x ELECTROMOTIVE ACTION IN NERVE 273 



other words, the alteration of excitability is present simultaneously 

 with the corresponding galvanic alteration. 



Subsequent experiments undertaken by different workers in 

 the hope of deciding this question (i.e. the absolute time occupied 

 by development of the electrotonic alterations in the nerve after 

 closure of the polarising current) have not so far produced any 

 congruous results. According to Wundt (33), who undertook a 

 comprehensive inquiry into the time-distribution of the electrotonic 

 alterations of excitability in the frog's nerve-muscle preparation, 

 these changes are not developed simultaneously with the closure 

 of the polarising current at all points of the nerve, but spread 

 from the poles with comparatively low and easily measurable 

 rapidity from section to section by an undulatory process analogous 

 with that of excitation. In this sense Wundt speaks of an 

 " anodic wave of inhibition " (i.e. an altered state of the nerve-sub- 

 stance, characterised by diminished capacity for response), trans- 

 mitted from the anode at a rate that varies with the strength of 

 the polarising current from 80 to 1700 mm. per sec. ; and a 

 kathodic wave of excitation (i.e. katelectrotonic rise of excitability), 

 of which the rate of transmission appears to correspond with that 

 of active excitation. In regard to method, it is sufficient to state 

 that it consisted essentially in exciting different points of the 

 myopolar part of the nerve, at different periods after the closure 

 of an ascending, or descending, polarising constant current, with 

 single induction shocks, and then recording the discharged con- 

 traction graphically. The differences which then appear in regard 

 to time-distribution, the magnitude (height), and duration of 

 twitches, before and after closure of the polarising current, form 

 the basis of conclusions as to the state of excitability at any point 

 of the nerve at a given moment. Wundt's observations, into which 

 we cannot here enter in detail, seem to have been little regarded ; 

 they are in direct contradiction with Pfliiger's experiment, as described 

 above, and also with certain experimental results of Griinhagen 

 (34), in which the commencement of the electrotonic alteration of 

 excitability coincides, at all points of the nerve, with the moment 

 of closing the polarising current. If (Fig. 209) a rheochord (rr l ) 

 and the primary coil of an induction apparatus are included in the 

 polarising circuit (JT), a branch of the primary current may be 

 led into the nerve of a nerve-muscle preparation (cd) in an 

 ascending direction. Although in itself inadequate to excite 



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