The effect of visible light on the development in mice of skin tumors and leukemia induced by carcinogens.

The absence of light enhances epidermal carcinogenesis in Swiss albino (9) and C57 black (10) strains of mice painted with a solution of 3,4-benzpyrene. It now appears that the presence or ab sence of light affects the response of mice of the dilute brown (DBA) strain to percutaneous ad ministration of either 3,4-benzpyrene or 20-methylcholanthrene by altering the incidence of not only skin carcinomas but leukemias as well. These mice are peculiarly susceptible to the leukemogenic action of several carcinogenic hydrocarbons, al though the incidence of spontaneous leukemia in the strain is low (2, 4-6, 11).