374 SURRA 
at any time. In 1906, it was brought to New York with the importa- 
tion of cattle from India but was suppressed by the slaughter of the 
animals at quarantine by the Federal Government. It was intro- 
duced into Australia with infected camels. For these reasons its 
nature should be understood by American veterinarians. 
Etiology. Surra is due to the presence in the blood of Trypanosoma 
evansi. 
“A motile trypanosoma 20 to 30u. in length to 1 to 2u.in breadth, somewhat blunt 
at the posterior end and gradually tapering at the anterior end. The undulating mem- 
brane is well defined, beginning at or near a small body (centrosome) in the posterior 
portion of the parasite and extending forward as a free flagellum. It is provided with a 
nucleus and a granular protoplasm.” 
This organism is invariably found during thé paroxysms of the 
disease in the blood of animals which have acquired surra either 
naturally or experimentally. Although blood containing these 
infusoria readily communicates the disease 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, susceptible animals even of different species with the unfil- 
tered blood of a diseased animal. The microscope reveals the try- 
panosomes in vast numbers moving with great activity in the blood. 
When this acute stage has passed the organisms disappear, the tem- 
perature 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 inoculation in about eighteen 
hours after death. 
Under the microscope, these parasites are detected in a drop of 
blood by an irregularly intermittent and characteristic quivering 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 
