576 COMPARATIVE ELECTRO-PHYSIOLOGY 



current, being thus concordant with the electrotonic current, 

 causes an increase of it, the so-called polarisation-increment. 



In Bernstein's experiment on polarisation-decrement, we 

 are confronted with a question of greater complexity, for 

 here we have to deal with changes of conductivity and 

 excitability at the same time. We shall first take the .case 

 (fig- 339) in which one electrode of the led-off circuit E is 

 under kat-electrotonus. E' is therefore relatively anodal, 

 and consequently more excitable. The excitation from the 

 stimulator S which reaches E' is in this case impeded in 

 reaching E by the fact that it has to travel electrically 

 downhill that is, from the ariodal E' to kathodal E. Thus, 

 owing to the greater excitation which reaches E', and owing 

 also to the greater excitability induced in it by the fact that 

 it is relatively anode, excitation induces a relatively greater 

 galvanometric negativity of that point. The thick arrow in 

 the figure indicates the excitatory current, which is opposite 

 in direction to the polarisation current, which latter is 

 indicated by the thin arrow. In the second case, when the 

 polarisation current is reversed (fig. 340), E is anodal, and 

 therefore relatively more excitable, and E' kathodal, and there- 

 fore less excitable. Unlike the last case, the excitation from 

 S, in order to reach E, has now to travel electrically uphill 

 from the kathodal to the anodal points. The excitation of E 

 therefore is in this case not impeded. Hence greater excit- 

 ability of E makes that point, on stimulation, galvanometrically 

 negative, and the responsive current, represented by a thick 

 arrow, brings about a diminution of the polarisation-current. 



It has thus been shown, in the course of the present 

 chapter, that the same electrotonic effects are exhibited in 

 the case of the plant, as in that of animal, nerves. It has 

 been shown that various apparently anomalous results may 

 be brought about by simple combinations of two different 

 factors. Thus, the so-called polarisation increment and 

 decrement are not mutually conflicting. They are, on the 

 contrary, due to the distinct and definite effects induced by 

 electrotonus on conductivity and excitability respectively. 



