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The greatest number of deaths in London and Aberdeen occurred in the first two years of life
when, as the Aberdeen figures showed, the fatality is greatest. Children at this age are not directly
exposed to infection at school, but the question needs to be considered what proportion of children
at this age owe their infection to older children who are themselves infected in school. Dr. Newman,
writing of Finsbury cases and deaths in 1905, states " In 1905 there were 75 cases and 14 deaths
in the second year of age. Of the total of 89 we have positive findings in 77 with regard to the
source of infection. It appears from these investigations that 55 of the 77 (or 71.4 per cent.) contracted
their infection at home from elder children in the same families (10 from children in their third year,
18 from children in their fourth year and 27 from children in their fifth year). Most of these infecting
children attended infant school."
The annual report of Dr. William Butler, Medical Officer of Health of Willesden, gives information
of much value as to the source of infection of 1,636 cases of measles occurring in that urban
district and which became known to him during the year 1905. Notification of cases of measles is
not obligatory in Willesden, but information as to the occurrence of this disease in school-attending
children is obtained from teachers in the schools, and inquiries are made in the homes by lady health
visitors. Of these 1,636 cases, 919 were primary attacks in families, the children attending the infant
school, where they had been exposed to infection. These 919 cases gave rise to 308 other cases, of
which 36 were under one year of age and 219 were from one to five years of age. Again, 66 primary
cases in families occurred among children attending the boys', girls', or mixed departments, where they
had been exposed to infection, and these gave rise to 14 secondary cases, of which two were under one
year of age and nine were from one to five years of age. There were, in addition, 87 primary cases
attending school, but not known to have been infected in school (from which 29 secondary cases
arose, of which one was under one year of age and 19 from one to five years of age), and 175 primary
cases in which the infected person was not attending any school. The 175 cases gave rise to 38 secondary
cases, 12 of which were under one year and 21 of which were from one to five years of age. Thus
985 children infected in school, in their turn infected 322 in the homes, 38 of whom were under one year
of age and 228 of whom were from one to five years of age.
The age distribution of the known Willesden cases is different from that of Aberdeen and,
therefore, probably different from that which would have been obtained by a system of obligatory
notification, for in Willesden only 46 per cent. of the cases are under five years of age while 58 per
cent. of the Aberdeen cases are of this age, and again, only 4.4 per cent. of the Willesden cases are
under one year of age, while 7.5 per cent. of the Aberdeen cases are of this age. The Willesden cases,
however, suffice to show the total primary and secondary cases which were known to be associated
with attendance at elementary schools in that district.
In the main, measles manifests increase of mortality in London in alternate years. The
intervals between successive prevalences correspond more closely to 18 months, or less, than to two
years, and these prevalences are, no doubt, associated with the accumulation of susceptible children
in the intervals, the incidence of mortality from measles being much greater on children in the second
year of life than on children of any other year of age. As will be seen on reference to diagram VII.,
there is a tendency for the occurrence of the maxima to alternate between the winter and the summer
and thus two maxima are produced when a composite seasonal curve is prepared which is based upon
the measles mortality of a series of years.
It is interesting to observe that if composite seasonal curves are prepared showing measles
mortality in successive groups of years, the summer maximum is in the later groups becoming greater
and is occurring earlier in the year. The intervals between successive prevalences is thus becoming
shorter and notwithstanding decline of measles mortality in 1891-1900 and 1901-5 as compared with
1881-90, and the continued fall in the birth-rate, deaths of children in the first two years of_ life constitute
in the last two periods a greater proportion of the total deaths from measles than in
1881-90. Indeed, the following table shows, with the exception of the period 1881-90, when the fall
in the birth-rate began, with its inevitable effect on the number of children in the early years of life,
the relative proportion of children dying from measles in the first and second year of life has increased
since 1851-60.

This shifting of measles mortality on to the first two years of life is, no doubt, the result of increased
aggregation of population in London and increased opportunity of infection, the result of aggregation
of children in schools ; for measles, in greater degree than scarlet-fever or diphtheria, spreads in the home
to the children of pre-school age if the disease be introducsd into the home by a school-attending child.
Hence, it is not matter for surprise that examination of diagram VII. shows that measles mortality frequently
declined after the Christmas holiday. Variations in the age-incidence of measles mortality
in London is further discussed in Appendix I.