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than at all ages; indeed, the proportion of severer cases is in
all the towns quite insignificant.
Before passing to another branch of the subject it will be
well to take account of the bearing upon one another of the facts
relating to the fatality, the attack-rate, and the type of the disease
of Small-Pox, which we have been considering. Between the
facts with which we have been concerned when investigating the
fatality of Small-Pox, and those which have engaged our attention
when considering the type of the disease, the connexion is obvious
and intimate.
In each of these cases we have had to deal with the same
classes of vaccinated and unvaccinated persons—indeed, we may
say with the very same persons—we have already pointed out that
it is more than improbable that on a division of the persons who
suffered from Small-Pox, into two such classes the fatality should
be so strangely different, unless there were something in the
condition of the one class which differentiated it from the other,
and rendered those within it less liable to suffer fatally from the
disease. What is to be said when it is found that, apart from the
fatality of the disease, its type in the two classes also differs, and
perhaps even more widely than its fatality does, and that the
milder type distinguishes the same class which exhibits the
smaller fatality ? That this should be a mere chance coincidence
is incredible when it is observed that the phenomenon is uniform
not only in the case of epidemics in five different towns, but in the
case of the same epidemic in different parts of the same town.
The facts surely afford strong corroboration of two propositions;
first, that a classification was, on the whole, accurately made in
these cases of persons whose condition in relation to Small-Pox
differed from one another ; and, secondly, that this difference of
condition was due to vaccination.
We cannot but lay stress on the force of the facts relating to
the fatality, the attack-rate, and the type of the disease, in the
vaccinated and unvaccinated classes, when considered in