iv ELECTROMOTIVE ACTION IN MUSCLE 445 



obtained by Hering from such experiments on the frog's sartorius 

 actually correspond throughout with this assumption. 



If the muscle is fixed at moderate tension, and current sent 

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

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

 longitudinal surface, the muscle current measured previous to ex;- 

 citation is found on opening the circuit to be considerably altered, 

 i.e. increased, diminished, neutralised, or reversed, in correspondence 

 with the direction, strength, and duration of the exciting circuit, 

 and the strength and direction of the original muscle current. If 

 the muscle current has previously been compensated, positive or 

 negative increase of the " polarisation currents "- corresponding 

 with the muscle current will appear, and may be positive or 

 negative, i.e. parallel with the exciting current, or opposed to it in 

 direction. Since these have their real origin in the anodic and 

 kathodic points of the muscle -substance, Hering distinguishes 

 between anodic and kathodic polarisation. The former may be 

 either positive or negative, according to the strength and duration 

 of the exciting current, the latter in the majority of cases is 

 negative only. 



With a short closure, very weak currents invariably yield 

 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 circuit. With stronger excitation currents, 

 on the other hand, and not too brief closure, positive polarisation 

 only results, which increases with the strength of current, and 

 finally far surpasses the strongest negative anodic polarisation. 



Very strong currents produce positive polarisation, even with 

 minimal closure, while weaker currents, with short closure, excite 

 negative, or diphasic (first negative, then positive) polarisation, 

 and produce a positive effect after prolonged closure only. In- 

 duction currents also cause a similar reaction to strong constant 

 currents, with minimal closure, since they only produce positive 

 anodic polarisation. 



All these polarisation effects (after-currents) are wholly want- 

 ing, or appear as a trace only, if both leading- off electrodes are 

 applied to the longitudinal surface of the muscle, without being 

 too close to one or the other end of it. 



Since, according to Hermann's alteration theory, excited 

 muscle-substance is negative towards unexcited substance, there 



