658 



TRYPANOSOMIASIS 



other organism, it can withstand short exposures to temperatures down to 

 - 191° C. ; it is quickly killed at 44° to 45° C. Novy and MacNeal suc- 

 ceeded in cultivating this trypanosome also, though here it was very 

 difficult to obtain a first growth from the blood on their blood-agar 

 medium ; once started, however, it was kept alive through many sub- 

 cultures, the optimum temperature of growth being 25° C, and it was 

 from these sub-cultures that the infection was obtained which definitely 

 proved the organism to be the cause of the disease. In cultures, as with 

 Tr. lewisi, short forms occur, and there is sometimes a rosette formation 



Fig. 196. — Trypanosoma brucei from blood of infected rat. Note in 

 two of the organisms commencing division of micronucleus and undu- 

 lating membrane, x 1000. 



with the tiagella directed outwards ; agglutination phenomena are also 

 observable in detibrinated blood. Under favourable conditions, involution 

 forms occur, the organism dividing frequently to form round flagellated 

 individuals. 



Nearly all laboratory animals are susceptible to infection, and the 

 duration of the illness corresponds to what has been observed in the 

 natural infection of these animals. The rat has been largely used for 

 experiment and usually succumbs in about ten days, there being very 

 few symptoms up to a few hours before death. A very important fact 

 has been observed with regard to this animal, namely, that individuals 

 which have gone through infection with Tr. lewisi and which are immune 



