SECONDARY ELECTROMOTIVE ACTION IN MUSCLE 499 



traction necessarily produces inequalities in the individual parts of the inter- 

 polar tract. Hence, there is no adequate reason for assuming an internal 

 polarisation of the muscle-substance in du Bois-Reymond's sense. On the 

 other hand, all the manifestations of negative kathodic polarisation are again 

 readily explained by chemical alterations (excitation or local fatigue) in the 

 kathodic points of the fibres collectively. 



Nor are the later experiments of du Bois-Reymond more convincing, in 

 which the application of a current from 10 Groves produced, after 15-25 

 minutes' closure, " a secondary E.M.F. in the reverse direction to the polarising 

 current, in every part of the muscle " its magnitude increasing with the 

 length of the tract led off. For the extent to which excitability and con- 

 ductivity in the muscle would be altered by such impossibly strong currents 

 is sufficiently attested by the appearance of the galvanic wave under similar 

 conditions, as also by the persistent excitation (often extremely marked, and 

 widety distributed over the intrapolar tract of the muscle) in the anodic 

 region, which depends, as was shown above, upon the effectuation of 

 secondary electrode points. Indeed there can hardly be a doubt, after the 

 preceding discussion, that experiments performed under such abnormal 

 conditions in no way contravene the clear and simple result of Hering's 

 investigations. 



The most striking proof that secondary electromotive phenomena are 

 pure polar effects of the current is, however, the fact that both positive anodic 

 and negative kathodic polarisation are abolished by killing the anodic or 

 kathodic ends of the muscle, exactly as occurs with the opening and closing 

 excitation. The negative, and still more the positive, polarisation current is 

 accordingly dependent upon the integrity of the kathodic or anodic points of the 

 excitable tissues. 



Hermann points this out in reference to the positive anodic after-current 

 only in muscle, designating this alone as " irritative," in contradistinction to 

 the negative after-current " resulting from true polarisation." Like du Bois- 

 Reymond, he derives the latter from the entire intrapolar tract, and after 

 partial passage of the current from the extrapolar tracts also, in consequence 

 of a polarisation which he takes to be equivalent with certain polarisation 

 phenomena (to be discussed below ; see vol. ii. pp. 309 ff.) that occur in medul- 

 lated nerve as also in a polarisable wire surrounded by an electrolyte, 

 through the sheath of which the current enters. He concludes that the 

 effects upon this core model coincide with the polarisation effects, both intra- 

 and extra-polar, of muscle (and nerve), the " polarisation after-current " being 

 in the first case heterodromous, in the second homodromous, with the 

 polarising current. 



We shall enter more fully into these relations in discussing the electrical 

 excitation of nerve ; for the moment it may be said that little as the phenomena 

 can be disputed under some conditions, yet that in muscle (within a certain, 

 so to speak, physiological limit of current strength) the negative kathodic 

 must, equally with the positive anodic after-current, be designated as " irrita- 

 tive," and resulting altogether from pure polar action of the current. 



Page 449, line 16, for has recently read subsequently. 

 Ib. line 24, for antagonistic read heterodromous. 

 Ib. line 30, insert designated as after is. 



