STUDIES ON PERMEABILITY OF MEMBRANES. I . INTRODUCTION AND TIlE DIFFUSION OF IONS ACROSS TIlE DRIED

When the different investigations on membrane potentials are taken into consideration, it seems that the theory of these potentials may be treated in three different ways. We may distinguish (a) phase boundary potentials, (b) ndxed electrode potentials, (c) diffusion potentials. The first theory assumes that the potential difference of each side of the membrane against the adjacent solution consists of a jump (a sudden, almost discontinuous fall or rise) of the potential at the boundary of two phases, the liquid being the one phase and the substance of the membrane acting as solvent for electrolytes being the other. The differences in the tendency of distribution of each single kind of ion between the two solvents which are in conflict with electroneutraL ity, produce the potential differences. This theory, first developed briefly by Nernst(1) and thereafter thoroughly elaborated theoretically and experimentally by Haber(2), has been applied to biological membranes by Beutner(3). The latter author also found different models in which he assumes the same mechanism, and at the same time, assumes that no essential part of the P.D. observed is produced within the membrane itself. He could reproduce membranes the potential of which depends on the concentration of any cation dissolved in the adjacent solution, and does not depend only on the concentration of one particular ion, as is the case with metallic electrodes and with the glass membrane, at least in certain kinds of glass such as Haber and