Scientific Memoirs by
certain local conditions this is no longer the case, and we need no longer expect
that in every case its appearance should be traceably connected with intercourse
with previously-infected localities. In the year 1871 the rainfall in Calcutta
was unprecedentedly excessive, and in consequence certain depressions in the
great open plain of grass-land within the limits of the town were for the time
being converted into pools of standing water, and in some of these plants of
Nymphœa made their appearance and flowered. Now, as the seeds of Nymphœa
mature subaqueously, and as the plant is not now native to any of the permanent
ponds within the area of the plain, there is no probability that the appearance
of these plants was due to the importation of seed into the hollows subsequent to
their occupation by the water, and there is every reason to believe that the phe-
nomenon was owing to the abnormal presence of the water acting upon seeds which
were already in existence in the soil. In other words, the appearance of the
plants was almost certainly the result of the presence of certain excotidenal con-
ditions of locality acting upon organisms which were already present, but which
under normal circumstances were kept in abeyance. But if the evidence of the
existence of a plant, such as Nymphœa, in a locality may only manifest itself
under the influence of certain exceptional and temporary conditions, there can be
no question that the evidence of the local existence of organisms of a nature
likely to be concerned in the manufacture of the primary cause of cholera may
only become conspicuous under similar circumstances, and, therefore, that the
appearance of the disease need not necessarily imply the fresh introduction of
the factors of its specific cause.
In any case, however, whether the appearance of the disease be connected
with the introduction of specific factors or with the presence of conditions favour-
ing the activity of specific factorswhich are already present, the influence of local-
ity remains alike the essential determinant of the result. It is the presence or ab-
sence of the favourable conditions in a locality that is the really important element,
for no amount of introduction of specific factors can give rise to any appreciable
result, if they do not encounter a congenial environment, and so long as such an
environment is wanting, any specific factors which are pre-existent in the locality
will remain permanently in abeyance. Intercourse with infected localities may
certainly be efficient to give rise to cases of cholera in localities of any kind so
long as it implies the introduction of a specific poison in a ready prepared form,
but, if the process of preparation be one which is normally conducted in the
environment, and not within the bodies of the sick, any already elaborated poison
will very rapidly be expended, and with this the occurrence of the disease will
cease. The same result will follow in cases where not merely the elaborated
poison but the specific factors concerned in its elaboration are imported into
any locality unfavourable to the latter, and it is only where intercourse with
infected localities implies the introduction of the factors of the specific poison
into a site favourable to them that it can efficiently contribute to determine
epidemic diffusion.
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