Mitotic Rhythm in Human Epidermis

Studies of mitotic rhythm, per se, have been few, although the number of mitoses found in various tissues has been used as an index of functional activity of these organs when subjected to various experimental conditions. The work of Loeb and his students 1 2 on the thyroid gland, using the mitotic index as a basis for the measurement of the effect of various chemicals and hormones upon this organ is most significant. All the work that has been done on plants, 3 4 5 6 mice and cats, 7 8 indicates the existence of a rhythm in cell division, which must obviously be taken into consideration in experimental studies; but, to the best of our knowledge, no observations have been reported on rhythmic periodicity of mitotic division in human tissues.

The relatively small number of mitoses that can usually be found in sections of human epidermis is striking, especially since the epidermis is known to be constantly renewed at a rather rapid rate, but as a general rule the sections of skin in which mitosis has been studied have been secured (by biopsy or by operation) during the day time. Consequently, the question arises whether more mitoses might not be observed in skin obtained during the night when, perhaps, cell division is occurring at a different rate than during the day.

The skin covering the prepuce of infants, which is removed at circumcision, was selected as a convenient tissue for experimentation. The babies were all of approximately the same age (8 days) and had been kept from birth under practically identical environmental conditions, at the St. Louis Maternity Hospital. The specimens were obtained at various hours throughout the day and night, through the courtesy of the Director of the Hospital, Dr. Otto Schwartz.