View report page

9
increased density of population naturally suggests itself, children of this age being less easily protected
from exposure to infection than before. Explanation is however still wanted for the relatively
increased incidence on the ages 3-, 4- and 5-. There is undoubtedly suggestion of some common cause
operating at these ages to produce parallel results with regard to the three diseases—measles, whooping
cough and diphtheria. In the case of diphtheria it will be observed that the increase also affects
the age 10-, but that this is not manifest in measles or whooping cough. The number of deaths from
those diseases at this age is, however, very small.
It is difficult to explain the fact that scarlet fever has not been affected in a similar manner at
these ages. Transference from diphtheria to scarlet fever, if proportionate at each age, would have the
effect of increasing the incidence of scarlet fever mortality on the earliest years of life, and would in
this way tend to obscure the result of increased incidence on ages 3-, 4— and 5- due to other cause, such
as that which has produced this increase in the other diseases. Whether it will be subsequently found
that the increasing feebleness of the scarlet fever virus, shown by the decrease in mortality, is operating
to prevent this cause from being manifested, the experience of future years alone can prove.
Apart from some such explanation as the above, it would be necessary to assume that the cause which
produced these changes in the other diseases was for some reason inoperative in the case of scarlet
fever.
The fact, however, remains as already pointed out, that irrespective of all questions of change in
nomenclature, there is increased incidence of mortality on the ages 3-, 4- and 5-, when the figures
relating to diphtheria, croup and scarlet fever are combined. The hypothesis that this increase is caused
by the aggregation of children at school is, I believe, the one most likely to be correct, and it does not
appear to me that the behaviour of the other diseases referred to militates against this hypothesis.
In connection with the hypothesis that increased attendance at school has led to relatively increased
incidence of diphtheria mortality on the school ages, the particular period at which this increased
incidence is first manifested becomes important. The Compulsory Education Act was passed in 1870,
and it will be seen from the following table (XI.) that in London there was marked increase
in the early years of the decade 1871-80, and that this increase has been practically continued since.
The table shows the diphtheria death rate at all ages, at the age period 3-15 years,* and the comparative
death rate of this age period, the death rate at all ages being taken as 100.

* The populations for the age period 3-15 have been calculated on the assumption that the rates of increase in intercensal
years have been constant. More precise figures would have been obtained by interpolating the populations by the
method of finite differences. This has been done for the years 1868-69-70 and 1872-3-4, also for the years 1880 and 1882, these
being the years in which the differences in the results obtained by the two methods of calculation would be greatest. The rates
for these years, calculated on either series of populations, are, however, practically identical.
[2]