The electronic variation with strong polarising currents / by G.N. Stewart.

  • Stewart, G. N. (George Neil), 1860-1930.
Date:
[1889?]
Catalogue details

Licence: Public Domain Mark

Credit: The electronic variation with strong polarising currents / by G.N. Stewart. Source: Wellcome Collection.

    6/20 (page 236)
    upon the work of which this paper is an account. But from certain experiments on the effect of stimulation on the intrapolar current during the flow, and on both extra and intrapolar currents after the opening of the polarising stream, I suspected that, if one of the galvanometer electrodes were placed very near the polarising circuit, and the strength of the current increased sufficiently, a positive electrotonic variation ought to appear on the side of the anode, hut not on that of the cathode. For the explanation of those experiments it was assumed, and the assumption was supported by direct experiments on muscular contraction, that during the flow of the polarising current the conductivity of the nerve for the excitatory change is less around the cathode than around the anode, and that, with increasing strength of current, complete block occurs sooner at the former than at the latter, although eventually it prevails at both. Whether, when this last stage is reached, the whole intrapolar area has lost its conductivity, was left an open question, and need not be considered here. Going back now to fig. 1, let us inquire what the effect would be on the side of the anode, i.e., with descending current, at a time wThen complete block was established there, and at the same time let us suppose that the galvanometer circuit is brought quite close to the anode, so that the lower galvanometer electrode is within the non-conducting region. If stimulation be now made at I, the excitation will pass A with a certain intensity, but will altogether fail before reaching B. B will, therefore, be strongly positive to A. We leave out of account for the moment any possible effect of the excitation on the electrotonic currents as such. There will be a current of action developed in the descending direction through the nerve—that is, in the same direction as the anodic electrotonic current. If this true action current be not masked by an over¬ whelming negative electrotonic variation, it will appear as a positive variation of the electrotonic current. Now let us take the case of the ascending current in fig. 1. Here the lower galvanometer electrode is in the cathodic region, and we know that even with comparatively weak currents the cathodic block appears. B will therefore, above a low limit of current density, be positive to A when the nerve is excited, and the true action stream will be descending. The cathodic electrotonic current,