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1918 in both diseases, although the decline will be seen to be greater for measles than
for whooping-cough.
The figures upon which the diagram is based have been approximately
corrected for the decrease in births caused by the war, but for reasons referred
to later the correction is only partial. In the past five or six years arrangements
have been made in most metropolitan boroughs for assistance in the
home nursing of children attacked by measles or whooping-cough, and the
arrangements made for admission of a proportion of the cases to hospitals of the
Metropolitan Asylums Board have also been more extensively made use of. The
segregation of a large number of cases in MA.B. hospitals, and the attendance on
other cases of trained nurses, must have tended both to reduce the mortality in the
cases dealt with and to diminish the spread of infection. It may be added that in
1916-18 measles, but not whooping-cough, was made compulsorily notifiable
throughout London.
The spread of measles and whooping cough is very largely governed by the
density of susceptible children. On this subject, so far as measles is concerned, reference
may be made to the discussion in the Annual Report for 1919 (Vol, III., p. 88).
The fluctuations in birth-rate during and after the war caused corresponding variations
in the density of the child population of London, and in preparing the diagram
the deaths after 1914 have been increased or decreased proportionately to allow
as far as practicable for the effect of the fluctuating births. It will, however, be
understood that the correction thus made does not fully eliminate the effect of the
fluctuations. For example, if in a row of 100 houses it be assumed that infection
spreads from a house to the next house but not to the next but one, then, if there
is a susceptible child in every house, one case will lead to all houses being invaded, but
if there is a susceptible child in every other house no spread of infection would occur.
In the latter case, while the susceptible population is only halved, the spread is reduced
to nil. The increase in the number of births from 70,976 in 1918 to 120, 529 in 1920
is sufficiently great to have an effect on the range of infection, and for this factor
no correction can practically be made. The excess of births during 1920 and the
remarkably low prevalence of measles last year result in there being at the present
time a large number of susceptible children, and it is to this circumstance that the
prolonged prevalence at the present time is due. The actual figures of mortality
for the first quarter of 1924 were not available in time for inclusion in the diagram
but the total deaths will be not far short of the total for the corresponding quarter
of 1915.
With regard to the diagram showing whooping-cough prevalence, the chief
point to be noted is the great weight of attack upon the year 1918, following upon
a year of low prevalence. The whooping-cough occurred shortly before the JuneJuly
prevalence of influenza and some months before the great October-November
influenza epidemic. There may have been occasional confusion between the two
diseases, especially in the middle of the year. There is, it will be seen from the
diagram no corresponding feature in measles. There appears to be some relationship
between the type of winter weather and the incidence of whooping-cough, the effect
of a prolonged period of cold weather in the winter being in some years to decrease
the immediate incidence of whooping-cough, and in all years to increase the
prevalence in the following winter. Since 1899 there have been several instances
of prolonged cold weather in the autumn and winter quarters; thus, in the winter
of 1890-91 the weekly temperature was below freezing point for six consecutive
weeks. In 1892-3, just at the turn of the year, the average temperature was below
freezing point for two weeks, and again in 1895 in the fifth to seventh weeks, the
average temperature in the sixth week of this year being as low as 22.4° Fahr.
Thereafter there were no similar periods of continued low temperature until 1917,
in the fourth to sixth weeks of which year the average was below freezing-point.