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preceding vaccination, has continued in those countries down
to the present time. We think this statement of the case
is accurate, notwithstanding that the present century has
witnessed epidemics of considerable severity, even in countries
where vaccination has largely prevailed. There has always been
in those countries a class, more or less numerous, of unvaccinated
persons who would, of course, be no less subject to the disease
than if their neighbours, like themselves, had remained unvaccinated.
Moreover, if it be true that experience has taught
that the protective effect of vaccination diminishes in force, or for
some purposes may even disappear, after the lapse of, say, ten
years from the date of the operation, there will be many of the
vaccinated class liable to be attacked, and to suffer more or less
from the disease, even conceding the protective effect of vaccination.
We cannot think, therefore, that the fact that epidemics
have from time to time occurred, and that deaths from SmallPox
continue, ought reasonably to be accepted as a proof that
Small-Pox is uninfluenced by vaccination. In referring to the
experience of the period which followed the introduction of
vaccination, we are, of course, speaking generally. We have
already considered the extent to which causes other than vaccination
may have contributed to the diminished mortality from
Small-Pox.
We observe next that there has been in the United Kingdom
a remarkable change in the age-incidence of Small-Pox. The
change does not appear to have been confined to this country,
but we limit our remarks to it, because we have not as precise
information on the point in the case of other countries. This change
in the age-incidence appears, on the whole to have become
increasingly marked as the infantile population came to be more
completely vaccinated. On the other hand, we have seen that
where vaccination has been neglected or practically abandoned,
a Small-Pox epidemic has been characterised by a very large
mortality among children, when compared with the mortality
exhibited in a well-vaccinated place visited by an epidemic of the