Mitoses in human epidermis. Clustering, sister cells, and findings suggestive of a spreading mitotic stimulus

40 sections 8 mum/thick from each of 60 biopsies of human skin were studied intensively by oil immersion microscopy. Mitoses occurred isolated, and as clusters of twos and threes. Some clusters consisted of or contained touching mitoses. These touching mitoses could result from sister cells of a prior mitoses staying together through a cell cycle and entering mitosis again together. However, even when these touching mitoses were excluded, the number of clusters left was significantly more than expected from chance. To account for the clustering we may postulate a mitotic stimulus spreading from mitotic cells in human epidermis.