J.
CARMICHAEL
187
50 mg. of culture of bovine origin given
subcutaneously is almost invariably sufficient to
overcome the resistance of English (Jersey)
cattle, and, with rare exceptions, produces genera-
lized tuberculosis of a severe type which proves
rapidly fatal, the results of the present experi-
ments would indicate that a certain proportion
of Indian calves equally small in size remain well
after similar infection, and, when autopsied,
show slight or minimal lesions, indicating that
they are possessed of very high powers of resistance
to tuberculosis as compared to English calves.'
Soparkar [1927], in a paper dealing with the
virulence of tubercle bacilli isolated from cattle
in India, reviews Sheather's [1921] results and
quite rightly draws attention to the fact that
Sheather used cultures which were six months
old, which of course detracts considerably from
the significance of his results.
Soparkar carried out inoculation experiments
on rabbits and calves, using both European and
Indian strains of tubercle bacilli. Of the Euro-
pean
strains
actively
growing
young
cultures were used, also cultures which were six
months old. Of the Indian strains only young
cultures were used.
It is difficult to draw definite conclusions
from the results, but it is quite evident that the
European strains six months old were not by
any means as virulent as the young cultures,
either in rabbits or calves. It is unfortunate
that six months old Indian strains were not
used in order to make a direct comparison with
Sheather's work.
Two series of calves were inoculated, one with
21-day-old European cultures (Table V), and
the other with Indian cultures of the same age
(Table VII).
On examination of Table V, i.e. the inocula-
tions with European cultures, 13 of the 24
calves died in an average period of 40 days
whilst Table VII, i. e., the inoculations with
Indian strains, shows that 15 calves died out
of 19, but the average period of survival was
71 days.
It is difficult to say on these results whether one
strain is more or less virulent than the other.
However, a number of calves inoculated with the
Indian strains did, in fact, die of acute generalized
tuberculosis in the same way as those inoculat-
ed with a known virulent strain of European origin.
This is important and indicates that the Indian
strain was not of markedly low virulence, and that
individual differences existed in the subjects
inoculated.
It will be recalled that none of Sheather's
[1921] calves died, and when killed they only
showed local lesions. All the Indian strains
proved highly virulent for rabbits in the same
manner as the type European strain.
Soparkar's findings are as follows:
"The
rarity of gross tuberculous lesions hitherto
observed among indigenous cattle and the usual
tendency of the lesions to remain localized in
affected animals, cannot therefore be ascribed
to any noteworthy difference in the virulence of
the infecting organisms."
It must be remembered that the indigenous
cattle of India are Zebu in type.
Experimental
The object of these experiments was to ascer-
tain how Zebu calves reacted to a test dose of viru-
lent bovine tubercle organisms with a view to
discovering whether any resistance to tuberculosis
did in fact exist in this breed of cattle. The
opportunity was also taken to test calves of the
Ankole breed for comparative purposes.
Technique. The dose of organisms was fixed at
50 mg. (Royal Commission on Tuberculosis)
and was given subcutaneously. All calves were
previously tested with tuberculin by the double
intradermal test and only non-reactors used
in the experiment. The strains used were B.V. 28
and B.V. 34, kindly supplied by Dr. A. S. Griffith
of Cambridge as being typical dysgonic virulent
bovine cultures of recent isolation. The strains
were highly virulent for rabbits in doses of 0.001
mg. intravenously and 10 mg. subcutaneously.
The cultures were grown on inspissated ox
serum and only young, vigorous cultures, not
more than 10 days old were used. As controls
to the actual injections of the calves, rabbits
and/or goats were inoculated with appropriate
doses of the same cultural growths.
It was intented to kill off all surviving inoculat-
ed calves after a period of 90 days and this was
done in a number of cases, but later the survival
time was allowed to extend, so as to ascertain
in what manner the tissues of a resistant calf
would react to a tubercle infection, and perhaps
enable the degree of resistance to be more accu-
rately assessed.
Experiment No. 1
ZEBU CALF NO. 3281 (weight 129 lb.) and
ZEBU CALF NO. 2562 (weight 110 lb.)
Inoculated subcutaneously with 50 mg. of
six-day-old serum grown culture B.V.28.
Controls. Two rabbits inoculated with 10 mg.
of the same culture subcutaneously. One rabbit
died 18 days later. Post-mortem examination
showed a tuberculous abscess perforating the
lumbar muscles into the peritoneal cavity. Liver,
spleen and lungs full of small tubercles.
The second rabbit died after 58 days. Post-
mortem examination showed acute generalized