THE TRYPANOSOMES 595 



fresh blood of a diseased animal. In infected animals 

 the trypanosome is generally abundant in the blood and 

 spleen. The Tr. Brucei can be cultivated, though with 

 difficulty, on rabbit-blood agar equal parts of melted 

 agar cooled to 45 C. and of defibrinated rabbit's blood 

 warmed to 45 C., allowed to solidify in the sloping posi- 

 tion (Novy and McNeal). The disease is conveyed through 

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

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

 transmitted 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 four hours after being withdrawn.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 biting flies belong- 

 ing to the genera Stomoxys, Hcematobia, and Tabanus. 



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, the wing venation is characteristic, the fourth 

 longitudinal vein making two bends, and the antennae are 

 peculiarly combed. 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 forest land in the vicinity of water (" fly-belts "). 



Tr. equinum attacks horses in South America, causing weakness 

 and paresis of the hindquarters (" mal 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 South 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 



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