ABSTRACTS
Studies with equine streptococci. 2. Experimental immunity to Str. equi.
P. L. BAZEBLEY, (1940). Aust. Vet. J. 16, 243
T HE author has explored the conditions under which a potent vaccine can be
produced having protective action against experimental Str. equi infection in mice.
The medium employed for the preparation of the vaccine was a nutrient broth made
from veal extract with one per cent proteose peptone and half per cent sodium chloride
to which 10 per cent horse serum and half per cent glucose were added. The final pH.
of the medium was 7.2 to 7.4. A fourteen to eighteen hour growth of Str. equi in this
medium was transferred to a similar medium previously conditioned at 37°C., the inoculum
being 10 per cent of the total bulk. After the stipulated period of growth the organisms
were centrifuged down through an angle centrifuge or other high speed centrifuge and
resuspended in Wright's fluid (0.1 per cent gelatine solution with a phosphate buffer of
pH. 7.6). This suspension was sterilized by heating at a temperature of 56°C. as early
as possible after suspension was effected.
The author's experiments include trials to determine the age at which the culture
has to be reaped for the realization of a potent vaccine and to ascertain the conditions
which govern heat-killing of the culture for the immuno-antigen to remain unimpaired.
Mice were used as the test animal and the results were evaluated by the application of
statistical methods.
The results may be summarized as follows :—
(a) Vaccines made from young cultures (3 to 6 hours' growth) of Str. equi were
found to possess greatly superior immunizing powers to the older culture
products, but the latter were not entirely lacking in this respect.
(b) The organisms from young cultures were capsulated and they sedimented very
slowly on standing, and it would appear that the immuno-antigen is
associated with the capsular structure of the streptococcus. Poor vaccines
were found to sediment very rapidly.
(c) Prolonged heating at 56°C. was injurious to the immuno-antigen. As short
a period as 0.9 minutes was sufficient to ensure the sterility of the vaccine
provided quick transference of heat to every organism was ensured by
adequate methods. But the immuno-antigen was not appreciably damag-
ed when 10 ml. quantities of the culture were heated in ¾ in. test tubes
for 10 to 12 minutes. At 16 minutes the immuno-antigen was significantly
impaired.
(d) Serum from a rabbit immunized by a series of injections with a potent vaccine
protected mice against lethal doses of Str. equi. [V. R. R.].
The pathogenesis of tuberculosis in the calf. E. G. WHITE and F. C. MINETT.
Brit. J. Tuberc. April 1941, 1-19
T HE authors refer briefly to the two contrasting views regarding the pathogenesis of
primary lung tuberculosis in the calf, viz. the view of the German workers who hold
that it is due to aspiration of infected material—either milk from cows with tuberculous
mastitis or sputum from cattle with ' open ' pulmonary tuberculosis—, and the view
of Calmette that such tuberculosis in calves as in other animals and men is due in the
great majority of cases to bacilli which have been ingested with the milk or other infective
material and have passed directly to the lungs without leaving any trace of their passage
through the intestine and mesenteric glands, after varying periods of sojourn in the latter
so-called ' latent' tuberculosis. The authors then describe in detail the results of
their own experiments which they carried out on a series of 24 calves from a tuberculin-
tested herd with a view to elucidating the position further. The calves were 5 to 7 days
old when they were obtained and were maintained throughout the experiments under
conditions which precluded the possibility of their acquiring natural tuberculosis.
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