an animal containing trypanosomes in its blood, only a relatively small proportion of the flies become infected, the number depending on a variety of conditions which are not thoroughly under- stood. Attention may be called to Miss Robertson's experiment with T. gambiense and G. palpalis, reproduced in tabular form on page 309, from which it appears that the percentage of flies in which the trypanosomes develop, depends to some extent on the stage of the infection in the vertebrate host. Yet another important condition is the interval that elapses between an infective and the subsequent feed. In the case of T. gambiense and G. palpalis, the trypanosomes that may have developed in the gut of the fly after the first feed are frequently swept out by the next influx of blood and thus no infection is produced. Strange as it may seem, from Miss Robertson's experiments there can be little doubt that when flies are fed every two or three days there is much less chance of them XVI] CONDITIONS AFFECTING TRANSMISSION t 251 becoming infective than if they are starved after a meal of infected blood. Probably temperature exercises a greater influence than any other known factor on the development of trypanosomes in the tsetse-fly. Kinghorn and Yorke have shewn that T. rhodesiense can only complete development in its invertebrate host, G. morsitans, at a temperature of at least 75° to 80° F. Similarly Kleine and Fischer on Lake Victoria were quite unable to transmit T. gambiense by means of G. morsitans, whilst on the warmer shores of Tanganyika, Taute, employing the same species, succeeded without much difficulty (vide p. 306). The observations on the natural infections of tsetse-flies have shewn that flies of different species frequenting the same district are not infected in the same proportions, nor in the same manner. Moreover these proportions, even for the same species, vary in different localities, as for example in West Africa. Thus Bouet and Roubaud found that in Lower Dahomey T. cazalboui predominated in G. longipalpis and palpalis, T. dimorphon in longipalpis and tachinoides, and T. pecaudi in longipalpis. On the other hand, in Upper Dahomey, T. pecaudi was most predominant in G. morsitans, and in Casamance T. dimorphon in morsitans. The number of G. palpalis becoming infected with T. cazalboui when fed on an animal suffering from this infection, was 40 per cent, in Middle Dahomey, and nil in Upper Casamance, although repeated attempts were made to infect the flies. These experi- mental results were confirmed by an examination of natural infections. In Middle Dahomey one fly in thirty was naturally infected with T. cazalboui, whilst in Upper Casamance out of 560 flies examined only one shewed infection of the pro- boscis. Souma (T. cazalboui) exists in both regions, but it is evident that some other species of tsetse besides palpalis must be responsible for its transmission in Casamance. From these data Roubaud deduces that the receptivity of a given species of Glossina for any particular virus, is not uniform throughout the region of the flies' distribution. In other words a virus is only endemic where there are receptive races of tsetse-flies. 252 GLOSSINA AND DISEASE [CH. From this point of view it is worthy of notice that, in spite of numerous experiments, up to the present no one has suc- ceeded in transmitting T. gambiense by G. palpalis — or any other tsetse-fly — on the west side of Africa. It seems that the West African races of G. palpalis, are more or less refractory to infection with T. gambiense, for the climatic conditions in Dahomey, Casamance and in Uganda, do not differ sufficiently to explain the difficulty of transmission in the two former districts. Thus the evolution of trypanosomes in the invertebrate host is a very complex problem and, before commencing pro- phylactic measures in any particular district, it is first of all necessary to determine, by careful experiments with the local races of Glossina, which species are responsible for the spread of the local strains of trypanosomiasis. If this is not done, there is a great danger of administrative efforts being wasted in the attempt to destroy a comparatively harmless species of Glossina, whilst the more important carrier escapes. The results of experiments in other neighbourhoods are of very little use, for, as mentioned above, in one district T. cazalboui is carried by G. palpalis, whereas in another all attempts to infect this tsetse with the same trypanosome have been unsuccessful. In the following pages we have summarized the available information concerning the bionomics of all species of Glossina that have been proved to carry any infection, together with a brief mention of the infections they are known to transmit. Further details of the experiments and observations on the latter point will be found under the heading of the various species of trypanosomes (Chapter XVIII). REFERENCES. Austen, E. (1911). Handbook of the Tsetse-Flies. British Museum, (Nat. Hist.) London. Newstead, R. (1911). Bull. Ent. Research, vol. n. p. 9. (1912). Ann. Trop. Med. and Parasit., vol. vi. p. 129. XVI] GLOSSINA TACHINOIDES 253 Glossina tachinoides Westwood, 1850. Synonyms. G. palpalis var. tachinoides Austen, 1903. G. decor sei Brumpt, 1904. Description. Glossina tachinoides is one of the smallest of the known tsetse-flies, the length of the female being from 6'8 to 8-4 mm. and of the male 6'O to 675 mm. Among those species having all the tarsi of the hind-legs dark, it may easily be recognised by its small size and its very distinctly banded abdomen. On the dorsum of the second segment of the abdomen there is a median quadrate pale area, which is very conspicuous and is one of the distinctive characters of the species. Distribution. G. tachinoides is widely distributed through- out West Africa having been recorded from the Senegal to the French Congo, including Gambia, Gold Coast, the Northern Territories, Togoland, French Guinea, Ashanti, German Came- roons, and Nigeria, where it is especially abundant in the north. In addition the species occurs in the French Sudan, on the shores of Lake Chad, and has been recorded from Southern Arabia and German East Africa. According to Neave, the tachinoides recorded from the last named locality may prove to be G. austeni, Newstead. Bionomics. G. tachinoides closely resembles palpalis in its habits, being found in the vicinity of water, especially along the banks of rivers. It generally prefers rather more open wooded tracts than palpalis and is not found in the groves of wild palms along the small streams. According to Simpson, the species is most abundant where the country is open, vegetation sparse, the dry season well-defined and the rain-fall slight. It is the predominant tsetse-fly occurring along the rivers in the region bordering on the Sahara and seems to have come from the north. Dr Alexander, in Northern Nigeria, found tachinoides in a large marsh consisting of elephant grass, with occasional clumps of palm trees and thick undergrowth, though he failed to find the fly on the banks of a river about three quarters of a mile away. 254 GLOSSINA TACHINOIDES [CH. Although usually confined to the vicinity of water, in Southern Arabia G. tachinoides occurs in thick belts of euphorbia, tamarisk and cactus, often some distance from the edge of any water, but is never seen in the date groves or along the patches of cultivation. Moiser has recently given an interesting account of the habits of G. tachinoides in the Bornu Province, Northern Nigeria, where the flies have existed for an indefinite period confined to the thick bush. In order to study the vertical range of the flies, men were posted up trees at heights varying from 10 to 25 feet, but in no case were any of the insects seen, although there were several on the ground. As a result of his observations Moiser comes to the following conclusions : — Deep shade and proximity to water appear to be the main factors influencing the distribution of the flies. Their natural resting place is on the lower side of twigs and branches of undergrowth, under the shade of large trees, at a height usually not greater than a foot above the ground. The flies are very restless and the observer is of the opinion that during the day they are continually moving about from place to place within the fly- belt and only for short periods rest on the under surface of twigs and small branches and perhaps on the ground. They do not usually travel higher than four or five feet and probably never as high as ten feet, therefore it is unlikely that the flies feed on monkeys or birds, but on the ground animals, e.g. the warthog, duiker or bushbuck. G. tachinoides requires a meal fairly frequently and accord- ing to Moiser cannot withstand starvation without water for longer than 24 to 30 hours. On the other hand Roubaud kept ten flies in saturated air and all were alive after three days, and three after ten days. In captivity they will feed on the bodies of other tsetse-flies and it is not improbable that in nature they feed on other insects, ticks, grasshoppers etc. Certainly in Arabia, Carter noticed this fly in localities where the chance of getting a feed of mammalian blood must be very slight indeed. The flies feed voraciously on human beings and are very troublesome, as they are quite active in dull weather and in the very early hours of the morning, when XVI] GLOSSINA TACHINOIDES 255 palp alls is usually quiescent. Moreover, according to Dr Alexander the flies bite after dark, at 7.0 p.m. he having had to take refuge in his mosquito net, and his boys remarked that the flies were more troublesome than mosquitoes. G. tachinoides is very resistant to heat, an exposure of one and a half hours in a stove at 40° C. being well borne. As a result the species is able to exist in very warm regions and occurs in the Sudan in localities that are too hot for G. palpalis. Reproduction. The flies copulate immediately after hatch- ing and at 25° C. the larvae are deposited at intervals of about eight days. The duration of the pupal stage in Dahomey (at 24° to 25° C.) was found by Roubaud to be from 28 to 35 days. Like palpalis, the pupae will resist immersion in water for a period of 20 hours, and are able to withstand a tempera- ture of 35° C. for ten hours in the day, so long as the experiment is only continued for a few days ; if it goes on for a month, all the pupae die. G. TACHINOIDES and Disease. This species is one of the main carriers of Souma (T. cazalboui] and T. dimorphon, in West Africa. Moreover, although direct experimental evidence is lacking, it is likely that tachinoides is able to transmit sleeping sickness. In Togoland on the Oti River, a tributary of the Volta, Zupitza believes that it takes the place of G. palpalis as a carrier of this disease. Prophylaxis. The methods that will be described for G. palpalis (see p. 315) are also applicable to tachinoides, and in Northern Nigeria experiments have been made on the effect of cutting down the undergrowth on the banks of rivers. One month after the clearing very few tachinoides could be found and pupae were sought without success. LITERATURE. Carter, R. Markham (1906). Brit. Med. Journ. Nov. 17, 1906, p. 1393. Moiser, B. (1912). Bull. Ent. Research, vol. in. p. 195. Neave, A. S. (1912). Ibid. p. 275. Roubaud, E. (1911). Compt. Rend. Acad. Sci. pp. 406 and 637. Simpson, J. J. (1912). Bull. Ent. Research, vol. in. p. 301. Zupitza. (1909). Cf. 5. 5. Bulletin, vol. n. p. 149. 256 GLOSSINA PALPALIS [CH. Glossina palpalis Rob. Desv. 1830. Synonyms. Nemorhina palpalis Rob. Desv. 1830. Glossina longipalpis Walker (nee Wiedemann), 1873. G. ventricosa Bigot, 1885. G. tabaniformis Bigot, 1885. G. maculata Newstead, 1907. G. fuscipes Newstead, 1910. Description1. " Length, $ 8 to 9 mm., ? 8-6 to 10-2 mm., width of head cf 2-4 to 2-6 mm., ? 2'5 to just under 3 mm. ; width of front of vertex, Mesnil and Brimont. (.soudanense, Laveran. The latter four trypanosomes are distinguished by their cross immunity reactions. XVII] AFRICAN PATHOGENIC TRYPANOSOMES 299 B. Trypanosomes in which the flagellum does not become free anteriorly. /Parasite distinctly dimorphic . . =dimorphon, Laveran and Mesnil. \ Parasite monomorphic . . . . Q >I ,-' • • • • • • = 2 f Monkeys, dogs, rabbits, etc., refractory to infection =nanum, Laveran. Monkeys and goats susceptible ; dogs, rabbits, etc., refractory to infection = simi(B, Bruce, Harvey, Hamerton, Davey, and Lady Bruce *. I Monkeys, dogs, rabbits, etc., susceptible to infection _ / congolense, Broden. ~ \pecorum, Bruce, Hamerton, Bateman, and Mackie. The latter two species are distinguished by cross immunity reactions. In addition T. pecorum is more virulent than T. congolense. C. Trypanosomes having forms with a free flagellum and forms without a free flagellum. /Trypanosomes immobilised by human serum . . =pecaudi, Laveran. \Trypanosomesunaffectedbyhumanserum .. .. .. =2 fin rats, trypanosome shewing a variable proportion of forms with the trophonucleus at the posterior end of the body = rhodesiense, Stephens and Fantham. I Trypanosomes never shewing any posterior nuclear forms I =gambiense, Dutton. * In this species the extreme tip of the flagellum may sometimes become free for a length of 2-3 microns. REFERENCES. Laveran and Mesnil (1912). Trypanosomes et Trypanosomiases , 2nd edition. MassonetCie. Paris. (Contains a very complete account of the literature on the subject.) 3°° SLEEPING SICKNESS [CH, CHAPTER XVIII GLOSSINA AND DISEASE (continued) SLEEPING SICKNESS (T. gambiense) Synonyms. African Trypanosomiasis (pro parte) ; African Lethargy ; Trypanosome Fever ; Sleeping Dropsy ; Morbus Dormitious ; Maladie du Sommeil ; Schlafkrankheit ; Doenga de Sonno ; Letargia dei Negri ; Malattia del Sonno. Also a very large number of native names. Definition. Sleeping Sickness is an acute or chronic infec- tion with Trypanosoma gambiense Button, characterised by an inflammatory condition of the lymphatic system, leading to a meningo-encephalitis and a meningo-myelitis. The disease is usually transmitted by Glossina palpalis Rob.-Desv., but G. morsitans and probably some other species of the same genus are capable of becoming infective. History. The first mention of this disease occurs in 1734, when John Atkins, a Naval Surgeon, gave a clear description of cases of the disease on the Guinea Coast. In the appendix to his book, entitled The Navy Surgeon, occurs the following passage : " The Sleepy Distemper (common among the negroes) gives no other previous Notice, than a want of Appetite two or three days before; their sleeps are sound, and Sense and Feeling very little ; for pulling drubbing or whipping will scarce stir up Sense and Power enough to move ; and the Moment you cease beating the smart is forgot, and down they fall again into a state of Insensibility, drivling constantly from the Mouth as if in deep salivation ; breathe slowly, but not unequally nor snort. ' Young People are more subject to it than the old ; and the Judgement generally pronounced is Death, the Prognostick seldom failing. If now and then one of them recovers, he certainly loses the little Reason he had, and turns Ideot . ..." " In Searching for the Cause of this Distemper it will be necessary to repeat what I have observed, that the Bulk of XVIII] HISTORY 301 Slave-Cargoes mostly consist of Country People, as distin- guished from the Coast People, apparently if the principal Way of Supply be considered. At Whydah more Slaves are brought than on the whole Coast besides ; and why ? The King of that Country, and his next neighbours, understand sovereignty better than others, and often make War (as they call it), to bring in whole villages of those more simple Creatures inland, to be sold at Market, and exchanged for the Tempting Commodi- ties of Europe, that they are fond and mad after. " The immediate cause of this deadly sleepiness in the Slaves is evidently a Super-abundance of Phlegm or Serum, extravased in the Brain, which obstructs the Irradiation of the Nerves ; but what the procatartick Causes are, that exert to this Production, eclipsing the Light of the Senses, is not so easily assigned .... "The cure is attempted by whatever rouses the Spirits; bleeding in the jugular, quick purges, Sternatories, Vesicatories, Acu-Puncture, Seton, Fontanels, and Sudden Plunges into the Sea ; the latter is most effectual when the Distemper is new, and the Patient as yet not attended with a drivling at Mouth and Nose." From this account there can be no doubt that the author had observed cases, of sleeping sickness, but no further mention of the disease occurs until 1803, when Winterbottom gave a fairly clear account of the malady as he saw it on the west coast of Africa, near Sierra Leone. Whilst the slave trade was in progress, some of the natives infected with sleeping sickness were carried across to the West Indies, and in 1808 Moreau de Jonnes recorded its presence amongst the negro slaves in the Antilles. In 1840, Clarke wrote a more complete account of the disease, based upon observations made at Sierra Leone, and during the next twenty years a number of English and French doctors published various descriptions of sleeping sickness. In 1869, Guerin met with the disease in the island of Mar- tinique among the slaves who had been imported from the west coast of Africa. The disease never spread in these countries to which it had been imported, and Guerin was able to shew 302 SLEEPING SICKNESS [CH. that in Martinique the infection was certainly not contagious. Dr Corre, in 1876, gave a good description of the disease as observed in the Senegal and attributed it to a kind of ergotism, or scrofula, and to the moral condition of the people. In addition he describes the ravages of sleeping sickness in the Senegambia, where whole villages had been swept away and many towns abandoned as a result of " Nelavane," the local name for the disease. Mense, in 1885 to 1887, found sleeping sickness widely distributed throughout the navigable reaches of the Congo as far up as the Stanley Pools, and the disease had not been lately introduced into this region for it was well known by the natives. In 1871, the first case of this disease appeared on the banks of Quanza, in Angola, and since that date thousands of victims have been claimed and numerous villages abandoned. Until this outbreak in Angola, for many generations sleep- ing sickness seems to have been confined to certain parts of the west coast of Africa, especially the Congo, which also formed its southernmost limit, and the Senegambia. Although the disease has now spread to the south into Angola, up to the present the region of the Gambia still forms its northern limit, and it is interesting to note that the natives of this region have a superstition that sleeping sickness came from the provinces to the south of them. In the eighties of the last century, the malady was still restricted to the west of Africa, but after this date began that opening up of Africa, that has resulted in sleeping sickness spreading inland as far as Uganda and the great lakes. It is believed that unwittingly Stanley, the African Explorer, was responsible for the introduction of the disease into the lake region during his expedition for the relief of Emin Pasha. In 1887, Stanley travelled up the Congo with a large force and eventually reached the shores of Lake Albert Nyanza where he found Emin Pasha. Regarding this expedition Mense states : " Stanley's expedition for the relief of Emin Pasha, which travelled in 1888 from the Congo to the Nile, and which hired carriers from the Lower and Middle Congo, must certainly have brought many infected men along with it to the XVIII] HISTORY 303 Lake region, and possibly introduced the disease there. I myself was the witness of sick men regardlessly abandoned, of dead and dying, who marked the way even in the Cataract region." After Stanley had met Emin they eventually proceeded to Zanzibar but a large number of soldiers and followers were left behind in a district to the west of the Lake Albert Nyanza. When Captain (now General Sir Frederick) Lugard arrived in Uganda in 1908, after deposing Kabarega, he went to Albert Nyanza and recruited a body of Sudanese, the remnants of those left behind by Stanley and Emin Pasha. About 400 to 500 able-bodied men were enlisted as soldiers and they, with their rabble of 7000 wives, children and followers, were settled in South Toro in 1891. A year later it was found advisable to move them to Busoga where they could be under better control, and for some years there continued recruiting of Sudan- ese soldiers brought to this province. Sleeping sickness was then unknown in this part of Africa for none of the chiefs or missionaries had ever seen it and the symptoms are so evident that cases could hardly have been overlooked. In 1901 the disease was first recorded from Busoga and on investigation Dr Hodges found that sleeping sickness had occurred in one district of this province for six years previously and that many hundreds of natives had already died of it. As many of the settlers in Busoga had originally come from the Congo with Stanley's force, there can be little doubt that they were responsible for the introduction of the disease. In the next seven years the epidemic assumed such proportions that in Busoga alone no less than 200,000 people out of a total population of 300,000 died of sleeping sickness. The disease was also prevalent in Uganda, occurring along the shore of Lake Victoria and on the islands. In 1901, Forde noticed some peculiar parasites in the blood of a patient who was admitted into the hospital at Bathurst, suffering from an unknown type of fever. The following year Button examined the blood of this patient and found the peculiar parasites noted by Dr Forde, and recognized that they were trypanosomes. Subsequently trypanosomes were also 304 SLEEPING SICKNESS [CH. observed in the blood of a native in the Gambia and therefore Button considered that it was probably a new parasite and gave it the name of Trypanosoma gambiense. In 1902, Button and Todd proceeded on an expedition to the Senegambia in order to make further investigations into the nature of this infection. They came to the conclusion that trypanosome fever, or trypanosomiasis, was in natives a particularly mild disease for many of those whose blood contained the parasites appeared to be in perfect health, and none of them were serious- ly ill. Owing to the fact that these investigators had to travel about, the cases could not be kept under observation for any length of time and the relation between trypanosome fever and sleeping sickness was not discovered. In 1901, an epidemic of sleeping sickness broke out in Uganda and the number of cases increased so rapidly that in 1902 the Royal Society sent out a Commission to investigate the causes of this outbreak. This Commission composed of Brs Castellani, Christy and Low, arrived in Uganda in 1902, and at once commenced to work on the etiology of the disease. Whilst Castellani was examining the brains and spinal cords of persons who had died of sleeping sickness in the attempt to find the cause of the malady, the other two members of the Commission travelled about and eventually proved that the area of infection was confined to a narrow strip of country surrounding the lake shores and on the islands of Lake Victoria. This restricted distribution had previously been noticed by Hodges, and clearly shewed that there was no relation between sleeping sickness and Filaria perstans, as suggested by Manson, for the areas of infection were quite different. In 1903, Castellani noted the presence of trypano- somes in the cerebro-spinal fluid of patients infected with sleeping sickness, and the same year Bruce and Nabarro arrived in Uganda to continue these investigations. Bruce at once recognised the possibility that this trypanosome might be the cause of sleeping sickness and on further examination Castellani found that 70 per cent, of the cases contained these parasites in the cerebro-spinal fluid. The parasite was described under the name of Trypanosoma XVIII] HISTORY 305 ugandense, as Castellan! considered that it was distinct from T. gambiense Button. Subsequently Bruce and Nabarro found trypanosomes in the cerebro-spinal fluid of practically all cases, but were puzzled by the fact that some natives shewed these parasites in their blood without presenting any very serious symptoms. Later, when patients suffering from trypanosome fever were kept under observation, it was found that this was merely an early symptom of sleeping sickness and that in the later stages the parasites appear in the cerebro-spinal fluid and the characteristic lethargic symptoms follow. The iden- tity of T. gambiense and T. ugandense was also established by means of inoculating animals with the two strains, when they were found to produce exactly similar effects. In 1903, Bruce and Nabarro shewed that sleeping sickness was carried by means of Glossina palpalis, and the manner in which they arrived at this discovery is of some interest. When it was proved that sleeping sickness was caused by the presence of a trypanosome in the blood, Bruce at once considered the possibility of the transmitting agent being a tsetse-fly as he had already proved to be the case in Zululand for another try- panosome disease, Nagana. Large numbers of tsetse-flies were found in the neighbourhood of Entebbe, but these belonged to a different species, Glossina palpalis, from the tsetse-fly of Zululand, G. pallidipes. The Commission, however, decided to find out the distribution of Glossina palpalis, in order to deter- mine whether it bore any relation to that of sleeping sickness, and with this object tsetse-flies were collected from all parts of Uganda together with any records of the disease. When all the information was put together the evidence in favour of the tsetse theory of transmission was almost overwhelming, for in every locality from which sleeping sickness had been recorded the tsetse-fly was found to be present. The final proof of this theory was obtained by feeding tsetse-flies on patients suffering from sleeping sickness, and subsequently, after various intervals, on healthy monkeys. The latter were found to become infected with T. gambiense, thus proving that Glossina palpalis can convey trypanosomes from sleeping sickness patients to healthy individuals. It was H. B. F. 20 306 SLEEPING SICKNESS [CH. next shewn that if large numbers of the wild tsetse-flies in the neighbourhood of Entebbe were caught and fed on healthy monkeys the latter became infected with sleeping sickness. The discovery that the tsetse-fly is the carrier of the disease explained why sleeping sickness had not spread in the West Indies in spite of the frequent importations of infected negroes. In the absence of its invertebrate host the disease could not be transmitted from the patients to other persons. In 1909, Kleine discovered the very important fact that T. gambiense undergoes a cyclical development in the body of Glossina palpalis, and that once infected the tsetse-fly may remain infective for a considerable period of time. In 1911, Taute, whilst experimenting on the shore of Lake Tanganyika, shewed that G. morsitans was also capable of acting as the invertebrate host for T. gambiense, and that the trypanosome underwent a cycle of development within the body of the insect resembling that in G. palpalis. Finally, Bruce, Hamerton and Bateman, in 1911, shewed that the wild game served as a reservoir for sleeping sickness, as antelopes and reed-bucks could remain infected, and infective, for long periods without presenting any signs of disease. The importance of this discovery from a prophylactic point of view cannot be over- estimated. Distribution. At the present time sleeping sickness extends along the west coast of Africa from St Louis in the Senegal, to Benguella in the province of Angola, and inland as far East as the Orno River (Brumpt) and the Victoria Nyanza. The main centres of the disease are the Congo Free State, French Congo, Cameroons, Angola, Senegal and Senegambia, Uganda and along the shores of Lake Victoria and Tanganyika. Life history within the vertebrate host — Endogenous cycle.— The life-cycle of T. gambiense has been elucidated by the researches of Minchin, Roubaud", Bruce, Kleine, and Miss Robertson. The last named investigator has given a complete description of all stages in the development, from which the following account is taken. In the blood the short forms (so-called female forms) about 13 to 20 microns in length (Fig. 75) are the adult type. They XVIII] LIFE-CYCLE OF T. GAMBIENSE 307 have the longest duration in the circulation and appear to be the type from which the individuals capable of carrying on the cycle in the intermediate host, are derived. The blood of a monkey is infective to Glossina only as long as this form is present in sufficient numbers and moreover in a healthy state, for at times, in very heavy infections, the flagellates seem to become exhausted. These short forms grow up into the so- called intermediate or " indifferent " forms, that are an ill- defined and artificial group, chiefly to be recognised by their increased length and longer free flagellum. The intermediate forms are merely a step in the development of the division forms, which are the culminating stage of this process. The long slender forms that have been known as the male forms, are merely the individuals that are about to divide. It is, therefore, incorrect to speak of male, female, and indifferent forms, as these are all stages in the development of the short forms. Multiplication takes place in the circulating blood and the details are as follows : the first sign of division is the doubling of the kinetonucleus together with the end-bead, situated at the posterior end of the trypanosome. The flagel- lum then splits longitudinally, but only for about two-thirds of its length, when it becomes free. Previous to division the trophonucleus shews two well-marked dark granules, one at each pole, and these are joined together by a fairly thick line to the karyosome. The nucleus then divides, the chromatin becoming aggregated about each pole. By this time the body has become long and slender in form and eventually this long trypanosome separates into two daughter individuals that are of the short form. No other mode of multiplication within the blood is known, although at times the nuclei may divide repeatedly without division of the cytoplasm. In such cases large multinucleate forms may be produced but they are merely the result of delayed division and not examples of true schizogony. In addition, certain authors have described various latent bodies or spores, small rounded nonflagellate forms, that are supposed to be capable of remaining dormant in the internal organs for considerable lengths of time and thus be the cause of the 20 2 308 T. GAMBIENSE [CH. relapses. It is possible that some latent forms are produced, but up to the present the evidence for their existence is inconclusive. One of the most noticeable features of the infection in the blood is the periodic increase and decrease in the number of trypanosomes in the peripheral circulation. It was formerly believed that the parasites completely disappeared from the circulation at certain times, but Ross and Thomson have shewn that when once a person becomes infected trypanosomes are constantly present in the blood. During the so-called negative periods the parasites are in such few numbers that their pres- ence can only be detected by the examination of large quantities of blood, either by centrifuging or some similar means. These alternating periods of increase and decrease in the circulating blood are of irregular duration, and the circumstances which bring about the disappearance of the majority of the parasites are not thoroughly understood. After a period of depression the following increase in the number of flagellates is always accompanied by division in the peripheral blood. These variations in the number of trypanosomes are accom- panied by differences in their infectivity when ingested by the tsetse-fly. Thus it has been shewn that monkeys infected with T. gambiense have negative periods during which they are not infective to the fly, and moreover the percentage of flies that become infected after any particular feed varies with the stage of infection. From this point of view, the following table, given by Miss Robertson, is of considerable interest. Monkey 113 was infected by wild G. palpalis from the shore of Lake Victoria, and first shewed trypanosomes in its blood on July 25th. From August 23rd up to the time of its death, fresh lots of flies were fed on this monkey and the percentage number of these flies that became infected is shewn in the table. It is evident, therefore, that there is a marked difference in the mlectivity of the parasite at different stages of its develop- ment, but in addition, different strains vary considerably in this respect. Thus, another monkey was infected by the direct injection of blood from a bush-buck which had been XVIII] LIFE-CYCLE 3°9 Monkey 113. Percentage f or - of flies Condition of blood examined laboratory bred Number of becoming Date alive flies flies fed infected Aug. 20-22 No trypanosomes seen in blood No flies fed 23 Few ,, „ ,, „ ioi o ,, 24 Numerous trypanosomes in blood + 45 IIT „ 25 „ „ „ '„ „ + 53 37 ,, 26 Very numerous trypanosomes in blood 89 o 27 Very few trypanosomes in blood No flies fed „ 28 J* No trypanosomes seen in blood Flies fed ,, 29 \ both days 25 o ,, 30 Few trypanosomes in blood 34 o 31 ,, „ ,, ,, + I07 **8 Sept. 1-3 Not examined 4 Very few trypanosomes in blood 32 o 5 ,, ,, ,, ,, ,, No flies fed 6 Moderate number of trypano- somes, dimorphism of broad and narrow forms very marked 49 o 7 Moderate number of trypano- somes . . . . . . No flies fed 8 Trypanosomes very numerous indeed ...... + 95 2'i 9 Fair number of trypanosomes but much fewer than on 8th No flies fed ,, 10 Not examined . . . . No flies fed ,, ii Few trypanosomes ,, 12 Trypanosomes vey numerous indeed . . . . . . + 70 1-4 ,, 13 Trypanosomes very numerous indeed . . . . . . No flies fed 70 i -4 14 Trypanosomes very numerous indeed . . . . . . ,, 15 Blood swarming with trypano- somes ...... + 20 10 infected with T. gambiense by laboratory bred flies. The bush- buck had harboured the trypanosome for about fifteen months. This monkey shewed infective and non-infective periods in exactly the same way as other infections, but the infective periods gave a remarkably large percentage of flies harbouring trypanosomes. Out of 150 G. palpalis that were fed on this monkey, 16 became infected, a percentage of 10-6 per cent., which is remarkably high, for Bruce, Hamerton, Bateman and Mackie found that the normal proportion of infected flies 310 T. GAMBIENSE [CH. produced by the Uganda strain of T. gambiense in monkeys was only about one in 40. Life history within the invertebrate host, G. palpalis — Exogenous cycle. — In addition to the initia linfectivity of the trypanosome mentioned above, several other conditions have a marked effect upon the development of T. gambiense in its invertebrate host, the tsetse-fly. A certain degree of warmth is essential and the more favourable results obtained on Tanganyika than in Uganda, in the transmission of T. gambiense by G. morsitans, can be explained by the differences in tem- perature between these two localities. One of the most important conditions affecting develop- ment is the interval that elapses between the feed of infected blood and the following meal. When a newly-hatched fly is fed, it usually ingests sufficient blood to fill both its crop and gut. The next feed, taken in two or three days later, may either entirely replace the undigested remains of the first meal, or some of the first feed may remain in the crop and the fresh blood be taken on top of it. Occasionally the blood may be taken directly into the gut without even going into the crop. If a fly has ingested trypanosomes at its first feed, the result of subsequent clean feeds varies in different individuals. The trypanosomes may be digested and disappear from the alimentary canal of the Glossina during the first 50 to 72 hours, without the intervention of a second feed. In other cases the flagellates survive in the gut in small numbers but disappear during the early stages of digestion of the new blood. It is evident from these two results that all trypanosomes cannot withstand the digestive processes and, of course, in such cases the fly does not become infected. In some flies the trypano- somes may survive and multiply in the gut in the blood retained from the first feed, although a second feed has been taken in on top. In these cases the trypanosomes may be swept out when the original blood is digested, and thus no infection be produced. The trypanosomes may survive and develop in the crop for as long as 12 days, providing that blood is con- stantly present. The gut of these flies may often shew no signs of flagellates, in which case the insect will not become XVIII] LIFE-CYCLE 311 infected, as there is never a permanent infection of the crop. When trypanosomes persist in greater or less numbers in the gut and crop of the same fly, the issue is somewhat doubtful as the flagellates may be swept out by subsequent clean feeds. A permanent infection of the fly is obtained when the whole material of the first feed has been displaced from the gut by the second feed, and the trypanosomes still persist. Once parasites are well established in the new blood the rate of multiplication is such that there is little chance of their being destroyed at the next influx of blood. There is no doubt that the critical time for the parasite is this influx of fresh blood after an infected feed. This is shewn by the very much larger percentage of infected flies found amongst those individuals that had only one feed and this the infecting one, than among those that had been subsequently fed every two or three days in the usual way. Out of 103 starved flies trypanosomes were found in 22 between the 6th and i2th day. 16 or 15-5 per cent, of these starved flies shewed a well developed infection of the gut, whereas under ordinary feeding conditions only about 3 per cent, of these flies became infected. In the early days of the cycle in the alimentary tract of the fly many forms of parasites may be observed, depending on the various conditions. The trypanosomes may persist without multiplying, under which circumstances they degenerate and disappear within three to four days. In other cases the parasites persist in small numbers and begin to multiply, but when the adverse conditions of a newr feed come upon them, they are unable to withstand them, and dividing and degenerating speci- mens may thus be found side by side. Persistence and quite normal development may occur in the crop and continue till the loth or I2th day, so that it is evident that the stimulus to development in the fly is not dependent upon the digestive action of the gut fluid upon the blood. The very large number of cases where the attempted multi- plication fails to establish an infection, indicates the presence of a general inhibiting property in the Glossina and is a fairly constant factor in experiments with freshly hatched flies. 3I2 T. GAMBIENSE [CH. 13 12 Fig. 75. (1-19). Trypanosoma gambiense. x about 2000 diameters. (After Muriel Robertson.) 1-4. Trypanosomes from the blood of a monkey. 5-6. Division of blood- types. 7-8. Trypanosomes in the middle intestine of Glossina, 36-48 hours after ingestion. 9-10. Slender proventricular types, final form of the gut development. 11-12. Specimens newly arrived in the salivary gland. 13-15. Typical salivary gland form, shewing the crithidial condition. 16-17. Division of salivary gland forms. 18-19. Final trypanosome types in the salivary glands, probably the in- fecting form. XVIII] LIFE-CYCLE 313 Individual strains of T. gambiense vary greatly in the percent- age of infected flies they produce, this being due to the greater or less vigour of the trypanosomes interacting with the inhibit- ing forces of the fly. The negative blood periods, during which the parasite is not in a fit state to carry on the cycle, are as well marked in very vigorous strains as in those of lesser vitality. When the conditions are favourable to development in the fly, the trypanosomes first become established in the posterior region of the mid-gut. Here multiplication takes place and trypanosomes of very varying sizes are produced, though the parasites rarely surpass a length of 34 to 35 microns. About the tenth day numerous trypanosomes are present, and the characteristic slender forms may begin to appear, but only in small numbers. The method of division in these forms is essentially similar to that in the circulating blood, but the final division of the protoplasmic body is very characteristic. Instead of the two daughter individuals swinging out so as to be arranged kineto- nucleus to kinetonucleus as in the majority of trypanosome divisions, there is no .longitudinal splitting of the parent organ- ism, but the young specimen is pushed off at the posterior end (Fig. 75, 17) and division is practically transverse. After the loth to the I5th day the slender forms that constitute the proventricular type gradually develop from the broader forms, and as their numbers increase move forward into the pro vent riculus, where they are the dominant type. There is only one important point in which they differ from their predecessors. The body is long and slender, the cytoplasm finely granular and much less dense than in the broader forms, but the trophonucleus shews a distinct change. The karyo- some has become much smaller and the membrane has become much more marked and stains deeply. In the fully developed slender types, division rarely seems to occur. The infection grows forward by sheer force of multiplication until it fills the whole of the middle and hinder intestine and the posterior part of the anterior intestine. The anterior portion of the anterior intestine and the proventriculus shew 3J4 T. GAMBIENSE [CH. the typical long slender forms and are only invaded about the middle of the developmental cycle. There seems to be some difficulty in the trypanosomes reaching the proventriculus and once arrived there they cannot maintain themselves if the fly is exposed to too long a fast. If there is any considerable interval before another meal the trypanosomes gradually ebb backwards to the posterior part of the anterior intestine and only gradually recover their position again after the next feed. The intestinal infection is thus the focus from which the sub- sequent stages are derived. Fig. 76. Transverse section (semi-diagrammatic) of the proboscis of an infected Glossina. The section shews the arrangement and aspect of the trypano- somes attached to the walls of the labrum (L) and the hypopharynx (Hyp.), (x about 700.) (After Roubaud.) ' L, labrum ; Hyp. hypopharynx ; M, M', muscles ; L. inf., under lip. After becoming established in the proventriculus the slender forms pass up into the hypopharynx and then along the salivary ducts into the salivary glands. The period at which this happens depends upon the virulence of the trypanosomes, and early infectivity is generally a character found in a strain which produces many positive flies. The trypanosomes settle down in the salivary glands in the cellular part of the lumen immedi- ately above the narrow tubular part of the duct. At first they are slender forms attached to the wall of the gland by their flagella, but later they gradually change into broad crithidial forms. XVIII] LIFE-CYCLE 315 These crithidial flagellates multiply and finally fill up large portions of the gland with flagellates in all stages from typical crithidial forms, attached by the flagellum, to free-swimming trypanosomes closely resembling the blood type. The fly never becomes infective until the trypanosomes have invaded the salivary glands. The proventriculus and gut forms when injected into monkeys never produce an infection. The inva- sion of the glands usually occurs about the 2oth day, but occasionally it may take place earlier, in one case a salivary gland being found infected on the I2th day. The Glossina seems to become infective two to five days after the trypano- somes have invaded the gland. During this period the para- sites pass through the crithidial cycle, which seems to be a necessary feature in the development of the trypanosome in the invertebrate host before the latter can become infective. The whole cycle from the ingestion of the trypanosomes to the appearance of young blood forms in the salivary glands generally occupies from 20 to 30 days, after which the Glos- sina becomes infective and probably remains so for the remainder of its life. When an infected fly bites an animal the young trypanosomes in the lumen of the salivary glands are passed down the duct together with the salivary secretion and thus injected into the wound caused by the mouth parts of the insect. Prophylaxis of Sleeping Sickness. In spite of the experimental evidence to shew that Glossina morsitans, G. fusca, and G. tachinoides, and probably the other members of the genus, are all capable of transmitting sleeping sickness, the epidemiological evidence in support of the view that G. palpalis is the main carrier, is overwhelming. Accord- ingly, for the time being, in combating the spread of the disease, the other species of tsetse-flies may be ignored. The prophy- lactic measures fall into two main classes. In the first place we may prevent the access of trypanosome carriers to fly areas, and in the second, we may attempt the destruction of the fly. With regard to the former of these two methods, the diffi- culties in the way of preventing the flies becoming infected SLEEPING SICKNESS [CH. have been enormously increased by the discovery that the wild game may serve as a reservoir for sleeping sickness. When it was discovered that the tsetse-flies along the shores of Lake Victoria were infected, the government of Uganda ordered the removal of all the population from the infested regions and by means of stringent regulations prevented any persons living on the lake shores or on any of the islands. Nevertheless three years later the tsetse-flies were still infected with sleeping sickness, although during this period they could not have had the opportunity of feeding on the blood of any human being suffering from the disease. It is evident, therefore, that the wild game serves as an efficient reservoir for sleeping sickness and as there is no possibility of exterminating all the mammals in the infected regions, the idea of eradicating the disease in this manner must be abandoned. Nevertheless, it is very important to prevent any infected person entering a fly area in which sleeping sickness does not already exist. The danger of this has been well exemplified in the case of Uganda, where, owing to the entrance of a few infected natives from the Congo, the disease was introduced among the previously uninfected Glossina palpalis, along the shores of Lake Victoria. Dr Bagshawe in his excellent article on this subject, advises the removal of healthy persons from the vicinity of the fly, or their protection from fly bites. This may be effected in a variety of ways amongst which may be mentioned the following : Whenever possible villages or markets should be removed to fly-free areas as has been done in Uganda. In many districts, however, the difficulties in the way of such a scheme are almost insuperable, and even in Uganda it has not been found practic- able to deal in a similar way with the infected districts near the Albert Lake and White Nile. Needless to add, any camps, whether temporary or permanent, should not be pitched in the fly regions. All occupations carried on in fly-areas should be discouraged or prohibited. The most important of these is fishing, as river and lake-side natives usually spend all their time in this occu- pation, unprotected by any clothes and constantly being bitten XVIII] PROPHYLAXIS 317 by the tsetse-flies. The rapid spread of sleeping sickness in Uganda was the result of the fishing habits of the natives. Fishermen should be recommended to cultivate the soil or raise stock, and regulations prohibiting fishing in fly infested regions should be enforced. Brumpt has suggested that the natives who live on fish might be persuaded to grow vegetables by importing dried sea fish in exchange for their vegetable produce. Rubber collecting in palp alls areas should also be abandoned and there is little doubt that the prevalence of sleeping sickness in the Congo is largely due to this occupation. During the heat of the day all fly areas should be avoided as the insects are especially active during these hours. Any visits to the water that may be necessary should be made either in the early morning or late evening. Whenever possible roads should be selected that do not traverse fly areas, and when travelling fly-infested ferries and fords should be avoided. If caravans are obliged to cross such rivers at hours when the fly is active, they should not be allowed to halt within a distance of at least 100 yards of the water. In the construction of railways, fly areas might also be avoided, for there is a great danger of these insects being carried very considerable distances in the carriages of trains. When trains have to travel through infested regions the carriages and trucks should be protected with wire gauze ; similarly, steamers that ply on fly-infested lakes or rivers should have some portion of the upper deck protected. The protective effect of clothing is well known and the comparative immunity of Europeans and native chiefs is mainly due to their practice of wearing clothes. The peasants who go about for the most part naked are particularly liable to the bites of the flies, and therefore they should be instructed as to the protective effect of clothes. Europeans when travelling through infested regions should take great care to protect their legs and arms, and if the flies are numerous it is advisable to wear both veils and gloves. It is possible that some substance may be found which will be repellent to the fly and when rubbed on the skin will keep it away, but up to the present no satisfactory repellent has been discovered. SLEEPING SICKNESS [CH. The instruction of the natives and also Europeans, as to the danger of being bitten by tsetse-flies, should be carried out systematically in all infected regions, for without the co- operation of all persons it will be impossible to prevent the occurrence of cases of sleeping sickness. It is most important that no person harbouring trypano- somes in his blood should be allowed to travel from one district to another. All sick persons should be segregated in treatment camps, away from any species of tsetse-fly. The employment of these segregation camps in Uganda has greatly reduced the number of deaths from sleeping sickness, but unfor- tunately such methods can never entirely eradicate the disease. It should be forbidden to recruit soldiers, carriers or labourers in infected districts and bring them into any other districts which contain fly areas. The importance of such pre- ventive measures in the case of uninfected districts containing G. palpalis is obvious, but. the passage of persons harbouring trypanosomes from one infected district to another should also be avoided. Dr Bagshawe has called attention to the impor- tance of this measure, for the strains of T. gambiense vary in virulence. There is some evidence that in consequence of the introduction of a virulent strain into a region where a mild strain previously existed, a small endemic focus of sleeping sickness has been succeeded by a great epidemic. It is also possible that an epidemic which is gradually losing its virulence and tending to die out may be kept alive by the introduction of persons harbouring virulent trypanosomes in their blood. The only effective way of suppressing sleeping sickness is by the extermination of the tsetse-fly, and, therefore, the most important of all prophylactic measures are those directed against the fly. In fact, the control of this disease is essentially a problem for the entomologists. There are no doubt enormous difficulties in the way of exterminating an insect ranging over some millions of square miles of Tropical Africa, but the manner in which Stegomyia and other mosquitoes are disappearing during campaigns against yellow fever and malaria should make one hesitate before considering such a task impossible. A complete knowledge of the bionomics of G. palpalis, including its natural XVIII] PROPHYLAXIS 319 enemies and diseases, would be of immense value, and yet up to the present comparatively little work has been done on this subject. Bagshawe advises the use of the following measures against the fly : (a) The clearing of fly-infested scrub. (b) The filling up or draining of pools when it is practicable. (c) The cultivation of plants noxious to the fly. (d) The destruction of animals on which the fly feeds. (e) The encouragement or introduction of animals or plants (Fungi) which attack the fly in its adult or pupal stages. (/) The collection or destruction of pupae or of the flies themselves. The clearing of fly-infested scrub has been found to be of great value in Uganda, but it is rather difficult of application over wide areas. As the natural range of palpalis does not exceed 30 yards from the water, a clearance of this strip will cause the disappearance of the fly. According to Roubaud, in the Congo it is sufficient merely to thin out the vegetation on each side of the water, but in most localities it is necessary to remove thoroughly all brushwood and scrub which shelter the fly and its pupae. The cleared areas must either be kept free from scrub-vegetation, or some crop planted which will not give the flies any shelter. Citronella is one of the most suitable, as the grass repays cultivation and its smell may be repugnant to the fly. No clearing should be attempted unless it is possible to make it efficient and keep the cleared spaces free from scrub, and before undertaking any such measure the locality should be carefully examined. The flies and pupae may be restricted to certain parts of the shore, in which case it is only necessary to clear these areas. It is advisable to clear the following locali- ties : boat and steamer landing-places on lakes or rivers ; dipping and washing places ; stations on railways that traverse palpalis areas ; ferries and fords ; and the sites of markets or camps. The clearing should be performed during the dry season, because the flies are then less numerous. In the Senegal, where clearing has been practised on a 320 SLEEPING SICKNESS [CH. large scale, whole tracts of country have been deforested, and in consequence, the streams have dried up and the tsetse-flies have disappeared. The destruction of animals on which the flies feed is a proposal that needs very careful examination. Koch advocated the destruction of the crocodile, but as mentioned above (p. 264) it is very doubtful whether this scheme would be of much use, and the available evidence is decidedly against it. The destruction of the big game is not likely to affect the numbers of G. palp alls, for it rarely feeds on these animals, as they mostly come to the water at early morning or late evening, when the flies are not about. The main food supply of this insect has not yet been satisfactorily decided. Minchin has suggested the introduction of jungle-fowl, which might scratch up the pupae and devour them, but it is possible that the birds might find plenty of other food. In any case the experiment might be tried, for at present we know very few enemies of this redoubtable insect. A knowledge of the insectivorous birds that prey upon the tsetse-fly is much to be desired, for we are almost in complete ignorance of this subject. With regard to the collection or destruction of the pupae or of the flies themselves, there is little hope of any considerable reduction in numbers being effected by these means. Dr Bal- four is of the opinion that fly-traps might be of some use and mentions an incident in support of this view. In the Sudan occurs a limited fly -belt, about twenty miles long and three or four miles in breadth. The fly is G. morsitans which in this locality haunts the neighbourhood of wells. ' This limited and peculiar distribution is said by the natives to be due to the fact that the fly was intentionally brought here from the river for purposes of revenge ! This may or may not be true, . . . but certain it is that at the present time the natives trap the fly in gourds containing blood as a bait, and then liberate them in spots where the cattle or horses of their enemies are grazing or are collected together. The trap is a spherical gourd with a hole cut in the top. It is half-filled with blood, and carefully watched. As soon as a number of flies have entered it in quest XVIII] REFERENCES 321 of food the native rushes forward and claps his hand over the aperture. He then closes the hole in some more permanent fashion, and carries off the flies in triumph for the future discomfiture of those with whom he has a feud. This native custom would certainly seem to indicate that a blood trap is a feasible method of dealing with one of the greatest pests from which Africa, the land of pests, has ever had to suffer." Mr Maldonado, manager of one of the estates in the Isle of Principe, caught large numbers of G. palpalis, by making his labourers wear a black cloth, coated with bird-lime, on their backs. -This method of trapping tsetse-flies, however, has not given good results in other localities, for it has been shewn that a single fly-catcher can capture far more flies in a single day than twenty or thirty fly-papers. REFERENCES. Bagshawe, A. G. (1908). Sleeping Sickness Bulletin, vol. i. Balfour, A. (1908). Third Report Wellcome Research Laboratories. Khartoum. Bruce and Nabarro (1903). Progress Report on Sleeping Sickness in Uganda. Reports S. S. Comm. of Roy. Soc. No. i. Bruce, Hamerton and Bateman (1911). Proc. Roy. Soc. B, 564, pp. 311-327- Bruce, Hamerton, Bateman, Mackie and Lady Bruce (1911). Eleventh Report of S. S. Commission of the Royal Society. H. M. Stationery Office, London. Castellani (1903). Rep. S. S. Comm. of Roy. Soc. 1903. Duke (1912). Proc. Roy. Soc. vol. LXXXV. pp. 156-69. Dutton (1902). Trypanosoma in man. B. M. J. Jan. 4, p. 42. and Todd (1903). First Report of the Trypanosomiasis expe- dition to Senegambia. Liv. Sch. of Trop. Med. Memoir xi. Kleine (1909). Deutsch. Med. Wochenschr. May 27, pp. 924-25. Laveran and Mesnil (1912). Trypanosomes et Trypanosomiases. Masson : Paris. Martin, Leboeuf and Roubaud (1909). Rapport de la Mission d'ttudes de la maladie du sommeil au Congo Francais, 1906-1908. Masson : Paris. Mense (1906). Handbuch der Tropenkrankheiten. vol. in. Minchin (1908). Quart. Journ. Micr. Sci. vol. LII. pp. 159-260. Robertson, M. (1912). Proc. Roy. Soc. B, 578, pp. 241-48. (1913). Trans. Roy. Soc. B, vol. 23, pp. 161-84. Ross and Thomson (1911). Proc. Roy. Soc. B, 563, pp. 187-205. Sandwith (1912). Sleeping Sickness. Macmillan & Co. London. Taute (1911). Zeitschr.f. Hyg. u. Infektionskr. vol. LXIX. pp. 553-558. H. B.F. 2I 322 TRYPANOSOMA RHODESIENSE [CH. Trypanosoma rhodesiense Stephens and Fantham, 1910. General account. Until 1909 it was generally supposed that human trypanosomiasis was restricted to regions in which Glossina palpalis occurs, for there were no records of any cases occurring outside such areas. In that year Hearsey published an account of six cases of trypanosomiasis in persons who had not visited any palpalis region. The infections in every case must have been contracted either in Nyasaland or North-Eastern Rhodesia, or Portuguese East Africa. Subsequently a number of additional cases were recorded, especially along the shores of Lake Nyasa and in the Luangwa Valley. In 1910, the first of these cases reached England and was studied at the Royal Southern Hospital, Liverpool. The history of this patient is of some interest as it was in his blood that this trypanosome was first observed, arid it is the only strain of the virus which has yet reached Europe. W.A., a male aged 26, first went to South Africa in July, 1904, living in Johannesburg till the end of 1906. He then went to vSalisbury for two years. About the end of November, 1908, he left Salisbury for North-Eastern Rhodesia with a view to prospecting for minerals. On the journey northwards he passed through Fort Jameson, Landazi, and Chinsali to Kasama, arriving at the latter place about the beginning of June, 1909. During this journey the patient traversed an area infested with Glossina morsitans. He stayed two months at Kasama, a place apparently free from tsetse-flies. On the return journey he called at Mpika (where Glossina morsitans occurs), Serenje and Mzaza (G. morsitans present). On September 10, he left Mzaza and travelling along the Luangwa River reached Feira on September 28. During this part of the journey he would pass through an area infested with Glossina fusca, between Mzaza and Hargreaves. The patient first became ill on September 2oth, but after a rest of two days continued his journey. A short stay was made at Feira and then the return jourriey was continued through the Hartley District to Salisbury, where it was found that he was XVIII] GENERAL ACCOUNT 323 suffering from trypanosomiasis, parasites oeing found in his blood on November ijih, 1909. The patient subsequently returned to England and in 1910 was admitted into the Royal Southern Hospital. The same year Stephens whilst examining a stained speci- men of the blood of a rat infected with this race of trypanosomes observed a marked peculiarity in its morphology, and in November, 1910, Stephens and Fantham gave a full description of this new species of human trypanosome under the name of T. rhodesiense. The announcement of the discovery of a new species of human trypanosome has given rise to a great deal of discussion as to the nature of T. rhodesiense and its relation to pre-existing species of trypanosomes. Whereas some authors tend to regard it as merely a variety of T. gambiense, hardly distinct, others consider it to be a form of T. brucei that has acquired patho- genic properties for man. The latter view seems rather unlikely, for on two or three occasions man has been shewn to be immune against experimental infection with T. brucei, and, moreover, human serum has a curative action on nagana in experimental infections. By means of cross-immunity reactions Laveran and Mesnil have shewn that rhodesiense is distinct from both gambiense and brucei, and therefore it must be regarded as a new species of human trypanosome. There can be little doubt that T. rhodesiense has arisen within the last few years and that it is an interesting example of the origin of a new species at the present time. As the transmitting agent G. morsitans is widely distributed through- out Rhodesia and East Africa, there is no reason why this disease, had it previously existed, should not also have had a wide range of distribution, instead of being restricted to one or two valleys in Nyasaland and Rhodesia, and the symptoms are so characteristic that the disease could hardly have re- mained unnoticed. Since the discovery of the trypanosome, however, its range of distribution has increased considerably and already cases have occurred south of the Zambesi. The sudden appearance 21 2 324 TRYPANOSOMA RHODESIENSE [CH. of this disease in one small region, followed by such a rapid spread, can only be explained on the supposition that it is an entirely new form of sleeping sickness. Moreover, its extremely deadly effect on its vertebrate host, man, is further evidence in support of the same view. T. rhodesiense is remarkably pathogenic to the majority of experimental animals, the duration of life of monkeys infected with this species being only about 8 to 14 days, as compared with 27 to 149 days in the case of T. gambiense. It is evident, therefore, that this new trypanosome is extraordinarily virulent, and it is also very resistant to treatment, atoxyl apparently having no effect on it. In man the course of the disease is much more rapid than in the case of ordinary sleeping sickness (T. gambiense) and death usually takes place within three or four months of infection. At present T. rhodesiense is restricted to Southern Nyasaland, North-Eastern Rhodesia, especially in the Luangwa Valley, and Portuguese East Africa, but it seems to be extending its range and unless effective preventive measures are discovered there is reason to fear that it may give rise throughout Africa to an epidemic, besides which the ravages of gambiense would appear almost mild in comparison. Morphology of the parasite. T. rhodesiense in most respects resembles T. gambiense, but is characterised by the occurrence of stout or stumpy forms in which some have the trophonucleus at the posterior end. Stephens and Fantham give the following account of the parasite : " Rats inoculated with this Rhodesian strain usually shew a few long thin trypanosomes in the peripheral blood in about three days. The stumpy forms of trypanosomes with the trophonucleus posterior appear about the fifth or sixth day and from this time onwards somewhat increase in number up to the seventh or eleventh day. They then form about six per cent, of the trypanosomes present, but may decrease again, varying from day to day." The dimensions of stumpy forms with a posterior tropho- nucleus vary from 17 to 21 microns in length by 2 to 3 microns in breadth. There is a well-marked kinetonucleus XVIII] MORPHOLOGY AND TRANSMISSION 325 and the flagellum terminates in a short free portion. The cyto- plasm is coarsely granular, especially at the anterior end. In addition Stephens and Fantham mention the occurrence of " snout " forms with an elongated posterior end. These forms are present especially during the first half of the infection, and although not absent from the ordinary strains of T. gam- biense are much more numerous in the case of rhodesiense. It is important to note that the posterior position of the trophonucleus has never been observed in trypanosomes in the blood of man, but only in experimental animals. Wenyon and Hanschell found that the percentage of posterior nuclear forms varies very much, not only with the stage of infection but also with the strain employed. In three strains of rhodesiense in rats the percentages of these forms were found to vary in one strain from o to 0-9 per cent., in the second from 3 to 7 per cent, and in the third strain from 13 to 40 per cent. T. rhodesiense, like gambiense, is markedly dimorphic, for there are long slender forms and short stumpy forms, together with intermediate forms. The numerical relations between these various forms are extremely variable, depending on the stage of infection. The dimensions of the parasites vary from 13 to 39 microns in length, but the majority of them fall between 17 and 30 microns. Mode of transmission. In 1912, Kinghorn and Yorke demonstrated the transmission of T. rhodesiense by Glossina morsitans, the experiments being carried out at Nawalia, Northern Rhodesia, on the Nyamadzi River, a tributary of the Luang wa. About five per cent, of the flies were found to become infected when fed on patients or animals containing trypanosomes. The development in the fly is of the cyclical type, the insect becoming infective after an incubation period of about fourteen days. Once infected a fly remains infective for the remainder of its life and may infect fresh animals at each successive feed. Temperature has a marked effect on the development of rhodesiense in the intermediate host as shewn by the following experiment. ' Two batches of wild G. morsitans, batch A 95 flies, batch 326 TRYPANOSOMA RHODESIENSE [CH. B 119, shewn to be non-infective by feeding upon clean mon- keys, were fed for three days on a rhodesiense-miected guinea- pig. Each batch was then fed on a healthy monkey until the fortieth day, the mean temperature being 59° F. Neither monkey became infected. The 42 flies remaining of batch A were placed in the incubator at 85° F., and the 58 flies of batch B were left at laboratory temperature. Of the batch A flies, on the 43rd day only six were alive. From the 4ist to the 47th day the flies of batch A were fed on a monkey (which died) ; from the 48th day on a rat. The rat became infected, shewing that batch A contained an infective fly on the 48th day, eight days after being placed in the incubator. The four flies still alive on the 53rd day were fed on four clean rats, three of which became infected. On the 6ist day the 38 flies of batch B, which had then failed to infect the monkey, were put in the incubator at 83° F., and from that day till the 75th were fed on a healthy monkey. The animal unfortunately died. All the flies were dissected as they died. One was found to harbour trypanosomes in the salivary glands and gut, and animals inoculated with the con- tents became infected. In the first part of the experiment the relative humidity in the incubator was 36 per cent., in the second, 72 per cent." This experiment clearly shews that at a comparatively low temperature the early stages of the trypanosomes may persist in the alimentary canal of the fly for sixty days, but that for the completion of the cycle of development a higher tempera- ture is required (75° — 85° F.). The necessity of a certain degree of heat, before the fly can become infective, explains why Kleine was unable to transmit T. gambiense by G. morsitans on Lake Victoria, where the temperature is not high enough. The life cycle of T. rhodesiense within the tsetse-fly has not been thoroughly worked out, but seems to present many points of resemblance to that of T. gambiense in G. palpalis. The trypanosomes first become established in the intestine and in every case the salivary glands are invaded before the fly becomes infective. The manner in which the glands become infected is uncertain, but it is apparently secondary to the XVIII] TRANSMISSION intestinal infection, and it only occurs when the trypanosomes in the gut have reached a certain stage of development, and even then only when the conditions of temperature are suitable for the further development of the parasites. It was found that on every occasion on which the salivary glands were infec- tive, the trypanosomes in the intestine were also virulent As a large number of the wild game harbour T. rhodesiense, in nature the fly is frequently infected. In the Luangwa Valley, Kinghorn and Yorke found that about 0-18 per cent, of the morsitans were infected with rhodesiense. Recently, however, Taute has published an important paper in which the validity of these results is questioned. This investigator carried out experiments at Lubimbinu, Portuguese Nyasaland, and found that a large proportion (16-2 per cent.) of the big game of that district was infected with a trypanosome closely agreeing with T. rhodesiense in its general characters. Nevertheless this parasite was shewn to be non-pathogenic for man, as Taute fed laboratory-bred Glossina morsitans on a monkey infected with the wild game strain, and subsequently on a number of animals and also himself. After the usual incubation period the flies became infective and all the experimental animals (goats, dogs, and monkeys) on which they were fed became infected and died of trypanosomiasis. On the other hand, although Taute fed these same tsetse-flies on himself for four days after they had been proved to be infec- tive for animals, yet he remained well. This experiment was repeated, with the same results, and in addition the author injected himself with 2 c.c. of blood from a naturally infected dog, without ever developing any symptoms of trypanosomiasis. These results suggest that game and domestic animals may not play the part in the spread of human trypanosomiasis that certain authors have supposed, and trypanosomes from such sources can only be regarded with certainty as factors in the spread of sleeping sickness when they have been shewn to be pathogenic for man. ^ oo 328 TRYPANOSOMA BRUCEI [CH. REFERENCES. Hearsey (1909). Nyasaland Sleeping Sickness Diary. Part vm. Kinghorn and Yorke (1912). Ann. Trop. Med. and Parasitology, vol. vi. pp. 1-23, 301-15 and 317-24. Laveran and Mesnil (1912) . Trypanosomes et Trypanosomiases, 2nd edit. Masson : Paris. Shircore, J. O. (1913). Trans. Soc. Trop. Med. and Hyg. vol. vi. pp. 131-42. Stephens and Fantham (1910). Proc. Roy. Soc. B, 561, pp. 28-32. Taute, M. (1913). Arbeit a. d. Kais. Gesundheitsamte, vol. LXV. pp. IO2-II2. Wenyon and Hanschell (1912). //. Lond. Sch. of Trop. Med. vol. 11. PP. 34-35 Nagana (T. brucei Plimmer and Bradford, 1899). General account. Nagana, or the " tsetse-fly disease," is the most widely distributed and best known of all the cattle trypanosomiases of Africa. For many years the common tsetse-fly, Glossina morsitans, was known to be the cause of the disease and the popular belief was that the fly injected into the bitten animal some poison that caused the well-known symptoms of the " fly disease." In 1895, Bruce, together with his wife, investigated the disease as it occurred in Zululand and discovered that it was caused by the presence of a trypanosome in the blood. This parasite was found to be conveyed from diseased to healthy animals by the common tsetse-fly, and was present in the blood of all affected animals. Bruce gives the following account of the infection. " Nagana, or the fly disease, is a specific malady appearing in horses, mules, donkeys, cattle, dogs, cats, and many other animals, and of which the duration varies from a few days to some weeks or even up to some months. It is invariably fatal in the horse, ass and dog ; but a small percentage of cattle recover. It is characterised by fever, by an infiltration of coagulated lymph into the subcutaneous tissue of the neck, abdomen or the extremities, giving rise to a swelling of these regions ; by a more or less rapid destruction of the red cells of the blood, an extreme emaciation, often blindness, and by the XVIIl] GENERAL ACCOUNT 329 constant presence in the blood of an intusorian parasite — a trypanosome." It is generally supposed that Bruce employed Glossina morsitans in these transmission experiments, but, according to Austen, from a consideration of the description and figures given in Bruce's Report on the tsetse-fly disease, or nagana, in Zululand, there can be little doubt that G. pallidipes was the species employed. T. brucei is one of the best known of all the trypanosomes, as a dog infected with the parasite reached England in 1898, and subsequently was sent to most of the laboratories of Europe. As a result this parasite is the one most often employed in treatment experiments and other observations on the biology of trypanosomes under experimental conditions. The disease is widely distributed in Africa, where, in addition to Zululand, it has been recorded from the basins of the Limpopo and Zambesi, Nyasaland, Northern Rhodesia, German and British East Africa, Uganda, Bahr el Ghazal, and in the region of the White Nile. It is also possible that the disease may occur in Somaliland and Galla, for the trypanosome causing the camel disease known as A ino is indistinguishable morphologically from T. brucei. Nagana is one of the most deadly of all trypanosomiases and the majority of animals succumb to the infection after a comparatively short illness. With regard to the virus as it occurs in the laboratories of Europe, Laveran and Mesnil divide the mammals into three groups according to their susceptibility. " (i) Animals in which nagana produces an acute infec- tion : mice, rats, marmots, hedgehogs, dogs and monkeys. (2) Animals in which nagana produces a sub-acute infection : rabbits, guinea-pigs, dormice, horses, donkeys, mules and pigs. (3) Animals in which nagana produces a chronic infection : cattle, goats and sheep." In nature the disease affects horses, ruminants and dogs, and also the wild game, such as antelopes, waterbuck, etc., 330 TRYPANOSOMA BRUCEI [CH. are frequently infected with the trypanosome. These wild animals, however, seem to have become immune against the disease, for they may harbour the parasite in the blood for long periods without suffering from any apparent ill-effects. The wild game, therefore, serves as a reservoir for the infection, as in the case of T. gambiense, and thus, in nature, generally a large proportion of G. morsitans and pallidipes are infected with T. brucei. The morphology of the parasite. In the living state, T. brucei displays active movements, as its undulating membrane is well developed. Its translatory powers, however, are far inferior to those of T. cazalboui and it rarely moves out of the field of the microscope. The dimensions of the parasite according to Bruce vary from 15 to 34 microns in length. Moreover the species is somewhat dimorphic, the short stumpy forms measuring from 2 to 5 microns in diameter and the elongated forms only about 1-5 microns in diameter. According to Laveran and Mesnil the average length of the parasite in horses is 28 to 33 microns and in dogs and the smaller rodents 26 to 27 microns. In stained specimens the protoplasm usually contains numerous granules, especially in the anterior region of the body. The kinetonucleus is distinct, and is generally situated near the posterior extremity, especially in the shorter forms. The undulating membrane is much folded and the flagellum usually becomes free at its anterior extremity. The trypanosome multiplies by simple longitudinal division. Mode of infection. The experiments of Bruce in Zululand shewed that Glossina pallidipes and morsitans were able to transmit T. brucei, but the exact mode of infection remained unknown until Kleine's observations were published. In 1909, Kleine shewed experimentally that G. palpalis is able to transmit this disease, and in addition that the trypano- some underwent a cyclical development in its invertebrate host. The account of the first experiment in which this important discovery was made is as follows : Since nagana did not exist in the Kirugu region (in German East Africa) some sheep and a mule were brought from a place XVIII] MODE OF INFECTION 331 seven days' march away ; these animals had been naturally infected with nagana by the bites of G. morsitans. Fifty G. palpalis were fed on three of these infected animals for three successive days and from the fourth day onwards daily on fresh healthy animals. From the fourth to the seventeenth day inclusive the flies fed on a new animal each day, but none of them became infected. From the eighteenth to the twenty- fourth day the flies fed on the same sheep, and from the twenty- fifth to thirty-ninth day on the same ox. On the twelfth day after the flies were put on this ox, numerous trypanosomes were found in the blood and the sheep was also found to be infected. All the other animals remained healthy. Continuing this experi- ment from the fortieth to the fiftieth day the flies, now reduced in number to twenty-two, were fed on two goats, two calves and two sheep. All these animals became infected after incu- bation periods varying from five to eight days. This experiment clearly shews that G. palpalis remains non- infective for many days after the ingestion of blood containing T. brucei, but that after this negative incubation period the flies become infective and may remain so for a considerable length of time. Later these experiments were repeated employing Glossina morsitans instead of palpalis. It was found that the animals bitten during the three days following the feed on an infected animal, all became infected, the transmission being direct, as in the case of the Zululand experiments. The animals bitten from the fourth to the tenth day remained healthy, whilst all those that were bitten by the flies from the eleventh to the forty-fourth day became infected. Moreover, Taute has shewn that Glossina morsitans may remain infective for at least 83 days. The evolution of T. brucei within the intermediate host has not been fully worked out, but the parasites seem to multiply within the alimentary canal and subsequently invade the proboscis in a manner similar to T. gambiense. 332 TRYPANOSOMA PECAUDI [CH. REFERENCES. Austen (1911). Handbook of Tsetse Flies. Bruce (1895). Preliminary Report on the Tsetse Fly disease or Nagana in Zululand. Ubombo, Zululand. Further Report, 1896. Bruce, Hamerton, Bateman and Mackie (1910). Proc. Roy. Soc. B, vol. LXXXIII. Kleine (1909). Deutsche Med. Woch. Nos. n, 21, 29 and 45. Kleine and Taute (1911). Arb. a. d. Kais. Gesundheitsamte, vol. xxxi. Laveran and Mesnil (1912). Trypanosomes et Trypanosomiases. Paris : Masson et Cie. Baleri (T. pecaudi Laveran, 1907). General account. In 1904, Cazalbou observed a trypanosome in the blood of a horse from the Bani region of Northern Nigeria. This animal was suffering from a disease known by the natives as Baleri. In 1907, Laveran described the trypanosome under the name of T. pecaudi, and since this time Baleri has been recorded from many parts of Tropical Africa. It is common in the Upper Senegal and Nigeria, especially in the basins of the Niger, Bani, and the Upper Volta. It has also been observed in the Lower Senegal, Ivory Coast, Dahomey, French Congo, and in the region of Chan. In Bahr el Ghazal, Balfour and Wenyon have observed in dromedaries and horses infections probably due to T. pecaudi. Baleri is especially a disease of horses and donkeys, but cattle are also susceptible to infection. The disease is charac- terised by the occurrence of febrile attacks that are repeated every three, four or five days. The trypanosomes are generally numerous during the first attacks, becoming rare towards the end of the infection. In horses the disease is practically always fatal, after a duration of from three to four months. Donkeys are less susceptible and may remain infected for nearly two years before death supervenes. A large number of animals may be experimentally infected with T. pecaudi and the symptoms vary according to the species. Cattle, goats, sheep and pigs are very resistant to the infection and generally recover. On the other hand, monkeys, dogs, cats, guinea-pigs, rats and mice are all susceptible and the XVIII] MORPHOLOGY AND TRANSMISSION 333 infection is invariably fatal. In these animals the parasites are numerous in the late stages of the disease. Morphology of the parasite. In the living state the move- ments of the trypanosome are very active. In stained preparations two types can be distinguished, namely, long thin forms and short broad forms. The long thin forms measure about 25 to 35 microns in length by about 1-5 microns in breadth. The posterior ex- tremity is drawn out to a point. The undulating membrane is very narrow and the flagellum anteriorly is free for about one-quarter of its length. The elongate trophonucleus is situated about the middle of the body and the kinetonucleus is some distance away from the posterior extremity. The cytoplasm is free from granules. The short forms measure from 14 to 20 microns in length by 3 to 4 microns in breadth. They are stumpy in ap- pearance and the undulating membrane is very well developed ; there is no free flagellum. The trophonucleus is large and round and the kinetonucleus is situated almost at the posterior extremity. The cytoplasm often contains numerous granules. In the Bahr el Ghazal strain, Wenyon found many forms in which the kinetonucleus was near to the trophonucleus and a few in which the latter was at the posterior end of the body. Both the long and short forms multiply by ordinary longi- tudinal division. Mode of infection. T. pecaudi is transmitted mainly if not entirely by tsetse-flies. The experiments of Bouet and Roubaud in Dahomey have shewn that, in this region, G. longipalpis is the most favourable intermediate host, but tachinoides, palpalis and morsitans, can also carry the disease. These two authors found that the longipalpis caught on the banks of the Oueme River, in the neighbourhood of Agouagon, were heavily infected with T. pecaudi. Thus batches of 45 flies and upwards, almost invariably produced infections of pecaudi when fed on susceptible animals. On the other hand, several hundred palpalis and tachinoides captured in the same area and similarly fed on susceptible animals never produced any infection, so it is evident from the epidemiological point 334 TRYPANOSOMA PECAUDI [CH. of view that longipalpis is the species which in this region constitutes the reservoir fly of T. pecaudi, to the exclusion of the others. The incubation period of the parasite in G. longi- palpis is about 23 days. In addition, 60 G. tachinoides were fed on a guinea-pig infected with T. pecaudi and then on a series of healthy guinea-pigs. Two of these guinea-pigs became infected, giving an incubation period in the fly of 26 days, whereas the others remained normal. In this region experi- ments with G. palpalis gave entirely negative results, but Bouffard previously succeeded in the transmission of T. pecaudi by means of this species, though only with difficulty. Fig- 77- Culture of T. pecaudi, in the intestine of G. palpalis ( x 1200). a, b, normal forms from the circulating blood ; 1-5 forms 18 hours after ingestion ; 1,2, involution forms ; 3, slender form ; 4, 5, large forms ; 6, 7, large forms 56 hours after ingestion. (After Roubaud.) In the Nigerian Sudan, Bouet and Roubaud, during the dry season, found that the morsitans of that region were naturally infected with T. pecaudi. It appears, therefore, that longipalpis and morsitans are the two most favourable hosts for this parasite, and that tachinoides and, exceptionally, palpalis may also be infected. Every infected fly that was dissected contained flagellates along the whole of the digestive tract from the proboscis to the hinder intestine. The trypanosomes multiply in the intestine up to 48 hours after ingestion in a modified form XVIII] TRYPANOSOMA CAZALBOUI 335 called by Roubaud the " intestinal trypanosome form." Under favourable conditions these multiply very rapidly and in seven to nine days invade the whole of the intestine as far as the pharynx. These flies are not infective until the parasites have invaded the proboscis and passed through the Crithidia and Leptomonas phase. These proboscis forms multiply and some reach the hypopharynx, where they assume the " salivary trypanosome form " and are then capable of infecting any susceptible animal. REFERENCES. Bouet and Roubaud (1910). Bull. Soc. Path. Exot. vol. in. p. 599. (1911). Ibid. vol. iv. p. 539. Bouffard (1908). Ann. Inst. Pasteur, vol. xxn. p. 15. Cazalbou (1904). Rec. de Med. Veter. vol. LXXXI. p. 615. Laveran (1907). Compt. Rend. Acad. Sci. vol. CXLIV. pp. 243-247. Balfour and Wenyon (1908). Rep. Wellcome Research Lab. Khartoum. Souma (T. cazalboui Laveran). General account. In 1904, Cazalbou described, from the Upper Niger Territories, a cattle trypanosomiasis known to the natives by the name of Souma. Two years later, Laveran described the trypanosome causing this disease under the name of T. cazalboui, and also gave an account of its biological properties. The disease has subsequently been observed in most of the provinces of West Africa south of latitude 17° N., especially along the upper valleys of the Niger and Volta. It is common in Uganda and has also been recorded from the French Congo, Congo Free State and Rhodesia. Souma is a very widespread disease affecting cattle, horses, mules, and donkeys ; goats, sheep and antelope are also suscep- tible to the infection, but contrary to the general rule for the group of trypanosomes to which it belongs, dogs, cats, monkeys, pigs, rabbits, guinea-pigs, rats and mice are all refractory, and this constitutes one of the principal means of distinguishing T. cazalboui from allied forms. T. vivax and T. uniforme are very closely related to this 336 TRYPANOSOMA CAZALBOUI [CH. species and may subsequently prove to be identical, but at present it is impossible to unite them without increasing the confusion of the subject. The incubation period is usually about seven days. The course of the disease is variable and may be either acute, subacute, or chronic. In the former case, cattle may succumb in as short a time as eight days after infection. The average duration of the malady is about two months, being terminated by the death of the infected animal, but in some cases the dis- ease lingers on for more than a year, and recoveries are not unknown. The parasites are usually rare in the peripheral circulation, but often increase in numbers previous to the death of the host. Morphology of T. cazalboui. The movements of the living parasite are very active and it frequently darts across the field of the microscope. It is a monomorphic species and its dimensions are very constant ; in stained specimens about 24 microns in length, by 1-5 to 2 microns in breadth. The trophormcleus is oval and situated about the middle of the body, whilst the distinct and spherical kinetonucleus is situated very close to the rounded posterior extremity. The undulating membrane is not markedly folded, resembling that of T. lewisi ; the flagel- lum is always free at the anterior extremity. Division is of the usual longitudinal type. Mode of infection. The principal agents for the transmis- sion of Souma are tsetse-flies, four species of which, viz., G. palpalis, tachinoides, longipalpis and morsitans, have been proved capable of carrying the infection. In addition, Bouffard's experiments have shewn that Stomoxys may serve as a direct carrier (vide p. 362). The distribution of Souma seems to shew that Glossina pal- palis is the usual intermediate host, and Bouffard found that in Upper Guinea this species was commonly infected with T. cazalboui. Experimentally, both G. palpalis and G. tachinoides have been proved to be very liable to become infected when fed on an animal containing the trypanosomes in its blood, for XVIII] MODE OF INFECTION 337 Bouffard found that out of 224 tsetse that ingested T. cazalboui, no less than 38-8 per cent, became infected. In Uganda, Bruce and his collaborators found that under similar circum- stances about 20 per cent, of palpalis shewed a development of trypanosomes in the proboscis. The effect of climate on the development of this trypanosome in the intermediate host is well shewn by the results of Bouet and Roubaud in Upper Dahomey and the Nigerian Sudan, during the dry season. In these regions only two species of Glossina, namely tachinoides and morsitans, were found during the summer, all palpalis having disappeared as a result of the dry weather. Experiments were undertaken to determine which of these species was most liable to infection with T. cazalboui. Although in Middle Dahomey tachinoides was as efficient a carrier as palpalis, in the dry regions of Upper Dahomey and the Nigerian Sudan the same species was only infected with great difficulty, the authors concluding that during the dry season, at any rate, G. tachinoides of the regions between 12° and 13° north latitude is unable, or only slightly able, to infect with the endemic viruses, or those which it is able to transmit outside these areas. On the other hand, about 50 per cent, of wild morsitans captured at random were found to be infected ; the development of the trypanosome in this species, however, is somewhat slower than in palpalis, tachinoides and longipalpis, respectively. In the Katanga district the mem- bers of the Belgian Sleeping Sickness Expedition (1912) found an equally large percentage of morsitans infected with cazalboui. The development of the trypanosome in the tsetse-fly is restricted to the proboscis, the flagellates never multiplying in any other part of the alimentary canal. Palpalis, tachinoides, and longipalpis, become infective about six to seven days after an infecting feed, whilst in the case of morsitans this developmental period is prolonged to eight to ten days. In Uganda, the development of T. cazalboui is much slower than in the West African Provinces, for the members of the Sleeping Sickness Commission at Mpumu, found that the non- infective period varied from n to 35 days. H. B. F. 22 TRYPANOSOMA CAZALBOUI [CH. It is possible that this remarkable difference in the rate of development may be accounted for by the difference in climate, for Bamako, on the Niger, the locality where Bouffard performed his experiments, is less than 1000 feet above sea-level, whereas Mpumu is more than 4000. Moreover, the mean temperature of Uganda is far below that of Bamako and the influence of this factor is most important. After being ingested some of the trypanosomes remain in the proboscis of the fly and change into Leptomonas or Crithidial forms. These become attached to the walls of the labrum and undergo rapid multiplication, resulting in the production of large clusters of flagellates, which may almost obstruct the cavity of the proboscis. Under the influence of the salivary secretion some of these fixed flagellates develop into small actively motile trypanosomes closely resembling the blood forms. These free trypanosomes are found in the hypopharynx and escape together with the salivary secretion when an infected fly feeds on any host. Once a fly becomes infected it may remain infective for at least two and a half months and probably for the remainder of its life. If the air is very dry, however, the flagellates may disappear from the proboscis and the fly cease to be infective. Thus Bouet and Roubaud found that in Upper Dahomey during the dry season about 50 per cent, of freshly caught morsitans shewed infection of the proboscis, but when these flies were kept and examined 20 to 31 days later the proportion of infected flies was only two in thirteen. Roubaud has performed some very interesting experiments on the effects of various conditions on the development of T. cazalboui in G. palpalis, which supplement the observations of Bouet and Roubaud in Upper Dahomey. Twelve G. palpalis, caught in nature, were placed in a dehydrated atmosphere. Twelve hours later and twice in the three succeeding days they were allowed to feed on a goat infected with T. cazalboui. Four days later they were fed on a healthy kid for two days. On the ninth day the flies were dissected and found to be uninfected and also the kid remained healthy. In another experiment eight flies were fed for two days on the infected goat and then XVIII] TRANSMISSION 339 placed in a partially dehydrated atmosphere. They were fed every day on a healthy kid until the ninth day when they were dissected and four were found to be infected. In another similar experiment three out of fifteen flies became infected and the kid succumbed to trypanosomiasis caused by their bites In two control experiments, during which the flies were kept in the ordinary atmosphere, eight out of twelve and eight out of nine flies shewed flagellates and also infected a succession of healthy kids on which they were fed. In another experiment, six flies hatched from pupae that had been kept in dry air from their formation, were fed on July 7, 8, and 9 on an infected goat and then returned to dry air. On the i8th and I9th they were allowed to bite a healthy kid and on the 27th and 28th yet another normal kid. The next day the flies were dissected and two out of six were found to be infected, moreover both kids suffered from a very severe attack of trypanosomiasis. Roubaud accordingly is of the opinion that if the modifying influence, such as dry air, acts for a long time before the infecting feed is given, the saliva regains its suitability as a medium for the development of the trypanosomes. The action of saturated air was similarly tested and respec- tively, one fly in eight and one infifteen became infected, without, however, infecting a kitten on which they were fed. These results tend to explain the author's observation that, in nature, during the dry season more flies were found to be infected than during the wet. REFERENCES. Bouet and Roubaud (1911). Bull. Soc. Path. Exot. vol. iv. p. 539. Bouffard, G. (1909). Bull. Soc. Path. Exot. vol. n. p. 599. (1910). Ann. Inst. Pasteur, vol. xxiv. p. 276. Cazalbou, L. (1905). Compt. Rend. Soc. Biol. vol. LVIII. pp. 564-565. Laveran, A. (1906). Compt. Rend. Acad. Sci. vol. CXLIII. pp. 94-97. (1910). Bull. Soc. Path. Exot. vol. in. p. 80. Rodhain, Pons, van den Branden and Bequaert (1912). Bull. Soc. Path. Exot. vol. v. pp. 45-50 and 281-84. Roubaud, E. (1909). These de doctor at es sci. nat. Paris, June, 1909. (1910)- Compt. Rend. Acad. Sci. 1910, pp. 729-32. 22 — 2 34° TRYPANOSOMA VI VAX [CH. Trypanosoma viyax Ziemann, 1905. In 1905, Ziemann described under the name of T. vivax a trypanosome occurring in the blood of cattle, sheep, and goats in the Cameroons. The symptoms of the disease it produces are almost identical with those of Souma, and moreover, in its morphology, T, vivax closely resembles cazalboui. But Ziemann definitely states that rats are susceptible to T. vivax, eight of them dying from the infection after eight, nine and eleven days. Also a dog and a pig both shewed a temporary infection. On the other hand, rats are absolutely refractory to T. cazalboui and this constitutes a method of distinguishing the two. Bagshawe has called attention to the resemblance between the two forms, and inclines to consider them as constituting a single species. This view has been opposed by Laveran, and certainly as long as " species " of trypanosomes are distin- guished mainly on the basis of cross-immunity reactions and the susceptibility of laboratory animals, it is impossible to unite two forms differing so markedly in the latter feature. Bruce and his colleagues on the basis of a microscopic exam- ination of Ziemann's slides came to the conclusion that T. cazalboui Laveran was synonymous with T. vivax Ziemann. Accordingly throughout their reports they have employed the latter name for a trypanosome which is undoubtedly identical with the T. cazalboui of the French and Belgian authors. A careful comparison of Ziemann's original description with the accounts of cazalboui, shew that although very closely related the two forms may be easily distinguished by their respective animal reactions. Thus, all small laboratory animals and the pig are refractory to cazalboui, whereas rats are very susceptible to vivax and die within eleven days ; also a dog and a pig shewed a temporary infection. As rats as well as the other small experimental animals are not susceptible to the Uganda virus, it is evident that the species of that region, which has been referred to as T. vivax, should be known correctly as cazalboui. XVIII] TRYPANOSOMA UNIFORME 341 Undoubtedly the two forms are closely related, but as long as the reaction of experimental animals constitutes one of the means of distinguishing varieties of trypanosomes, it is only increasing the confusion of the subject to unite vivax and cazalboui on purely morphological grounds. REFERENCES. Bruce, Hamerton, Bateman and Mackie (1910). Proc. Roy. Soc. B, vol. 556, p. 368 and vol. 561, p. i. Bruce, Hamerton, Bateman and Lady Bruce (1911). Eleventh Report Sleeping Sickness Comm. of Roy. Soc. Yorke and Blacklock (1911). Ann. Trop. Med. and Parasit. vol. v. P- 413- Ziemann, H. (1905). Centralbl. f. Bakter. I. Orig. vol. xxxvm. p. 9. Trypanosoma uniforme Bruce, Hamerton, Bateman and Mackie, 1911. This parasite was first noticed in the blood of oxen in Uganda. It closely resembles T. cazalboui, but may be distin- guished by its smaller size. T. uniforme causes a very fatal disease, for two naturally infected cattle died after 5 and 79 days respectively. Goats inoculated with the parasite lived on an average 29 days, but out of three sheep inoculated only one became infected. Fraser and Duke found that two out of 30 bushbuck and sitatunga (Tragelaphus spekei), obtained within two miles of the shore of Lake Victoria, were naturally infected with T. uniforme. Monkeys, pigs, dogs, cats, guinea-pigs and white rats are all refractory to this parasite, another characteristic in which this species resembles cazalboui. According to Laveran and Mesnil, uniforme is probably the same as cazalboui, but its small size seems to be a sufficient means of distinction. Morphology. T. uniforme is a small and active trypanosome with marked translatory movement, though inferior to that of cazalboui. The parasites are remarkably uniform in size and appearance, the average dimensions being 16 microns in length by 1-5 to 2-5 microns in breadth. The extreme range of variation in the length is only from a minimum of 12 to 342 TRYPANOSOMA DIMORPHON [CH. a maximum of 19 microns. The free part of the flagellum is from I to 5 microns in length. In all other characters T. uniforme is the same as cazalboui, with the exception that there is no marked narrowing opposite the trophonucleus as in the case of the latter species. Mode of infection. Fraser and Duke have shewn that the Glossina palpalis in the neighbourhood of Lake Victoria are naturally infected with this trypanosome, for after 1020 flies from the lake-shore had been fed on a goat it became infected with T. uniforme. Also it was shewn experimentally that laboratory-bred palpalis were capable of transmitting this species of trypanosome from infected to healthy animals. Of six experiments four were successful. The flies became infective in from 27 to 37 days, and the infection in the fly was always limited to the proboscis as in the case of cazalboui. REFERENCES. Bruce, Hamerton, Bateman and Mackie (1911). Proc. Roy. Soc. B, 563, p. 176. Fraser and Duke (1912). Ibid. B, vol. i.xxxv. p. i. Trypanosoma dimorphon Laveran and Mesnil, 1904. Synonyms. T. confusum Montgomery and Kinghorn, 1909. T. frobeninsi Weissenborn, 1911. General account. In 1902, Button and Todd in the course of their expedition to the Gambia observed trypanosomes in the blood of some of the horses in that region. Under the title of " Horse trypanosome " they described and figured the parasites occurring in one of these horses. The .emarkable feature about the infection was the occurrence of small tadpole-shaped trypanosomes without any free flagellum. side by side with long and slender forms with a long free flagel- lum. Button and Todd did not name their horse trypano- some, a fortunate omission, since there is practically no doubt that several distinct species were in their hands. One of these infected horses was sent over to Liverpool and from here the strain was sent across to Laveran and Mesnil in Paris, where they studied the morphology of the trypanosome, and, in 1904, published a description of it under the name of T. dimorphon. XVIIl] GENERAL ACCOUNT 343 The name T. dimorphon, therefore, is only applicable to the trypanosome which reached Europe and was described by Laveran and Mesnil. This parasite, as pointed out by the authors, differs considerably from Button and Todd's description of the " Horse trypanosome," especially in the absence of any forms provided with a free flagellum. T. dimorphon Laveran and Mesnil, is the ordinary dimorphon of the laboratories of Europe, and it is important that the use of this name should be abso- lutely restricted to trypanosomes agreeing with Laveran and MesmTs original description (1904). Montgomery and King- horn wish to reserve the name T. dimorphon for the forms described by Button and Todd and apply the term T. confusum to the parasite described by Laveran and Mesnil. Such a course, however, is illegitimate, for the name dimorphon was only applied to the latter, and never to Button and Todd's original description. The occurrence of mixed infections in many animals is a source of great difficulty in identifying the species of trypano- somes, for Yorke and Blacklock have shewn that dimorphon and cazalboui may occur side by side in horses from the Gambia. T. dimorphon is widely distributed throughout West Africa and has been recorded from the following localities : Gambia, Senegal, Casamance, Upper Gambia, French Guinea, Sierra Leone, Ivory Coast, Togoland, Bahomey, French Sudan and French Congo. In the Congo Free State, Rhodesia, Zululand, Portuguese East Africa, Zanzibar, Bahr el Ghazal, and Somali- land, trypanosomes of the dimorphon type have been observed, but it is difficult to say whether they should all be referred to T. dimorphon Laveran and Mesnil. Horses, mules, cattle, goats, sheep, pigs, dogs, cats, mon- keys, and all the smaller laboratory animals are susceptible to infection with T. dimorphon. As a rule, in the larger animals, the course of the disease is slow, and death only occurs after trypanosomes have been present in the blood for several months. In some cases the animals recover and trypanosomes may be present in the peripheral circulation for some years, without apparently producing any pathogenic symptoms. 344 TRYPANOSOMA DIMORPHON [CH. Morphology of the parasite. In the fresh state, the dimorphic nature of this species is easily recognisable. The most common forms are only 12 to 14 microns in length and I micron in breadth, with a rounded posterior extremity and a body which gradually tapers towards the anterior extremity. These short forms present a somewhat characteristic movement ; after progressing forward for some little distance, wriggling after the manner of a tadpole, they stop abruptly, and then move on again in the same fashion. The undulating membrane is very slightly developed. The long forms of dimorphon are less common than the pre- ceding and may occasionally be absent. They range from 20 to 25 microns in length, by 1-5 microns in breadth. The undulating membrane is only slightly developed and the parasites, although more active than the short forms, do not present as lively motions as T. brucei. These two forms are connected by intermediate stages, and therefore the short trypanosomes might be regarded as a young form of the large, were it not for the fact that they both reproduce by longitudinal fission. In Giemsa-stained specimens, a remarkable feature of dimorphon is the extremely dense blue colour of the protoplasm. The kinetonucleus is situated close to the rounded posterior extremity. The undulating membrane is never very marked and in every case the protoplasm is continued along to the extremity of the flagellum. This latter feature, together with the dimorphism, is very characteristic. Division is of the usual longitudinal type. Mode of infection. Bouet, in 1907, succeeded in transmitting T. dimorphon by the bites of Glossina palpalis that had fed on an infected animal 24 hours previously. In this experiment the transmission was merely mechanical. In Dahomey, Bouet and Roubaud have demonstrated the part played by G. palpalis, tachinoides and longipalpis in the transmission of this parasite. Palpalis captured in nature, were fed on two dogs, a sheep, and a kid, and these animals became infected with dimorphon after incubation periods vary- ing from 14 to 20 days. The same flies were fed on guinea-pigs XVIIl] TRANSMISSION 345 but produced no infection, thus shewing that these animals are only slightly susceptible to this trypanosome. G. morsitans is also capable of transmitting T. dimorphon, and thus four species of tsetse-flies in West Africa are all efficient intermediate hosts for the parasite. The experiments with regard to the infection of the fly are somewhat inconclusive, but from an examination of " wild " tsetse it appears that longipalpis is the most often infected, then tachinoides, whilst the proportion of palpalis containing dimorphon is very much less, being only about one per cent. In Dahomey, the negative period of incubation in the fly is said to be more than 18 days, but as Bouet and Roubaud worked entirely with wild flies the exact period could not be decided. The infection in each species of fly is what is known as " total." The trypanosomes become established in the hind intestine and gradually extend forwards until they reach the proboscis, when they become fixed and assume the Leptomonas or Crithidial form. These proboscis forms of dimorphon may be distinguished from those of congolense by the frequent occur- rence of giant forms like those of cazalboui, but differing in the flattened appearance of the posterior prolongation. The inocu- lation of intestinal forms produced no infection, whereas when the proboscis was inoculated a positive result was obtained. It is evident, therefore, that the evolution of T. dimorphon in Glossina longipalpis, tachinoides, palpalis, and morsitans, respectively, is of the usual type, first a multiplication of try- panosomes in the intestine, during which period the fly is non- infective, followed by an invasion of the proboscis where the Leptomonas or Crithidial stage is gone through, after which the fly becomes infective. REFERENCES. Bouet (1907). Ann. Inst. Pasteur, vol. xxi. p. 474. and Roubaud (1910). Bull. Soc. Path. Exot. vol. in. p. 722. Dutton and Todd (1903). Liverpool Sch. of Trop. Med. Memoir xi. Laveran and Mesnil (1904). Compt. Rend. Acad. Sci. vol. cxxxvm. p. 732- Montgomery and Kinghorn (1909). Lancet, Sept. 25, 1909. Yorke and Blacklock (1911). Ann. Trop. Med. and Parasit. vol. v. p. 413 and vol. vi. p. 107. 346 TRYPANOSOMA PECORUM [CH. Trypanosoma pecorum Bruce, Hamerton, Bateman and Mackie, 1910. General account. In 1910, Bruce and his collaborators observed a trypanosome in the horses and cattle of Uganda. This parasite was supposed to be identical with T. dimorphon and T. congolense, and, therefore, all three were united under the name T. pecorum. Laveran, however, has shewn by means of cross-immunity reactions that T. pecorum is a distinct species, but is closely related to dimorphon, congolense and nanum. Recently Kinghorn and Yorke have found T. pecorum present in the wild game of the Luangwa Valley, North-Eastern Rhodesia. The incubation period in cattle inoculated with T pecorum is on an average about six to seven days. The duration of the disease may vary from 26 up to as long as 287 days. It is invariably fatal, the symptoms being weakness and emacia- tion, accompanied by anaemia. Cattle, goats, sheep, monkeys, dogs, rabbits, guinea-pigs, rats and mice are all susceptible to infection with T. pecorum, and this constitutes a means of distinguishing it from nanum. Duke's experiments have shewn that the bushbuck is also susceptible and may remain infective for at least 323 days, therefore the wild game may serve as a reservoir for this trypanosome. Morphology of the parasite. In the living state T. pecorum is remarkable for its habit of exhibiting alternate periods of quiescence and activity. When quiescent it usually buries itself under clumps of red cells and is thus difficult to detect. The movements are active but, as in the case of T. congolense, not translatory ; therefore, the parasites do not travel across the field of the microscope. In stained specimens the trypanosome is practically indis- tinguishable from T. nanum and T. congolense. It is a monomorphic species ; the extreme variations in length are 8 to 18 microns, but the average dimensions, comprising the majority of individuals, are 14 microns in length by about 3 microns in breadth, including the undulating membrane. The posterior extremity is rounded ; the anterior XVIII] TRANSMISSION 347 is more or less tapering. The undulating membrane is well developed, being larger than that of T. nanum, and there is no free flagellum. The oval trophonucleus is situated about the middle of the body and the small spherical kinetonucleus is at the posterior extremity. The cytoplasm is generally homo- geneous and not very granular. Mode of infection. The results of Kinghorn and Yorke in the Luangwa Valley have shewn that Glossina morsitans is probably the most important agent for the spread of this infection. By collecting large numbers of these tsetse-flies and feeding them on healthy monkeys, out of 3202 flies at least two were found to be infected with T. pecorum. Under experimental conditions, Glossina palpalis can also serve as the intermediate host for this species and animals may be infected by the bites of palpalis that have previously ingested blood containing T. pecorum. The mode of transmission is indirect, that is to say the trypanosome undergoes a cyclical development within the alimentary canal of the fly, but this development is so extremely slow that it is evident that G. palpalis is not the usual intermediate host of this parasite. It is also significant that wild palpalis has never been found naturally infected with pecorum. The stages in the develop- ment of T. pecorum in the alimentary canal of G. palpalis have been observed by Fraser and Duke, and also by Miss Robertson. Although these two species of Glossina have thus been proved capable of transmitting this infection, there is considerable evidence to shew that the disease can exist in the absence of tsetse. Thus Bruce and other members of the Sleeping Sick- ness Commission saw an outbreak of T. pecorum infection under the following circumstances. The cattle belonging to this Commission grazed at the foot of Mpumu Hill, half to the east and half to the west. Tabanus and Hcematopota were occasionally seen but always in very small numbers. In September, 1909, swarms of Tabanus secedens Walk, suddenly appeared to the west of the hill and a month later to the east. Soon afterwards the cattle, which had been healthy for a year, shewed signs of T. pecorum infection, first those which grazed to the west, then those which grazed to the east. It should be 34-8 TRYPANOSOMA NANUM [CH. noted that there were a few pre-existing cases of infection in the herd. Afterwards a few Glossina palpalis were found at the foot of the hill. Nevertheless, although this circumstantial evidence is so strong, all attempts to transmit the disease experimentally by the bites of either Tabanids or Stomoxys have given uniformly negative results. Development within the intermediate host. The development of T. pecorum within the alimentary canal of Glossina palpalis in all essential features resembles that of T. nanum, but is excessively slow, so that it seems probable that this species of tsetse only exceptionally serves as its intermediate host. The parasites develop in the hinder intestine and give rise to a large number of trypanosomes of very varying size. Eventually, the slender forms are produced and these are extraordinarily attenuated ; in addition the nuclear changes occurring at this stage in the cycle of T. gambiense, also take place in T. pecorum. The invasion of the proventriculus usually occurs about the 45th day and no proboscis infection was found before the 76th day. The Crithidial phase is passed through in the proboscis, as in the case of T. nanum, and the salivary glands are never invaded. LITERATURE. Bruce, Hamerton, Bateman and Mackie (1910). Proc. Roy. Soc. B, vol. LXXXII. p. 468. Duke, H. L. (1912). Proc. Roy. Soc. B, vol. LXXXV. p. 554. Kinghorn, A. and Yorke, W. (1912). Ann. Trop. Med. and Parasit. vol. vi. pp. 301 and 317. Laveran, A. (1910). Bull. Soc. Path. Exot. vol. in. p. 718. Robertson, M. (1913). Trans. Roy. Soc. B, vol. ccm. pp. 161-184. Trypanosoma nanum Laveran, 1905. General account. This parasite was first discovered by A. Balfour in 1904, in the blood of cattle from the Anglo- Egyptian Sudan. It has since been recorded from various other localities of this region and also in Uganda, where Bruce and his collaborators found it in the blood of cattle. XVIII] MORPHOLOGY 349 Kleine and Fischer, in the region of Lake Tanganyika, have found both sheep and antelopes naturally infected with a try- panosome that seems to agree with nanum in its characters. In cattle, T. nanum produces a disease which develops slowly ; the main symptom is the well-marked anaemia, which is accompanied by a gradual emaciation and usually ends in the death of the infected animal. The parasites are usually present in the peripheral circula- tion, sometimes in considerable numbers, and can be easily recognised. T. nanum can readily be inoculated into cattle and goats, but all the smaller laboratory animals are refractory to infec- tion, for monkeys, dogs, rats and mice have been inoculated without becoming infected. Morphology of the parasite. Laveran has given the following diagnosis of Trypanosoma nanum : ' The trypanosomes measure 10 to 14 ^ in length, by 1-5 to 2 ^ in breadth. Their structure is that of flagellates belonging to the genus Trypanosoma ; yet, contrary to the rule, the protoplasm is prolonged at the anterior end, in such a manner that there is no free flagellum, or the free part of the flagellum is extremely short. The undulating membrane is very narrow and in consequence only slightly evident. The posterior extremity is conical, not drawn out, otherwise a little variable in form." " The oval nucleus is situated about the middle of the body of the parasite. The centrosome (= kinetonucleus) , rounded and rather large, is found almost at the posterior extremity. ' The protoplasm is homogeneous, without granulations. " Some of the forms, a little larger than the others, shew two centrosomes and a flagellum divided for a greater or lesser extent from the origin in the centrosome ; these are evidently multiplication forms." In Uganda the length of the parasite may extend up to 16 microns as shewn by Bruce, Hamerton, Bateman and Mackie, and also by Duke. Mode of transmission. The experiments of Duke in Uganda have shewn that Glossina palpalis may serve as the intermediate 35O TRYPANOSOMA NANUM [CH. host for T. nanum. Laboratory bred flies were fed on an infected sheep and subsequently on a calf, which developed a typical infection with this trypanosome. About five per cent, of the flies fed on this sheep were found to be infected. Kleine and Fischer are of the opinion that Glossina morsitans is the intermediate host of T. nanum in the region of Lake Tanganyika. Development of the parasite. In the blood the trypanosome multiplies in the usual manner by means of longitudinal division. When taken into the gut of G. palpalis the resulting changes are exactly comparable with those that take place in the case of T. gambiense, described above. The trypanosomes begin to develop in the hinder intestine and by the loth day numerous parasites may be found in the hinder and middle intestine. The slender forms begin to be produced from the loth to the I4th day onwards, and the proventriculus is usually invaded about the 20th day. The proventricular forms are not quite so uniformly slender as in the case of T. gambiense. Moreover, there are no marked changes in the appearance of the nuclei of T. nanum. About the 25th day the trypanosomes invade the proboscis, where they may be found attached to the labrum, often lying in clusters. They then pass through the Crithidial phase, many of them being extremely long and slender. Subsequently trypanosome forms are produced which may be found free, sometimes in the hypopharynx and at other times in the labrum. The salivary glands never become infected in the case of T. nanum, the proboscis infection apparently playing the same part as the gland infection in the cycle of T. gambiense. LITERATURE. Laveran, A. (1905). Compt. Rend. Soc. Biol. vol. LVII. p. 292. Balfour, A. (1904). B. M. J. Nov. 26, 1904. Bruce, Hamerton, Bateman and Mackie (1910). Proc. Roy. Soc. 1910, B, vol. LXXXIII. p. 180. Duke, H. L. (1912). Proc. Roy. Soc. B, vol. LXXXV. p. 4. Kleine and Fischer (1911). Zeitschr. f. Hyg. u. Infectionskr. vol. LXX. p. 18. Robertson, M. (1913). Phil. Trans. Roy. Soc. B, vol. ccin. p. 161. XVIII TRYPANOSOMA CONGOLENSE 351 Trypanosoma congolense Broden, 1904. This parasite, which very closely resembles T. pecorum and T. dimorphon, was first described by Broden, who found it occur- ring in the blood of a donkey and sheep in the Congo Free State. Subsequently the parasite was also observed in the blood of cattle and dromedaries in the same locality and also in cattle, sheep, goats and dogs in the French Congo, where, according to Martin, Leboeuf and Roubaud, it is widely distributed. In North-East Rhodesia, Montgomery and Kinghorn have observed T. congolense in the blood of cattle. It is doubtful whether the trypanosomes occurring in dogs on the shores of Tanganyika should be referred to this species or to T. pecorum. T. congolense is only distinguishable from T. pecorum by cross-immunity reactions, for Laveran and Mesnil shewed that a goat immune against T. congolense was susceptible to infec- tion with pecorum. Otherwise the two forms are practically identical and it is questionable whether they should be regarded as distinct species. Fig. 78. Culture of T. congolense in the intestine of G. palpalis. ( x about 1600). a, b, normal forms from the circulating blood ; 1,2, forms 24 hours after ingestion ; 3, 5, forms after 48 hours ; 6, 7, forms after 56 hours. (After Roubaud.) In addition to cattle, sheep, goats and dogs, all the usual experimental animals may be infected with congolense, but the course of the disease is usually very slow, resembling that of dimorphon. The constant susceptibility of guinea-pigs is, however, in marked contrast with that of other laboratory 352 TRYPANOSOMA CONGOLENSE [CH. animals, for Laveran and Mesnil found that the average duration of the disease in this species was only two weeks and invariably resulted in the death of the animal. Morphology of the parasite. The living parasite exhibits active wriggling movements without, however, progressing across the field of the microscope. The trypanosomes are often attached to the leucocytes by their anterior extremities. The dimensions of the majority of the individuals vary between 10 to 13 microns in length, by i to 2 microns in breadth, and the largest forms are never more than 17 microns in length, a means of distinguishing this species from dimorphon. In stained specimens the posterior extremity is rounded and anteriorly the body of the parasite gradually tapers, the protoplasm being prolonged to the extremity of the flagellum. The trophonucleus is situated about the middle of the length of the parasite ; the kinetonucleus is very distinct and is usually close to the posterior extremity. The protoplasm is somewhat clear and rarely contains chromatophilous granules. Mode of infection. There is some little doubt as to whether G. palpalis is capable of transmitting congolense, for the only positive experiments with this species of tsetse-fly that have been recorded up to the present are those of Roubaud, and this author states that the observations were made with " T. con- golense (vel dimorphon}." In the alimentary canal of G. palpalis Roubaud observed the commencement of a development of this trypanosome somewhat resembling that of T. gambiense, but the parasites all disappeared by the end of the third day. Rodhain, van den Branden, Pons and Bequaert, found that the G. morsitans in the Katanga region were naturally infected with congolense. In addition an experiment was made with 23 flies born in the laboratory. These were fed on an infected goat and subsequently on healthy animals. After an incubation period of 23 days one of the flies became infective. This individual on dissection was found to present an " infec- tion tot ale " of the alimentary canal. The parasites in the intestine were nearly all of the trypanosome type and some were of the blood form. In the proboscis the hypopharyngeal XVIII] TRYPANOSOMA S1UI1E 353 tube was filled with small trypanosomes of the congolense type without any free flagellum, whilst the parasites that swarmed in the labrum were of the Leptomonas type. REFERENCES. Broden, A. (1904). Bull. Soc. d'£tudes Coloniales, Bruxelles, February, 1904. Laveran and Mesnil (1912). Trypanosomes et Trypanosomiases. Montgomery and Kinghorn (1909). Ann. Trop. Med. and Parasit. vol. in. p. 349. Rodhain, van den Branden, Pons and Bequaert (1912). Bull. Soc. Path. Exot. vol. v. p. 281. Roubaud (1909). These de doct. es sci. nat. Paris, pp. 153 and 161. Trypanosoma simiae Bruce, Harvey, Hamerton, Davey and Lady Bruce, 1912. Synonym. T. ignotum Kinghorn and Yorke, 1912. General account. This species of trypanosome has been recorded from Nyasaland, Central Angoniland, and North- Eastern Rhodesia, where a large percentage of Glossina mor- sitans are naturally infected with the parasite. Its pathogenic properties are very remarkable, since it only affects such widely different animals as monkeys and goats. Oxen, baboons, dogs, guinea-pigs, and white rats, seem to be immune. In goats T. simice sets up a chronic disease, but in monkeys the infection is rapidly fatal, for in a series of 19 the average duration of life after the trypanosomes were first seen in the blood was only 2-9 days. Morphology. When living the parasite shews active pro- gressive movements, some individuals passing completely across the field of the microscope. The dimensions of the trypanosomes as found in the monkey and the goat, are found to vary from 14 to 24 microns in length, by i to 2-75 microns in breadth, the mean being 18 microns in length by 1-75 in breadth. The parasites are monomorphic and, as a rule, fairly uniform in shape. The authors give the following summary of its characters : " Elongated, narrow, undulating body ; posterior extremity bluntly pointed or rounded ; anterior extremity pointed ; H. B. F. 23 354 TRYPANOSOMA SIMIM [CH. nucleus oval ; micronucleus small, round, situated about 1-5 microns from posterior extremity, placed laterally, protuberant ; undulating membrane marked, thrown into bold folds ; flagel- lum frequently not projecting beyond undulating membrane, sometimes i to 2 microns of the extremity apparently free." Fig. 79. Trypanosoma simice. Successive stages in the division shewing the peculiar manner in which the two daughter trypanosomes seem to " slip " past each other, until they are only joined by their non-flagellate ends. (After Bruce, Harvey, Hamerton, Davey and Lady Bruce.) In the blood of the monkey these trypanosomes swarm in enormous numbers and numerous division forms can be seen, often four or five in a field. When dividing the trypanosomes appear to slip past one another until they are only joined by their posterior extremities, as shewn in Fig. 79. Multiplication often takes place so rapidly that the individual trypanosomes have not time to disengage themselves and thus large multi- Fig. So. Trypanosoma simia. Large multinucleate form. (After Bruce, Harvey, Hamerton, Davey and Lady Bruce.) xvni] STOMOXYS 355 nucleate masses are produced, sometimes filling the whole field of the microscope (Fig. 80) . The life history of this parasite in its intermediate host, Glossina morsitans, has not yet been worked out. Its extreme pathogenicity in monkeys is very remarkable and suggests that T. simicE is a species that has only recently become adapted to its present mode of life. LITERATURE. Bruce, Harvey, Hamerton, Davey and Lady Bruce (1912). Proc. Roy. Soc. B, vol. LXXXV. p. 477. Kinghorn and Yorke (1912). Ann. Trop. Med. and Parasit. vol. vi. pp. 301-315 and 317-324. CHAPTER XIX STOMOXYS General description. The members of the genus Stomoxys may be distinguished from other blood-sucking Muscidae by the following characters : The proboscis protrudes horizontally in front of the head and is pointed towards its anterior extremity. The maxillary palps are cylindrical and slender, less than half the length of the proboscis. The first longitudinal vein opens into the wing about mid-way along its length, almost opposite the small transverse vein. The first posterior marginal cell opens widely at the tip of the wing. Between the posterior transverse vein and the margin of the wing the fourth longitudinal vein is arched like a bow with the concavity facing the third longi- tudinal vein (Fig. 81). The flies belonging to this genus are all moderate sized (5 to 7 mm.) dull-coloured insects that generally feed on the blood of cattle. They closely resemble the house-fly (Musca domestica] in general appearance, but may be readily distin- guished by the presence of the proboscis, and also Stomoxys rests with its wings widely divergent whilst in Musca they are 23—2 356 STOMOXYS CH. held closer together. The most abundant species is Stomoxys calcitrans, the common stable-fly of this country, but in addition to this insect, 5. nigra is also supposed to be concerned in the spread of disease. Auxiliary v,ein Anl-erior cross-vein Fig. 8 1. Wing venation of Stomoxys calcitrans. Stomoxys calcitrans Linn. General description. This insect closely resembles the common house-fly in colouration and general appearance, but as mentioned above, may be easily recognised by the pres- ence of the biting proboscis and the attitude of the wings. In addition 5. calcitrans is distinguished by the following characters : Fig. 82. Side view of head of Stable-fly ; A, proboscis in resting position B, proboscis extended. (After Graham-Smith.) XIX] DESCRIPTION 357 The lower part of the face is white, frequently with a yel- lowish tint, which is especially visible upon the sides of the forehead. The latter is marked with black or reddish-brown stripes ; the antennae are brown, at times lighter dorsally. The maxillary palps are short, scarcely protruding, and yellow in colour. The dorsal surface of the thorax is marked with four dark longitudinal stripes, two on each side, extending from the shoulders to the scutellum, but interrupted in the middle of their length by the transverse suture. The abdomen has a yellowish-brown tint and is marked with three indistinct dark spots on the second segment and some on the following segments. The legs are blackish-brown with reddish-yellow knees. According to Austen, the African examples of this species are smaller than British specimens and the abdominal spots shew considerable variation in size and shape. The insect varies from about 5-5 to 7 mm. in length. Fig. 83. Stable-fly, Stomoxys calcitrant (Y 5). On the left, magnified view of antenna. On the right, view of the fly in its resting position. (Nat. size.) (After Graham-Smith.) Distribution. S. calcitrans has been recorded from almost every part of the world, occurring throughout both temperate and tropical countries and even extending as far north as Lapland. It is especially abundant, however, in warmer countries, or during the summer months of more temperate regions. Habits. The common name of this insect, the stable-fly, 358 STOMOXYS [CH. gives a true indication of its usual habitat, and during the sum- mer large numbers of Stomoxys may generally be found around the cow-sheds and stables of any farmyard ; in warm weather, however, it may be found wherever cattle are grazing ; and during late summer and autumn they are frequently found in houses, where they are known as "Biting House-flies." When resting on a wall, Stomoxys generally points the head upwards, and thus may be distinguished from the house-fly which usually takes the opposite position. The fly may feed on the juices from any decaying organic matter, and also on the blood of vertebrates. It is possible that its blood-sucking habits have been somewhat over-esti- mated, for Newstead kept a careful watch on both horses and cattle in a farmyard where Stomoxys were plentiful without seeing even one settle on an animal. During hot weather, however, the flies become very troublesome to animals and may even attack human beings. The voracious habits of Stomoxys are well shewn when a number are kept together in captivity. Under these circumstances if an individual suffers any injury, the others at once try to feed on it and, if success- ful in piercing the integument, suck all the contents out of their unfortunate companion. Unlike many blood-sucking flies, the female Stomoxys will lay fertile eggs without ever having fed on blood. Life history. Newstead has recently given a complete description of the metamorphosis of this insect from which the following account is taken. The female generally lays its eggs a few inches below the surface in stable manure, decomposing vegetable matter, or similar materials. Although the flight of this insect is usually noiseless, when the female is preparing to oviposit the noise of its wings is distinctly audible, resembling the hum made by most other members of the Muscidae. The eggs are generally laid in an irregular heap and their number is usually about 50 to 70. The egg is i mm. in length, very elongate, shaped somewhat like a banana, being curved on one side and deeply grooved on the other. This groove widens towards the anterior end. The colour of the egg is white when first laid, but subsequently becomes creamy-white. XIX] LIFE HISTORY 359 The larva escapes by splitting the egg membrane at the broad end of the groove. During August, with an average tempera- ture of 72° F. in the day and 65° at night, the incubation period varies from two to three days. The young larva is round, smooth, and almost transparent, and of the usual acephalous muscid type (Fig. 6, p. 20). It may be distinguished by the appearance of the two posterior stigmata, which are small, circular and situated rather far apart. Its length when full grown is about n mm. The duration of Fig. 84. Stomoxys calcitvans. Eggs. The small group in the top left hand corner represents their natural size. (After Newstead.) the larval stage under favourable conditions, is from two to three weeks, but the absence of plentiful moisture or exposure to light retards the development very considerably, to at least a period of 78 days. Such larvae produce abnormally small pupae and correspondingly small adults. The process of pupation is completed within two hours. The larva first burrows to some little depth and then shortens itself by contraction of the front segments, thus becoming barrel-shaped (Fig. 9, p. 22). The colour of the pupae is at first terra-cotta, but it subsequently darkens to a chestnut- 360 STOMOXYS [CH. brown. The length varies from 5 to 5-5 mm. The duration of the pupal stage varies from nine to thirteen days under favourable conditions, but may be considerably prolonged by cold. A few days before the emergence of the insect the pupal case darkens and splits anteriorly along the lateral and median lines and also across the fourth segment. The front region then falls away and the fly escapes after undergoing a final moult within the puparium. On emergence the fly at first tries to make its way to the surface of any rubbish with which it may be covered. This is chiefly accomplished by means of the frontal sac, which is alternately inflated and deflated, and at the same time the insect pushes itself forward by means of its legs. After it has become free the hairs of the arista are care- fully combed out, and also the .frontal sac and rudimentary wings are cleaned by means of the front pair of legs. Subse- quently the frontal sac contracts and the head assumes a more normal appearance, and then the insect stretches itself to the full extent and pumps air into its body. This air is forced along the nervures of the wings and these finally unfold, being aided by the use of the hind-legs. The fly then remains qui- escent for some time and when the integument and wings are sufficiently hardened it takes flight. The duration of the whole life-cycle from egg to imago varies from 25 to 37 days, under favourable conditions of temperature and moisture. Methods of destruction. The methods which have been used for the destruction of the common house-fly are also appli- cable to StoniO'ys, with this difference, that whereas in the case of the former, middens and ashpits are notorious breeding places, the stable-fly rarely selects these localities, but chiefly breeds in stable manure and heaps of decomposing vegetation. The numbers of the insect would be considerably reduced in any particular locality, if all stable manure, etc. were care- fully removed at least every seven days, during May to October inclusive. By this means the fly would be prevented from breeding, as the immature stages would be removed together with the manure. In the case of farmyards and country XIX] STOMOXYS AND DISEASE 361 districts, where the removal of manure is impracticable, the manure heaps should be sprayed periodically with some insec- ticide, in order to destroy any eggs, or larvae, that may be present. REFERENCES. Austen (1909). African Blood-sucking Flies, London : Brit. Mus Bouffard, G. (1907). Compt. Rend. Soc. Biol. vol. LXII. p. 71. Newstead, R. (1907). Ann. Trop. Med. and Parasit. vol. i. p. 76. Tulloch (1906). Proc. Roy. Soc. vol. LXXVII. B. p. 523. CHAPTER XX INFECTIONS TRANSMITTED BY STOMOXYS i. Trypanosomiases. There is no doubt that under experimental conditions the direct transmission of various trypanosomiases from infected to healthy animals, is comparatively easily effected by means of the bites of Stomoxys, but with regard to the importance of this insect in the spread of disease, opinion is still very divided. Surra (T. evansi) is generally stated to be transmitted by Stomoxys as well as Tabanus, and yet Mitzmain in the Philip- pines made a most exhaustive series of experiments on the transmission of this disease by Stomoxys calcitrans and obtained uniformly negative results. In Africa, Bruce, Grieg and Gray, Bevan, and others have also been unsuccessful in attempts to transmit various trypanosomiases by this insect. Nevertheless a number of observers are of the opinion that Stomoxys plays an important part in the transmission of certain infections. Thus in Java, according to Schat, Surra is mainly spread by the agency of Stomoxys calcitrans Linn, and Lyperosia exigna de Meijere, but experimental proof is lacking. Similarly, Musgrave and Clegg stated that in the Philippines it has been " conclusively shewn that Stomoxys calcitrans and other biting flies transmit the disease," but this statement is somewhat exaggerated. 302 STOMOXYS AND DISEASE [CH. Bouffard at Bamako on the Upper Niger experimented on the transmission of Souma, a trypanosomiasis of cattle caused by T. cazalboui (vide p. 335). A calf was inoculated with this parasite and shewed numerous t^panosomes in its blood on the eighth day. A healthy calf was then segregated with the other calf in a fly-proof stable, the animals being separated by a distance of one and a half metres. Forty wild Stomoxys were then put in the stable and were observed to feed on two after- noons, after which they died. Twelve days later trypanosomes appeared in the blood of the healthy calf so that it seems evident that Stomoxys is able to carry T. cazalboui. Whether the flies were naturally infected or not when caught, was not decided. In French West Africa, Bouet and Roubaud succeeded with difficulty in the direct transmission of T.' cazalboui and T. pecaudi by means of Stomoxys, but failed to transmit T. dimorphon. On the other hand, the trypanosomes of the Sahara were easily transmitted by means of this insect as shewn by their results. Employing T. soudanense, out of five experi- ments performed under laboratory conditions, with no intervals between the bites of the flies, four gave positive results. In another experiment at least 24 hours were allowed to elapse between the feed on the infected and on the healthy animal, in this case a dog. This animal became infected a month later shewing that the flies were still infective after 24 hours. In addition one experiment was made under natural conditions. A healthy puppy from which all ectoparasites had been carefully removed was kept on a chain during the day beside an infected dog in a place infested with Stomoxys ( ? calcitrans and nigra) ; at night it was removed and placed in a fly-proof cage to prevent any nocturnal flies feeding on it. The experiment lasted from the nth to the igth of August and both animals were frequently bitten by Stomoxys. On August 24th the puppy became infected. The results were similar on employing a strain of T. evansi (Surra) obtained from some camels at St Louis. In three experiments the Stomoxys were transferred from an infected to a healthy rat and a minute later to another healthy rat. In two XX] TRYPANOSOMIASIS 363 cases the first animal became infected whilst the second did not ; but in the third experiment, in which only a single Stomo- xys was used, both animals became infected after one bite. In addition positive results were obtained in the transmission of this virus after intervals varying up to at least three days. As Dr Bagshawe remarks, these experiments demonstrate that the trypanosomes of the Surra type in French West Africa may be transmitted by Stomoxys and that the flies may retain the infection for at least three days. But it is so obvious that some of the flies may have been infected when caught, that definite conclusions as to the period during which Stomoxys retains infection, may be as misleading as were those drawn from similar experiments with G. palpalis. Nevertheless, the fact that a single Stomoxys was capable of transmitting the infection shews that under certain conditions this insect might be an important agent for the spread of the disease. By means of interrupted feeding, that is, the fly beginning its meal on an infected animal and at once finishing it on another, various authors have succeeded in the experi- mental transmission of T. brucei, T. gambiense, T. equiperdum, in addition to T. evansi, T. cazalboui and T. soudanense. In India, Leese is of the opinion that Surra (T. evansi) may be naturally spread by the bites of Stomoxys, but the results of experiments shew that Tabanus is a much more efficient carrier as far as direct transmission is concerned (vide p. 237). In Mauritius, where Stomoxys nigra Macq. is very abundant, this species is believed to be concerned in the spread of the same disease, but experimental evidence is lacking. Finally it should be noted that in practically all experiments with Stomoxys in Africa, no distinction has been made between 5. calcitrant and 5. nigra both species being used indiscrimi- nately. REFERENCES. Austen, E. (1909). African Blood-sucking Flies. Bagshawe, A. G. (1912). 5. 5. Bulletin, vol. iv. p. 273. Bevan, LI. (1910). Ibid. vol. n. p. 252. Bouet and Roubaud (1912). Bull. Soc. Path. Exot. vol. v. p. 544. Bouffard (1907). Compt. Rend. Soc. Biol vol. LXII. p. 71. 364 FILARIA LABIATO-PAPILLOSA [CH. Bruce, Hamerton, Batemanand Mackie (1910). Proc. Roy. Soc. B, 558, p. 468. Greig and Gray (1905). Rep. S. S. Comm. Roy. Soc. No. 6. Leese, A. S. (1912). Journ. Trop. Vet. Sci. vol. n. p. 19. Manders, N. (1905). Journ. R.A.M.C. vol. v. p. 623. Martin, Leboeuf and Roubaud (1908). Bull. Soc. Path. Exot. vol. i. P- 356. Minchin, Gray and Tulloch (1907). Reports S. S. Comm. Roy. Soc. No. 8, p. 124. 2. Filaria labiato-papillosa Alessandrini, 1838. Synonyms. Filaria cervina Dujardin, 1845. F. terebra Diesing. Stomoxeos von Linstow, 1875. Habitat. The adult worm inhabits the peritoneal cavity and occasionally the eyes of cattle and various species of deer. The embryos are constantly present in small numbers in the peripheral circulation. Description. The adult filaria is white and filiform with the integument shewing fine transverse striations. The body tapers towards both extremities, the anterior being blunter than the posterior. The mouth is surrounded by a chitinous ring and immediately behind it are four small depressions, from each of which arises a tactile papilla. The male measures 4 to 6 cms. in length. Its tail is especially twisted and on each side are three pre-anal, one ad-anal and five post-anal papillae, behind which is situated a well-developed conical process. The female measures 6 to 12 cms. in length Its tail is also twisted but not so much as in the male. The caudal extremity bears a large number of fine processes, in front of which are situated two strong conical processes. Life history. This filaria is viviparous and the embryos when born measure 140 to 250 microns in length. Noe has investigated the further evolution of these embryos and finds that it takes place in the body of Stomoxys calcitrans. When this fly ingests blood containing the embryonic filariae, the latter bore through the gut wall and make their way into the thoracic muscles. Here they accomplish their larval develop- ment and when it is complete, the young filariae travel into the XX] POLIOMYELITIS 365 labium of their intermediate host. When an infected Stomoxys bites another animal the filarige escape from the labium and probably bore through the skin of the host in the same way as F. bancrofti, but this part of the life-cycle has not yet been observed. Noe found that in Italy, where his experiments were performed, only three to four per cent, of the Stomoxys became infected, the remaining 96 to 97 per cent, being appar- ently immune to infection. Although there is little doubt that 5. calcitrant is capable of transmitting this filaria, it is important to add that up to the present no one has been successful in actually infecting cattle by the bites of infected flies. REFERENCES. Alessandrini. Rendiconti Accad. d. Lincei, vol. xn. pp. 387—393. Neumann-Macqueen (1905). Parasites and Parasitic Diseases of Domesticated Animals. London : Bailliere, Tindall & Cox. Noe, G. (1903). Studi sul ciclo evolutivo della Filaria labiato-papillosa. Rend. Accad. d. Lincei, vol. xn. pp. 387-393. Poliomyelitis. Synonyms. Epidemic Poliomyelitis ; Infantile Paralysis ; Epidemische Kinderlehrnung. History. Poliomyelitis has been endemic in Northern Europe for many years, especially in Scandinavia, but it was only in 1907 that the disease suddenly began to extend its range of distribution. During the past two or three years many countries in different parts of the world have been visited by epidemics, the origin of which has remained quite unexplained. In America there is no previous history of a general epidemic until 1907, although local outbreaks had occasionally been noticed. Since this date, however, the dis- ease has been prevalent during the summer and autumn in many parts of the United States and Canada. It is possible that the infection may have been introduced from Scandinavia, for the two great centres of the recent epidemic were the Atlantic coast towns and the state of Minnesota, both of which received large numbers of Scandinavian emigrants. But there is no apparent reason why the disease should not have broken out 366 POLIOMYELITIS [CH. previously to 1907, for large numbers of emigrants had been arriving for many years before that date, and also why the infection should have suddenly appeared in many other parts of the world. Since this date, however, the disease has taken on fresh activities in its original home, and in 1911, Sweden was visited by a very severe epidemic. Distribution. Poliomyelitis is especially prevalent in Scan- dinavia and Northern Europe but, in addition, epidemics have occurred in England, France, Germany, Italy, Austria, and Spain ; in America large numbers of cases have been recorded from New York and Boston in the east, to San Francisco in the west, and a large outbreak occurred in Cuba in 1909. The disease has also been recorded from various parts of Australia. Causal agent. Although the most varied methods of staining and cultivation have been employed, no parasite has ever been detected in patients infected with poliomyelitis, but the scarcity of polymorphonuclear leucocytes in the altered cerebro-spinal fluid and spinal cord and the large increase in the number of mononuclears suggest that the parasite is protozoal in nature. The filterable nature of the virus has since been demonstrated, for if the spinal cord of a recently paralysed monkey is made into an emulsion with either distilled water, or normal saline, and passed through a Berkefeld filter, the resulting filtrate is still infective. Moreover, its activity is very considerable, for one thousandth of a cubic centimetre of a filtered 2-5 per cent, suspension of the spinal cord of an infected monkey is sufficient to produce infection and paralysis when injected into another monkey. The resistance of the virus is extraordinary, for in dust, especially within protein matter, it remains virulent for months. In diffuse day- light it survives indefinitely and resists the action of pure glycerine and 0-5 per cent, phenol for many months. The virus may be preserved by passage through monkeys, as these animals are easily infected by the intra-cerebral injection of an emulsion of the brain or spinal cord of an animal suffering from poliomyelitis. The susceptibility of monkeys has enabled Flexner, in conjunction respectively with Lewis and Clark, and also Landsteiner and Levaditi, to make some XX] CAUSAL AGENT 367 observations on the development of the virus within the body of an infected subject. The disease is essentially one of the central nervous system as evidenced by both the clinical and pathological features of the infection. If the virus is injected into the sciatic nerve of a monkey, it has been shewn that it multiplies in the nerve, first at the site of the injection and then progresses along the nerve until it reaches the spinal cord, when it causes paralysis of the hind-quarters. When the virus is placed on the unin- jured nasal mucous membrane, the infective agent travels up the olfactory nerves and subsequently causes general paralysis. It is evident, therefore, that nervous tissue is the one in which the organism chiefly multiplies. From the brain and spinal cord it passes into the cerebro-spinal fluid and thence into the blood circulation and lymphatic system, but in these positions it does not seem to persist for any length of time, except in the lymphatic nodes. The presence of the virus in the lymphatics explains why the nasal secretion becomes infected, for it has been shewn that poliomyelitis escapes with the secretions of the nose and throat and the discharges from the intestine of an infected person. Method of infection. Considering the infect ivity of the various secretions of a patient suffering from poliomyelitis, it is only reasonable to suppose that the disease may be directly transmitted from one person to another without the aid of any intermediate host. Flexner supports the view that the nasal mucous membrane is the chief site of infection, for the virus is able to survive in the form of dust and thus might be inhaled, and, in fact, the sweepings of a room occupied by a poliomyelitis patient have been shewn to be infected. On the other hand, as a result of very thorough epidemio- logical studies conducted by the Massachusetts State Board of Health, evidence has been collected which supports the theory that the disease is spread by insects. Rosenau has recently (1912) been able to transmit poliomyelitis from infected to healthy monkeys by the bites of Stomoxys calcitrant. Several monkeys infected with the disease by intracerebral inoculation were daily exposed to the bites of several hundred Stomoxys, 368 POLIOMYELITIS [CH. at the same time exposing twelve healthy monkeys to the bites of these flies. Of these twelve monkeys, six developed symp- toms characteristic of poliomyelitis, namely, illness, followed by more or less extensive paralysis. Two monkeys died, and in the spinal cord of one of them was found the characteristic lesions of this disease, i.e., perivascular infiltration and des- truction of the motor cells of the anterior cornu. Anderson and Frost have confirmed these experiments of Rosenau and their results will be given in detail. On October 3rd, a rhesus was inoculated intracerebrally with an emulsion of the spinal cord of a monkey that had died of poliomyelitis. Two hours after inoculation it was exposed to the bites of about 300 Slomoxys collected in Washington. Each day until the death of the monkey on October 8th, it was exposed for about two hours to the bites of these flies, together with additional ones that were added as they were caught. This monkey developed the characteristic complete paralysis on October 7th and died on October 8th. Another monkey similarly inoculated on October 5th was then daily exposed to the bites of the same lot of flies from October 7th until October gth, when the second monkey died. Thus from October 4th to the gth inclusive, the Stomoxys had been able to feed on two monkeys infected with poliomyelitis. Beginning on October 4th, two fresh monkeys (Java and rhesus) were exposed daily for about two hours to the bites of these same flies ; and on October 5th yet a third monkey (rhesus) was similarly exposed. On October i2th the Java monkey was found completely paralysed and died the same day. The second rhesus monkey also developed paralysis during the day and was anaesthetised. The first rhesus monkey died on October I3th after presenting the typical symptoms of poliomyelitis. Thus three monkeys exposed daily to the bites of several hundred Stomoxys, which at the same time were allowed to feed on two infected monkeys, developed typical symptoms of poliomyelitis seven, eight and nine days, respectively, from the date of their first exposure to the bites of the flies. These results are of great interest and shew that the XX] LYPEROSIA 369 disease may be transmitted by the bites of Stomoxys. It should be added, however, that the transmission has only been effected under experimental conditions and it remains to be seen whether this is the usual method of infection in nature, for cases of poliomyelitis have occurred in the absence of any Stomoxys. REFERENCES. Anderson and Frost (1912). Transmission of poliomyelitis by means of the stable-fly (Stomoxys calcitrans). Public Health Reports, Washington, vol. xxvn. No. 43. Brues and Sheppard (1912). The possible etiological relation of certain biting insects to the spread of infantile paralysis. Journ. Econ. Entom. vol. v. No. 4. Kling, Wernstedt and Pettersson (1912). Recherches sur le mode de propagation de la paraiysie infantile epidemique. Zeitschr. f. Immunitdtsforschung, vol. xn. pp. 316-323 and 657-670. Kling and Levaditi (1913). Etudes sur la poliomyelite. Publ. de I'Inst. Pasteur. 126 pp. Paris : Maretheux. Rosenau (1913). Public Health Reports, Washington, vol. xxvn. CHAPTER XXI LYPEROSIA General description. The genus Lyperosia is closely related to Stomoxys, from which it may be distinguished by the shape of the maxillary palps, which are more or less spatulate, and as long, or almost as long, as the proboscis. When the insect is resting the palps ensheath the proboscis, as in the case of Glossina, and as a result the combined structures appear as a stout rod-like process in front of the head. The proboscis is long and tapering, chitinous throughout, and the labella are small. The arista is feathered only on the dorsal surface. The third longitudinal vein is without bristles and the fourth longitudinal is gently curved distally so as to leave the first posterior cell wide open. All the known species of Lyperosia are small, dull, incon- spicuous insects, not exceeding about 4 mm. in length. H. B. F. 24 370 LYPEROSIA [CH. They are very common on domestic animals and generally cluster on any small sores. They also take advantage of the wounds caused by the bites of Tabanids, etc. In the Philip- pines, Mitzmain has observed these insects to wait for a Tabanus to finish feeding and then immediately suck up the drop of blood that oozed from the open wound caused by the larger insect. They are also capable of obtaining blood for themselves, and the only European species, L. irritans Linn., has the habit of clustering in a dense mass about the base of the horns of cattle. Lyperosia rarely attacks man, but regarding a Uganda species, L. punctigera, Austen records the following observation by the collector (the late Dr W. A. Denshaw) : " These flies were noticed in great numbers in one camp only near the Nile, and were very troublesome to my boys early one sunny morning ; they clustered thickly on any small sore, and quickly filled themselves ; though preferring to feed in this way, they seemed also to insert the proboscis into sound skin." Life-cycle. The life-history of Lyperosia irritans Linn, has been investigated in America by Riley and Howard. The eggs are laid singly on the surface of freshly dropped cow-dung. They are light reddish-brown in colour and vary from 1-25 to 1-37 mm. in length, by 0-34 to 0-41 mm. in breadth. As soon as they hatch the larvae penetrate into the dung and in this situation complete their development. The fully-grown larva is dirty white in colour and about 7 mm. in length. The posterior stigmatic plates, situated on the terminal segment, are large, very dark brown, and almost circular, but with their inner adjacent margins almost straight, and each has a circular central opening. On the ventral surface of the anal segment is a dark yellow chitinous plate bearing six irregular paired tubercles, and the whole plate is surrounded by an area of coarsely granulated skin. The pupae are found in the ground beneath the dung, at a depth of about 2 cms. The puparium resembles that of the house-fly, being dark brown in colour and barrel-shaped. Its dimensions vary from 4 to 4-5 mm. in length, by 2 to 2-5 mm. in breadth. XXI] LYPEROSIA AND DISEASE 371 LYPEROSIA and Disease There is no direct experimental evidence in support of the view that Lyperosia carries any infection, but certain authors have suggested that this fly may occasionally be responsible for the spread of various trypanosomiases of animals. Schat is of the opinion that Lyperosia exigua de Meijere, takes a part in the spread of Surra in Java. Montgomery and Kinghorn, in Rhodesia, record an outbreak of trypanosomiasis occurring under the following circumstances. A herd of cattle in Northern Rhodesia which had been in good health for a year was kept on a farm two-and-a-half miles from the nearest tsetse area. In April six bullocks were sent on a journey and as they passed through a fly belt were prob- ably bitten by tsetse. These bullocks returned to the farm a few days later. In June, three of these animals and also one which had not been away shewed trypanosomes. In July, fifteen animals were infected so all the healthy cattle were isolated in a place that seemed free from biting-flies. Five more of these animals shewed trypanosomes in August and were removed, but the balance continued to remain uninfected. The average duration of the disease was about 30 days, and the parasite is described as T. dimorphon. The authors write : " From an examination of all conditions, we think it prob- able that one or more of the six cattle that went to Mwomboshi in April contracted the disease on the road and brought it to the farm, where, in the presence of Stomoxys and Lyperosia in the kraals, the animals, including cows and bulls, which did not leave the place, became infected, and that the segregation from these flies checked its spread to the fourteen cattle which remained healthy." Montgomery and Kinghorn believe that in this case, Lyperosia was partly responsible for the transmission, the trypanosomes being directly carried from infected to healthy animals. In India, Leese has given an interesting account of an out- break of Surra in the Bikanir State in the desert of Rajputana. During this outbreak the Imperial Service Camel Corps, out of 500 camels, had only 205 survivors and of these 130 were 24—2 372 HIPPOBOSCID.E [CH. suffering from chronic Surra. Only 40 camels had been out- side the State and the great majority of them had been in the Corps so long that they could not have been infected when purchased, therefore the infection must have chiefly spread within the State itself. Bikanir is about 200 miles square, and there is only one small locality in which Tabanus is known to occur. Leese proved that the outbreak occurred and spread when the camels were grazing in the desert portion of the State at least 100 miles from any fly zone. In this region the only biting fly present was Lyperosia minuta Bezzi, which swarmed on the animals and caused great irritation so that the camels rubbed against each other in order to dislodge them. It seems probable, therefore, that Surra can spread in the presence of Lyperosia alone, and Leese believes that the transmission is probably mechanical. REFERENCES. Austen, E. (1909). African Blood-sucking Flies, p. 160. Leese, A. S. (1912). Journ. Trop. Vet. Sci. vol. vn. p. 19. Montgomery and Kinghorn (1908). Ann. Trop. Med. and Parasit. vol. n. p. 130. Riley, C. V. and Howard, L. O. (1889). Insect Life, vol. n. p. 93. Schat, P. (1903). Mededal. Proef station Oost-Java, 3rd ser. No. 44. CHAPTER XXII Family HIPPOBOSCIDAE (Tick-Flies). Description. The members of this family may be regarded as Muscidae that have become adapted to an entirely parasitic mode of life on birds and mammals. As a result certain marked changes in structure and reproduction have taken place and the flies form such a distinct group that they are frequently placed in a separate sub-order, the Pupipara, characterized by their viviparous mode of reproduction. The Hippoboscidae may be distinguished by the following charac- ters : XXII] DESCRIPTION AND BIONOMICS 373 The head is generally flattened and usually fits into an emargination of the thorax. The antennae are apparently one- jointed and are inserted in pits or depressions, situated near the border of the mouth. The maxillary palps ensheath the proboscis, which closely resembles that of Glossina, but never projects in front of the head. The eyes are round or oval, and are widely separated in both sexes ; ocelli may be present or absent. The thorax is flattened, strongly chitinised, and leathery in appearance ; the scutellum is broad and short. The abdomen is unsegmented. The legs are rather short and very strong, broadly separated by the abdomen and end in powerful claws. The wings may be well-developed, rudimen- tary, or entirely absent ; when present the veins are always concentrated towards the anterior margin. The halteres are small or rudimentary. The length of the adult insect may vary from about 3 mm. up to ii'5'mm. Bionomics. The Hippoboscidae live amongst the fur or feathers of either mammals or birds, and by means of their strong legs and claws are enabled to cling to their hosts. As a result of the adoption of this parasitic mode of life, the wings have gradually become rudimentary and in Melophagus ovinus, the common " sheep-ked," they are entirely wanting. They run about on the surface of their hosts, and even when possessing well- developed wings make little use of them. They feed entirely by sucking the blood of birds and mammals, and except for some special reason, such as the death of the host, rarely leave its body. The bites of Hippoboscidae are not very painful to man, but the sensation produced by their sharp claws hanging to the skin is most unpleasant. However, none of the species, except fortuitously, ever attack man. Reproduction. As in the case of Glossina, the female Hippoboscid at certain intervals gives birth to a fully grown larva which at once proceeds to pupate. The body of the larva exhibits practically no trace of segmentation and thus differs from those of the true Muscidae. The female may deposit its larva either amongst the hair of its host (e.g. Melo- phagus) or on the ground (e.g. Lynchia), but precise information 374 HIPPOBOSCIDAE [CH. on this subject is lacking. After a variable incubation period the pupa, which is of the usual Cyclorrhaphous type, splits off a cap at the anterior end and the perfect insect emerges from the circular aperture thus formed. Hippoboscidce and disease. Up to the present no truly pathogenic organisms have been shewn to be carried by Hippo- boscidae, but two species of Hippobosca are said to transmit Ttypanosoma theileri occurring in cattle in the Transvaal, and three species of Lynchia have been shewn to carry the pigeon halteridium, Hcvmoproteus columbce. The insects, therefore, are of little importance from the point of view of disease- carriers, but some of them are of economic interest because of the harm they do to domestic animals, through mere irritation. Classification. The Hippoboscidae may be divided into thirteen genera as follows : Synopsis of the genera of Hippoboscidce after Speiser1. A. Wings well developed and functional. /Claws with the usual two points (heel and tip) ; parasitic on mammals = 2 \ Claws with three teeth ; parasitic on birds . . . . . . . . =3 r Head of normal form, not broadly impinging on thorax, freely movable ; ocelli absent ; wings always present . . . . = Hippobosca. | Head flat, broadly impinging on thorax ; ocelli present ; wings sometimes I becoming detached (in female) leaving only a shred =Dipoptena. /Ocelli present .. .. .. .. .. .. .. .. = 4 ^ \Ocelli wanting (no anal cell) . . . . . . - ,y 350, 363 Life-history in vertebrate host — Endogenous cycle 306 Life-history within the inverte- brate host — Exogenous cycle 310 Trypanosoma himalayanum 384 ignotum See T. simice indicum 384 lewisi 11, 12, 294, 296 muktesari 384 Trypanosoma nanum 30, 270, 299, 346, 347. 348 Development 350 General account 348 Mode of transmission 349 Morphology 349 References to literature on 350 INDEX Trypanosoma pecaudi 30, 31, 234, 235, 270, 275, 286, 299, 332, 362 Mode of infection 333 Morphology 333 Trypanosoma pecorum 29, 30, 233, 270, 286, 299, 346, 351 Development within the inverte- brate host 348 General account 346 Mode of infection 347 Morphology 346 References to literature on 348 Trypanosoma rhodesiense 30, 251, 285, 294, 299, 322 General account 322 Mode of transmission 325 Morphology of 324 References to literature on 328 rutherfordi 384 Trypanosoma simice 30, 286, 296, 299, 353 General account 353 Morphology 353 References to literature on 355 Synonyms 353 soudanense 29, 31, 233, 235, 298, 362, 363 Trypanosoma theileri 31, 374, 379, 384 General account 384 Mode of transmission 385 Morphology 384 togolense 298 transvaaliense See T. theileri ugandense 305 Trypanosoma uniforme 335, 341 Mode of infection 342 Morphology 341 References to literature on 342 Trypanosoma vivax 335, 340 References to literature on See 4r. Trypanosoma vivax Bruce cazalboui wrublewskii 384 Trypanosomes 293 Trypanosomiasis 361 Trypanosomiases, Conditions affect- ing transmission by tsetse-flies 250 Tsetse- Flies 243 Tsetse-Fly Disease See Nagana Typhus icteroides See Yellow Fever Udenocera 230 Uranotcsnia 109, in Uranotaeninae 76 Utricularia 72 Venation 15 Verruga Peruviana 26, 42 Wyeomyia smithii 66 Yellow Fever 8, 28, 176, 177 Causal Agent of 186 Development of virus within mosquito 187 Distribution 179, 182 Endemic centres of 182 General account and history 177 Immune serum 189 Mode of infection 184 References to literature 189 St Nazaire epidemic 183 Synonyms 177 Vaccination 188 Virus of 10 Yellow Jack See Yellow Fever CAMBRIDGE: PRINTED BY JOHN CLAY, M.A. AT THE UNIVERSITY PRESS THE CAMBRIDGE PUBLIC HEALTH SERIES UNDER THE EDITORSHIP OF G. S. GRAHAM-SMITH, M.D., AND J. E. PURVIS, M.A. Flies in Relation to Disease. Non-Bloodsucking Flies. By G. S. GRAHAM-SMITH, M.D., Lecturer in Hygiene in the University of Cambridge. 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