THE FORM OF THE EPITHELIAL CELLS IN CULTURES OF FROG SKIN, AND ITS RELATION TO THE CONSISTENCY OF THE MEDIUM.

1. Fragments of skin from the leopard frog (Rana pipiens) were cultivated in media of varying consistency. A mixture of frog plasma, frog muscle extract, chicken plasma, and chicken embryo extract usually produced a very firm medium; a mixture of frog plasma, frog muscle extract, and chicken plasma, one less firm (semi-firm); and a mixture of frog plasma and frog muscle extract a medium of a consistency varying from soft to liquid. 2. (a) In a firm medium the cells which migrate into the medium are polyhedral (polygonal when seen from above) in form, which shape they retain permanently. They remain united in a compact membrane, the central parts of which consist of several (three to four) layers of cells. Migration of isolated cells into the medium does not take place. (b) In the semi-firm media the cells situated at the edge of the membrane become fusiform in shape, gradually detach themselves from the membrane, and stray out individually into the medium. This causes the membrane to become loose in character, and to contain holes, while its edges at the same time become very irregular and send out pointed projections. (c) In a soft medium the cells are fusiform or thread-like in shape. The migration of isolated cells is much more pronounced than in the semi-firm media, as a result of which the membrane undergoes constant and rapid loosening up. By this means whole portions of the membrane become detached and their separate parts are at first united by the thread-like columnar cells, which become drawn out in the form of long threads upon the separation of the individual sections of the membrane. The loosening up of the membrane is further assisted by liquefaction and the consequent formation of vacuoles; the latter process likewise results in the formation of thread-like columnar cells. (d) Liquid media contain only round cells. 3. This serves to explain numerous internal processes of the organism, especially certain changes of form observed by Leo Loeb in transplantations of wound scabs and of skin; the conditions artificially produced by Leo Loeb must have effected a change in the consistency of the medium. 4. It has been shown that it is unnecessary, for a satisfactory explanation of the above findings, to have recourse to the theories of "functional stimulus" or "inhibiting influences," by means of which Champy wished to account for the variations in the morphological character of the cells.