It is commonly agreed that the malignant tumor is emancipated from the controls to which cell proliferation is subject in the normal tissues, however hypothetical the existence of such controls may be. The autonomy of the cancer cell is thought to be the result rather than the cause of its cancerous transformation. The present study was stimulated by Bullough's (1) finding that the mitotic frequency in mouse epidermis is considerably higher in middle-aged than in young animals even before they

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... ave reached full size. This finding contradicts the common concept of aging, according to which bodily processes slow down and the regenerative capacity of the tissues diminishes with age. If Bullough's observation should prove to hold for other epithelia this would point to the possibility that the mechanisms by which normal cellular proliferation is controlled are weakened in the older individual. The incidence of cancer increases with age. One might suspect that the full emancipation from control of the full-fledged malignant cell is prepared for by the partial emancipation from control which occurs with age. The present study was undertaken in order to determine whether human tissues in which maintenance depends on the perpetual proliferation of cells resemble similar tissues in mice in showing higher regenerative rates in older individuals. Gingiva was chosen because of the ready availability of biopsy material from this site. It was anticipated that many variables other than age would influence the individual mitotic frequencies. It was therefore thought advisable not to study the entire human life span, but to concentrate on two separate stages. MATERIAL AND METHODS The study was based on 60 human biopsy specimens of the attached gingiva measuring from 1 to 5.5 mmin length after fixation. 30 specimens came from men ranging in age from 25 to 34 years, and 30 from men ranging from 50 to 78 years of age. A clinically normal region of gingiva in the anterior region of the mouth was used for biopsy. The biopsy specimens were taken between 2 p.m. and 4 p.m. except for a small number of specimens which were obtained in the later hours of the morning. The tissue was immediately fixed in Zenker's solution, sections