CHAPTER XXXIX 



ELECTROTONUS 



Extra-polar effects of electrotonic currents on vegetal nerve Electrotonic 

 variation of excitability Bernstein's polarisation decrement Hermann's 

 polarisation increment Investigation into the law of electrotonic variation 

 of conductivity Investigation on variation of excitability Conductivity en- 

 hanced when excitation travels from places of lower to higher electric potential, 

 and depressed in opposite direction When feeble, anode enhances and kathode 

 depresses excitability All electrotonic phenomena reducible to combined 

 action of these factors Explanation of apparent anomalies. 



WHEN an electrical current is Jed through a portion of a 

 nerve entering, say, at A, and leaving by K it is found that 

 electro-motive changes are induced by it in the extra-polar 



E El 



A-n ^ ^ 



FIG. 336. FIG. 337. 



Extra-polar Kat- and An-electrotonic Effects 



Fig. 336 shows kat-electronus, E near K being galvanometrically negative. 

 Fig. 337 shows an-electronus, E near A being now galvanometri- 

 cally positive. 



regions. On the kathodic side, the electric potential near 

 K is found to be lowered in reference to a point further away. 

 On the anodic side similarly, the electric potential of a point 

 near A is found to be raised. These changes induced in the 

 electric potential are indicated by the galvanometric nega- 

 tivity of the point near the kathode, and positivity of that 

 near the anode (figs. 336, 337). In the tissue itself the 

 current is assumed to flow in a direction contrary to that in 



