PROTOZOA IQI 



Trypanosoma Lewis! (Lewis, 1878). Found in rats; not 

 fatal to them, though often equaling the red corpuscles in 

 number. The infection continues for two months without pro- 

 ducing any illness, and the animal is then immune. 



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

 rat is probably infected by the bite of a flea or louse. (See Fig. 

 117.) 



Trypanosoma Brucei (Bruce, 1894) causes nagana, or 

 tsetse-fly disease, a disease affecting horses, cattle, and dogs 

 in certain regions of South Africa. The trypanosome of Bruce 



Fig. 117. Trypanosome from blood of gray rat; stained with a 2 per cent, 

 aqueous solution of methylene-blue (Boston). 



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 blood 

 of infected animals contains the organism, and can, if injected, 

 produce the disease without the agency of the fly. So far the 

 tsetse fly alone is responsible for the spread of the infection. 



