320 THE SO-CALLED SECONDARY ELECTROMOTIVE 



the prolonged breaking- excitation reveals itself at the anode by 

 the bulging of the tissue 1 . 



There is no doubt that this excitation is strongest at the anode 

 and decreases in intensity in proportion as the distance from the 

 anode increases. According, therefore, to the law of currents of 

 action, nerve and muscle, after the break of a sufficiently strong 

 current, must be the seat of currents of action which are directed in 

 the tissue away from the anode on both sides. 



For completeness it may be further stated that another current 

 of action may be present after the break of a current of very short 

 duration, namely, the action-current produced at the kathode by 

 the make of the pola rising-current. This will undoubtedly be 

 present during the early part of the time of closure, and there is no 

 decided reason why it should not continue longer than the polaris- 

 ing current if the time of closure of the latter is very short ; it 

 certainly would not be of marked character, since, in the first place, 

 the polarisation opposed current is unfavourable to the persistence 

 of the kathodal excitation (the kathode now becoming the anode) ; 

 and, in the second place, I have never been able to see after short 

 closures any bulging of muscle at the kathode, which would remain 

 synchronous with a bulging at the anode. 



This kathodal action-current would evidently be opposed to the 

 polarising current when intrapolar, + when extrapolar; it has, 

 therefore, in all cases the same direction as the polarisation after- 

 current, so that it could be differentiated from the latter at most 

 by its longer duration. As however such long duration is not 

 observable we may omit this current, and therefore it will be disre- 

 garded in what follows. It will be referred to once again later on. 



C. Combination of the polarisation and excitation after-currents. 

 Explanation of the secondary electromotive phenomena. 



The anodal current of action is similarly directed to the polarising- 

 current (i.e. +) in the intrapolar, oppositely directed (i.e. ) in the 

 extrapolar region, it completely fails in the kathodal extrapolar region. 

 Whenever it appears, it is, therefore, opposed to the polarisation after- 

 currents and comes into conflict with these. 



The whole relation is seen at a glance by means of the 

 following schema, in which the arrow P indicates the polarising 

 current, A and C the anode and kathode. 



1 See ' Handbuch,' Hermann, vol. i. p. 93. 



