554 



TRYPANOSOMIASLS 



is, without the agency of the fly ; that the latter had no inherent 

 power to produce the disease ; that it could, however, by 

 successively biting infected and healthy animals transmit the 

 disease to the latter ; and that specimens of the insect caught in 

 infected areas harboured the parasite and were thus infective. 

 The question remained as to how the flies might become infected 

 in nature. It had been observed that in districts where the 



FIG. 168. Trypanosoma Brucei from blood of infected rat. Note in two 

 of the organisms commencing division of micronucleus and undulating 

 membrane. x 1000. 



tse-tse fly lived the prevalence of the disease in imported animals 

 was related to the presence in the locality of wild herbivora. 

 Bruce now found that, if considerable amounts of the blood 

 of the latter were taken to another locality and injected into 

 dogs, these in a proportion of cases contracted nagana, and from 

 this he deduced that the wild animals harboured the parasites 

 in small numbers in their blood and thus kept up the 

 possibility of infection. A further and as yet unexplained 

 fact was that other blood -sucking flies besides the tse-tse 



