View report page

70
Blind alley
employment
of adolescents
in
relation to
phthisis
death-rates.
In a paper by Dr. M. Greenwood, entitled " The Epidemiology of Pulmonary Tuberculosis,"
which appears in the 1919-20 report of the Chief Medical Officer of the Ministry of Health, a question is
raised concerning blind alley employment of adolescents in relation to phthisis death rates, which opens
up some far-reaching considerations.
We have been reminded elsewhere by Dr. Greenwood that " the epidemiologist is concerned
with disease as a mass phenomenon ; his business is not with individuals but with aggregates." This
view has of late years certainly received increasingly wide acceptance. We are beginning to appreciate,
too, the fact that the mass consists of living beings, and is, in fact, an organism whose constituent units
are here to-day and gone to-morrow, now susceptible and anon immunised. Before approaching the
particular case of phthisis in young persons a word may be said concerning some other scjiool diseases.
Thus, as a case in point, the extent to which, in London elementary schools, the " under fives " are
mainly important when measles and whooping cough are in question, while, on the other hand, older
children are also largely implicated when scarlet fever and diphtheria are concerned, and so on, has for
some years past been increasingly realised. But beyond this there is now seen to be urgent need for
study of the varying resistances encountered by epidemics at one and another point of time, or in one or
another part of London, according to the degree of immunity (natural or acquired) of the population
at risk. In the annual report for 1914, a first attempt was made to grapple with the problem, in so far
as the behaviour of scarlet fever in London is concerned. Study was made of the paradoxical phenomenon
that the good elementary schools suffer more from scarlet fever than the poor schools, and in
the annual report for 1918 (p. 46) further examination was made of scarlet fever prevalence in the poorest,
the less poor, and the least poor areas of London. The conclusion was reached that the children under
school age are exposed to a markedly excessive extent, in the poorest areas, to infection by scarlet fever ;
and then later, in virtue of acquirement of immunity, they actually suffer distinctly less at school age
than the children of the next higher social grade, those belonging to the less poor areas; they suffer,
indeed to no appreciably greater extent at the school age than the children in the still higher grade,
those living in the " least poor areas."
In the same report (p. 47) comment was made upon Dr. John Brownlee's study of scarlet fever
incidence in Glasgow in relation to "social conditions." Dr. Brownlee was confronted with a somewhat
similar paradoxical result to that above mentioned, and the bearing of his observations upon the
London problem was accordingly illustrated (loc. cit.). Again, in the annual report for 1918 problems
involving similar considerations relating to tuberculosis, scarlet fever, and influenza were considered.
In last year's report the same theme was again touched upon in regard to measles. Dr. Brownlee
had treated measles as he had before treated scarlet fever and tuberculosis, in the mass, concerning
himself not with individuals but with aggregates ; but he had not attempted in one and the same enterprise
to secure the aid and assistance to be derived from field methods in combination with his statistical
method, and thus it would seem had not fully recognised that "epidemiology is not a mere branch
of mathematics." The song is, as we have been told, of the man as well as of the arms, "the conditions
of human life—both as we now say environmental and eugenic—(are) quite as important to the epidemiologist
as the materies morbi." To lay undue emphasis upon the germ is to miss the full significance of
interplay between germ and environment; and, indeed, to obscure the factors which operate in producing
actual variations in the germ itself. We are in danger of being led away from the straight path
by being induced to step aside to explore the potentialities of strains of measles paramcecia or to chase
will o' the wisp varieties (young adult, middle age, and old age) of tubercle bacilli; and this despite the
fact that the track, narrow and rugged though it be, stretches right ahead, past the landmarks set up
by numbers of epidemiologists who have explored this difficult tract of country.
But, now, to come to the point raised by Dr. M. Greenwood with reference to blind alley employment.
In an analysis of the London borough statistics, which is contained in section X. of his paper,
he has dealt with figures relating to three different age periods (15-25, 25-45, 45-65) in the two sexes.
The attempt to interpret the meaning of the partial correlation coefficients, which are obtained between
Tuberculosis and Overcrowding, Tuberculosis and Other Diseases, and Tuberculosis and Factory Employment—in
males and females belonging to these three age groups—compels him to take arms against a
sea of troubles; inter alia, the paradoxical result emerges that, taking the percentage of population in
a borough living more than two to a room as a rough measure of domestic conditions, "there is a negative
correlation between the index of overcrowding and the death rate from tuberculosis. ' in both males
and females at ages 15-25; in other words "the worse the home conditions (so measured) the lower
the death-rate from phthisis in adolescents." Dr. Greenwood, however, hastens to reassure us by
pointing out that correlation does not necessarily mean "completely isolated covariation, unless we are
certain that the two variables are not correlated with a tertium quid not included in our system of
measurements." And then he goes on to suggest that this unknown correlated factor may possibly
be ready to hand in "blind alley employment." "If," he says, "it were at all generally true that the
adolescents of the worst-housed families—in general these are the families dependent upon casual and
unskilled labour for subsistence—have for a few years more money to spend than their coevals in skilled
industry, then we have introduced a positive correlation between bad housing and certain advantages
of adolescents (more money to spend, less confinement in factories, more out-of-doors life), and these
advantages will in turn be negatively correlated with the death rate from tuberculosis.
And this leads Dr. Greenwood to the hypothesis outlined in the sentence quoted on p. 53 of the
present report. " Spending one's boyhood on the tail of a van, driving a milk cart, or carrying telegrams
may be a very bad preparation for the economic future; but it may be a good thing for one's health as
a boy or girl." Dr. Greenwood, however, continues—" I am alive to the insecureness of this argument,
which will be proved or disproved by further statistical analysis."