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or origin of this tendency. Generally it confines itself
for a time to some one of these affections, it may be to
small pox in one year, to scarlet fever in another, and
to measles in a third; although not unfrequently
epidemics of two diseases appear in the same community,
and, whilst concurrent in point of time, may not
be of equal intensity. The epidemic in one town may
differ from that in another, and the same epidemic in
different towns varies in some respects, whilst in the
same town the death-rates from the prevailing epidemic,
from unknown causes, fluctuate from week to week.
Of some of these diseases, thus liable to become
epidemic, it may be said that they are always with us.
Year after year they claim their complement of sufferers
; and ever and anon, with something like cyclic
regularity, they operate upon a wider field with startling
capriciousness and with greater malignity.
The small pox epidemic of 1876-78 has been no
exception to the rule. It followed that of 1871-72,
which was preceded by those of 1866-67 and of 1863.
The periods between those years were intervals of comparative
exemption from the disease, and served as a
gathering time for the accumulation of fresh material
to be used up on the recurrence of the next epidemic.
Such susceptible material was the train ready for the
match. It was fuel prepared for ignition. As to the
source of the material upon which epidemics of small
pox depend for their existence, one has not to go far to
find it. Those who had evaded the law in respect to