April i6, 1896J 



NATURE 



567 



poison-matter. It will be seen that this conclusion is substan- 

 tially correct. 

 ^- ^ Mysterious as has been the connection between the Tsetse 

 gl and the animal-disease endemic in its haunts, there has been 

 s never any reason to doubt that a properly-conducted investiga- 



tion would throw much light on the subject. At last, on behalf 

 of the Natal Government, such a research is being made by 

 Surgeon-Major Bruce, and the results of the first three months' 

 work are just published. They are of great interest, and are 

 full of promise that our knowledge of this disorder will be 

 placed at least on a level with that of kindred diseases. 



Dr. Bruce, in a somewhat brief recapitulation of the charac- 

 teristics and habits of the fly, adds one important new fact, 

 of which he appears scarcely to recognise the significance. The 

 f?y investigated, which is not necessarily Westwood's species, 

 is viviparous, giving birth to an adult larva (Fig. i, b), which 

 creeps about actively in search of a hiding-place, where, in the 

 course of a few hours, it changes by the usual skin-hardening 

 to a jet-black puparium (Fig. i, c). Hitherto the accounts of 

 Bradshaw and Chapman have asserted, on native authority, that 

 the maggot lives in buffalo-droppings, and a statement of 

 Edwards, quoted by Castelnau,^ that the Bushmen declared 

 and demonstrated the Tsetse to be viviparous, has gone almost 

 unnoticed. 



This fresh observation must be accepted with some reserve, 

 as the fly has not yet been bred from the puparium. Assuming 

 it to be correct, it is of two-fold interest ; the mode of 

 reproduction is substantially that which exists in the Pupipara, 

 though, to judge from Dr. Bruce's account and rough figures, 

 the newly-extruded Tsetse-larva, though equally mature, is 

 somewhat less abnormal than that, for instance, oi Melophagiis.'^ 

 A transitional series from oviparous forms has been described in 

 Muscidae by Portschinsky,* and viviparous Oestridae are well 

 known to occur. Nevertheless, this peculiarity of Glossina, 

 which could not have been prognosticated on systematic grounds, 

 sufficiently demonstrates the unsoundness of separating the 

 Pupipara from Muscidae on account of developmental differences. 



Moreover it shows that the Tsetse, unlike most blood-sucking 

 insects, such as the flea or mosquito, is absolutely dependent 

 for its continued existence upon the food taken in the imaginal 

 state, and, unless it is capable of feeding upon other matters 

 than blood, which, though unlikely, should not be disregarded 

 in the inquiry, its life is bound up with that of the indigenous 

 mammalia. And this both confirms and explains the observa- 

 tion made by Livingstone, Selous and others, that it is con- 

 stantly associated with large game, such as the buffalo, and 

 ceases to frequent districts from which they retreat. 



Fly-disease or Nagana (a Zulu term, aptly signifying to be 

 low or depressed in spirits) is due, according to Dr. Bruce, to 

 the presence in the blood of a flagellated infusorian. This 

 hxmatozoon (Fig. 2) is of elongate form, about 10-20 /* long 

 by 2 /* wide, furnished with a membrane or "fin" running 

 along one side of the body, and a flagellum at one end. 



It is intimately allied to, if not actually identical with, Try- 

 panosoma evaiisi, the haematozoon of " Horse Surra." At pre- 

 sent Dr. Lingard, the leading authority on that Indian animal- 

 disease, hesitates to regard the two complaints as the same, 

 because Surra does not attack cattle. But when it is recollected 

 that Nagana pursues a much slower course in cattle than in 

 horses, and that wild game are immune to it, just as African sheep 

 are to anthrax, the objection does not seem very formidable. 



The haematozoa of Nagana make their appearance, which is 

 signalised by a rise in temperature, in the blood after an in- 

 cubation period of 7 to 20 days, swimming actively among, and 

 apparently " worrying " the corpuscles. With the progress of 

 the disease they increase in numbers and, at the time of their 

 host's death, may amount, in the dog, to 310,000 per cub. mm. 

 of blootl ! Neither reproductive nor any other stages of the 

 parasite are yet known, nor has it been found in the blood 

 of any wild animal, inoculation of which (the best test for the 

 presence of the haematozoon ) has hitherto failed to produce 

 disease. 



Dr. Bruce has demonstrated that it is possible repeatedly to 

 feed Tsetse on a healthy dog without producing disease in that 

 animal — that is, the flies possess no specific venom ; but that, 

 if allowed to draw blood from a diseased animal or the carcase 

 of one, they will communicate Nagana to any healthy animals 



1 Compt. rend., 1858 (i), pp. 984-986, 

 -' Leuckart, Abh. Naturf. Gcs. Halle, 

 Saturg. 1893, i. pp. 151-200. 

 ' Osten Sacken, Berl. ent. Zeitschr., 1887, pp. 17-27 



NO. I 38 1, VOL. 53] 



pp. 145-226; and Pratt, A rcA. 



on which they are subsequently fed, and the same result is 

 obtained by inoculation of diseased blootl, or, in dogs, by feed- 

 ing them on the flesh of an animal dead of Nagana. 



Thus far is the cause of the disease ascertained, as is the fact 

 that the Tsetse can serve as a transmissive agent ; but the 

 natural source, other than diseased animals, which are not known 

 to occur in a wild state, whence the flies obtain the parasite is 

 still undetermined, nor is it proved that, unlike malaria, the 

 disease cannot be acquired by breathing the air of the fly- 

 country. 



Repeating an old experiment of Captain Vardon's, Dr. Bruce 

 has shown that a few hours' sojourn in a fly-district is sufiicient 

 exposure to induce the disease in a horse, which is prevented 

 from eating and drinking there ; but tcj complete the proof that 

 the flies are indispensable as carriers of infection, it has further 

 to be shown that domestic animals, if protected from their bites, 

 can remain in such a region with impunity. As yet Dr. Bruce 

 has not been able to make the experiment, but it may be ob- 

 served that the concurrent testimony of many travellers, that 

 animals can safely cross a fly-country on nights when the insects 

 are inactive, goes to prove that the infection is not air-borne. 



If Dr. Lingard's very voluminous report on Surra ' be com- 

 pared with the one under consideration, the points of identity 

 between the two diseases will be found to be remarkably 

 numerous, though not quite universal, and the fact that two such 

 investigations are in progress by workers in touch with each 

 other ought materially to quicken and extend the results arrived 

 at. The complete life-history of the Surra parasite has yet to be 



Fig. 2.— Ha:matozoa of Nagan.-i in the blood of a horse (after Bruce). 



published, and in discussing the etiology of that complaint. Dr. 

 Lingard attaches much importance to the eating of grass from 

 swamps and marshy ground, and the drinking of stagnant water, 

 and but little to fly-infection, which he considers to occur chiefly 

 when healthy and diseased horses are crowded together. Such 

 infection is, therefore, regarded as being of the purely trans- 

 missive form of fly inoculation found in anthrax and possibly 

 other septic diseases. 



But a more intimate relationship of the fly and the parasite, 

 at least in Nagana, suggests itself. In 1884, Dr. Manson 

 .showed - that the mosquito is the intermediate host of filaria, 

 and applying his observations to the building-up of a working 

 hypothesis as to the life-history of the malaria parasite ( Laveran's 

 ha;macytozoon) outside the body, he suggested, in 1894, that the 

 mosquito also served as host for that form, and that the " flagel- 

 lation-stage " a.ssumed by a certain number of the parasites in 

 drawn blood was an incipient change designed for life in the 

 mosquito. In a ccurse of lectures,^ in process of being delivered 

 as we write, for the unpublished text of which we have to return 

 him our warm acknowledgments, this theory is developed in 

 greater detail, and is supported by the observations of Surgeon- 

 Major Ross, that examination of the blood imbibed from a 

 malarial patient by mosquitoes shows, shortly after its extrac- 

 tion, that not a few, but the majority of parasites undergo 

 flagellation. That the destiny of the flagella is still untraced is 

 due to the extreme difiiculty of the observations. 



Dr. Manson's theory still awaits its final proof or disproof, 



1 "Report on Horse Surra," vol. i. (Bombay, 1893); and "Summary of 

 further Report on Surra." (Bombay, 1895). 



- Tians. Linn. Soc. (2), II. pp. 367-388, pi. xxxix. 



3 "The Goulstonian l^ectures on the Life-History of the Malaria Germ 

 outside the Human Body," delivered before the Royal College of 

 Physicians of London, March 1896, by Dr. Patrick Manson. 



