ELECTROTONUS 



569 



effects balance each other. The galvanometric effect is 

 then zero. But if one of the two have its excitability en- 

 hanced in any way, this balance will be disturbed, and a 

 resultant current will flow through the circuit, the more ex- 

 citable contact becoming galvanometrically negative. I now 

 took a long piece of isolated vegetal nerve and connected 

 it with the galvanometer at E and E' I} a secondary coil, 

 giving equi-alternating electric shocks, being also in the 

 circuit (fig. 348). The 

 two longitudinal con- 

 tacts E' and E being 

 more or less equally 

 excitable, there was at 

 first no resultant re- 

 sponse to stimulation. 

 E' was now made the 

 anode, an E.M.F. of 'I 

 volt being used for the 

 purpose, and a perma- 

 nent current was found 

 to flow in the galvano- 

 meter in the direction 

 of E'GE shown by the 



ability at Anode, and its Depression at 

 Kathode, when the Acting E.M.F. is 



FIG. 349. 



Figs. 348, 349. Experimental Arrangement 

 to Exhibit the Enhancement of Excit- 



feeble 



Fig. 348 shows enhancement of excitability 

 at anode ; Fig. 349, the depression ot 

 excitability at kathode. 



Inside thin arrow indicates direction of polaris- 

 ing current. Outside thick arrow, direction 

 of excitatory current. Note that in both 

 there is a so-called polarisation-decrement. 



thin inner arrow, E' 

 being galvanometrically 

 positive. On now ap- 

 plying equi-alternating 

 shocks, the balance was 

 found to have been dis- 

 turbed, and the re- 

 sponsive current to be in the opposite direction, namely, 

 EGE', as shown by the thick arrow ; E' now undergoing an 

 excitatory negative variation. This shows that the ex- 

 citability of E' has become enhanced by being made 

 anode. E' was next made kathode, in consequence of 

 which the permanent current in the galvanometer was now 

 in the direction of EGE' (fig. 349). E' is now the kathode, E 



