A study of the branched cells of the mammalian epidermis with special reference to the fate of their division products

Abstract

The branched cells of the superficial epidermis of mammals are divisible into two classes: those that occupy a position in the basal layer, and those that occur in more superficial layers. The first class comprises melanocytes visible in the living epidermis after its enzymatic fission from the corium; cells that blacken upon exposure to dihydroxyphenylalanine; cells that maintain quinoneimine dyes in the oxidized state in living skin; and clear cells. It is shown that these are merely different preparation images of the same cell, the melanocyte. The second class comprises cells that may be more or less specifically impregnated by metallic gold (Langerhans’ cells); cells stainable in living skin by quinone-imine dyes; and the ‘clear cells’ of superficial strata. It is shown that these, too, are so many preparation images of the same cell. It is argued that the branched cells of superficial strata, which have never been seen to divide, represent effete melanocytes which, having discharged or otherwise lost their pigment, participate in the general outward movement of epidermal cells to be cast off at the skin surface. This argument is supported by evidence of their similarity of structure, mode of branching, and relationship to neighbouring Malpighian cells; by their position in the epidermis; by their one-to-one correspondence of number; and by their coincidence of distribution.