SECONDARY ELECTROMOTIVE ACTION IN MUSCLE 497 



If (as already set forth) each alteration of chemical activity in any part 

 of the muscle-fibre necessarily implies the appearance of electromotive action, 

 we should anticipate that on sending current through a muscle with parallel 

 fibres, the chemical alterations in the contractile substance at the physio- 

 logical kathode and anode would initiate differences of potential. And these 

 differences must be manifested when one or the other end, so altered, of the 

 muscle is led off in connection with a point on the otherwise uninjured 

 surface. The results which Hering obtained from experiments on the 

 frog's sartorius did, in fact, correspond in every particular with this 

 assumption. 



If, namely, this muscle is fixed at moderate tension, the current being 

 passed through it from the stumps of bone on either side, then on leading off 

 from one or the other tendon-end, and from a point on the longitudinal 

 surface, the muscle current measured previous to the passage of the current 

 will, on breaking the latter, be found to be considerably altered. It is 

 increased, diminished, neutralised, or the reverse, according to the direction, 

 strength, and duration of the exciting current, and the strength and direction 

 of the original muscle current. When the muscle current has been pre- 

 viously compensated, " polarisation currents " make their appearance in 

 correspondence with the positive or negative modification of the muscle 

 current. These may be positive or negative, i.e. homodromous or hetero- 

 dromous to the exciting current. Since they are really initiated at the 

 anodic and kathodic points of the muscle-substance, Hering distinguishes 

 between anodic and kathodic polarisation. The former may be either positive 

 or negative, the latter is in most cases negative only. 



With a brief closure, very weak currents invariably give a negative 

 polarisation current in fresh muscle, so long as only the anodic tendon-end, 

 and a point at about the middle of the muscle surface, are in the galvanometer 

 circuit. With stronger exciting currents, on the other hand, and not too 

 brief a closure, positive polarisation alone results, and increases with the 

 strength of current, until finally it far exceeds the strongest negative anodic 

 polarisation. 



Very strong currents produce positive polarisation at once, even with 

 the shortest possible closure. Weaker currents, with brief closure, give 

 negative or diphasic (first negative, then positive) polarisation, and the pure 

 positive effect only appears after prolonged closure. Induction currents are 

 like strong constant currents, with minimal closure, and produce positive 

 anodic polarisation only. 



All these polarisation effects (after-currents} are wanting, or at most appear as 

 a trace, if both leading-off electrodes are applied to the longitudinal surface of the 

 muscle, and not too close to one or the other end of it. 



Since, according to Hermann's "alteration theory," excited muscle- 

 substance is negative to unexcited substance, there can, when we consider 

 the conditions and the character of the opening excitation in muscle, be no 

 doubt that positive anodic polarisation is the expression of the latter. " The 

 positive polarisation current produced by alteration of the anodic points of the 

 contractile substance is an action current, due to the break excitation starting from 

 the anode " / albeit, an action current that behaves very differently from the action 

 current due to the make stimulus, that has so far exclusively concerned us. 



The long persistence of negativity at the anodic points is remarkable in 

 VOL. II 2 K 



