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 
suffering 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 role 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 hundred 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 1902-1905. 
