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incidence of fatal Small-Pox on the ages under and over five) can
be attributed to the superior sanitary conditions of what are
termed the " healthy districts," it is necessary to define what is
meant by sanitary conditions, and also to see how the case stands
with regard to other diseases. A supply of pure water, good
drainage, sufficient light and air and cleanliness, these and the like
are usually regarded as the elements which render one area
superior to another in its sanitary condition. Different areas may
be better or worse in these respects or some of them, and this
superiority may largely influence zymotic disease.
But in relation to diseases of this class, there are other
respects in which a great town differs from rural districts. In the
former, a large population is collected in close proximity, whilst
in rural districts the population is scattered over a wide area, and
the people collected in close proximity are comparatively few in
number. The necessary effect of this, as we shall presently show,
is that the cases of zymotic disease would be more numerous in
the former area than in the latter districts, and that, as regards
certain zymotic diseases, a larger proportion of the deaths would
occur under five years of age.
In the outbreak of Small-Pox in London in 1892-3, of the
vaccinated under 10—110 were attacked, none of whom died.
Of the unvaccinated of a similar age, 228 were attacked, of whom
61 died, or 26.7 per cent. Of the vaccinated over 10 years of age,
1,643 were attacked, of whom 39 died, or 2.3 per cent. Whilst of
181 unvaccinated of a similar age who were attacked, 38 died, or
20.9 per cent.
Mr. Marson's observations, made during 32 years in respect
of 19,467 cases at the Small-Pox Hospital, showed a fatality
among the unvaccinated of 36.5 per cent., whilst the highest
death-rate amongst those having vaccination marks, viz., those
having one vaccination cicatrix only, was 12.8 per cent. We
shall have to revert to his figures presently, when considering the