Prophylaxis 517 



period of lethargy seems to coincide with that at which the parasites 

 are invading and injuring the nervous tissue. 



Prophylaxis. Reasoning from knowledge of the successful cam- 

 paigns that have waged against yellow fever and paludism, it at 

 first appeared as though the prophylaxis of sleeping sickness ought 

 to be based partly upon measures taken to prevent the infection 

 of men by tsetse-flies, and partly upon those taken to prevent the 

 infection of the flies by men. 



To prevent the infection of men by the flies is extremely difficult 

 where naked or half-naked savages are to be dealt with. For 

 Europeans, the customary dress, the avoidance of exposure in bath- 

 ing, the use of mosquito guards, etc., are to be recommended, as well 

 as the erection of habitations and the building of roads, etc., as 

 far as possible from the fly districts. The destruction of the grass 

 and reeds along the river banks, the use of drainage, and the intro- 

 duction of chickens, to pick up the larvae and pupae, have been 

 recommended. 



To prevent infection of the flies with Trypanosoma gambiense is 

 impossible where, as in some sections of Africa, 50 per cent, of the 

 population of some of the villages already harbor the parasites, 

 and still more impossible when, as is the case with Trypanosoma 

 rhodesiense, the wild animals, especially antelopes which are ex- 

 tremely numerous, continually harbor the parasites and act as 

 reservoirs from which the flies receive a continuous supply. 



The importance of undertaking radical measures for the prevention 

 of the disease may be imagined when it is understood that in the 

 last few years no less than a half-million of the natives of the infected 

 districts have died of sleeping sickness. 



TSETSE FLIES 



The Tsetse flies are dipterous insects belonging to the family Glossininae, 

 and included in a single genus Glossina. With one exception, G. tachinoides, 

 the entire family lives in tropical and subtropical Africa. About sixteen 

 species of Glossina are now described, for the rough and ready identification 

 of which the following table from Brumpt ("Precis de Parasitologie " 1910, p. 

 630) will be found useful. For those who desire more accurate information, 

 Austin's "Handbook of the Tsetse Flies," the "Sleeping Sickness Bulletin," 

 and Patton and Cragg's "Text-book of Medical Entomology" will prove useful 

 books of reference. 



Tsetse flies are easily recognized by their fly-like appearance, by their hori- 

 zontal proboscis, slender but swollen at the base, and by their habit of resting 

 with the wings crossed like the blades of a closed pair of scissors. 



The greater number of the flies occupy sections of country, spoken of as 

 "fly belts" or "fly districts," some of which are permanently infected, others 

 temporarily infected. Such "belts" are usually deep forests along the banks of 

 streams or on the shores of lakes. The adult flies seem to love the shade, though 

 they fly from it into the hot sun to seek their prey. The large game animals 

 seem to be the natural prey of the flies, though a number of them bite human 

 beings, and one, Glossina palpalis, seems to prefer human blood to all others. 

 The flies seem to attack moving animals by preference. So long as the creature 

 moves they pursue. When it stands, many of them fly away to the shade again. 



Both males and females 'bite. The latter distend themselves with blood until 



