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49
about the period of puberty is all (putting out of the
question a certain small number of exceptional cases) that
is really needed to protect a person for life. This is very
likely true; but it is obvious that trustworthy statistics in
reference to this point must be very difficult to obtain;
and meanwhile I suspect that it is on the whole wise, notwithstanding
a second successful vaccination at puberty,
to submit to further vaccination if some years after that
period there should be, or should threaten to be, special
exposure to the small-pox poison.
I have used the term successful vaccination more than
once, and I have used it advisedly; because it is not
sufficient that the operation of vaccination should be performed,
but it is essential that some visible result should
follow the operation. It is no proof that a person operated
upon is insusceptible of cow-pox or of small-pox, when the
puncture made with the lancet dies away like the ordinary
prick of a pin—it is simply a proof either that the lymph
has lost its virtue, or that from bleeding or some other
cause it has failed to become lodged in the substance of
the skin. Under such circumstances the operation should
be repeated, and if necessary repeated again.*
The present epidemic of small-pox, while it proves
conclusively that the great majority of persons living in
the Metropolis are fully protected by vaccination
*Let me add the fact, that the latent period of small-pox is longer
than the time which intervenes between the performance of vaccination
and the ripening of the pock which results; and that it is therefore
possible for a person who has already caught small-pox to be vaccinated
and to have at the proper time a well-developed pock, and
within a day or two afterwards a severe attack of small-pox.