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34
The most important feature perhaps, is not so much the
actual form of the various curves, but that there is a marked
semblance in those for each disease.
The following facts relating to the incidcnce of infectious
disease for this Estate need correlating.
1. That there is a large, recently imported, population
resident here of a peculiar age distribution, being particularly
deficient in representation of the age groups
above 45 or 50.
2. That the population has come largely from congested
Metropolitan areas to a newly erected Estate in which
each house has its garden and the whole area provided
with wide streets and open spaces.
3. That for a period of over 2 years the incidence of the
two diseases Scarlet Fever and Diphtheria, a rate based
on the standardised population, has been much above
normal.
4. That this excess incidcnce is most marked amongst
the population after a period of residence of some 6
months to 2 years.
5. That this exccss incidence did not appear until about
the 5th year of the development of the Estate. Up to
that time the incidence of the diseases was below what
might have been anticipated. About the 5th year,
however, the prevalence of both diseases became
apparent and has remained above normal ever since.
The excess, however, is becoming less -marked, the
incidence of both infections becoming more closely
normal.
As an explanation of these facts the following hypothesis
is suggested: —
The principle of active immunisation of the population
by repeated sub-linimal doses of infection is accepted
and that these immunisation doses are given off largely
by the immune members of the population.
2- That the population in this locality, lacking as it doe.;
its due proportion of adults over 45, who form such a
great proportion of the immunes in an ordinary population,
is thereby deprived to a large extent of its sublethal
immunising doses