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19
In the Annual Report for 1920 reference was made to a paper by L. I. Dublin Environment
and C. W. Baker on Tuberculosis Mortality and Racial Susceptibility. Dr. Dublin tubercu.ty
(who is statistician to the Metropolitan Life Insurance Co. of New York) a few
months ago delivered an interesting address on the " Causes of the Decline of
Tuberculosis." He analysed the evidence forthcoming in support of two distinct
ways of looking at the question under consideration, as follows:—
"The first emphasises the importance of the environmental factors in the
causation of tuberculosis and credits the improvement in the death-rate to those
human activities which have centred around the amelioration of the environment
of the great body of people. The second emphasises the importance of stock and
ascribes the decline to secular changes in the germ plasm of nations and of races,
which follow from the full interplay of natural forces rather than from the conscious
interference of man with nature. The data are so numerous and often so clear.cut
that we should have little or no difficulty in determining which of the hypotheses
we have outlined has the better of the argument.
"Geographical Variation in the Tuberculosis Death-Rate.—The first fact is the
great variation in the amount of fatal tuberculosis in various parts of the United
States. Tuberculosis is pre-eminently an urban disease. It is, of course, present
in rural sections of the country, but to a lesser degree . . . Here, then, are our first
facts. Let us try to square them with the two explanations. The environmentalists
approach this phenomenon of extreme variation in the tuberculosis death-rate
without hesitation. They are familiar with it and have, in fact, based much of
their assurance on it. Those who live in the country—the rural population—
they say, might be expected to have a lower rate. They are engaged in more
healthful occupations ; they live in less congested places ; they live more normal,
happier lives; they enjoy a larger and better supply of food and lead altogether
a more wholesome existence. Those who live in cities, on the other hand, are in
more congested quarters and, therefore, more subject to infection ; they are often
engaged in industries which are more distinctly hazardous to general health ; they
are on the whole poorer and less well supplied with good food and fresh air. Life
is harder and more hazardous in the cities and there are more chances for the natural
resistance of the individual to break down.
"The geneticists or the constitutionalists, on the other hand, have not made
much of the facts of geographical variation, and it is difficult to summarise the views
that they hold in explanation of these facts. Obviously, it would be necessary
for them to assume that the differences in the death.rates represent differences
in the innate stocks, with various degrees of immunity or resistance to tuberculosis
in the several parts of the country. They are compelled to posit a hierarchy of
constitutional vigors corresponding to the low rates and the high rates. They must
assume that the population in the rural areas is constitutionally better selected than
that in the cities ; that the population living in Nebraska, for example, is a fitter
population than that living in Delaware or in New York ; that the people living
in Akron are innately more vigorous than those living in Providence. It must be
clear, I think, that on the score of variation of the death-rate, the environmentalists
have very much the better of the argument on the first count.
"Sex and Age Variations.—But, of course, geographical variation is only one
and the first test. Another fact about the tuberculosis death-rate which is almost
universal is the marked difference in the death-rate in the two sexes. Tuberculosis
mortality is much higher among males than among females . . . How do the two
explanations square with this fact ? The environmentalists would say that the
boys and girls in our country are pretty much the same as to exposure and as to
resistance. The higher rate for females at the ages of adolescence and early adult
life they would explain on the assumption that at this period, developmental changes
in the organism involve greater hazards than among males. . . .
"On the other hand, those who sponsor the theory of the constitutional factor