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The Medical Research Committee s Rep ort on the Epidemiology of Phthisis.
The Medical Research Committee recently issued Part III of a report, by Dr. Brownlee, on an
investigate on into the Epidemiology of Phthisis in Great Britain and Ireland (Special Report Series, No. 46)
Parts I and II were discussed in last year's report, and it was suggested that Dr. Brownlee's three types
of phthisis, namely, the "young adult" the "middle-age" and "the old-age" phthisis were not three
different strains of disease, but the same disease manifested in differing populations, rural and urban.
This view appears to be strongly supported by much of the material contained in this the final part
of Dr. Brownlee's report, to which is attached an appendix giving the mortality rates which have formed
the basis of his painstaking research.
It was pointed out last year as a curious fact that no attempt had been made in the report to gauge
the effect of movement of population upon phthisis mortality at various ages. This omission is still
unsupplied in the third part of Dr. Brownlee's report.
The present instalment, however, contains a discussion of results concerning the bacteriological
analysis of London milk carried out on behalf of the London County Council since 1907. Dr. Brownlee
limits consideration to those counties the deliveries from which have been examined on not less than
500 occasions, and excludes years after 1914. This gives fairly stable figures relating to twelve counties.
The percentage of samples of milk found to be tuberculous varies from 31 in the case of supplies from
Oxfordshire, to 15-6 in that of Derbyshire. Dr. Brownlee finds that if the death-rate of a county be
taken as a criterion of the healthiness of a county, "the correlation between this and the percentage of
the samples of milk found to be infected is '82; in other words the same conditions which determine
unheal thiness in man determine the presence of tuberculosis in animals. Man's want of care of his own
hygiene is therefore reflected not only in his own ill-health but also in the ill-health of his beasts." He
further finds "that the total number of deaths from tubercle under five years of age stands in a yet
higher relationship to the percentage of infected milk samples, the correlation being '90."
The correlation between percentages of infected milk and the "young adult" type of phthisis
was found to be minus .76, and for "middle age" phthisis -50."It would seem, therefore," Dr.
Brownlee states, "that the amount of tuberculosis in children is markedly associated with the amount
in cattle, that the same relation holds with regard to the ' middle age' type of phthisis, but that much
tuberculosis in cattle is negatively correlated with the amount among 'young adults.' .... Apparently
the only reasonable assumption to account for this relation is that some degree of immunity
may be developed during childhood which persists in the 'young adult' age. The larger the number of
children, therefore, exposed to infection in childhood, the smaller the number found to take phthisis
at the early adult ages." The high positive correlation between the death-rate from all causes, and
the infant tuberculosis death-rate, on the one hand, and the negative correlation found between the
" young adult" phthisis and the percentage of tuberculous milk on the other, form as it were the nucleus
of the summary with which Dr. Brownlee's report concludes.