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13
These zymotic diseases have a special interest for sanitarians,
arising out of the fact that, being admittedly of a more or less
preventable character, the absence or the prevalence of certain
of them is regarded as a test of the sanitary condition of a
district. But, without under-rating the importance of this test,
it must be said that there are limitations to its applicability
necessary to be borne in mind in drawing inferences from mere
numbers. What I mean may be best explained by an
illustration, founded on our own local experiences within
the last few years. Thus, Measles was very prevalent in 1885,
the deaths being considerably above the average: it was the
zymotic disease that gave a special character to the year. In
the year 1886, on the other hand, the deaths from measles were
below the average: but the lowered mortality, regarded as
evidence of the diminished prevalence of the disease, was the
result of its excessive prevalence and fatality in the preceding
year. In saying this, I must not be thought to ignore the fact
that one epidemic of a zymotic disease may be more severe
than another; or that the severity of an epidemic may be
influenced by the measures taken, or the neglect to take any
measures, to check the spread of infection. Again, the rate of
mortality in the Metropolis from Whooping-cough in 1881
was the lowest on record; it is not surprising to find,
therefore, that in 1882 the disease was excessively fatal.
In our own Parish the large total of 185 deaths from this
disease in 1878 followed the minimum return of 34 in the
previous year.
Diarrhœa may be cited as an illustration of quite another
kind. The mortality from this disease, amongst infants, was
excessive in 1878; the mortality in 1879 was much below the
average; but the diminished mortality in 1879 had no relation
to the excessive mortality in 1878. The conditions were
altogether different: the summer of 1879 was cold and wet, and,
as always happens in these circumstances, the mortality from
infantile diarrhoea was low—just as it is always high when the
summer is hot and dry, as in 1878.