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being the first cause of an outbreak in horses, for surra in
horses is not so generally distributed. In my opinion
it is unlikely to act that way because the powers of the
fly to transmit are never great, and as cattle usually have
the trypanosomes so scanty in the blood or apparently absent
from it, the chance of the fly transmitting from ox to
horse are reduced to zero. But the case is quite different
when, by Tabanus, surra is already started amongst a stud of
horses from an ox. Trypanosomes are often numerous in the
horse with surra, and Stomoxys is numerous and is often dis-
lodged during a feed on these animals and seeks a new victim.

The transmission is rendered easier since horses are
often standing close together in lines, or working in double
harness in tongas. In these circumstances (i.e., surra
already started amongst a stud of horses), the Stomoxys is
probably an active agent helping in the spread of the disease.

The explanation therefore of the difficulty that, although
in the 1907 Kathgodam outbreak it was found at every
stage on the road, but surra only at Kathgodam and Bojia-
ghat, seems to depend upon the foregoing facts. Local
opinion insisted that Tabanus, when present, was confined to
these two stages, and no doubt they may have been responsible
for the occurrence of the outbreak (i.e., bringing the try-
panosomes from the ox) and after they had disappeared,
Stomoxys was only able to carry on the outbreak amongst
the ponies in the stages in which surra was already rife. The
close of the outbreak corresponded with the disappearance of
the latter.

I think, that in camels it may also be an agent for
the spread of surra, although of much less importance
than Tabanus.

A Stomoxys, as I have said, more often finishes his
feed on one camel than on one horse.

Late in the surra season at Mohand I exposed a newly
purchased healthy pony with the surra ponies to its bites
for about an hour a day on 20 days with negative result; but
as Tabanus was then still present, the exposure could only
be made at times and places where biting-flies of all kinds
were not very numerous, and I do not attach any importance
to the negative result of the experiment,