Medical Officers of the Army of India.
45
absence and presence of the factors whose efficiency is affected by these. Within
the endemic area regularly recurring fluctuations in seasonal prevalence manifest
themselves, but there is clearly never either an entire absence of the actual
manufacturing agents nor of conditions allowing of their exercising their
activities. The very regularity with which fluctuations in prevalence succeed one
another is in itself very strong evidence that the process of manufacture is
carried on in the environment, and not in the bodies of the sick, for there is
certainly not a trace of evidence to show that the periods of maximum prevalence
coincide with periods in which there is any specially close crowding together
and association of the population. On the contrary, whilst the periods of
maximal prevalence occur in March and April, and again at the close of the
rainy season, the periods of minimal prevalence occur during the rainy season
and at the period at which atmospheric temperature falls to a minimum. In
other words, maximal prevalence coincides with periods when the population
is least likely to be specially closely associated and minimal prevalence when
aggregation of the population is at a maximum. During the height of the rainy
season and again in the middle of winter the natives at night remain crowded
together and cooped up within their huts, whilst during the hot weather
and again subsequent to the cessation of the rains and before nocturnal tem-
perature falls low, a very large number of them spend their nights al fresco.
With regard to localities lying outside the endemic area, it is of course
possible to regard the phenomena of prevalence from two distinct points of view.
We may ascribe them to alternating absence or presence of the agents manu-
facturing the poison, or to the absence or presence of local conditions favouring
or repressing them in carrying on the manufacture. According to the crude
contagionist opinion the former explanation is the true and sufficient one, and
the absence or presence of epidemic diffusion is simply due to absence or pre-
sence of importation of the factors of the poison ; according to the extreme
localist opinion the phenomena are to be accounted for simply as the result
of the action of fluctuations in the conditions of the environment acting on
factors which are constantly present and ready to manufacture the specific
poison whenever they encounter favourable surroundings. But there are good
grounds for refusing to accept either explanation as sufficient, for if we adopt
the contagionist theory, we are unable to account for the fact that constant and
free communication with the endemic area or with infected areas lying outside
it is only occasionally followed by any epidemic diffusion of the disease, whilst
from the purely localist point of view it is impossible to explain the phenomena
which appear certainly to indicate that intercourse with infected localities is to
a certain extent an appreciable factor in determining epidemic diffusion. Werethe
specific cause of cholera normally manufactured within the bodies of the sick,
we should be left without any sufficient explanation of the fitfulness with which
general epidemic diffusion occurs, and of the fact that so often repeated im-
portation of cases of the disease is followed by no appreciable result ; were all