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Thus we see that, except in the last period (which has been
one of increasing default in regard to vaccination), and then only
in the case of those under five years of age, there has been no
substantial reduction of small-pox mortality, while at all ages over
five the mortality from small-pox has been actually greater in the
last three periods than in the first. Such saving of life as there
has been in London in the period 1851-88 was most noticeable
in the period 1881-88, and was confined to children under five
years of age.
It has been urged that the observed changes in age incidence
of small-pox mortality point to vaccination rather than sanitary
reforms as the cause of the difference, since sanitary reforms should
operate equally upon all ages, while vaccination might be expected
to effect especially the young. There are, however, some considerations
which prevent the acceptance of this explanation, at
any rate for the whole of the facts. The increased death-rate
from small-pox in persons above the age of childhood might, with
equal reason, be ascribed to vaccination, or at least seems incompatible
with the belief that the influence of vaccination against
fatal small-pox is of an abiding character. Moreover, it has
been pointed out by the Registrar-General in his report for the
year 1879 that sanitation operates differently upon the general
mortality of persons at different age periods. He calls attention
to the fact that " while the mortality in early life has been very
notably diminished, the mortality of persons in middle or
advanced life has been steadily rising for a long period of years."
He adds, "That the sanitary efforts made of late years should
have more distinctly affected the mortality of the young is only
what might be naturally anticipated; for it is against noxious
influences to which the young are more especially sensitive that
the weapons of sanitary reformers have been chiefly directed."
He further suggests that the enhanced mortality at later ages may
in part be due to the indirect influence of sanitation by preserving
from early death a vast number of children of permanently
unsound constitution who so diminish the healthiness and add to