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41
three to six are shown to be still susecptible. These results can
be explained by consideration of the individual immunity of
the children of the different ages before receiving their protective
doses. Three doses apparently protect children only who have
some anti-toxin in their system. The older children would be
in this state by reason of having been previously exposed to subliminal
doses of infection and so are immunized by their reaction
to the additional toxin added to their system. Very young
children already possess some immunity ; presumably at the time
of inoculation some anti-toxin still remains in their system and the
combined effect of this and the inoculation is sufficient to render
them Schick-negative. Children of 3 to 6, however, have, at the
time of receiving their inoculations, lost their natural immunity of
babyhood and have not been sufficiently exposed to sub-lethal
doses of infection to develop their further immunity ; three inoculations
in them will not be sufficient to awaken a response of that
degree that will render them Schick-negative. If this is the
explanation of these differences at the different ages, then it seems
very probable that these younger children who are Schick-negative
will, after a period of years, become again susceptible to infection.
Whilst the conclusion might be arrived at that a case of diphtheria
occurring in a house does have some effect on the Schickreaetion
of the remaining occupants, this influence seems slight
compared with the definite effect produced by the immune contacts
as shown by the decreasing percentage of Schick-positives at any age
occurring with an increase in the number of immunes in the family.
This effect of the immunes, who presumably act as healthy carriers,
probably only intermittently, supports the suggestion previously
made, that the outbreak which occurred in this district in the years
1927-28, was due to the fact that the children, on coming to reside
here, lost what immunity they had acquired previous to transerring
to this district.
Scarlet Fever.
424 eases of scarlet fever were notified during the year. This
|s an incidence rate of 4.66 per thousand population or 10.34 per
thousand population under 15 years of age. The corresponding
'jxures for England and Wales were 2.05 and 8.09. The compara-
mc'f'euee rates in the two groups were, therefore, 2.27 and
The distribution was fairly even throughout the year, there
Hl"f! no periods of very heavy incidence.
In the early months of the year, the shortage of hospital
accommodation was again felt, though the difficulties were much
relieved by the admission of cases to other Isolation Hospitals.
The diffulties were not comparable to those in previous years as all