490 A MANUAL OF BACTERIOLOGY 



bites of a tsetse-fly (Glossina morsitans). The trypanosome 

 is believed to live in the big game, from whence it is trans- 

 mitted to horses entering the infected localities. The 

 blood loses its infective properties usually within twenty- 

 four hours after being withdrawn. 



Surra attacks horses in Burma, Mauritius, and the 

 Philippines, and is pathogenic to the same animals as 

 nagana, and in the blood a parasite (Tr. Evansi) similar 

 to that in nagana. but more active, was observed by 

 Evans. Surra is probably spread by certain biting flies 

 belonging to the Tabanidce. 



The tsetse flies (Glossina) belong to the house-fly order (Muscidse) 

 and have a general resemblance to a house-fly, but when at rest 

 the wings fold completely over each other. The proboscis is long 

 and straight and the wing venation is characteristic, especially the 

 fourth longitudinal vein, which makes two bends. Instead of laying 

 eggs, the female extrudes a single full-grown larva. They are 

 confined to Africa and Arabia ; some sixteen species have been 

 differentiated, and they occur in the vicinity of water on the edge 

 of forest land (" fly-belts "). 



Tr. equinum attacks horses in South America, causing weakness 

 and paresis of the hindquarters ("ma/ de caderas"). Cattle are 

 immune, most other animals susceptible. 



Tr. Theileri, the largest trypanosome known (50-60 p in length), 

 is found in cattle in ISouth Africa, and is not pathogenic to any 

 other animal. 



Tr. dimorphum occurs in two forms, large and small, in horses 

 in Africa. Is pathogenic to most animals. 



Dourine, a venereal disease of the horse met with in North Africa, 

 Spain, and Hungary, is due to the Tr. equiperdum, which is conveyed 

 by direct contact, and is mainly confined to the lesions, being 

 scanty in the blood. It is pathogenic to the ordinary laboratory 

 animals. 



In rats a non-pathogenic trypanosome was found by Lewis 

 (Tr. Lewisi). It is especially met with in sewer-rats, but also 

 occurs in field-rats (Crookshank). It is somewhat shorter and 

 thinner than the Tr. Brucei, and there are other small differences 

 between the two forms. With the exception of rats and mice, 

 and to a less Extent guinea-pigs, other animals cannot be infected 

 with the Tr. Lewisi. It may be kept alive for long periods in the 



