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Adding, therefore, together the cases of inoculated Small.Pox, and
the cases of natural Small.Pox of which the inoculated cases were
in one way or other the cause, it seems probable that inoculation
did tend to increase the prevalence of Small.Pox; but there are no
recorded data to show that this really was the case, and this
supposed influence may have been counter.balanced by other
influences.
The general conclusion which may be drawn seems to be
that inoculation had a double influence, one favourable, the other
unfavourable, as regards Small.Pox; and, owing to the conflict
between these two influences, it produced but little effect upon
the prevalence of or mortality from Small.Pox.
There is no adequate evidence that inoculation did increase
the mortality from Small.Pox. There was certainly, so far as the
evidence goes, no such increase of Small.Pox, coincident in point
of time with the increase of inoculation, as to justify the decrease
of the latter being considered the main cause of the marked
decline of the former. Nor is there sufficient even to show that
it was a distinct subsidiary cause.
It is to be observed that some opponents of vaccination,
whilst insisting that the decline in Small.Pox mortality in the
first quarter of the present century was due to the discontinuance
of the practice of Small.Pox inoculation, have contended that
what was supposed to be vaccination during that period was in
reality inoculation with Small.Pox virus. It is obvious that
these theories are mutually destructive. If the so.called vaccination
was in truth Small.Pox inoculation and the latter practice
increases the prevalence of Small.Pox, the disease should have
increased and not diminished during the period under review.
Another view has been put forward attributing the decline
in question to the improvement of sanitary conditions.
The question how far the behaviour of Small-Pox in the