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29
An examination of the statistics relating to diphtheria shows that the case mortality of
diphtheria is subject to similar seasonal variations. Tables for this purpose have been prepared in the
same manner as those relating to scarlatina, namely, to the notifications of each month are applied the
deaths registered in a month beginning a week later. The following figures are in this manner obtained.
The rates of 1891-94 are obviously more reliable, inasmuch as they are calculated on larger figures.

It will be seen from these tables that the seasonal variations in the case mortality of diphtheria,
although proportionately less than the seasonal variations shown in the case mortality of scarlet fever,
are yet of a character sufficiently marked to suggest some definite cause or causes for their occurrence.
With a view to ascertaining whether the age and sex distribution of the cases notified is
responsible in any degree for the differences exhibited by the figures, I have selected the three months
of 31 arch, May and October, in the year 1894, for comparison in this respect. The following table
shows the actual age and sex distribution of the cases notified in each of these three months with the
deaths in each instance, which would have occurred had the case mortality for each age and sex been
the same in each of the three months as for the whole year 1894.