206 ESSENTIALS OF BACTERIOLOGY 



be described. The infection continues for two months with- 

 out producing any illness, and the animal is then immune. 



Injection of infected rat blood into healthy rat causes the 

 latter to become infected. 



The injection of serum from an immune rat will prevent 

 the disease in normal rats. 



Cultivated best at 20 C. and is very resistant to cold. 

 The rat is probably infected by the bite of a flea or louse. 

 (See Fig. 105.) 



7 



w 



Fig. 104. Pure culture of trypanosomes of mosquitos Crithidia 

 fasciculata. Elongated crithidia from same preparation as preceding 

 (Novy, MacNeal, and Torrey). 



Trypanosoma Brucei (Plimmer and Bradford, 1894) 



causes nagana, or tsetse-fly disease, a disease affecting horses, 

 cattle, and dogs in certain regions of South Africa. The 

 trypanosome of Bruce is less motile than that of Lewis. It 

 has been cultivated at 25 C., and is less resistant to cold. 

 All laboratory animals subject to infection. The rat dies in 

 ten days. 



In the natural infection Bruce discovered that the tsetse- 

 fly transmitted the disease, but that it did so by first biting 

 some animal whose blood contained the trypanosome. The 



