318
Multiplication of B. Anthracis and Cl. Chauvœi
flasks varied in the different experiments from about 100-600 organisms per
gm. of wet soil, except in one case where a very light seeding was used, viz.
about 40 organisms per 100 gm. soil, and from 400 to 1000 organisms per c.c.
of water. The number of organisms introduced into the soil or water was
again checked immediately after seeding and was found to agree reasonably
well with the expected number. In fact, in spite of the presumably large
sampling error, the results throughout have been fairly concordant and should
suffice to show all that was required, viz., whether growth was negligible or
abundant. At intervals of from 5 to 49 days, soil or water samples were
again examined. There were four separate experiments. It is unnecessary
to give full details, for except in one instance, growth was slight or inappre-
ciable, both in sterilized and in natural soil or water. The findings were
consistent enough to indicate that, even with large seedings, growth, if occur-
ring at all, is as a rule very restricted, usually not more than 10 times, occasion-
ally as high as 100 times. There was an exceptional case where, in the pre-
sence of lime, superphosphate and horse manure extract, growth of chauvœi
took place in one bottle from a very light seeding up to 2 million times within
15 days. From this experiment the impression was gained that growth was
assisted by the presence of the lime, superphosphate and horse manure mix-
ture but this could not be confirmed. Nor was there any real evidence that
multiplication of chauvœi was enhanced by aerobes present in natural soil or
water.
DISCUSSION
In considering the possibilities of pathogenic organisms multiplying in
soil under natural conditions one has to take into account physical, chemical
and biological factors. Soils vary in their composition, chemical reaction,
temperature and water content, while various kinds of living organisms are
present. Soil temperature and water content show great differences accord-
ing to countries and seasons. The temperature is also to some extent de-
pendant on moisture ; in moist soil temperature rises are smaller than in
dry soils, owing to the greater specific heat of moist soils. In the case of
pathogenic organisms that might gain entrance, the surface layers would
be mainly concerned. To deal with the temperature factor alone in illustra-
tion of the variability of conditions in soil at the surface the difference between
daily maximum and minimum temperatures is large but the difference rapidly
diminishes with increasing depth ; at 6 in. depth at Rothamsted the daily
fluctuations are practically inappreciable in winter but are marked in summer
[Keen, 1926]. In England, according to Keen and Russell [1921], the mean
temperature at 6 in. depth is about 20°C. in summer and 5°C. in winter. In
subtropical countries such as India, the temperatures are, of course, much
higher. Dravid [1940] has recently recorded that, at Poona, which has black
soil and therefore absorbs greater amounts of heat through solar radiation
than lighter-coloured soils, at 5 cm. depth the temperatures reach 30-32°C.
in January, 32-42°C. in February-March, 47°C. in April and 31°C. in August.
At 10 cm. depth the corresponding figures are : 26-28°C., 30-34°C., 40°C. and
62C°. During the summer in Poona, surface temperatures as high as 75°C.
are occasionally recorded.