MASTIGOPHORA 745 



There the parasites in large numbers are found attached to the 

 epithelial cells by their flagella. Rapid multiplication takes place by 

 repeated fission and the parasite becomes crithidial in form, that is, 

 it loses its undulating membrane, becomes short and stubby, and the 

 kinetonucleus moves forward close to or in front of the trophonucleus. 

 Ultimately some change back to minute trypanosomes, and these, 

 when regurgitated or passed in the feces, serve to infect the next vic- 

 tim. The rectal phase, when once established, lasts for several months 

 or perhaps indefinitely, making every infected flea a chronic carrier. 



Trypanosoma evansi. Surra is a disease of horses and mules, 

 camels, elephants, buffaloes, and dogs, which prevails in India and 

 other parts of Asia, and also in the Philippines and Northern Aus- 

 tralia. The Philippine outbreak was traced to animals returned from 

 China after the Boxer outbreak; for at that time American troops 

 came into contact with native Indian troops and their animals. 



The trypanosome causing the disease was discovered by Evans in 

 1880. The clinical course of the disease is marked by an irregular 

 recurring fever, with many remissions, during which the parasite can- 

 not be demonstrated in the blood, although it is not difficult to find 

 during the febrile period. The animal is anemic, weak, emaciated, 

 and may show an ecchymotic eruption on the abdomen. The course of 

 the disease may be either short or long, but leads almost invariably to 

 death. In camels it lasts from two to four years, often without symp- 

 toms until near the end, and these animals probably act as chronic 

 carriers. 



Morphology. Morphologically, the parasite is very like the Tryp- 

 anosoma brucci of Nagana, yet, as a rule, the trophonucleus lies- 

 nearer the anterior end than in b'rucei, although it may be impossible 

 to distinguish in smears between the two. 



The disease is carried by biting flies, tabanidm and' stomoxys, and 

 also by fleas. 



Trypanosoma brucei. Nagana is a well-known horse and animal 

 disease of Africa, which causes an enormous economic loss and has 

 greatly interfered with the development of the country. The para- 

 site was discovered by Bruce in 1895. Among the natives it is known 

 as tsetse fly disease, and investigation has incriminated Glossina mor- 

 sitans as the carrier. Clinically, the disease in horses is much like the 

 Surra of India ; the native name for the disease, nagana, means weak- 

 ness. Nearly all the larger animals are susceptible to either natural or 

 artificial infection, yet man is apparently immune. 



