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139
suggested by the evidence which we have already passed under
review.
We have hitherto, save for a cursory reference to the bearing
of some of the facts upon one another, treated the various tests
which have been applied to ascertain whether vaccination has a
protective effect separately and independently. We have found
that in each case the result of the test has been to suggest an
affirmative answer to the question. In order to estimate the
value of the evidence aright, it is necessary to consider in
conjunction all the tests which have been adopted, and the results
which they exhibit. They are, it is true, independent of one
another, and have been separately applied in a number of cases.
But the greater the number of tests employed, and the greater the
number of cases to which they are applied, the more certain is it
that the play of chance, or the influence of other causes, will be
excluded, and the more safely may the conclusions to which they
lead be acted upon. The cumulative force of a number of
independent pieces of evidence, all pointing in the same direction,
is very great indeed. Even if a more or less plausible answer
could be suggested in the case of each one of them standing
alone, the cumulative force of the testimony might still be
irresistible. We think those who have denied the efficacy of
vaccination have often lost sight of the circumstance that investigations,
which have followed so many different roads, have all
led to the same end.
We have not disregarded the arguments adduced for the
purpose of showing that a belief in vaccination is unsupported
by a just view of the facts. We have endeavoured to give full
weight to them. Having done so, it has appeared to us impossible
to resist the conclusion that vaccination has a protective effect in
relation to Small-Pox.
We think—
1. That it diminishes the liability to be attacked by the disease.