134 DISEASES DUE TO PROTOZOA 



This infection may continue for the rest of the life of the fly. 



One case retained its infection for ninety-six days, but some lose 

 their infectivitv and become harmless. 



Trypanosomes are never found in the proboscis except immediately 

 after a meal. 



The greatest development is found in the fore, mid and hind gut, 

 first degenerate blood forms, then comes a dominant type, a long, 

 broad form with a narrow, simple, undulating membrane and a 

 very short flagellum, if one at all. This appears to rise from a pink- 

 coloured body near the kineto nucleus, a condition or phase never seen 

 in ordinary blood trypanosomes. There are masses of these at all 

 times in all parts of the gut. When the blood supply runs low these 

 degenerate and disappear. When there is fresh blood supply they 

 multiply and increase at an astounding rate, hence there are at the 

 same time trypanosomes in all phases of their development which 

 beggars description. 



Trypanosomes appear in the salivary glands on the twenty-fifth 

 day and remain present there. They arrive there b}' way of the 

 proboscis and salivary duct or hypopharynx. Trypanosomes have 

 never been found in the body cavity. As soon as the trypanosomes 

 reach the salivary gland they revert to the original blood forms and 

 become infective. 



Conclusions. 



Trypanosomes taken into the alimentary canal of tsetse flies retain 

 their shape and infectivitv for some eighteen hours. 



They then degenerate and lose their power of infectivity. 



Thev disappear in the majority of cases within five to six days. 



In a small percentage of flies, the female and the male, the try- 

 panosomes retain their position, multiply, swarm in the gut, but do 

 not resemble the original trypanosomes. 



After some twenty days the trypanosomes reach the salivary gland, 

 resume their original blood form, and regain their infectivity. 



Reservoir. 



When men were numerous about the shores of Lake Victoria 

 Nyanza, 20 per cent, to 50 per cent, of the natives were infected. (The 

 epidemic there has since died out.) Months after the natives had been 

 removed the flies were still infective. Animals were then suspected 

 and examined. Cattle were found heavily infected, but showed no 

 sign of the disease, but healthv susceptible animals could be infected 

 from them by tsetses. The same can be said of antelopes. Animals 

 not showing the trypanosomes microscopically would infect susceptible 

 animals. Five years after the removal of the population from about 

 certain parts of the shores of Lake Xvanza antelopes were still carrying 



