Incorporation of Tritiated Thymidine Into the Skin and Hair Follicles

The incorporation of tritiated thymidine into the skin has been studied after the initiation of new hair growth by plucking. Techniques are described whereby the incorporation into hair follicles and into the basal layer of the epidermis can be studied independently. Fluctuations are observed in the levels of incorporation in both cell populations through the hair growth cycle. These fluctuations show great regularity. the early fluctuations have been attributed to synchronous progression of cells through the cell division cycle. the significance of the fluctuations is discussed with particular reference to (I) possible persistence of cell cycle synchrony, (II) regulatory feedback mechanisms controlling DNA synthesis, perhaps through specific mitotic inhibitors, (III) the existence of G o , G 1 and G 2 cell sub‐populations.