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47
diagram XX. has been prepared to show the relative mortality from these diseases in
the several sanitary districts in London arranged in order of overcrowding. The
decrease of mortality from phthisis as the line travels from the most to the least overcrowded districts
is well marked, and the same, but in less degree, is also seen in the mortality from "all
causes." The mortality from tubercular meningitis manifests this fall in much less degree, and
that from tabes mesenterica still less. The relation of overcrowding to mortality from diarrhoea and
the principal zymotic diseases is not particularly apparent, while the mortality from cancer does not
appear to have any relation whatever to overcrowding. There is therefore suggestion that it will
be found that while associated with overcrowding is a tendency of the population to die from
disease generally, this tendency is especially manifested in the case of phthisis, and is not manifested
in the case of every disease. Probably this difference in behaviour will be found to depend
upon differences in causation and age distribution of particular diseases.
The question whether increase of mortality from other diseases than phthisis in association
with overcrowding especially manifests itself at the same ages as in phthisis may be considered by
reference to diagram XXI. The ages mostly affected in phthisis are 20—25—35and 45—,and it
will be seen that these ages are mostly affected in mortality from "all causes."
In explanation of this diagram (XXI.) it may be stated that the London sanitary districts
have been arranged, with regard to the amount of overcrowding into seven groups as in the preceding
tables. The death-rates obtaining, at each age-period, for the least overcrowded group of
districts—represented in the diagram as a dotted line—have been adopted as a standard of comparison,
the death-rates of the more overcrowded groups being represented by curves. The distance
of each point of these curves above or below the dotted line represents the increase or decrease per
cent. in the death-rates obtaining for the particular group of districts dealt with, above or below
the corresponding death-rates obtaining in the least overcrowded group. Eact square in the
diagram represents ten per cent.
Two curves are shown in the diagram for each group of districts, one (black) relating to
death-rates from "all causes," the other (red) relating to death-rates from "all causes" exclusive
of phthisis. It will be seen that the red curves are very similar to the black, except for the fact
that the increase at ages 25— 35— and 45— is less conspicuous. That this increase would be less
conspicious in the case of all causes excluding phthisis is, of course, apparent from the behaviour of
the figures previously referred to relating to phthisis. The height of the vertical column shows
the excess per cent. of the death-rate at "all ages" in each group of districts over that of the least
overcrowded group.
The Reduction of Prevalence of Diphtheria and Scarlet-fever in the Month of August.
I have, in recent reports and in the present report, referred to the reduction of prevalence
of diphtheria and scarlet-fever in the month of August, and have attributed this to the closure of
schools during that month. I have also expressed the opinion that while the usual exodus from
London in August may in some degree have contributed to this reduction, this hypothesis is insufficient
explanation of the reduction which actually occurs, and which must be attributed to
diminished opportunity for infection at school.
For the purpose of learning to what extent migration from London may have affected the
number of cases notified in August it would be well to take, for the purpose of comparison with
scarlet-fever and diphtheria, some disease the prevalence of which is not affected by
season, and which is never communicated from one person to another. Obviously
no such disease is notified, and hence it is necessary to fall back upon the notified
cases of enteric fever, which for this purpose need not be thought of as a disease communicable
by school attendance. There are now the statistics of seven years available, and although
at the separate ages the numbers notified are not sufficient for conclusions of too precise a
character, the behaviour of enteric fever in August may be profitably compared with that of
diphtheria and scarlet-fever. It will thus be seen that while there is an actual decrease in the
number of cases of diphtheria and scarlet-fever notified in August as compared with the number
notified in July, and which especially affects children at school age, there is no evidence of
similar decrease in the number of notified cases of enteric fever.