5 02 



NER VE. 



262. 



repetition of the classical transmission experiment of Helmholtz, with 

 the addition of a polarising current on the central side of both exciting 

 contacts (Fig. 262). 



During the passage at A of an ascending galvanic current (of at 



most 0*5 Daniell), the 



I I. [/ |/ maximal muscular re- 



*W If 1L ^--gL--_^ sponses evoked by excita- 

 tion, with adequate in- 

 duced current at the 

 proximal and distal points 



B and C, are separated by a much larger interval than is normally the 

 case ; if the current is descending, the interval is less than the normal, 

 von Bezold found that both currents increased the difference, but 

 Eutherford found that the descending current diminished it, and the 



present writer can fully 

 confirm this observation. 

 The curves in Fig. 263 

 are instances of such 

 cathodic acceleration and 

 anodic retardation ; G being 

 cathodic, A anodic, and 

 the uppermost curves 

 normal. 



It will be observed that 

 by this method the excit- 

 ing stimuli are applied to 

 the extrapolar region. If 

 the whole polar region is 



f~ -^ ^ interposed between the 



FIG 263 exciting electrode and the 



muscle, the conditions are 



far more complex. I have been unable to find evidence of any marked 

 alteration in propagation rate, unless the polarising current is intense 

 or of prolonged duration, in which case it is always retarded. The 

 presence of two polar regions, a cathodic accelerating and an anodic 

 retarding, causes the one change to counterbalance the other : when, 

 however, the conditions are such that the anodic effect is intense and 

 the cathodic diminished, then retardation is observed, von Bezold's 

 experiments involved the use of currents of considerable intensity and 

 duration, hence the retardation found by him in all cases. 



Even the opening changes can be seen to influence the rate of 

 propagation. I have found that the opening cathodic retards more 

 than the opening anodic, provided that the current has been of small 

 intensity, short duration, and that excitation by induced currents occurs 

 within one second of the opening. 



Another proof of such polar effect on the rate of propagation is 

 furnished by the increased duration of the delay of the indirect muscular 

 response to polar excitation of its nerve by the galvanic current. 



It is evident that the only cases of marked increase in delay are those in 

 which the cathodic closing and anodic opening excitation are situated, so that 

 the intrapolar region lies between them and the muscle, and the galvanic 

 current is of some intensity. It appears to the writer that the chief factor in 

 the production of the more marked delay is the slower propagation which 



