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16
another; or that the severity of an epidemic may he influenced
by the measures taken, or the neglect to take measures, to check
the spread of infection. Again, the number of deaths from
Whooping-cough in 1889 was the lowest on record; it is not
surprising to find, therefore, that in the immediately preceding
and succeeding years the disease was fatal above the average.
The large total of 185 deaths from this disease in 1878, moreover,
followed the then minimum return of 84 in the previous year.
Diabkhcea 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.
Again, the significance of a high rate of prevalence of
Enteric Fever varies widely in different circumstances. This
disease may be constantly present in one district as a result of
drainage defects or of a polluted water supply; whilst in another
district its introduction may be wholly accidental, as when it is
due to casual pollution of water, or to a specifically contaminated
milk supply introduced from without.
These and like circumstances must be kept in view if we
would draw sound conclusions from a high or a low rate of
prevalence of zymotic diseases, particularly in relation to the
sanitary condition of a district.
Subject to corrections for local circumstances, for climatic
influences, and for high rates in previous years, the concurrence
of a low zymotic death-rate with a low general death-rate
furnishes just ground for satisfaction. For some years past the
general rate and the zymotic rate had both been below the