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years of age cxpericnce a mortality above the average rate, and so do
men of the age of 5 4 and upwards while boys and men of 5 years of
age and below 54, die at less than the average rate. In the
country, in cities, under tlie same sanitary conditions this
universal law prevails; infants and old people die off more
rapidly; boys and girls as well as men and women in the prime
of life, less rapidly than the average rates imply.
The general rates of mortality, as they are usually given, may
differ therefore in two populations, merely because the ono
contains more of the population under 5 and above 55 than the
other. When the births exceed the deaths, the effect is to
increase the number of children under 5 years of age ; and it is
conceivable that a novice in these inquiries may rush to the
conclusion, that the effect of an excess of births is to increase
the general rate of mortality ; whereas it is found by observation
to have the contrary effect. The mortality of a population with
an excess of births over deaths is lower than the mortality of a
stationary population where the births and deaths are equal.
And the reason on reflection is obvious. The births take place
steadily year by year in a city ; and if they are in excess of the
deaths, they throw into it not only additional children under
5 years of age, but also children and adults above that age;
and hence there is less than the due proportion of old people in
the whole population; hence also the mortality appears below
what it would be in the same population, under the same
sanitary conditions, if the births and deaths were equal. In all
England the births are to the deaths as 3 to 2; and this has the
effect of reducing the rate of mortality to 22 in 1000. By the
English Life Table, in which the people of different ages are
distributed as they would be if the births and deaths were
constantly equal, the correct rate is found to be 24 in 1000.
In Liverpool when the rate of mortality was 34, the corrected
rate was 39 ; in the same year the rate for London was 24, the
corrected rate 27.
Immigration has the effect of reducing the general rate of
mortality; as it swells the excess of persons at ages of low
mortality.
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