MECHANISM OF MOVEMENT OF EPIDERMIS, ESPE-CIALLY ITS MELANOPHORES. IN WOUND HEAL-ING, AND BEHAVIOR OF SKIN GRAFTS IN FROG TADPOLES EARL H. HERRICK ZOOLOGICAL LABORATORY, HARVARD UNIVERSITY Probably no other animal tissue is more active than an epidermis in repairing lost or damaged parts. The process is not primarily one of growth. A deficiency, either large or small, in the epidermis is rapidly covered by centripetal movement of the surrounding epithelium, and later, by reorganization and growth, the original condition is re-stored. Rand (1915) in considering the wound reactions of actinians says (p. 207) : " In general, an epithelium will not tolerate a free edge. When such an edge arises, accidentally or otherwise, the epithelium ex-tends until, if possible, the free edge meets and unites with some other portion of the same layer or with another epithelium. The essential function of an epithelium is to cover a surface continuously." The investigations of Fraisse (1885), Barfurth (1891), Born (1896), Morgan (1901), Loeb and Strong (1904), Rand (1905), Eycleshymer (1907), Matsumoto (1918), Loeb (1920), Arey (1925), and Collins and Adolph (1926) point unanimously to the conclusion that wounds are at first covered by movement of the surrounding epithelial cells and that proliferation occurs later to restore the original thickness of the layer. The cause and mechanism of the cell movement are not so well agreed upon. Born (1896) believed that the cells flatten to cover a larger surface than previously. Rand (1905), however, referring to wound healing in earthworms, says (p. 46) : " There certainly is little evidence in favor of supposing that the concentric advance of the epidermis is due to the tendency of the individual cell to spread itself over the greatest possible surface." Barfurth (1891) proposed that, while the movement of the epidermis might be in part a passive " Verschiebung " due to relief from lateral pressure in the layer, it was in the main an active movement of cells which had become "embryonal beweglich (amoboid) ' (p. 417). Oppel (1912) described epithelial movement as an active movement often a " Massenbewegung ' ; resulting from change of form of the 271
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