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comparative atmospheric dryness, and. little rainfall. 2nd. That a rise of mean
temperature above 60°, and a fall below 42°, tend to arrest an existant epidemic.
3rd. In the spring, the spread of measles is promoted by comparative coolness and
dryness of the atmosphere, with excess of rainfall; and in the autumn, by
comparative warmth and dryness of the air, especially when the rainfall is small.
Last year, the spring epidemic was lessened in duration and extent by the
comparatively high temperature of the season, the severity of the epidemic due that
year being reserved until the temperature fell to below 49° in the beginning of
November. December being very mild, the disease extended most in that month.
Scarlet Fever furnished 160 deaths to our Mortuary Table, so that, taking into
account the additional week, it was quite as fatal as in 1867. The number of cases
recorded in the public practice of the parish, however, was smaller, namely, 494
against 641 in 1867. The disease, then, must be regarded as probably more deadly,
though less extended, than it was in 1867. The experience of 12 years led me to
expect that the disease would have abated in the course of the winter of last year,
and that the year 1868 would not have been marked by a continuance of the
epidemic. Scarlatina is essentially an autumnal disease. An analysis of my records
from 1857 to 1868 has led me to the following inferences respecting it:—1st. That
a mean atmospheric temperature about 60°, or between 56° and 60° is that most
favourable to its outbreak as an epidemic. 2nd. That for its free development, it
is necessary that the humidity of the atmosphere shall not exceed 86, or much less
than 74 (saturation = 100). 3rd. That while a higher mean temperature than
60° does not appear to be in itself unfavourable to its spread, a fall of mean
temperature below 53° tends to arrest an epidemic of the disease. 4th. That in all
seasons of the year,—but more decidedly in the winter and spring,—seasons in which
scarlatina is not commonly epidemic—its extension is favoured by a mean
temperature above the average. Applying these results of my experience to the
events of last year, a sufficient explanation is afforded of the continuance of the
epidemic. This epidemic commenced with an outburst of the disease in the autumn
of 1866. It subsided a little during the winter quarter of 1867, but then increased,
as it usually does, month by month, from April until October, upon which month,
the chief violence of the epidemic was expended. A partial subsidence of the disease
then occurred, continuing through January, February, and March, 1868. The
spring months of this year—which, with the winter months, were remarkable for
high temperature—saw, however, the epidemic reviving, and it was as severe, to say
the least of it, in the spring and summer of last year, as in those of 1867. After
September, the susceptibility of the population having been tolerably exhausted, the
epidemic declined. Unless we have a recurrence of the remarkable seasons which
marked 1868, we may expect now to be free, for some time, from any severe epidemic
of this disease.
Hooping Cough prevailed extensively in 1868, especially in June and December.
There is nothing cyclical in the recurrence of epidemics of hooping cough; nor does
it appear to prefer for its extension one season of the year much before another. All