Abstract
SUMMARY.— The predominant pigment of the comedo appears to be melanin. The darkness of the tips of comedones, apparent in vivo, has been confirmed by examination of expressed comedones with the dissecting microscope. Histochemical techniques, applied to comedones from many different sources, confirm that the dark tip results from melanin granules within the horny cells which form the foundations of the comedo and which are more tightly packed toward the tip; the granules, which are visible with the light microscope can be blackened or bleached by methods appropriate for melanin. The amount of pigment within the comedo and of melanin staining parallels the intensity of general skin pigmentation of the donor, is absent from albino comedones and very dark in specimens from Negro skin. Extraneous pigments including carbon and metallic particles have been found in some comedones. The source and significance of the pigments found is discussed.
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