September, 1951]
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absorption varying from 78 to 83 per cent. Another point of interest in the coat
colour is that the black coat also helps loss of heat specially when the animal is kept
in cold. The larger the surface of the body, the greater the amount of absorption
of solar radiation. Adult animals were preferred to the young, as the response
to antigen for the antibody formation is greater in the former than in the latter.
Lastly, the males were considered more suitable than the females for inducing
photosensitization during the period of exposure to the sun, as the thermogenesis
is more perfect in the males than in the females. But the stock of rabbits available
at the time of the experiment at Mukteswar was limited and, therefore, the choice
was restricted.
NATURAL ANTITOXIN
Parish, O'Meara and Clark [1934] and Dolman and Kitching [1935] found
antitoxin in the blood of normal rabbits and guinea pigs. But, Bryce and Burnet
[1932] found none in the domestic rabbits. Since the occurrence of natural anti-
toxin plays an important part in the development of active immunity, it was con-
sidered necessary to discover whether the rabbits selected for the experiment
contained any amount of detectable antitoxin. The haemolytic method of estimating
staphylococcus antitoxin was used in the investigation described below: The
rabbits were bled for serum. A few tubes were arranged in the rack. Each tube
contained 0.5c.c. of double dilution of serum. 0.5 c.c. containing 2 M.H.D. of
toxin (original 3,200 M.H.D. per c.c.) was added to each tube. The tubes after
standing on the bench for 30 minutes were incubatd in a water bath at 37 °C. for
30 minutes. The rack was then removed from the bath and 0.1 c.c. of 10 per cent
suspension of washed rabbit red cells was added to each tube, and the rack was return-
ed to the bath for an hour, being shaken at the end of the first half hour. Reading
was taken before removing the rack from the bath and finally after one hour's stand-
ing on the bench. All the tubes were found to be completely haemolysed, thus
indicating the absence of any detectable amount of antitoxin in the blood serum
of normal rabbits selected for immunization with alum-precipitated staphylo-
coccus toxoid.
Immunization of rabbits with alum-precipitated toxoid
Smith [1936] conducted experiments on groups of rabbits and gave two spaced
injections of staphylococcus toxoid @ 2.5 c.c. per kg. body weight. The injections
were spaced 3 to 4 weeks apart and the animals were bled 14 days after the 2nd
injection. The degree of immunity conferred, as judged by the level of antitoxin
in the immune blood serum of the rabbits was satisfactory. He further worked
on the comparative efficiency of the different routes of injection and found that the
subcutaneous route proved to be 5.7 times more efficient than the same dose given
intravenously. Having regard to the conclusive findings, noted above, all the 20
rabbits were injected subcutaneously with two doses of toxoid @ 2.5 c.c. per kg.
body weight at an interval of 3 weeks and 14 days after the 2nd injection all the
rabbits were bled for immune serum. Besides formation of a small swelling at the
site of injection in a few rabbits, no other systemic disturbance was noticed. The
local swelling disappeared in a week's time without any treatment.