266 



SURRA 



to be introduced into this countr}-. For this reason its nature 

 should be understood b}- American veterinarians and pathol- 

 ogists. 



§ 199. Etiology There 

 is little or no doubt that surra 

 is due to the presence in the 

 blood of a flagellated infu- 

 sorian, Tiypanosouia Evansi. 

 This organism is invariably 

 found during the paroxysms 

 of the disease in the blood of 

 animals which have acquired 

 surra either naturally or ex- 

 perimentally. Although blood 

 containing these infusoria 

 readily communicates the dis- 

 ease to susceptible animals it 

 entirely loses its virulence 

 when it is filtered through 

 porcelain, so as to free it from 

 the parasite. The disease can 

 be transmitted to healthy, sus- 

 ceptible animals even of differ- 

 ent species, with the unfiltered blood of a diseased animal. 

 The microscope reveals the infusoria in vast numbers moving 

 with great activity in the blood. When this acute stage has 

 passed the organisms disappear ; the temperature falls ; the 

 severity of the symptoms abates ; and there is an intermission, 

 during which, at the beginning of the attack, the patient may 

 appear in good health. Although the blood during an inter- 

 mission may appear under the microscope to be absolutely free 

 from the parasites, its inoculation into susceptible animals will, 

 as a rule, produce the disease. The blood of surra affected 

 horses loses its power of transmitting the disease by inocula- 

 tion in about eighteen hours after death. 



Under the microscope, these parasites are detected in a drop 

 of blood by an irregularly intermittent and characteristic quiver- 

 ing of some of the red blood corpuscles, which become much 



Fig. 67. Trypanosoma Evansi, 

 highly magnified. {After Evans). 



