Tak slUbY- OF CANCER 27 
are not capable of easy solution in the mouse. One can use 
the organism as an indicator of the nutritive needs and meta- 
bolic activity of cells, because in studying propagated cancer we 
have such a large number of tumour cells of the same kind in 
one animal. Conversely,as I have shown above, we can use the 
tumour cells as indicators of changes in the animals. So far 
as these results go they encourage further experimental investi- 
gation into the growth of cancer as a problem of cell nutrition, 
in which the organism as a whole is implicated, although the 
demand proceeds from a circumscribed area, limited in the first 
place to a little bit of tissue no bigger than a pin’s head at the 
time of inoculation. It is obvious that this line of inquiry may 
have ultimately direct bearings on certain aspects of the disease 
in man; but I must enforce caution in drawing conclusions, 
and above all warn the layman that I have said nothing in 
favour of popular views on diet or disordered digestion as 
causes of cancer. 
This is an opportune stage at which to terminate an outline 
of the firstfruits of the experimental investigation of cancer, to 
the development of which the Imperial Cancer Research has 
very materially contributed. In 1905, 137,128 deaths of males 
occurred in England and Wales above the age of 35; of these 
11,908 were due to cancer. In the same year there were 138,477 
deaths of females above 35 years of age, of whom 16,875 died 
of cancer. Therefore of persons dying above the age of 35, 
one out of every eleven men died of cancer, and one out of every 
eight women. Is this great frequency as a cause of death to 
be explained as due to communication of the disease from 
one person to another? Our experimental investigations have 
revealed no analogy with any known form of infection. The 
chance of ultimately dying of cancer is one in eight for women 
and one in twelve for men above the age of 35. A simple 
calculation shows the probabilities of the occurrence of one or 
several cases of cancer in families of whom few or many survive 
beyond the age of 35. Murray and myself have pointed out 
that when the full facts are known, the incidence of cancer in 
some animals will probably approximate to that in man, 
although the forms of cancer to which different species are 
most liable may differ. Since the greater frequency of cancer 
coincides with the later years of life, the span of life of human 
beings has long been one of the obstacles preventing a final 
