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Table III. shows that in England and Wales there has been, relatively to the diphtheria mortality
at all ages, a considerably increased incidence of the disease upon the population at ages above 3 and
under 10, in the period 1871-80 as compared with that in the period 1861-70. The table also shows
that this is true generally for each of the groups of populations, except that in the "urban" (excluding
London) there is practically no increase at 3-4.* The increased incidence upon children in this
population at the age of 4-5 is, however, strongly marked.
It has been possible in the cases of England and Wales and of London to give the figures for a
further decade 1881-90. It will be seen that the increase, absolute and relative, of diphtheria mortality,
in the former population has been maintained in the period 1881-90 as compared with 1871-80, at each
age-period from 3-10 years. In the latter (London) there has been a trifling relative fall at ages 5-10
years, but at ages 3-5 years the increase has been very marked, as in the case of England and Wales.
The question whether this change in the age incidence of diphtheria may be due to any alteration
in nomenclature deserves to be considered. The following table relating to croup and diphtheria
in London has been prepared for this purpose—
This table (IV.) shows that when croup and diphtheria are taken together, in the periods 1871-80
and 1881-90 as compared with 1861-70, there has been a relative increase of diphtheria in the ages 3-10
years. Moreover, the trifling relative fall at ages 5-10 years in diphtheria mortality in 1881-90, as
compared with 1871-80, is not found to have occurred when croup and diphtheria are taken together. It
is indeed interesting to observe how closely the mortality from croup follows that of diphtheria, leading
to the conclusion that under the name of "croup" much diphtheria is still registered.†
* It is a well recognised fact that the figures given in the census volumes as to persons living at ages under
5 are unreliable and can only be considered as approximations. An examination of the age distribution of the
population of " urban " (excluding London) shows that the proportion of children aged 3-4 to those aged 0-5 in
the period 1861-70 was 18 96 per cent., and in the period 1871-80 19 36 per cent. Had the former percentage been
maintained in the latter period the figures shown in Table III. for " urban " (excluding London) age 3-4 would
have been 499 instead of 489.
f The relative mortality in any district or groups of districts at various times is best ascertained by
combining diphtheria and croup. This is the practice of the Medical Department of the Local Government Board,
and the Registrar-General, writing in 1889, says: "It is probable that some part of the increase under diphtheria
may be due to diminution under the heading croup, which in accordance with the classification of the College of
Physicians, is separated from diphtheria, and placed with the respiratory diseases. But this can only be a partial
explanation of the rise which was far greater than the falling off under croup." (Annual Summary of Causes of
Death in London, 1889). The deaths registered as being due to diphtheria and to croup do not, however, include
the whole of the deaths due to diphtheria. Thus it was the experience of the Medical Department of the Local
Government Board in 1889 that deaths, presumably due to diphtheria, had been found after local inquiry to have
been attributed to mumps, croup, tracheitis, laryngitis, measles, scarlatina, tonsillitis, ulcerated throat. Inclusion
of deaths due to these causes would, however, produce—inasmuch as they are not by any means all diphtheria—
a dilution or obscuration of the facts respecting diphtheria mortality.