I say the known relations, because
it is evident that there are many unknown relations of which at present we
have had the merest glimpse. For instance, small-pox, while of an ordinary
type, and producing only a comparatively small proportion of deaths to
those attacked, will sometimes suddenly assume an epidemic form, and
spread with great rapidity at a time of year and under the meteorological
conditions when it usually declines in frequency. There are, however, in
this country known relations between the temperature and, I may say,
almost all diseases. As far back as 1847 I began a series of elaborate
investigations on the mortality from scarlet fever at different periods of
the year, and the relations between this disease and the heat, moisture,
and electricity of the air. I then showed that a mean monthly temperature
below 44.6 deg. F. was adverse to the spread of this disease, that the
greatest relative decrease took place when the mean temperature was below
40 deg., and that the greatest number of deaths occurred in the months having
a mean temperature of between 45 deg. and 57 deg. F. Diseases of the lungs,
excluding consumption, are fatal in proportion to the lowness of the
temperature and the presence of excess of moisture and fog.
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