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20
These facts are suggestive of two things, namely:
1st. That vaccination is often imperfectly performed,
and therefore fails of its prophylactic
power; and
2nd. That even when it has been well performed
in infancy, the effect of it is weakened
by time.
Looking, indeed, at the ages of those who have
been attacked with small-pox in the City, I find that
of the 1,150 that had been vaccinated, 158 were
under five years of age, 508 were at from five to fifteen
years of age, and as many as 484 were at fifteen
and upwards—so that of every 100 cases of
small-pox after vaccination 13.7 were at the first
period of life, 44.2 at the second, and 42.1 at
the third. It is manifest from this that the
protective power of vaccination has failed, either
from its having been imperfectly performed, or
from its having been weakened by time. In the
epidemic of 1864, the statistics of Berlin showed
that 64.6 per cent. of all the cases of small-pox were
among persons at twenty and upwards, and that
40.7 per cent. of the deaths were at these ages. The
mortality of the cases in the City of London during
the last thirteen years has been in the proportion of 43.1
por cent. among infants, 16.2 at from five to fifteen