Abstract
The physico-chemical nature of the intracellular electromotive system is not deducible from electromotive force measurements alone, although many investigators have drawn conclusions from such data. Critical evidence has been provided by Lund and his students 1 that the E.M.F. arises from an oxidation-reduction system. This, and direct evidence by the writer, 2 are interpretable only in terms of a conductor of the first class (plasma membrane, or analogous structure or phase boundary) in electron equilibrium with a dissolved ion or ions. Under these circumstances the effect of electric currents upon cells acquires diagnostic significance. Mast 3 has recently confirmed Kühne's observation that passage of current through the epidermal cells of Tradescantia causes acidity at the cathode end and alkalinity at the anode end. The cells contain a natural pH indicator; the color change begins at the inner boundary of the cell membrane and extends slowly inward. The writer has also confirmed these experiments. The color change is a qualitative test of the nature of the electromotive system.
Four physico-chemical systems must be interrogated as to their behavior on electrolysis (the diffusion potential will not explain the facts in Tradescantia). The membrane potential and the phase boundary may be treated together under the Donnan equilibrium. In this system electrolysis causes accumulation of the non-diffusible ion at one membrane and diminution at the other. The non-diffusible ion tends at equilibrium to expel ions of like signs and to attract in ions of opposite sign.
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