FURTHER STUDIES ON MELANOCYTES AND MELANOGENESIS IN THE HUMAN FETUS AND NEWBORN

[摘要] In the Negro fetus, the first mature melanin granules are produced in melanocytes of eyelids, external auditory meatus and in specific areas of the oral mucosa. This occurs in the latter part of the 3d fetal month, approximately 1 month earlier than in the epidermis of trunk regions. Cephalo-caudal direction in the maturing process of melanocytes supports the view that melanoblasts originate from the neural crest. Attempts to stain human melanoblasts in the dermis, before they reached the epidermis, have failed. Below the head region, there are few and widely scattered immature melanocytes in the epidermis at the 3d fetal month. Early in the 4th month there are approximately 104/mm2. In the 5th fetal month the number of melanocytes increased to 316/mm2. Approximately 1/3 (114/mm2) of the latter are mature melanocvtes containing melanin. Maturing process of melanocytes in the epidermis is protracted. In the 7th fetal month there are approximately as many mature melanocytes per mm2 as there were immature pigment cells in the 5th month. In epidermal spreads of newborn Negro skin there are approximately 1030 dopa positive melanocytes per mm . This number corresponds roughly to that determined in adult skin (Szabo). Fetal melanocytes have fewer secondary dendrites and are more uniform in shape than those of adult skin. Vertical sections of late fetal Negro skin revealed pigment in the basal cell layer (silver impregnations). Horizontal spreads with dopa stain, however, showed no evidence of pigmented basal cells; all the melanin granules were within melanocytes. Gold impregnations of melanocytes in white fetuses were unsuccessful before the 6th month. Those revealed in later stages were identical with gold impregnated melanocytes of Negro fetuses and of the newborn.