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Scientific Memoirs by
certain local conditions favourable to its factors, so the secondary one cannot
be manufactured in the absence of favourable conditions within the intestinal
tract.
In order to the development of the primary poison in any locality, it is
necessary that certain organisms should be present, and that they should en-
counter conditions favourable to their growth and multiplication. The mere
presence of the organisms will be incapable of producing any appreciable effects
in the absence of favourable local conditions, and the latter may be present in
the highest degree without implying the presence of cholera so long as the
organisms which are the actual factors of the specific cause of the initial symp-
toms of the disease are wanting. Within the truly endemic area there can be
no reasonable doubt that the actual factors of the poison are constantly present,
and yet the activity of the process of manufacture is unequivocally entirely re-
gulated by seasonal variations in the conditions of the locality ; on the other
hand, in many sites situated beyond the endemic area, there is every reason to
believe that local conditions may at times be most favourable to the develop-
ment of the disease, and yet no actual development of it occurs in the absence
of the specific factors of the poison. At the same time there can be no doubt
that the phenomena of epidemic diffusion indicate most clearly that the pre-
sence or absence of conditions favourable to the development of the specific
cause of the disease is not solely dependent on purely localised causes, but is
regulated by certain widely-diffused influences. On the assumption that the pro-
vision of favourable conditions is purely dependent on strictly localised influ-
ences, it is as difficult to account for the fitfulness with which general epidemic
diffusion takes place, as it is if the crude contagionist point of view be adopted.
The actual conditions in any locality are liable to be affected not merely by
influences of strictly local origin but by generally diffused ones, and it may be
necessary that both should co-operate in order to determine that the environment
shall be adapted to the requirements of particular organisms. Where perma-
nent local conditions are constantly more or less favourable, and the actual factors
of the poison are indigenous, we are dealing with an endemic locality ; where
local conditions are permanently unfavourable we have an exempt area ; where
local conditions are such that with the co-operation of certain widely-diffused
influences they are capable of providing a congenial environment for the factors
of the poison, then all that is necessary in order to secure the epidemic occur-
rence of cholera is the presence of the factors during the period at which such
co-operation is extant. In certain cases the factors may be previously present,
but in a state of abeyance up to the time at which conditions favouring their
multiplication and exercise of activity are provided, in others they may be
absent, and the development of any local epidemic will then depend on their
introduction into the locality during the period at which it provides a congenial
environment for them. We have thus to distinguish between localities which