The effect of the age of mice on the incidence of skin cancer.

The plausibilities of two hypotheses explaining the increased cancer incidence rate in old age caused by a constant dose of carcinogen were compared using a mouse skin painting experiment in which two groups of mice started treatment at different ages. It was shown that the hypothesis of the increased rate being caused simply by increased vulnerability of old animals was not as plausible as the alternative hypothesis of the carcinogen acting to some extent cumulatively.