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(IV).—The ingestion of corn soiled with the excrement of the Rat and Bandicoot.
In 1891, experimental inoculation of equines proved that out of twelve animals inoculated with
soiled rat's blood, four or 33 per cent. contracted Surra and died of a virulent form of the disease in an
average of seven days. The above experiments raised the question as to how rats could cause the disease
in horses, for the food would rarely, if ever, be soiled with the blood of these small animals. It, there-
fore, only remained to be tried, whether the excreta of rats, in whose blood the infusorian was present
at the time of its collection, could cause the disease when mixed with grain. Experiments with this
end in view were carried out, and one Australian horse contracted Surra in 1893, the incubation period
occupying some time between June and September during which the animal received daily rat
excrement mixed with its ration of corn. This was evidence that when a horse is made to ingest soiled
material day by day, Surra may finally be contracted; but whether the disease was ever actually
produced in the natural course of events by this means at that time there was no testimony forthcoming.
Enquiries were instituted in different parts of India in order to discover whether any folk-lore existed
on the subject and syces and keepers of horses were interrogated for a similar purpose. In June 1895,
one gentleman with many years' experience in India stated " that it was a fixed idea in the minds of
many natives in the North-West Provinces and Oudh that if horses were allowed to eat corn soiled
with rat excrement, some of them would be more than likely to die within a few months." Again the
following statement was made by an old syce—"It is a common belief among syces that rat's dung in
the corn given to horses makes them ill." Further testimony with regard to small animals was obtained
to this effect. "Some years ago we lost a couple of goats, and the native who tended them said,
death was due to the rat's dung we found among the stock of gram the animals had been fed upon."
From the above statement it will be gathered that animals can acquire the Trypanosoma or
organism of Surra by different means, the thousands of equines which have succumbed to that disease
in the Punjab alone have to shift for themselves, and under no circumstances obtain anything as
fodder but the grass they can find, and water from the nearest source. Therefore, the question of rat
excrement can be at once excluded as a factor in the causation of the disease in that class of animals.
But with regard to the question of Surra being communicated by the bite of a fly, we know that when
once the disease is started it may be re-produced to any extent by these insects. The evidence put
forward with regard to the effect of rat excrement in corn is also of great importance to the horse-
owner in India.
C.— Classification of certain species of flies caught upon the bodies of animals,
in India and other countries.
All species of flies may become dangerous by transferring disease germs, which adhere to their
mouths and limbs, from one animal to another, as when alighting and feeding upon the blood of a
Surra patient they transfer their attentions to equines with some exposed wound or slight solution of
continuity of the skin.
In such a case it is almost inevitable that the healthy animal will contract Surra. The species of the
Diptera, which are essentially dangerous on account of their forminable bite, are provided with pointed
instruments as sharp as needles, with which they pierce the cuticle and draw blood with the greatest
ease. These species of flies are able to obtain for themselves, in the absence of sores on the bodies of
the affected animals, the soiled material with which they may inoculate the healthy animals they bite.
The flies which infest equines the most, during different seasons of the year in this country, appear
to be as follows :—all through the year the Hippoboscidæ, two varieties (i) which principally attacks
bovines and equines, (ii) a smaller variety which infests dogs. In the plains at the beginning of the
rains, the Mhet (Burmese), a species of Tabanus, was always observed, also in Poona and the Mohand
Pass (North-West Provinces).
In the hot season, especially towards the end of May and the beginning of June, before the rains
set in, the large green-eyed fly the Tabanus-lineola, or an allied species, is present in great force.
Sometimes it re-appears during a spell of fine weather, during the monsoon season, in September or
beginning of October, but directly the cold weather sets in, these flies may be found dead by hundreds.
Several fairly large varieties of the Muscidæ have been caught on diseased animals, with their
body cavities distended with blood, which, when submitted to microscopical examination, have been
found to contain innumerable Surra hæmatozoa. These flies, up to the present, have not been identi-
fied and placed to their respective species.
At Poona the Surra animals, especially mules, and at the Surra Camp at Karnal, the horses were
annoyed night and day by mosquitoes (culicidæ) which were only kept in abeyance by making fires
to windward of the animals and allowing the smoke to envelope them.
In the plains of India the commonest variety is the 'louse fly,' which infest horses, cattle, sheep
and other animals, especially dogs. They belong to the family Hippoboscidæ, "head prone; neck
lying on the prosternum" which is again sub-divided into six genera, of which Hippobosca, the first,
is frequently separated as a sub-order under the term Pupipara on account of the curious method
of re-production.
The following notes, with regard to the above mentioned families of Diptera, have been abstracted
principally from the works of the chief British and American authorities on this branch of the science.