38 REPORT OF THE IMPERIAL INSTITUTE OF VETERINARY RESEARCH,
the inoculation of massive doses of culture, traces of which proved virulent to the more
susceptible animals, and no success was obtained in endeavours to exalt cultured strains
for dogs. The only certain means of killing dogs was found to be by the inoculation
of blood rich in anthrax bacilli from fatal cases of the disease, but inoculation with such
highly virulent material overwhelmed the defences of vaccinated dogs to the same extent
as those of controls. However, it is believed that the vaccination must have conferred
some degree of immunity in addition to that naturally possessed by the dog, but that the
virulence of the attack necessary to break down surely the natural immunity also over-
whelmed the additional acquired immunity. Analogous phenomena were commonly
observed at the laboratory in tests upon blackquarter vaccination, when the test animals
employed were mature hill bulls. It was most difficult to demonstrate the efficacy of
the protective systems under test by the use of such animals, as the doses of virulent
material required to kill controls, already possessing high natural resistance, also broke
down the defences of the vaccinated animals ; large doses of anti-serum were the only
agents which seemed to display a real capacity for warding off such highly virulent test
deses. In tests of hæmorrhagic septicæmia serum the lesson again had been that while
the most conspicuous evidence of the value of good serum could be obtained by employing
animals, such as hill bulls, of moderate susceptibility, care must be taken to titrate the
dosages of the test virus to be employed so that it was not " overwhelming." In black-
quarter tests it seems that the use of guinea-pigs, which possess a fairly uniform, and
fairly high susceptibility, is the method most conducive to obtaining information in regard
to the protective value of an inoculation system, and for tests of the value of the protective
action of anti-serum in particular against anthrax it seems that a careful selection of
host and titration of the infective virulent test material must be made.
(d) Contagious bovine abortion. In the. preceding Report it was stated that attempts
were made to vaccinate against this affection at one of the Government Military Dairies
(Lucknow) where the herd had shown for some time a high incidence of abortion. Vac-
cination, performed by the inoculation of massive doses of an English strain of B. abortus
that had become greatly degraded in virulence did not prove satisfactory. Although it
was fully realised that deductions drawn from the incidence of abortion before and after
the application of an attempted system of preventive treatment, owing to the tendency
of the affection to self-limitation, were fallacious, and that the only proper method of
evaluation would be to insist upon the allotment simultaneously of untreated " controls,"
yet the decrease in incidence, following upon treatment in the above manner was not
thought to be sufficient to warrant the assumption that distinct benefit from the practical
standpoint had been conferred by it. It was hoped that the institution of a modified
procedure, using the maximum safely tolerated doses of virulent cultures of the organism
isolated from cases of abortion at the Dairy itself might lead to better results. Towards
the end of December 1923, the new method was applied to the herd by inoculating
females about two months prior to service with two successive doses (5 and 10 c.c. res-
pectively, " SO 16 " agar emulsion) at an interval of 9 or 10 days. The full results of this
vaccination are not yet available, but enough information has been obtained to indicate
that the procedure falls short of expectations. In a communication received from the
Dairy authorities in February 1925, the position regarding vaccination with the Indian
strain was reported to be :—
(a) Adults vaccinated .
.
.
Calved normally
.....
Aborted
(b) Young stock heifers vaccinated (in May 1924)
Calved normally
Aborted
.
.
147
16
11
34
nil
8
The proportion of heifers that aborted is exceptionally high, but in the case of four
it seems that the vaccine was applied either early during pregnancy or too soon before
pregnancy.
The results of the application of the English vaccine on cows concerning which the
histories were traced during 1923-24 were :—
Number of cows vaccinated
....
Calved normally .
Aborted
Prematurely calved
Barren
. .
. .
.
. . .
. .
117
89
24
1
3
During the year prior to attempts at vaccination, 1922-23, the figures were :-
Total number of cows under observation
Aborted
..
.
.
.
.
.
156
48