ELECTROTONUS 567 



I next undertook an investigation into the effect on 

 conductivity, of variations of intensity in a moderate polaris- 

 ing current. This is shown in fig. 346, in which excitation 

 travels electrically downhill that is to say, from the anodic to 

 the kathodic region. In a we have the normal response 

 before the passage of the current. In b we have the re- 

 sponses reduced by the diminution of conductivity con- 

 sequent on the application of 'I volt for polarisation. On 

 the application of '5 volt in c, there was a tendency towards 



FIG. 346. Photographic Record of Modification of Conduction during 

 Passage of Excitation from Anodic to Kathodic Region, under Increasing 

 Intensity of Polarising E.M.F. 



a, Normal response ; d, Diminished response where terminal E.M.F. was 

 i volt ; c, Response still further diminished and rendered diphasic 

 under *5 volt ; d, Response reversed under I volt. 



reversal, the response being now diphasic, positive followed 

 by negative. Finally, on the application of I volt in d, we 

 see the response reversed to positive, the conduction of the 

 true excitatory effect being here altogether abolished. 



In a second set of experiments, carried out on a fresh 

 specimen, I investigated the effect of an increasing intensity 

 of the polarising current, when the excitation was made to 

 travel, electrically uphill, from the kathodic to the anodic 

 region. It will be seen, from figure 347, that the application 

 of a polarising E.M.F. of *i volt increased the conductivity, 

 as seen in the heightened responses shown in b, as compared 



