in ELECTRICAL EXCITATION OF MUSCLE 293 



Since it is a well-established fact that on closure of current 

 excitation occurs only at the point where it leaves the muscle, 

 the proof that excitability increases at the anode after polarisa- 

 tion, lies essentially in the fact that the effects of excitation are 

 augmented with closure of a polarising current in the opposite 

 direction. It is conceivable that such changes in excitability 

 might extend over a larger or smaller part of the tract of muscle 

 traversed, although the complete failure of electrotonic alterations 

 of excitability in the intrapolar tract during the passage of the 

 current renders it a priori very improbable. Direct electrical exci- 

 tation of different points in the continuity of a previously polarised 

 muscle, moreover, affords direct proof that just as little as the 

 negative after-effect of polarisation extends beyond the physio- 

 logical kathode, does the positive after-effect pass beyond the 

 limits of the physiological anode, provided only that the polarising 

 current is not too powerful, otherwise a complex of disturbances 

 might arise through the formation of secondary electrodes. 



Undoubtedly the alterations of excitability in question during, 

 and after, the passage of current through a muscle, stand in very 

 close relation with the effects of excitation and inhibition already 

 described, being indeed only another aspect of the same facts. 

 We have seen that when the electrical current acts as a 

 continuous excitation at the kathode, the alterations of excita- 

 bility, or capacity of response observed are its necessary conse- 

 quences, and equally under all conditions must we predicate 

 depression of excitability at the anode whenever an existing 

 excitation is inhibited during closure. The complete reversal 

 at break of the polarising current follows as cogently from the 

 reversal of polar manifestations of excitation and inhibition. 

 Since neither excitatory nor inhibitory phenomena are produced 

 by the direct action of current within the intrapolar area, but only 

 appear as changes induced at the poles, or by the effectuation of 

 secondary electrodes, it is a priori certain that there can be no 

 question of alteration of excitability within the intrapolar tract by 

 direct action of current in v. Bezold's sense nor, as we shall see, 

 does any such alteration exist. 



Nor is there legitimate ground for assuming changes of 

 conductivity within the intrapolar tract, and the experiments of 

 v. Bezold in this direction can hardly be regarded as convinc- 

 ing. He investigated the effect of polarising a tract of muscle 



