On the ionic basis of electrical stimulation.

Abstract

In their attempts to develop a physical theory of electrical stimulation, Nernst 1 and A. V. Hill 2 have supposed the current to act by carrying the ions within the tissue against a membrane barrier. The resulting heaping up of the ions at the membrane constitutes the first step in excitation. If we assume, as the work of Loeb 3 shows we have a right to do, that the positive ions are the effective ones, then according to the views of Nernst and of Hill stimulation must occur at the cathode when the current is made. This is a statement of Pflüger's law and is valid for frog tissue, with which Pflüger worked.

A consideration of cases in which Pflüger's law is reversed suggests that a somewhat different and more general picture of the ion mechanism of electrical stimulation is necessary. In the ctenophores Beroe and Mnemiopsis, when the galvanic current is passed through a trough of sea water containing them, the result is a luminescent glow on the anodal side of the animal. 4 This glow occurs on the make and lasts for some seconds during the flow of the current. If an incision is made in the animal transversely with reference to the direction of the flow of the current, then anodal stimulation occurs also at the cut surface. These results mean that galvanic stimulation takes place only at the protoplasm-sea-water surface, and that stimulation is referable to the blocking of positive ions of the sea water at that surface. These ions, therefore, impinge on the protoplasmic membrane from outside. It is a remarkable fact that in ctenophores which consist so largely of included sea water there is no apparent stimulation as a result of internal ionic movements.