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33
Greenwich to Wandsworth; it existed also continuously,
but in far less intensity, and with comparatively
little extension inland, along the northern
side of the river from Poplar to Chelsea; and it
existed very intensely in several independent centres,
scattered about those healthier levels of the metropolis,
which, by their better position, ought to have
been exempted from such a reproach. The Cholera
struck in the same proportion as this atmosphere
prevailed; and herein, I repeat, lies that definite
local condition, except for which—to the best of
my knowledge and belief, the migratory ferment
(whatever it may be) would pass harmlessly through
the midst of us.
For, towards the chemical constitution of local
atmospheres, it seems that the several principles of
epidemic diseases stand in the same sort of fixed
respective relations, as do the several principles of
infective fevers towards certain elements in the
blood of individual persons. Just as the infective
ferment acts on man, so appears the epidemic
ferment to act on locality. We know that, in a
given group of human beings, small-pox chooses
one victim, scarlatina another, measles a third, by
reason of some material quality in each person
respectively, which his blood possesses, and which
his neighbour's does not possess. By virtue of this
quality—not the less chemical because chemists
have 110 name for it, that specific exterior agency,
D