ETIOLOGY 267 



altered in form. The leucocytes remain unchanged in appear- 

 ance. After a further and careful examination of this slightly 

 quivering blood a minute thread-like organism with eel-like 

 movements, emerges from the niass of corpuscles. It may be 

 seen apparently tugging with all its might at a red corpuscle 

 endeavoring to detach it from its rouleau. The question of the 

 manner in which these parasites interfere with the health of 

 the affected animal has not yet been settled. When they are 

 outside the animal body and in a dry state, they are killed or 

 rendered inert by prolonged atmospheric heat. 



Fig. 68. Photograph of blood of horse containing Trypanosoma . 

 ( Taken by Smith and Kinyoun. ) 



The contagium of surra is fixed and can be conve3-ed only 

 by inoculation or ingestion. Stagnant water and grass growing 

 on recently inundated land form favorable resting places for 

 this organism. It is probable that flies act as carriers of surra 

 from infected animals to sound ones, especially if the latter 

 have open wounds. 



§200. Symptoms. The symptoms as given by lyingard 

 are as follows. "The chief symptoms, in addition to the 



