G. D. Maynard 
293 
these rates were to be compared in relation to deaths in occupations — soldiers at 
the front with men in garrison — no positive correlation would be observed. Thus 
under the heading of occupations we may be measuring rather the determining 
causes of the type of breakdown, than the fundamental cause of the disease. 
I may perhaps be allowed briefly to refer to the theory which has been adopted 
as a working hypothesis in the present investigation. As far as this investigation 
is concerned there does not seem to be any evidence as to the infectious nature of 
cancer. Nor has any evidence been adduced that would lead to this belief with 
the possible exception of cancer-houses, while on the other hand, all the improve- 
ment brought about by public health i-eform, in the way of reducing over-crowding, 
abolition of back-to-back houses, &c. has not been followed by any reduction of the 
disease, on the contrary an actual increase has been taking place. That nervous 
centres do exercise an extraordinary influence over tissue cells is a matter of 
common knowledge and that some nervous disturbance may affect the cell 
metabolism in diabetes, and the cell growth in cancer does not seem to me 
impossible, even if a novel view. This suggestion does not necessarily exclude the 
presence of an organism as the determining cause, and several analogies will occur 
to the reader. For instance in a disease like scurvy, which is almost certainly of 
infectious origin, the organism does not usually obtain a footing until the soil has 
been prepared by errors of diet. 
It must be understood that the strain occasioned by modern competition is 
only regarded as an exciting factor, in so far as it leads to a breakdown of nervous 
origin. This breakdown of course may occur without any undue strain, but will in 
the aggregate do so more frequently when this factor is present. The heredity 
factor, i.e. the constitutional weakness, is of course of primary importance. 
Problems connected with the occurrence of cancer in animals are at present 
difficult to deal with statistically. That malignant tumours occur in vertebrates 
is well known, as the following extract from the Third Report of the Cancer 
Commission shows: — "Cancer is ubiquitous in man and vertebrate animals. It 
has been shown that cancerous tissue of a species of animal retains the characters 
of that species, whereas in infective tumours (e.g. tubercle) occurring naturally 
in separate species, the biological characters of the newly formed tissue are 
determined by the common infective agent and not by the tissues of the affected 
animal." 
Again, the question of cancer in African Natives requires more study, and the 
increasing rates for these races as observed in America are of interest. The 
phlegmatic nature of the Bantu in Africa is well known. The prevalence of 
Diabetes among Jews is another problem of interest that awaits explanation. 
This race, however, seems particularly liable to certain nervous complaints, as for 
instance various forms of insanity, and Amaurotic Family Idiocy. 
Since writing the above I have been looking through the small literature of 
insanity at my disposal and have been struck with the following sentences : — " It 
Biometrika vii 38 
