402 SURRA 



Under the microscope, these parasites are detected in a 

 drop of blood by an irregularh' intermittent and characteristic 

 qnivering of some of the red blood corpuscles, which become 

 much altered in form. The leucocytes remain unchanged in 

 appearance. After a further and careful examination of this 

 slightly quivering blood a minute thread-like organism with 

 eel-like movements emerges from the mass 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 

 action. 



The period of incubation seems to be liable to great varia- 

 tion. It may be put from six to eight days after inoculation 

 or ingestion of blood taken from an animal suffering from 

 surra. It appears from Lingard's investigation that the 

 period of latency may be prolonged to thirteen days, if the 

 blood used for inoculation has been taken from a dead animal. 

 When the parasites have been given in water, by the mouth, 

 symptoms of surra may not appear for even seventy-five days. 

 We have no exact data for determining the time required for 

 the disease to manifest itself under natural conditions from 

 drinking surra contaminated water. 



^ 313. Means of transmission. The contagium of 

 surra is fixed and can be conveyed only by inoculation or 

 ingestion. Stagnant water and grass growing on recently 

 inundated land are said to form favorable resting places for 

 this organism. 



Lingard considers the ingestion of stagnant water and of 

 grass from land subject to inundations a source of infection. 

 Salmon and Stiles do not think this method of infection is 

 sufficiently proven to look upon it seriously. Lingard stands 

 almost alone in the belief that infection can take place through 

 healthy mucosae. 



The most couunon demonstrated natural methods of 



