Correlation of Initial Changes in the Mouse Epidermal Cell Population with Two Stage Carcinogenesis—A Quantitative Study

The behaviour of the normal epidermis of mice on the first 5 days of exposure to a single application of carcinogens and cocarcinogens has been investigated by simple quantitative measurements of cell population, size of cells and thickness of the epidermis. Irritant substances and promoting agents both produce cellular hypertrophy but the respective responses can be distinguished by the much greater incidence of degenerate cells associated with irritant treatment. Urethane treatment is characterized by induction of a transient hypoplasia which is not in agreement with the level of cellular division. This response has also been demonstrated after treatment with mild carcinogens or low doses of potent carcinogens. Higher dose levels are followed by a reduction in the mitotic index after about 27 hours. The possibility of developing a preliminary screening test for carcinogenic substances is discussed in the light of these observations.