THE PATHOGENIC PROTOZOA 285 



T. Evansi. A disease of horses known as surra, which is very 

 prevalent in India, was shown by Evans to be due to a trypanosome. 

 Experiments have shown that the disease is transmitted by flies. 



T. Brucei. Nagana or tsetse fly disease is prevalent in South 

 Africa and especially in Zululand, where it affects chiefly horses, 

 cattle, and dogs. In 1894 Bruce discovered that the blood-in- 

 fected animals swarmed with the trypanosomes now known by 

 his name. The disease, which is similar to the surra of India, is 

 characterized by a watery discharge from the eyes and nose, swell- 

 ings on the surface of the abdomen and legs, and an increasing 

 emaciated and anemic condition which generally results in death 

 after several weeks. It had been noticed that the disease was 

 frequently contracted by horses passing through hot, damp, fly- 

 infested areas, and the cause was thought to be due to a poison 

 secreted by the fly and transmitted in the act of biting. After 

 a number of experiments Bruce was able to demonstrate conclu- 

 sively that while the tsetse fly was responsible for the transmission 

 of the causal agent the latter was not a poisonous secretion but 

 living trypanosomes. Bruce found that the organisms are more 

 or less harmless parasites of the big game animals of South Africa. 

 Consequently he concluded that it is from them the tsetse flies 

 derive the parasites with which they infect domestic animals. 



T. Equiperdum. A trypanosomiasis known as dourine occurs 

 among horses in various parts of Europe, and has occasionally 

 developed in some of the northern states of America and western 

 Canada amongst imported horses. A characteristic of the disease 

 is that so far as is known it is transmitted by coitus and not by 

 biting insects. The disease is usually of a chronic nature ; the 

 animal becomes paralyzed and death occurs as a rule in from two 

 to ten months. ' 



T. Gambiense. Within comparatively recent years the im- 

 portant discovery was made that the terrible disease known as 

 sleeping sickness, which affects the natives of South Africa and also 

 Europeans, is a form of human trypanosomiasis. The parasites 

 found by the first investigators are grouped together under the 

 name T. gambiense. They closely resemble T. equinum and T. 



