The Effect of Ultraviolet Radiation on the Production of Spontaneous Mammary Tumors in C 3 H Mice *

cages and fed Purina Dog Chow and water ad libitum. Litter mates were distributed evenly among the experimental groups, which were also carefully balanced for weight and age. Ultraviolet radiation including the carcinogenic wave lengths (5) was given by a quartz mercury arc (General Elec tric Uviarc) at 21 inches. At this distance an exposure of 2.5 minutes produced a minimal erythema on human skin. When radiated, the mice were placed in small individual wide wire mesh cages in which a wire mesh trap kept the animals at an approximately constant distance from the light source. They were able to move about, however, during the exposure. All animals were weighed once a month. There was no sig nificant difference in the weights in different groups. The mice from the light room ate less and wereless active. The firstdefiniteappearance of the tumors was noted. When a tumor had grown to a moderate size the animal was killed, and the tumor was removed, sectioned, and examined micro scopically. As the mammary tissue is wide spread, tumors ap peared in many different locations—axilla, groin, back of neck, jaw, base of tail, etc. The histologic appearance of the carci nomas conformed to the types described by Dunn (6), which occur regularly in mice of the C3H strain.