Kinetics of epidermal cell proliferation in experimental skin carcinogenesis.

It is well known that there exists a daily rhythm in the mitotic count in the epidermis of the mouse. It has also been emphasized that the mitotic rate cannot be estimated correctly from the mitotic count unless the mitotic duration is constant.In this paper it is shown that applications of 3-methylcholanthrene to the skin cause great variations in the mitotic duration of the epidermal cells. The Colcemid technique is used to study the mitotic duration in the untreated epidermis of hairless mice during a 24-hour interval, and it is shown that the diurnal and nocturnal variations in the mitotic count are the effect mainly of variations in the mitotic duration and not of variations in the mitotic rate.