28 _ SCIENCE. PROGRESS 
settlement of the question whether there is or is not a family 
liability to the disease. This obstacle is inoperative in the case 
of the mouse, with a short life of two to three years. Statements 
have been made of the greater frequency of cancer in the mice 
housed in certain cages, but no account has been taken of the 
total population of the cages for the period during which the 
tumours were observed, nor of the sex and age-constitution of the 
mouse population. In short, the data necessary to justify state- 
ments of relative frequency have not beenascertained. To baldly 
assert that epidemics occur, or that the disease must have been 
conveyed from one mouse to another because so and so many 
cases of cancer have occurred in one cage, as has been done in 
the most positive manner by the New York State Laboratory, 
Buffalo, U.S.A., is to ignore the rudiments of statistics. By 
breeding and in-breeding mice of cancerous stock we hope to 
finally settle the importance attaching to the apparent frequency 
of cancer in some strains of mice as compared with others. 
We have long had such observations in progress; but, since 
statistical studies on the incidence of cancer in animals require 
to be conducted with all the precautions accurate statisticians 
employ in dealing with the incidence of cancer in a human 
population, we are not yet able to institute comparisons between 
different communities of mice. These observations do not lend 
support to assertions of infection, any more than do our studies 
on the nature of experimental transference, and the means 
whereby immunity or protection may be conferred. The 
universality of the disease in man and animals, the biological 
law of its age incidence, the unique character of the proliferation 
and its continuation on transplantation, the peculiar nature of 
the measures which protect mice, as well as the intimate 
relations between normal and cancerous tissue, and the increased 
digestive activity induced to compensate for the building up of 
protoplasm in the tumours borne by otherwise normal animals, 
all point to the probability that cancer arises de novo in the 
individual attacked. This statement may seem to be mere 
dogmatic reiteration of an oft-expressed hypothesis ; but experi- 
ment has removed this conception of the relation of cancer to 
the individual from the realms of hypothesis to the level of a 
well-considered theory, harmonising many isolated facts, and 
fruitful as the basis of further inquiry. 
Finally I may point out, that if the comparative and experi- 
