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the valleys' of low prevalences was due to school influence. Again, Dr. Brownlee, in his paper of February,
1919, gave a diagram (X), exhibiting the average seasonal distribution of measles in London for three
periods, 1840-56, 1857-74, and 1875-93. In commenting upon this (loc. cit., p. 119), I suggested
that the fact that the summer maximum, in London in recent years, had moved forward from June
to May or even April, might be in part attributable to preventive measures. There is undoubtedly
something to be said for this. It is true it has been pointed out that the measles epidemics of recent
years have recurred at intervals falling only a little "short of a period of two years, and this fact by itself
might perhaps tend to favour the antedating of the summer maximum commented upon. But
the complete explanation of the recent maintenance of a regular series of biennial explosions is still to
be sought, and I am inclined to think that the tendency to stereotype the date of attainment of the
summer maximum, in London, in April (or in some years even as early as March) may be in part attributable
to the attempt made to prevent spread of measles in the schools. It is difficult in this critical age
to obtain even a hearing for the view that preventive measures can accomplish very much in the case of
measles. Yet the following suggestions are, perhaps, deserving of consideration.
Those who have studied closely for some years past the behaviour of measles in London must have
been puzzled by the, at first sight, seemingly strange phenomenon observable, at any rate since 1907,
that following upon the spread of measles in the school population, which commences after the summer
holiday, and extends across the shorter Christmas holiday into January, February and March, the
succeeding decline almost always starts many weeks in front of the closing of schools for the July-August
holiday. This decline must, presumably, represent in part the result of growing exhaustion of susceptibles,
and in part that of increasing exercise of preventive measures as the epidemic gradually extends.
It needs in fact to be recognised that school influence operates partly in the direction of favouring and
partly in that of preventing prevalence of measles. The former effect is generally admitted, the latter
has been especially insisted upon by Dr. C. J. Thomas (see Roy. Soc. Med., Epidem. Sect., vol. VI.,
p. 145). Where school attendance is adequately enforced, Dr. Thomas points out that the susceptible
material is swept up as it were into little heaps, leaving spaces between, over which the flame has some
difficulty in passing, " instead of having one sheet of flame of equal intensity, there were progressive
series of definite explosions. Heap after heap exploded, but there was a certain amount of resistance
offered in passing from heap to heap, and occasionally a heap missed fire altogether." This resistance,
plus the control over spread of measles in the schools, exercised by virtue of knowledge of what is going
on in the schools themselves, must, it would appear, help to determine the decline in measles prevalence,
and may account for the fact that in recent years this has almost always antedated by some weeks
the time of commencement of the summer holidays.
Admission
Examinations,
Defective children.
The total number of examinations conducted under the special Acts during the year was 5,494
as compared with 4,264 for 1918. Of these 1,319 (677 boys and 642 girls) were deemed suitable to attend
elementary schools, 81 (37 boys and 44 girls) a blind school, 338 (142 boys and 196 girls) schools for
myopes, 1,184 (638 boys and 546 girls) P.D. schools, 1,604 (875 boys and 729 girls) M.D. Schools, 12 (7
boys and 5 girls) open-air schools, 80 (32 boys and 48 girls) hard of hearing schools, 124 (61 boys and
63 girls) deaf schools; 24 (9 boys and 15 girls) epileptic colonies, 601 (297 boys and 204 girls) were
invalided from school attendance, 73 (41 boys and 32 girls) were imbecile, 13 (9 boys and 4 girls) feebleminded,
23 (10 boys and 13 girls) idiot, 3 (1 boy and 2 girls) M.D. and P.D., 1 (boy) blind and deaf,
and 14 (9 bovs and 5 girls) were deaf and defective.

Age of P.D.
children at
time of onset
of morbid
conditions.
Dr. Shrubsall and Dr. Hogarth have made an analysis of the medical record cards relating to
the children in the P.D. schools to show the age of the children at the time of the first symptoms of
the morbid condition which has led to their being certified as physically defective.