Examination of the Epidermis by the Strip Method

Abstract

Although it may seem surprising that such a basic question has not been answered long ago, the mechanism of epidermal regeneration has come under renewed scrutiny during the past few years. There is indeed a classical answer which states that the epidermis replaces the desquamating keratinized cells through mitotic division of the cells of the basal layer (F. Pinkus (1)). Thuringer (2) and Cowdry and Thompson (3) reported that mitoses occurred also in the prickle cell layer. They even found that the cells of the rete Malpighi above the basal layer showed three times as many mitoses as the latter. Still Cowdry (3, 4) defended the basic thesis that all epidermal cells are derived from the basal cells, which he called vegetative intermitotics, even though the prickle cells—the differentiating intermitotics—boost the total number of cells available for kera-tinization and desquamation. This basic concept was attacked from two sides and for two different reasons. One reason was an apparent paradox in cutaneous carcinogenesis which Eichen-laub and Osbourn (5) recently expressed as follows: "If we consider the basal cells as the parent cells of the prickle cells, then we have the more primitive cell giving rise to the less malignant tumor". The other reason was the small number of mitoses which was found in normal epidermis, and which was held insufficient for replacement of the constant loss of cells. The supposedly insufficient number of mitoses led Andrew (6) to postulate that lymphocytes migrated into the epi-dermis and there transformed into prickle cells through the intermediary state of the so-called cells of Masson (7) which most authors consider to be specific pigment forming cells in the epidermis (melanoblasts, dendritic cells, melano-genocytes) (8). Andrew based his conclusions on the interpretation of sections of rat and human skin stained with hematoxylin and eosin. Eichenlaub and Osbourn (5), on the basis of examination of embryonic pig skin, concluded that the lowest