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.

    11/20 (page 241)
    different in purpose from mine and essentially different in method, found that the cathodic block took time for its establishment, and that, when it appeared, it appeared suddenly. In the example given in Experiment 5 the initial positive effect is seen to change in 30 into a negative effect thrice as great, and this negative effect then gradually increases with still longer time of closure. In order to diminish, as far as possible, the irregularities in the deflection, which are always a source of trouble with strong electro¬ tonic currents, especially on the anodic side, I thought of using the currents led off to the galvanometer from two separate nerves of the same frog to compensate one another, a method resembling some¬ what in principle that which Hermann has used in some of his polarisation work. Then, on exciting one of the nerves, one ought to get the stimulation effect, weakened, of course, by the extra resistance of the second nerve. The same battery was connected with both nerves, so that irregularities in the battery itself might be eliminated. The result was very satisfactory. Figs. 3 and 4 show the arrangement. In the arrangement of fig. 4 two nerves were placed on two separate sets of electrodes A, B, D; A', B', D', a compensator (Com.) being introduced into the galvanometer circuit. Fig. 3.—G is the galvanometer ; Bat., the battery ; I, the stimulating electrodes. The pieces of nerve BD, B'D' were made as nearly as possible equal in length, and therefore the current would have nearly the same density in each. The electrotonic currents in AB, A'B' would be nearly equal, and they would pass through the galvanometer in opposite directions. The balance was completed by means of the compensator. In the arrangement of fig. 4 the polarising current passed to vol. xvi. 16/7/89 Q