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11
changeable weather of winter and spring; while
the period for the greatest activity of tabes and
scrofula, the other members of the tubercular class,
is summer and autumn. And so also of zymotic
diseases, there is the greatest difference in their
manifestations of power at different seasons: scarlatina,
for example, is most virulent in autumn, and
least so in winter. The same is the case with
continued fever, and with measles, and with the
diarrhœa of adults. But the diarrhœa of infants
is most fatal in summer—so much so, that of a
total number of 80 deaths in the year, 65 occur in
the summer quarter, and these mostly in the hot
months of August and September. On the other
hand, there are some forms of zymotic disease
which are most virulent in the colder months of
the year. This is so with small-pox, which is by
far more fatal in the mild weather of spring and
early summer than at any other time; and so also
of whooping-cough, croup, and erysipelas, which
arc especially the zymotics of winter.
The explanation of this is not altogether clear;
indeed, there is much to be done in the classification
of these facts before any notion can be formed
of the laws which govern the manifestations of
these diseases. That, however, which we do perceive
is, that whensoever the start is given to any one of
them, it is more likely to run into an epidemic,