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106
of intercourse. Whilst, then, there is ample reason to regard the
decrease in the case of Typhus and Typhoid Fever (and it may,
perhaps, be said of fever generally) as the result of improved
sanitary conditions, since each of these is specially dependent on
conditions which sanitary improvements have removed, there is no
adequate reason to attribute the decrease of Small-Pox in the
nineteenth century to a similar cause, though we fully recognise
that sanitary improvements have had an effect in reducing the
mortality from Small-Pox as from the other diseases to which we
have just been referring. This view is strongly confirmed by
the fact that, in spite of sanitary improvements, the mortality
from Measles and Whooping Cough has remained undiminished,
and the diminution in the mortality from Scarlet Fever has only
been apparent in comparatively recent years.
It has been maintained that the decline in Small-Pox
mortality is largely due to more frequent and systematic attempts
to isolate those suffering from Small-Pox. We think an answer
to this contention is to be found in the fact that, as we
shall presently show, it is only in quite recent years that
there has been any systematic practice of isolating Small-Pox
patients, and that it has been confined even then to a very limited
number of localities. The fact to which we are about to call
attention in greater detail than hitherto, that the decline in the
deaths from Small-Pox is found almost exclusively among those
of tender years, appears also to militate against the contention.
The risk of contagion is not confined to children. Adults also are
subject to it. If a better system of isolation had been a main
cause of the reduced mortality, we should have expected to see it
operate in the case of adults as well as of children. At the same
time we are far from thinking, as will appear when we come to
deal with that subject, that the efforts at isolation which have
characterised recent years have been without a beneficial effect on
Small-Pox mortality.
A study of the age incidence of Small-Pox mortality is very