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18
Those in certain occupations are exposed to increased risks of contracting
cancer of the lung. Certain coal mines have high levels of radioactivity.
Those exposed to lubricating oils and to metallic dusts and
fumes and those working with tars and oils obtained by the destructive
distillation of coal are more at risk. But all these comprise small numbers,
and most people are not exposed in this way. While important to the
individual, then, they are not of concern to the general body of the
population.
For some years now in other countries and in this, attention has
been focussed on smoking as a factor. Many statistical enquiries have
been carried out and much research into the recognition of carcinogens
and the presence of carcinogens in various substances. In 1954 a Ministry
of Health report indicated that: " It must be recorded as established that
there is a relationship between smoking and cancer of the lung; but though
there is a strong presumption that the relationship is causal, it is not a
simple one." There is the complication of the effect of atmospheric
pollution. There is also the higher incidence amongst those engaged in
certain occupations. Then, too, there is the well-known fact that some
of those who suffer from cancer of the lung have never smoked, while
many heavy smokers have lived to great ages without suffering from this
complaint. Of the enquiries in this country, perhaps the best known is
that of Professor Bradford Hill and Dr. Doll based on the information
of the smoking habits of members of the medical profession and correlated
with the findings of the causes of their deaths. This enquiry
showed there was a higher mortality in smokers than in non-smokers, a
higher mortality in heavy smokers than in light smokers, a higher mortality
in cigarette smokers than in pipe smokers, and a higher mortality in those
who continued smoking than in those who gave it up. Two series of
figures might run parallel, but without there necessarily being any relationship
between them, either directly or indirectly. On the other hand,
while there may be no direct relationship, there can be some common
cause. But when the findings are broken down to the detail that they
were in this report and still retain their correlation, they can only point
to smoking being a factor. As the report of the Medical Research Council
issued last year says: " In the opinion of the Council the most reasonable
interpretation of this evidence is that the relationship is one of direct
cause and effect." Those who, while not disputing the correlation of the
figures, are not prepared to accept that that is the position, suggest the
explanation might be either that both smoking and cancer of the lung
are due to some common factor, or perhaps that the tendency to cancer
of the lung might be responsible for the individual smoking. But this is
not merely a matter of statistics. Recent reports are that there are at
least five chemical substances in tobacco smoke known to be capable ot
cancer in animals, and local application of tobacco tar can result in skin
cancer in mice.
Although so many people have given up smoking, there is no
reduction in the consumption of tobacco. It is said that one in eight o
those men who are smoking 20 cigarettes a day will develop cancel o
the lung, as contrasted with a ratio of one in three hundred of nonsmokers.
Without any further increase in prevalence, cancer of the lung