=Epidemiology.=—Practically the only method of transmission of the disease is by the bite of infected tsetse flies. The female gives birth to a single, yellowish brown, motile larva, which is almost as large as the mother and which, upon reaching the ground, bores its way into a coarse, sandy soil for a depth of about two inches and then becomes a pupa. The larval stage in the mother lasts about two weeks and the pupal stage about a month. The tsetse fly is much like _Stomoxys_, but has a branching of the feathering of the arista, long palps, a bulb to the proboscis and a characteristic upbending of the fourth longitudinal vein to meet the mid-cross vein. The female deposits her larva near a shady place upon loose, dry, sandy soil. Moisture and sunlight are not favorable for pupal development, the sun being particularly injurious, so that pupae, buried only an inch deep and away from shade, are killed. This fact has been utilized in prophylaxis by cutting down the trees. The trouble is that the bush growth which soon follows is favorable as providing shade for the pupae. Male and female flies bite and transmit the disease. They bite in the daytime, usually from 9 A.M., to 4 P.M., and will bite in the sunlight. It has been stated that tsetse flies are attracted by persons wearing khaki clothing. With a view to eradication of the disease certain areas have been depopulated, but upon examining the flies caught in the district a year or more later, infected flies have been obtained. This would indicate some other reservoir than man. It is now generally conceded that the trypanosome strain in the antelope is the same as _T. rhodesiense_, both being transmitted by _G. morsitans_. Taute, however, believes them different as he not only injected blood containing such trypanosomes into himself, with negative result, but also allowed flies which had fed on antelopes, which were infective for laboratory animals, to feed on himself, likewise with negative result. It is a well-known fact that men in good condition are refractory to trypanosome infection so that this courageous experiment does not prove the antelope strain to be different from the human one. One measure that has been proposed is to kill off the big game from a certain area with a view to depriving the flies of their main source of infection. The probabilities of an animal reservoir for _T. gambiense_ however is not so well settled. Many think that we may have trypanosome carriers and that such persons in the enjoyment of health may act as reservoirs of the virus. Koch suggested that crocodiles were important factors in the life of the tsetse flies and recommended the destruction of the crocodile eggs.