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67
other standards is considered healthy. All members of the population are
exposed to infection by the tubercle bacillus. Not many years ago, most
had been exposed to and had overcome their infection before they had
reached school-leaving age. When an adult succumbs to infection, it
may be that what is overcoming his resistance is a fresh infection, or it
may be that it is the result of a reawakening of his childhood infection
which had for many years remained dormant. Probably most frequently
the latter has happened. There are many sorts of conditions which
might bring about a lessening of the resistance which had been keeping
the infection in check or which may have brought about an increase in
the powers of invasion. An acute illness such as pneumonia or influenza
might be the determining factor. So very often, though, there is no
history of any such condition, and in these it can only be assumed that
the battle has been lost because of some adverse environmental factor
which in one case might be housing, in another nutrition, in yet another
the conditions of work. And yet, if these are the important factors
causing the breakdown of the resistance of so many, it might have been
expected that the high rate of notification would have been paralleled
by a lowering of the standards of the health of the population as indicated
by the ordinary vital statistics. Then, too, in so many instances there is
nothing which suggests that any of these factors have had any bearing on
the onset of the disease. If the development of the disease in the adult is
the result of a fresh infection rather than the result of a reawakening
of an attack in childhood, opportunities for these added infections would
be important. In a number of instances there is a family history of
infection. Sometimes the greatest opportunity of transmission of bacteria
is at the place of work ; but again enquiries bring to light little evidence
of these possibilities. The effects of family contact are likely to have been
greater in childhood and do not in the new cases of last year seem to
have been responsible for many of the adult infections. Some of those
afflicted work in trades which have an unenviable reputation in regard to
the risks of the employees contracting tuberculosis ; but there were not
many so employed. Because so little is known of why each of these
300-odd persons did in fact succumb to the invasion by the tubeicle
bacillus, it is not possible to do anything specifically directed to this
end to prevent the onset in others. The mere fact that the incidence
is diminishing will itself lead to a further reduction as there will be that
many fewer sources of heavy invasion in others. That this position is
being reached is confirmed by the findings of the tests in children which
show that the annual invasion rate of children is very much lower than
it was only some few decades ago, with the result that many children
now reach school-leaving age without having been exposed to, or having
been given an opportunity to overcome, invasion. This suggests that it
is all the more necessary to keep under close observation the adolescent who
might now at the time of many stresses be meeting the tubercle bacillus
for the first time. This is one of the steps that can be taken to try to
control the disease, by detecting in these susceptibles the infection in its
earliest stage when it is both curable and possibly not infective. For
the rest, it would seem that reliance must continue to be placed on
improving the environmental conditions of all members of the population,