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18
become ill. Later again it was appreciated that even when a person,
proved to be susceptible, was exposed to a virulent organism, he even
then did not necessarily succumb; there was some other factor which
could operate in certain conditions and which apparently could cause a
person who had resisted infection many times previously to succumb on
some occasion. This change could cause the Superintendent of an isolation
hospital who had been in and out of the wards in which there were
infectious patients day after day for years, on one day to fall ill with
scarlet fever. It is something of this sort which probably accounted for
the not really explained increase in the incidence of tuberculosis during the
war years. It may be that just as some succumb to any infections going,
others subjected to the same exposures remain free. In the same way,
it may be that the population can be divided into those likely to and the
other group not likely to contract cancer. In the group liable to contract
it, it can be assumed that something else is needed to trigger-off the
condition—that without this inherent susceptibility, perhaps cancer does
not develop, but the triggering is needed, and this will decide not only
that cancer will develop but also where it will occur. That there is something
in the general make-up of an individual which might affect the
liability to develop cancer would seem to be the view of Ogilvie who
claimed that the happy man never got cancer. That there is something in
the physical make-up is suggested by the correlation of the incidence of
cancer of the stomach and the 'A' blood group. Some have suggested a
familial predisposition, because of the occurrence of an unusual number
of cases in a family. These however, are probably coincidental occurrences.
An environmental factor was suggested when it was seen that the incidence
might be heavier than average amongst those living near some rivers. The
only instance of diet having any relationship would seem to be the high
incidence of stomach cancer amongst those living in North Wales; any
association there could be more the result of the irritant effect of certain
foodstuffs on the stomach wall than of any general effect of diet. In these
cases it would perhaps be only those who have their predisposition in
whom the disease would develop. Many a woman who has developed
cancer of the breast has attributed its origin to a blow. Usually this
explanation has been brushed-off with a comment that it was the blow
which led to the recognition of the existence of the growth and not to its
origin. That explanation though would not account for instances of
malignant growths developing following an injury to the nose or a
fracture of a bone. Examples of chronic irritation which have led to
cancer are those of the old clay pipe smoker, the chewer of betel nut and
the chimney sweep. Cancer occurring in those working in certain industries
might be due to a specific irritant such as chrome or spindle-oil
The man with a gastric ulcer is more prone than the man free from it to
develop cancer of the stomach. Some irritants then are non-specific;
others are more specific substances. Those liable to be followed by
cancer are classed as carcinogens.
Cancer and Education of the Public. There are different varieties
of malignant growth. Some are so slow growing as to be almost innocent;
about some nothing can be done because their spread is so rapid or because
of the inherent malignancy of the type. There is a wide range in the rate