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

  • George Neil Stewart
Date:
[1889?]
Catalogue details

Licence: Public Domain Mark

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

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    action will pass through the galvanometer from B to A.* This will have the opposite direction to the electrotonic current, and will therefore look like a diminution or negative variation of that current. Similarly, if C he the anode, and the current be descending, the excitation will pass over B in greater intensity than over A, and again there will he a negative variation of the electrotonic current. Hermann, as already stated, seemed at one time to suppose that this was a complete explanation of the phenomena. But he was afterwards led by rheotome researches to modify his view, and, while retaining the law of “ polarisation increment ” as an essential factor in the explanation, to postulate besides, as Bernstein had previously done in a somewhat different form, an actual diminution in the polarisation, a negative variation, so to say, in the capability of the nerve to take on polarisation between core and sheath. (“ Untersuchungen liber die Actionsstrome der nerven,” Pfliiger’s Archlv, Bd. xlii. s. 246, &c.). According to Hermann, the electrotonic currents are branches of the polarising stream which spread beyond the electrodes, owing to the transverse resistance caused by polarisation between this hypothetical core and sheath. The greater the polarisation coeffi¬ cient is, the more widely do these branches spread, the stronger are the electrotonic currents. If stimulation diminishes this polarisa¬ tion coefficient it will, in general, diminish the electrotonic currents. If the excitation be confined to special parts of the nerve, then it will depend upon the ratio of the transition resistance between core and sheath to the longitudinal resistance of the nerve, and upon the magnitude and position of the unexcited or relatively unexcited parts, whether the electrotonic variation (as we may for shortness call the variation of the electrotonic currents produced by stimula¬ tion) will be negative or positive. All this he deduces from his theory, and supports by experiments with the “ Kernleiter Modell,” He looked, in vain, however, for a positive phase in his rheotome work on nerve, the experimental difficulties being very great. It was not from Hermann’s theoretical standpoint that I entered * Strictly speaking, if E(A), E(b), represent the intensity of excitation at A and B, fE(A)dt is >jB^)dt for corresponding limits. Considering time- integrals, B may, therefore, be looked on as positive to A during the tetanus. The galvanometer deflection produced by stimulation will be a measure of the difference of these integrals.