MUKTESAR, FOR THE YEAR ENDING THE 31ST MARCH, 1925
39
That vaccination with the more highly virulent type of organism represented by the
Indian strains employed was not a sufficient protection against the onset of clinical abor-
tion is illustrated by the following cases selected from the records.
Name
Yankei .
York
.
Heifer No. 126
Heifer No. 459
VACCINATED
1st dose
9th Feb. 1924.
30th
April
1924.
11th
May
1924.
11th
May
1924.
2nd dose
18th Feb. 1924.
10th
May
1924.
19th
May
1924
21st
May
1924.
Served
May 1924 .
July 1924 .
15th
July
1924.
5th
Sept.
1924.
Aborted
18th Nov. 1924.
30th
Nov
1924.
2nd Dec. 1924.
8th
Jan.
1925.
The mode of vaccination that had hitherto been considered worthy of application,
judging from the published reports of eminent authorities in other parts of the world
would therefore appear to lack the degree of efficacy that would commend its adoption
as a practical measure in a herd faced with very virulent type of infection such as prevails
in the Dairy under observation. Laboratory investigations were therefore prosecuted
in order to determine in the first place some ready means of testing the various procedures
susceptible of adoption in the light of existing bacteriological knowledge, for observations
with regard to the efficacy of any system in natural conditions must of necessity be pro -
longed and often difficult of control. Moreover, the laboratory records seemed to indi-
cate that buffaloes and indigenous cattle possessed a higher degree of resistance than did
cattle with a large admixture of European blood. A factor that must be considered
however, in forming an estimate of individual or breed susceptibility is the probability of
considerable variation in the virulence of the micro-organism to which the different herds
or types of cattle are exposed. It has been stated in the preceding Report that in the
course of a large number of agglutination tests carried out by Mr. Bennett upon indigenous
cattle in the Punjab early in 1924 about 10 per cent. of the animals were found to be
infected with the common cause of bovine contagious abortion, but none were discovered
to have actually aborted due to this infection. A number of milk samples was taken
from reactors and tested by inoculation of guinea-pigs ; none of these small animals subse-
quently developed agglutinins, or showed any evidence of infection with B. abortus on
post-mortem examination after some months' interval. It is now known that strains of
very low virulence may fail to provoke any reaction when tested in this manner, so that
the negative results of guinea-pig inoculation do not necessarily preclude the presence
of the specific organism in the milk.
It is conceivable that use might be made of the production of lesions or even death in
these small animals for testing the efficacy of a vaccination procedure. However, a
method was devised at the laboratory which seems capable of furnishing more reliable
information. In smears from one of the cows that had succumbed at Lucknow from the
effects of the virulent, Indian vaccine evidence of an acute septicæmia was observed.
It was then believed that probably the intensity of invasion subsequent to infection might
be gauged by the degree of septicæmia, or " blood flush " that arose. Much painstaking
work was being undertaken in studying this " flush " at the laboratory in connection with
the passaging of the rinderpest virus through rabbits and of the surra trypanosome through
buffaloes in attempts to exalt virulence. It was then thought that blood cultivation, on
the lines adopted for the isolation of the organism allied to that of bovine abortion from
the blood of human subjects suspected to be affected with Malta fever, could be applied
with equal facility. In the first experiment attempted the English strain of very low
virulence and an Indian strain recently isolated were injected into cattle and the blood
plated out daily. It was found in reality that the more virulent strain produced a dis¬
tinct flush for some days, while the one of low virulence produced no such flush. With
the virulent strain indigenous cattle (hill bulls), cross-bred European cattle, and buffaloes
were injected, and the flush estimated for several days (three weeks). It was found that
a variation in the " flush " occurred comparable with what was suspected in regard to
susceptibility from field operations. Moreover, various strains were tested in regard to
their properties for causing the " flush " in cattle of the same species.
A system was then devised for estimating the efficacy of various procedures of vac-
cination on the assumption that suppression of the flush subsequent to the inoculation