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of deaths; the mortality from Group II. cancers among females falls considerably
earlier in life than that in other groups, while the excess of male mortality in Group I.
is relatively higher at middle age. The mortality in Group III., on the other hand,
has a very similar age-distribution in both sexes. See Section A of diagram on p. 19.
(The Group I. female deaths and Group II. male deaths are not shown, as they are
relatively negligible.)
The relationship between Groups I. and II. in regard to age-incidence of cancer
mortality suggests the possibility that the higher mortality from Group II. cancers
among women at the earlier ages may be a determining factor in the extent of the
excess of mortality from Group I. cancers among males; for, if the earlier mortality
among women has proportionately reduced the number of those with a tendency
to cancer, the survivors later in life, even if equally exposed to carcinogenic conditions,
will respond less to them than the male survivors of the same age. This raises the
question of the influence of constitutional predisposition to cancer, or cancer diathesis
; and if this is the governing factor, there would be grounds for qualifying
the hypothesis which naturally suggests itself that some particular male habit is
responsible for the higher mortality for Group I. cancers among men. Unfortunately,
complete data to establish a complementary relationship between the
excess of female Group II. cancers in earlier life and the excess of male Group I.
cancers, among survivors from the same stock, are not available in London, as the
tabulation of deaths according to locality by age and sex was not made before 1911,
or before 1901 in England and Wales. There are, however, certain features of the
cancer mortality of all sites which bear upon this possibility.
mortality in In thereport of the County Medical Officer for 1923, page 38, the London cancer
different mortality-rates are shown for eight successive equidistant three-year periods from
generations 1850-62 to 1920-22 inclusive, per thousand living at different age-periods for both
sexes. In the following table these death-rates are rearranged in such a way as
to enable the mortality in successive periods of life among persons born in the same
years to be readily followed. In column (1) the death-rate among persons who were
born between 1805 and 1817 is shown as they passed through the successive ageperiods,
35-45, 45-55, 55-65, etc., and in column (2) similar figures axe shown in
respect of persons born ten years later, and so on.

It will be noted that there is a clear indication of a maximum mortality having
been attained among females born between 1835 and 1857, so far at any rate as
they can at present be followed, i.e., up to the 65th year of age; and, notwithstanding
the wide variation in the male mortality, the relative incidence at each
age-period is much the same in each column, that is to say, for each generation;
among females the variation in mortality is not so great, but here, also, there is
similar relative movement in each separate age-period.
The female mortality for cancer is shown to be definitely declining in London
among the survivors of those born since about 1851, while among males there is