5
Although the latent period of Rat Surra was so prolonged in the first instance,
when inoculated from rat to horse (average 40.7 days), it immediately returned
to the normal period (average 7 to 8 days), when a second horse was inoculated
with the blood of the first affected. The latent period however becomes still
more reduced (5 days), when a third animal is inoculated with the blood of the
second.
2. Horses unsuccessfully inoculated, and re-inoculated subcutaneously with
the Bat hæmatozoon, when subsequently inoculated with Horse Surra blood,
show no protection from the former, but acquire the disease after an incubation
period of six to ten days.
3. Animals other than horses, which contracted the disease, were:
Bovines, monkeys, and field rats; while the rabbit, guinea-pig, fowl, cat, dog,
and donkey proved refractory to the rat hæmatozoon. But all the above animals,
with the exception of the fowl, were very susceptible to the rat hæmatozoon,
when it had first been passed through the horse.
(b).—Experiments on the gastric ingestion of Rats excrement.
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 animals. It therefore 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.
2. In 1892 experiments were undertaken at Poona, on the Deccan plateau,
where the disease is not enzootic, and where the difficulty of producing it was
fully recognized, owing to the dryness of the situation at that period of the year
(December to February). These experiments as expected proved negative.
3. At a later date, during the latter half of the hot season and the rains
of 1893, further experiments with the same end in view were carried, out in
Bombay, where the climate is favourable from its humidity, and the disease is
enzootic. From these, positive results were obtained, the incubation period
occupying four months (about June to September); but the incubation period of
the disease will probably be found to vary with the amount of moisture present
in the atmosphere, and amount of materies morbi ingested by the animal.
This points to the probability of a number of the Surra cases in Bombay being
contracted through the ingestion of rats' or bandicoots' excreta mixed with the
corn. Although not yet definitely proved, it is more than likely that the
excreta of young and half-grown bandicoots have the same power of producing
the disease, as the hæmatozoon is also frequently present in their circulation.
III.
BOVINES.
A, Bull, No. I. inoculated successfully with Surra in 1892, and whose
case was included in Vol. I. of the Report, was re-inoculated subcutaneously
with Surra, one year and a half after the first inoculation. The animal proved
refractory to the disease, and apparently was still protected against another
attack.
B.—Transmission of the hæmatnzoon from the Mother to the
offspring through milk,
A cow, with a calf three weeks old at her side, contracted Surra. The
blood of the mother was found to contain the hæmatozoon for a period of 120
hours.
The calf was allowed to suckle three times in the 24 hours, and the milk
from each teat was daily examined microscopically for the presence of the
organism; but this was never discovered. However, on the 38th day from
the appearance of the hasuiatozoon in the circulation of the mother, it appeared
in the blood of the calf, which up to that date had been free. The organism
remained in the circulation for 24 hours only, and had not re-appeared 123 days
later.
B 678—2