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93
conditions, (b) climatic influences, and (c) errors in
feeding, but they will not be taken separately.
It has been shown by English observers that
diarrhœa does not become epidemic until the temperature
of the earth, as indicated by underground
thermometers, has reached a definite point, about
60° F. at 1 ft. and 56° at 4 ft. This fact appears to
be independent, to a certain extent, of the air
temperature, i.e., that high air temperatures are
efficient in producing diarrhœa only so far as they
cause high temperatures of the soil. It has been
observed that the temperature of the soil does not
follow that of the air in a regular manner, and
there is little doubt that the amount of moisture in
the soil influences the effect of the high air temperatures.
The evidence as to the connection between
the soil and this disease is as yet incomplete, but it
would appear that in addition to a definite maximum
temperature there must be pollution of the soil with
either sewage or garbage or both. The disease is
undoubtedly due to micro-organic life, and therefore
it may be supposed that the micro-organism multiplies
in the soil when it is at or near its maximum
temperature, and by some means or other the
organism or its products finds its, or their, way into
the human body.*
Granting that the disease is due to a filth
* The curve of the disease follows that of the temperature of the earth at
an interval of about a week, a fact which supports the view that the disease
is due to the development of a micro-organism in the soil.