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In last year's report reference was made to the fact that, among other problems of reconstruction, The new
there had been a tendency of late to examine anew the foundations upon which the practice of preventive epidemiology.
medicine is built, with the result that the whole question of nomenclature had come under critical review,
and that it was now recognised that the diagnosis of an epidemic involved something more than does the
diagnosis of disease in individual instances. Attention has for years past been concentrated Upon the
"materies-morbi" ; it is now agreed that the "conditions of human life, both as we now say environmental
and eugenic," also merit the attention of the epidemiologist. Some ways of viewing the questions
at issue, as they present themselves when regarded from different angles, are exhibited, and may be
studied, in recent articles and letters which have appeared in the " British Medical Journal" ("The New
Epidemiology," March 19th, 1921 ; " The Science of Etiology," April 9th, 1921 ; and correspondence
arising in connection therewith). There seems to be general agreement that " an exact knowledge of
causes is one of the most difficult and elusive of all quests in medicine." But it is now becoming recognised
that there is scope for all, for the field men as well as for the laboratory men. We have been told that,
for Sydenham, " personal knowledge of the facts was the prerequisite of epidemiological theory." Just
as personal knowledge of the facts must also be a prerequisite for the theory of germs, visible and ultravisible.
The dispute which has arisen between the new epidemiologists and a few laboratory and clinical
workers " is a very pretty quarrel as it stands ; we should only spoil it by trying to explain it." It is
at least clear, however, that the champion of the new epidemiology, Dr. Greenwood, has maintained
his position in the face of the criticisms " from the pen of a distinguished bacteriologist written ... in
consultation with a no less distinguished clinician " ; and his success must be attributed, like that of
his legendary prototype who fought with the giants of old, " to his four marvellous possessions—an
invisible coat, a cap of wisdom, shoes of swiftness, and a resistless sword."
There comes plainly to light, however, from this correspondence, the disconcerting discovery
that-the new epidemiology stands under some suspicion of being content merely with "postulating
causes " without systematically testing its hypotheses " by the stern reality of experience in its widest
sense." Under such a suspicion no epidemiologist can rest undisturbed ; for epidemiology, old or new,
has always been inevitably dependent upon close observation of the behaviour of epidemics. Conceptual
reason has its uses, but those who study epidemics' must keep their feet on solid ground. As
William James says, " Our ideas and concepts and scientific theories pass for true only so far as
they harmoniously lead back to the world of sense."
And yet we must not forget that a belief in human reason does not, or should not, merely mean
a belief in our own reason; it means a belief in human reason as a whole. The bacteriologist and
clinician are warned by the " British Medical Journal" that they certainly seem to imply that they
" limit the term research to experiments in bacteriological and chemical laboratories." And the new
epidemiologist must, of course, on his part, pay the closest attention to the teachings of bacteriology.
All mechanisms must, in the long run, square with the facts, for, as it has been aptly said, " So long
as a suggested mechanism accounts only for the phenomena which gave rise to it, it can only claim to
be a possible solution of the riddle. It is when a mechanism is found also to accountfor other phenomena,
widely different from those that suggested it, that it first becomes entitled to claim to be regarded as
the actual solution." This clearly is the corner stone of epidemiology, and of bacteriology and clinical
medicine too, upon which they must base their right to rank among the sciences.
A.—Vitat. Statistics.
The population of London County at the census of 3rd April, 1911, was 4,521,685, and it was Population.
estimated by the Registrar-General to have fallen to 4,518,021 in the middle of 1914. Returns furnished
to the Registrar-General of data obtained under food rationing schemes have enabled him to estimate
the civil population for 1920 to be 4,531,971. The estimated number of men still on service is about
21,000. From these figures it would be expected that the census to be taken this year should show an
increase in the population belonging to London of over 31,000 since the census of 1911.
The births since 1914 exceed the deaths in this period by about 180,000; and assuming the
number of Londoners who fell during the war to have been about 80,000 the increase in London population,
apart from migration, would be about 100,000. Returns made in respect of rate leakages in
London show that while in the financial year 1913-14 there were about 28,000 empty houses in the
county, the number had fallen to 21,294 in 1918-19, and in 1919-20 more than half these houses had
become occupied. Most of these houses would be in the better class districts, and the margin of empties
in smaller houses must have reached an irreducible minimum. Since the conditions are the same
in the rest of Greater London practically the whole of the natural increase since 1914 must now be housed
within the county.
Marriages.
The marriages registered in London during 1920 numbered 49,185, as compared with 50,222 in
1919, the approximate marriage rate being 22 per thousand of estimated population for both years.
It will be seen from the diagram facing page 5 that the marriage-rate of 1920, although not reaching
the exceptional level of 1915 is nevertheless well above that of the years immediately preceding the
great war. The average number of marriages annually during the six years 1909—1914 was 40,765,
as compared with 47,313 in the last six years.
Births.
The births in London during 1920 numbered 120,529, the corresponding figure for 1919 being
82,525, and for the pre-war period 1911—1914, 110,951. The actual number of births was greater
than in any year since 1908.
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