84 
Eq uine Tt'upanosomiasis 
where they could become infested by ticks. Saddle-horses were the 
only animals from which ticks could be collected, because they were 
used out along the trails and other locations where they could, and did, 
become infested with ticks. For a period of six months, before the true 
nature of the disease was recognized, the saddle-horses and some of the 
mules were stabled in a long shed, the stalls of the horses being opposite 
those of the mules, so that only a few inches of partly open space 
separated the heads of the horses from the mules. At this time mules 
kept coming down with the disease, though their near neighbours, the 
saddle-horses, never became infected. It was concluded from this that 
ticks did not transmit the disease under these conditions. 
Among the biting flies only two species were found within the corral 
district— Stomoxys calcitrans and Tahanus sp. S. calcitrans was breeding 
near some of the corrals and could always be taken in the corrals. This 
fly did not breed in the corral because the horse droppings were removed 
daily. Very few Tabanids were ever seen within the corrals. A few 
were taken near the isolation corral and in the new corral at Ancon, 
which lie on the outskirts of the district near woods, but no Tabanids 
were ever seen in the old corral at Ancon, which lies within the 
populated district, nor at the corral at Gatuu, which lies away from the 
woods. 
During the height of the epidemic among the mules, several specimens 
of S. calcitrans were taken at the Ancon corral with mule’s or horse’s 
blood in their intestinal tracts, and Stomoxys could be collected here 
every day. Now as at this time I had a naturally infected work-horse 
already under observation and I was confident that horses were as sus¬ 
ceptible as mules, though practically all the infected animals were 
work-mules, I felt therefore that S. calcitrans was not transmitting 
the infection, because the saddle-horses would otherwise have become 
infected. 
At this time I obtained several condemned animals, including two 
horses, for experimental purposes. One of the horses was placed in an 
isolated stable with three expeximentally infected mules. In this stable 
the droppings were not removed, and .S. calcitrans was permitted to 
breed so that the flies could be collected every day. This horse was 
exposed to the infected mules, and to S. calcitrans in this stable for 
10 months, and did not become infected. At the end of this period, 
the horse was experimentally inoculated with trypanosomes to determine 
if it was susceptible or not; the animal developed the disease after an 
incubative period of 8 days and died 79 days after inoculation. 
