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malady is now, I think, generally admitted. Dr. Thomson has alluded
to cancer of the lip in persons who have been in the habit of smoking
a short and dirty clay pipe in support of this contention. In the case
of primary malignant disease of the gall bladder, where the liver for the
time being has escaped, gall stones are present in probably 90 per cent.
of the cases. This is not only true of man, but also of the lower
animals. I have seen the association of the two in horses. There was
on the part of many members of the medical profession, years ago, the
tendency to discount the association of injury and cancer, but the
opinion is growing that in many instances there is a causal relation
between the two events. That chimney sweeps cancer is a consequence
of the irritating action of the soot is now widely accepted, and
in addition to the mode of cellular in vasion mentioned by Dr. Thomson,
there is also the probability that the presence of arsenic in the soot is
not without a harmful influence. The malady is occasionally met with
in the hands of gardeners who are in the habit of sprinkling soot upon
the soil around plants. Dr. Thomson, in support of the irritation as
causative of cancer, has drawn attention to the presence of malignant
disease in the alimentary canal, and there is certainly a sufficiently large
number of cases to support the view that cancer has developed on the
site of an old or of an unhealed ulcer. Fortunately, the occurrence is
less frequent than might be expected.
That the disease may be due to a germ is more than likely. The
parasitic theory has many adherents, but although microscopic bodies
have been described and photographed, no one and definite object has
yet been found in all cases. Much light will be thrown on this subject
by further research and by the study of the growth of embryonic and
other tissues apart from the living body. It is an interesting fact that
of all the various kinds of tissue which can thus be grown, watched and
experimented upon in the laboratory, one of the most rapidly-growing
tissues is that taken from a cancerous tumour.
As regards the infeotivity of cancer, I have cases where there was
a strong suggestion of such having taken place. I discussed the subject
with Sir William Macewen, who was convinced of the probability of
cancer of the rectum having been conveyed by an enema tube which had
previously been used by a patient suffering from the disease and who
had apparently, by this means, passed it on to other persons.
It is gruesome to think that there is the possibility of cancer germs
lurking in houses. Without going into details I will simply give a few