Tsetse-flies and Nagana 215 



injected the excrement into healthy animals. Moreover, he had 

 found that the experimental flies were infective only during the first 

 forty-eight hours and that if wild flies were taken from the infected 

 region, "kept without food for three days and then fed on a healthy 

 dog, they never gave rise to the disease." 



Koch had early described what he regarded as sexual forms from 

 the intestine of the fly but it remained for Kleine (1909) to experi- 

 mentally demonstrate that a part of the life cycle of the parasite 

 was undergone in the fly. Working with Glossina palpalis, he found 

 that for a period of ten days or longer after feeding on an animal 

 suffeiing from nagana it was non -infective, but that then it became 

 infective and was able to transmit the disease for weeks thereafter. 

 He discovered and described developmental stages of the parasite 

 within the intestine of the insect. In other words, the tsetse-fly 

 (in nature, Glossina morsitans), serves as an essential host, within 

 which an important part of the life cycle of the parasite is undergone. 

 These conclusions were quickly verified by Bruce and numerous 

 other workers and are no longer open to question. Klein and Taute 

 are even inclined to think that mechanical transmission plays practi- 

 cally no r61e in nature, unless the fly is interrupted while feeding 

 and passes immediately to a new animal. 



Tsetse-flies and Sleeping Sickness of Man — ^About the beginning 

 of the present century a hitherto little known disease of man began 

 to attract great attention on account of its ravages in Uganda and 

 the region of Victoria Nyanza in South Africa. It was slow, insidu- 

 ous and absolutely fatal, characterized in its later stages by dullness, 

 apathy, and finally absolute lethargy all day long, symptoms which 

 gave it the name of "sleeping sickness." 



It was soon found that the disease was not a new one but that it 

 had been known for over a htindred years on the west coast of Africa. 

 Its introduction into Central and East Africa and its rapid spread 

 have been attributed primarily to the development of the country, 

 the formation of new trade routes and the free mingling of native 

 tribes formerly isolated. It is estimated that in the first ten years 

 of the present century there were approximately two hundred 

 thousand deaths from the disease in the Uganda protectorate. In 

 the British province Bugosa, on the Victoria Nyanza there were 

 thirty thousand deaths in the period from 1 902-1 905. 



