448 ELECTRO-PHYSIOLOGY CHAP. 



extent to which the excitability and conductivity of the muscle 

 is altered by such impossibly strong currents is sufficiently 

 attested by the appearance of the galvanic wave under these 

 conditions, as well as by the persistent excitation (often excess- 

 ively marked and widely distributed over the intrapolar muscle 

 tract), in the region of the anode, which depends, as was shown 

 above, upon the effectuation of secondary electrode points. But 

 there can hardly be a question, after the foregoing 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 pheno- 

 mena are pure polar effects of current is, however, the fact that 

 killing the anodic or kathodic points of the muscle hinders the 

 appearance of both positive and negative kathodic polarisation, 

 exactly as occurs in the opening and closing excitation. The 

 negative, and still more the positive, polarisation current thus 

 implies integrity of the kathodic or anodic points of the excitable 

 substance. 



Hermann pointed this out in regard to the positive anodic 

 after-current in muscle, designating it in consequence an " irrita- 

 tive " negative after-current, vs. that " derived from true polarisa- 

 tion." Like du Bois-Eeymond, he derives the latter from the 

 whole interpolar tract, and, after partial passage of current, from 

 the extra -polar region also, in consequence of a polarisation, 

 which he takes to be equivalent with certain polarisation pheno- 

 mena (infra) that occur in medullated nerves, and can be 

 reproduced upon a polarisable wire surrounded by an electrolyte, 

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

 the effects upon this (" core ") model coincide with the polarisation 

 phenomena, both inter- and extra-polar, of muscle and nerve, the 

 " polarising after-current " being in the first place heterodromous, 

 in the second place homodromous, with the polarising current. 



We shall enter more fully into these relations when dis- 

 cussing the electrical excitation of nerve ; for the present it is 

 enough to say that just as these effects are indisputable under 

 certain conditions, so too in muscle, within a given " physio- 

 logical " range of strength of current, the negative kathodic must, 

 equally with the positive anodic, be designated an " irritative " 

 after-current, due entirely to polar current action. 



