In 1880 Evans had found a trypanosome in the blood of horses affected with surra and several years afterward Bruce discovered that nagana, a fatal disease of cattle, was due to a trypanosome, _T. brucei_. In 1890 Nepveu found a trypanosome in the blood of a man in Algeria but owing to vagueness of description the discovery did not attract attention. [Illustration: FIG. 25.—Geographical distribution of African trypanosomiasis.] In 1901, Forde found a parasite in the blood of a patient in the River Gambia Colony who had a fever and in 1902 Dutton recognized the parasite as a trypanosome and gave it the name _T. gambiense_. In 1902, Castellani, finding a trypanosome in the cerebro-spinal fluid of a patient with sleeping sickness, brought about the establishment of the connection between the trypanosome in the blood (trypanosome fever) and the trypanosome in the cerebro-spinal fluid (sleeping sickness). In 1903, Bruce and Nabarro reported that this disease was spread by a tsetse fly, _Glossina palpalis_. In 1910 Stephens and Fantham brought forward the existence of a more virulent trypanosome, _T. rhodesiense_. =Geographical Distribution.=—The disease exists on the West Coast of Africa, from Senegal to Mossamedes. It is also present in the Congo basin and particularly in Uganda. The more virulent form is found in Rhodesia. ETIOLOGY AND EPIDEMIOLOGY =Etiology.=—The African trypanosomiases follow infection with two species of trypanosomes; the more virulent type of the disease, occurring in South Central Africa, being due to _Trypanosoma rhodesiense_, transmitted by _Glossina morsitans_ and that of less severe type, but of more general distribution, being due to _T. gambiense_ and transmitted by _Glossina palpalis_. The very important _Trypanosoma brucei_, which is the devastating agent in the African horse, dog and cattle disease, nagana, is also transmitted by _Glossina morsitans_ and there exists the opinion that this trypanosome is identical with _T. rhodesiense_. Macfie has reported a new trypanosome, _T. nigeriense_, from young persons in Nigeria. It is said to be less virulent than _T. gambiense_, and to be transmitted by _Glossina tachinoides_. [Illustration: FIG. 26.—_Trypanosoma gambiense_ (slide presented by Professor F. G. Novy) (From Todd.)] Bruce considers _T. nigeriense_ as being _T. gambiense_. Macfie noted many short stumpy forms in animals inoculated with _T. nigeriense_.