456 ELECTRO-PHYSIOLOGY CHAP. 



As regards preparations which are as far as possible free from 

 tonus (relaxed), we find as a rule, as in striated muscle, on leading off 

 from the kathodic end and middle of the muscle, that negative 

 after-currents predominate ; these, in consequence of the slow 

 disappearance of the persistent closure contraction, are very 

 protracted, and are always most pronounced when the conditions 

 are most favourable to the closing excitation. On fresher and 

 more tonic preparations, on the other hand, a positive kathodic 

 after-current predominates ; it either appears alone, or is intro- 

 duced by a negative fore-swing. Like positive anodic, positive 

 kathodic polarisation is found to be dependent upon the strength 

 and duration of the exciting current, and increases, generally 

 speaking, in ratio with it. There is, moreover, an alternation 

 between the antagonistic effects of polarisation at the kathode 

 precisely similar to that at the anode, since the negative after- 

 current retreats into the background in proportion as the positive 

 is stronger, and vice versa. As a rule, it is not difficult to find 

 in any given case a strength of current and duration of closure, 

 at which mouophasic positive effects alone are visible on the 

 side of the kathode. But even then repeated excitation with 

 homodromous currents soon brings about a diphasic action, since 

 the positive after-current becomes steadily weaker, with simul- 

 taneous increase of negative polarisation. 



In regard to the anodic after-current there is almost perfect 

 correspondence between monomerous striated, and smooth mollus- 

 can muscle, save that every effect, including the galvanometric 

 consequences of excitation, makes its appearance at a much 

 higher current intensity in the latter. As a rule the negative 

 anodic polarisation of molluscan muscle increases with increase in 

 current intensity, but only within a certain range, beyond which a 

 rapidly increasing positive after-current appears, so that there is 

 once more a diphasic effect with diminishing phase of negativity, 

 terminating with a simple positive variation. This latter, in 

 striated muscle, is essentially dependent upon the actual excitability 

 of the preparation, i.e. appears earlier, at less strength of current 

 and duration of closure, in proportion as the muscle is more 

 excitable. With regard to all the characteristics of positive 

 anodic polarisation its dependence on the state of excitability 

 of the preparation, strength and duration of closure of the 

 exciting current, localisation at the anode, and greater permanence 



