32
REPORT OF THE IMPERIAL BACTERIOLOGICAL LABORATORY,
A further line of research into the etiology of the disease was to endeav-
our to view its characteristics from a different angle, as it were, by
implanting it upon a different species of host. The rabbit was chosen
for this purpose, but no tissue change was seen after massive local
infection, except after intra-ocular injection, when a change was seen
for some days in the iris somewhat similar to that seen in specific
ophthalmia in horses. After massive intravenous inoculation of virulent
ox blood a scarcely perceptible rise in the temperature of the rabbit
took place on the following days. It was thought, however, possible
that the reaction might be capable of intensification; hence, at various
days after inoculation, blood was taken from the originally infected
rabbit and " passaged " intensively intravenously through a series of
rabbits at various intervals. After a few passages, a very pronounced
thermal reaction was manifested by the injected rabbits, usually
reaching its maximum on the second or third day, and then subsiding
rapidly; sometimes a very slight febrile relapse was seen towards the
ninth day. Outward, clinical disturbances were not appreciable,
and mortality was rare, and no constant macroscopic lesions could
be seen post-mortem. In this way, " strains " of rabbit virus were
kept up at the laboratory by " passages" at intervals of 2 days,
3 days, 4 days, and 7 days for 14 months, after which our stocks
of rabbits died out on account of a natural outbreak of pasteurellosis
among them. During this period the infectivity of each strain of the
rabbit virus was tested upon cattle from time to time, and it seemed to
remain virulent throughout; the degree of reaction in the cattle varied
from types that were almost symptomless or merely febrile in character,
and left a powerful immunity, to those which were nearly as severe as
the disease set up by the injection of virulent ox blood, but there was no
progressive degradation in virulence. The modified virus never became
" safe " for the vaccination of cattle by itself, although it was generally
much feebler, and had the advantage of being a " pure " virus,—not
contaminated with accompanying virulent piroplasms.
Staining of blood films by all known methods that might lead to the
demonstration of an organism was then attempted, and ultimately
by the adoption of special silver impregnation method (Warthin-
Starry's hydrogen-peroxide silver-agar method) forms were seen in
the thinnest parts of thin blood films from the rabbit which showed a
most extraordinary resemblance to the minute pleomorphic granule-
vibrio-lepto-spirillary forms depicted by Bordet (1910) in the figures
published by him of his researches into the morphology of the organism
of contagious bovine pleuro-pneumonia. In order to confirm this belief,
impression preparations were made from the brains, kidney, liver,
and blood of a normal rabbit and an infected rabbit and after staining
given to a visitor to the laboratory (Mr. W. Harris, Superintendent, Civil
Veterinary Department, Assam) to be handed to me in a haphazard
manner and the results of the examination of each smear were to be noted
in writing immediately. The brain and kidney preparations of the in-
fected rabbit were stated undoubtedly to contain the organism, the