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7
old alchemists believed in the transmutation of metals. Be this as
it may, the fact remains that, as a rule, when one zymotic disease
is very active the others are to a greater or less degree in abeyance,
and thus after a violent eruption like that of small pox in 1871-2,
it is not uncommon to witness a considerable temporary reduction
of mortality from zymotic diseases generally. Why is this ?
Can it be that a particular element in the blood which we may
reasonably suppose to be that which the zymotic poison attacks,
and upon which it grows and multiplies, becomes exhausted, or
worked out in the individuals liable to, and who contract the
disease, and therefore in the population generally ? This would
seem to be the case as a rule, quoad the individual, and with respect
to each disease, for it is notorious that the same person rarely
suffers twice from the same disease, though it is equally obvious
from common experience that the same person may take all of
them consecutively—a fact, by the way, which militates against
the theory of the unity of the zymotic poison. It is true that
small-pox, scarlet fever, &c., may attack the same individual twice
or oftener, at long intervals ; and it does not seem far-fetched to
suppose that in such cases the particular element in the blood
before referred to, as the food or nidus of the zymotic poison
may have been renewed, or possibly was never quite eliminated.
I am aware that this is not the view commonly entertained, but it
appears to me equally reasonable with the more popular one which
ascribes the cessation of an epidemic, e.g., of small-pox, to a gradual
decrease in the virulence of the poison, and a progressive inability
to propagate itself, so that after a fearful inflation of the mortality,
tho deaths diminish more and more till the disease scarcely
appears in the weekly mortality returns. To me it seems equally
probable that, the disease having selected for its victims those
who were fitted to receive the poison, gradually dies out, because
it finds no more food—for the epidemic extends from town to
town, from country to country, and from continent to continent,
going through the same stages of increase, maximum virulence,
and decline alike in all. The subject is full of difficulty, but the
experience of each year and of each epidemic, may be expected to
throw additional light upon it, and it is satisfactory to know that
earnest and able men are making it their peculiar study—for of
this we may be sure our present immunity from zymotic diseases
will not last, but will be followed sooner or later by a serious
outbreak—whether of Scarlet fever, or, as seems not improbable,
Cholera, it is impossible to tell. Our duty is clear, viz., to do
what lies in our power to be prepared for the worst, that the
enemy may not come and find us wanting. It may be mentioned
in passing, that the very abundant rains of the latter part of 1872
and the early part of 1873 have been credited as active agents in
reducing zymotic mortality, by washing out the sewers and
removing the sources of malaria. I think we may fairly ascribe a