ELECTROMOTIVE ACTION IN NERVE 241 



a loss distance between the exciting (or leading-off; electrodes. 

 Accordingly the breach in the series of opening twitches is much 

 plainer in the first case than in the second (Ludinilla Nemer- 

 owsky, 16). Griitzner (I.e.) proposes to explain the phenomenon 

 as follows : " The exciting current may be less than, equal to, or 

 greater than the nerve current. In the first case the nerve 

 current will diminish at closure of the exciting current, and when 

 the latter is opened will return to its original height. When the 

 exciting current is equal to the nerve current, the nerve current 

 (in the deriving circuit) sinks to zero at closure of the exciting 

 current. On opening the latter the nerye current returns from 

 zero to its original height. Lastly, where the exciting current is 

 stronger than the nerve current, its closure sends into the 

 nerve a current less than, and opposite in direction to, the nerve 

 current. At break, on the contrary, this reduced exciting cur- 

 rent disappears, and the nerve current rises again from zero in 

 the momentarily isoelectric nerve." According to Griitzner, 

 an exciting current weaker than the nerve current as well 

 as one that is stronger excites when the circuit is opened. In 

 tlie first case the excitation is discharged at a point which has 

 been rendered considerably more excitable by the kathode of the 

 intrinsic current ; in the second, on the other hand, the action of 

 the voltaic alternative comes into play, since a current traverses 

 the nerve shortly after the passage of a heterodromous current. 

 The disappearance of a current just sufficient to compensate does 

 not excite, because the current which rises from zero does not 

 find exit at any especially excitable point. This coincides with 

 the fact that the " breach " in the opening twitches never appears 

 at isoelectric points of the nerve, unless these have been polarised 

 by the previous passage of stronger currents. In such cases the 

 breach reappears, if exciting currents are employed which are 

 heterodromous to the polarising current passing through the 

 nerve. 



Lastly, we must reckon among the phenomena of interference 

 between nerve current and artificial exciting current the charac- 

 teristic reaction which (as first investigated by Hering, 11) appears 

 in nerves that are stimulated with induction currents in the 

 proximity of the cross-section. " If the electrodes from the 

 secondary coil of an induction apparatus are placed at a distance 

 of only 23 mm. upon the freshly divided or ligatured nerve, in 



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