. Electro-physiology. Electrophysiology. ix ELECTRICAL EXCITATION OF NERVE 145 and yhi. Here again the true form of the curve is uncertain, and this merely represents the general relations. The curve abc shows that nearly the whole of the intrapolar tract is thrown with minimal currents into a state of augmented excitability (katelectrotonus), while the indifferent point in this case is near the anode. Excitability increases gradually from this point on the one side, while on the other it is correspondingly diminished. The alteration reaches its maximum in the immediate proximity of the two el
. Electro-physiology. Electrophysiology. ix ELECTRICAL EXCITATION OF NERVE 145 and yhi. Here again the true form of the curve is uncertain, and this merely represents the general relations. The curve abc shows that nearly the whole of the intrapolar tract is thrown with minimal currents into a state of augmented excitability (katelectrotonus), while the indifferent point in this case is near the anode. Excitability increases gradually from this point on the one side, while on the other it is correspondingly diminished. The alteration reaches its maximum in the immediate proximity of the two electrodes, whence it declines again to 0. The curve (clef} from currents of medium strength is essentially the same, but is distinguished by the larger tract of nerve which it embraces, and by higher ordinates, while the indifferent point lies about midway in the intrapolar region. These differences correspond. FIG. 185. with the fact that the electrotonic alterations of excitability increase in intensity and extent of diffusion with the strength of the polarising current. The same applies to the curve (glii} of strong currents, which contrasts with abc, inasmuch as the indifferent point lies near the kathode, so that almost the whole intrapolar tract is in a state of anelectrotonus. It would also be easy to record the after-effects of an- and katelectrotonus, since the excitability of every point, at all events immediately after breaking the current, is exactly opposite to the effect at closure. We have up to this point considered only the effect of strength of polarising current upon magnitude and diffusion of electrotonic alterations of excitability, yet, as Pniiger has shown, the length of tract traversed, as well as the time-relations of the passage of the current, are not unimportant factors. The first of these two (besides the older experiments of Humboldt, Eitter, and others) was investigated by du Bois-Eeyrnond. According to Ohm's law, the intensity of an electrical cur
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