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proved that any such protection or immunity has been enjoyed by
the vaccinated. The latter is manifestly the more important
point. If the facts which have been accumulated, when fairly
and impartially viewed, do really show that the vaccinated are either
less liable to be attacked by Small.Pox, or if attacked suffer less
severely, than the unvaccinated, any theory which rests on the
basis that there is no possible connexion between vaccination and
susceptibility to Small.Pox must evidently be regarded with
distrust. If the protective effect of vaccination be thus estabtablished,
then, even if the relation of vaccination to Small.Pox
could not be explained, nor the reason why or the manner in which
it affects human susceptibity to Small.Pox contagion, elucidated, it
would still be quite reasonable to accept and act upon the conclusions
to which experience directed us. The reason why the introduction
of a particular drug into the human body produces certain
phenomena may be incapable of explanation, but that it operates
to produce these phenomena may be none the less certain. If,
then, it be shown that vaccination has a protective influence
against Small.Pox, or modifies the character of the disease, it is
not necessary for the purpose of the inquiry upon which we are
engaged to determine what is the true theory by which the effect
is to be accounted for. To embark on such a scientific inquiry in
any detail would be beyond the scope of our functions. If, again,
experience does not warrant the assertion that vaccination tends
to prevent the spread or mitigate the effects of Small.Pox, it is
obviously immaterial whether this was a priori to be expected.
At the same time, as it has been asserted with much confidence
that science forbids a belief in the protective influence of
vaccination, we have not thought it right to abstain altogether
from dealing with this question. We shall, however, for the
reasons we have given, discuss it much less in detail than the
question what inferences ought to be drawn from the facts
accumulated by the history of vaccination and Small.Pox in the
period, now nearly a century, during which vaccination has been
in use.