316
Multiplication of B. Anthracis and Cl. Chauvœi
It was not considered necessary to try to obtain any very accurate data
as to the rate or extent of growth under the different conditions. Multipli-
cation may go on up to 13 or 14 days at 25°C. but it is only occasionally that
it is continued beyond that time. After 13-14 days, the number of colonies
which develop tends to remain stationery ; this, in conjunction with the
observation that most of the organisms resist 60° or 70°C. for 30 minutes,
indicates that they have passed into the spore phase. A glance at Table II
will show that, under favourable moisture conditions, the number of orga-
nisms may increase by several thousandfold—in two cases by 25,000 and
30,000 times, representing a final count of 4.5 and 5.5 millions per gm. wet
soil. Good growth also takes place when blood from guinea-pigs dead of
anthrax is used as seed. There is, however, much variation in growth among
the bottled soils kept under the same conditions and even in the absence of
recognizable aerobic contamination.
A few attempts were made to demonstrate growth in parallel with the
cultural results by inoculation of white mice and rats. This succeeded in
some cases with mice but as previously remarked, the susceptibility of these
animals is not uniform. As was expected, white rats were useless as test
animals.
An endeavour was also made to determine the most favourable tempera-
ture range for the anthrax bacillus in soil. The results, shown in Table III,
were somewhat erratic but two points were clear :—(i) that 15°-17°C. is too
low ; (ii) that good growths are obtainable at 25° and 30°C. There was a
tendency for growth to be comparatively poor at 37°C. but this finding should
be treated with reserve.
Experiments were conducted on soil to which certain ' manures ' (horse
dung, vegetable manure, ammonium sulphate, lime, superphosphate) were
added. It was ascertained that the anthrax bacillus would grow in sterilized
soil containing these substances individually or in mixture. Whether the
organism grew better in the presence of some or all of these substances was
not determined. The making of exhaustive observations on these points
would have entailed much time and labour, which would have been scarcely
justified by the results, especially as much difficulty was encountered in
efficiently sterilizing soil containing the organic manures. One would expect,
however, that such substances would assist growth and Erdman [1928], in
studying the effect of various manurial treatments on the number of micro-
organisms in soil, found that the addition of manure+lime+superphosphate
brought the greatest increase in numbers. From the data in Table IV, it is
seen that the anthrax bacillus grows in soil to which these substances severally
have been added—in amounts larger no doubt than would be used in agricul-
tural practice—though in some cases the results are erratic. The addition
of lime appears to be especially advantageous, maximal growth occurring
at 30°C. within 13 days.
Growth in soils from other localities in India.—It was of interest to ascertain
whether the anthrax organism was capable of multiplying in sterilized soil,
differing in composition from that at Mukteswar. For this purpose, 9 different
types of soil were obtained from the Imperial Agricultural Research Institute,
New Delhi, and 6 soils from the Agricultural College, Coimbatore, Madras.