ACTION OF VOLTAIC CURRENT ON MUSCLE. 429 



If a voltaic current is led through such a muscle, with the cathode on 

 the excited and veratrinised end, no effect is produced so long as the 

 current is closed, but on opening it the anelectrotonic state manifests 

 itself by relative positivity of the anodic part. 



In the adductor muscle of Anodonta, which is normally in a state of 

 tonus, Biedermann has shown that the cathodic relaxation which follows 

 the opening of a polarising current is accompanied by a corresponding 

 electrical state (relative positivity), but this observation does not bear on 

 the question whether or not, in the absence of tonus (produced either 

 naturally, by veratrine, or by other chemical agencies), an inhibitory 

 after-effect, marked by relative positivity and muscular relaxation, can 

 be observed at the cathode in normal skeletal muscle. 1 On this point 

 the only information we possess is derived from certain observations of 

 Hering to which reference is made by Biedermann. 



In all experiments on polarisation care must be taken to select 

 muscles which are free from tendinous inscriptions, for, as Hering 

 conclusively showed, these exhibit the physiological properties of 

 cathodes and anodes. At each inscription the current leaves the 

 muscular substance to enter tendon, and again leaves tendon to enter 

 muscle. An after-effect in the same direction may consequently 

 manifest itself even when both galvanometer electrodes are at a distance 

 from the cathode and anode, provided that an inscription occurs in the 

 region from which the effect is led off. 



J o' 



In nerve the phenomena of polarisation can be studied more advantageously 

 than in muscle, and are of greater physiological importance. The reader will 

 therefore find it useful to refer to the Article on Nerve, in connection with 

 the preceding paragraph. 



Polar effects on excitability during and after the passage of a 

 voltaic current. — If a curarised sartorius be so arranged that during 

 the flow of a battery current from end to end, an induction current is 

 led through the same electrodes in the same direction, it is observed 

 that the response to the induction current is much augmented. Thus 

 an induction current of which the strength is such as to produce a 

 minimal contraction when the voltaic current is open, at once evokes a 

 maximal response if this current has previously been closed, — a fact 

 which led v. Bezold, who first observed it, to the erroneous supposition 

 that a general increase of excitability of the muscle is produced by 

 the flow of a voltaic current through it. 2 



The arrangement of this old experiment will he best understood from the 

 description of the diagram (Fig. 243), with the addition that the metallic 

 electrodes originally used should be replaced by non-polarisable ones. It 

 affords evidence that during the passage of a current, excitability is augmented 

 at the anode, diminished at the cathode, but gives no indication of the state 

 of the region between the poles. 



As in the case of nerve, so also in that of muscle, the observation of 

 interpolar excitability by means of electrical excitation is attended with great 

 difficulty, consequent on the interference of the testing current with the 



1 With reference to the apparently similar case, in which a polarising current is led 

 through a sartorius with a devitalised tibial end, see Locke's paper, Arch. f. d. ges. 

 Physiol., Bonn, Bd. liv. S. 520. 



-" Biological Memoirs. " Oxford, 1887, " On the Phenomena of Inhibition, etc., and 

 on Positive Cathodic Polarisation," p. 331. See also " Electrophysiologic," S. 386; 

 Translation, vol. i. p. 454. 



