22 INFECTION AND IMMUNITY 



transmits the parasite from diseased to healthy animals 

 " surra disease." The tsetse-fly disease of Africa is 

 transmitted in the same way and is very fatal to 

 horses and also to the ox, the dog, the ass, and the 

 sheep, but not to wild animals indigenous in the 

 region where the tsetse fly is found. The parasite is 

 present in great numbers in the blood of infected 

 animals, and the fly simply acts as a carrier of this 

 parasite from diseased to healthy animals. 



