16
Scientific Memoirs by
not find that it has been specially sterilised for them, it is already fully occupied
by native Schizomycetes with which a struggle must be maintained, and under
normal circumstances, even in localities such as Calcutta, the experimental
evidence goes to show that they very rapidly succumb to it.
But this Laboratory evidence is quite in accordance with that which
presents itself on a large scale in connection with the phenomena of the
occurrence of epidemics of cholera. As we have already seen, Koch has
recorded a striking example of the rapidity with which Comma-Bacilli will
disappear from large bodies of foul water to which they have gained access,
and, if we are to regard the commas as in any way causally related to cholera,
the proportion of cases in which they die out rapidly in localities to which they
have gained access must be very great.
Under normal circumstances the local conditions, then, would appear to be
so unfavourable to their multiplication and persistence that, however efficient
they may be as producers of choleraic symptoms, they can neither persist or
multiply sufficiently to give rise to any appreciable effects. The normally
unfavourable conditions in any locality must to a great extent be of two classes
—1st, conditions tending to diminish the amount of suitable nutritive materials
for the Bacilli in the media to which they gain access; and, 2nd, conditions
tending to increase the intensity of the struggle for existence to which they are
exposed. The actual intensity of the struggle must, of course, depend in part
on the numbers and in part on the nature of the organisms present in the media
at the time of access. In regard to India, at all events, there can be little doubt
that it is the latter class of conditions which, except in certain desert areas,
must be the influential ones, the general quality of soil and water in most places
certainly not being such as to render it likely that the repressive agent is a
want of nutritive material. It is of course, however, possible that elsewhere, in
localities with specially pure water and soil, want of nutritive material may really
play an important part in this respect.
Be this as it may, what the experimental evidence goes to prove is that
under normal circumstances local conditions of soil and water are such as to be
very inimical to the persistence or multiplication of Comma-Bacilli, and that,
therefore, under normal conditions of locality, the latter are not likely to be able
to establish themselves to such an extent as to give rise to any appreciable
effects in the production of cases of cholera. In order, then, to the occurrence
of cholera in epidemic fashion in any ordinary locality, and assuming the Bacilli
to be really causally related to the disease, it is clear that we must have alter
-ations in the local conditions. Such alterations are necessary according to
Koch's theory in order to permit of the presence of commas in sufficient
numbers, and also to give rise to the development of abnormal dyspeptic con
-ditions in the inhabitants, of a nature to render them suitable recipients for them.
Here the commas themselves clearly are reduced to playing a very subordinate