572 



COMPARATIVE ELECTRO-PHYSIOLOGY 



means of ' down ' and that of the right hand contact E by 

 means of 'up' responses. An E.M.F. of '5 volt was now 



I 



FIG. 351. 



FIG. 352. 



Figs. 351, 352. Experimental Arrangement demonstrating the Joint Effects of 

 Variation of Conductivity and Excitability by Polarising Current 



employed to induce polarisation, the anode being in the first 

 case to the left. Here we have a greater excitability induced 



at E' by the proximity 

 of the anode, that of E 

 being depressed by the 

 proximity of kathode. 

 Of the two waves of ex- 

 citation, moreover, which 

 proceed in opposite di- 

 rections from the stimu- 

 lator S, that towards E' 

 is moving electrically 

 uphill, or towards the 



FIG. 353. Photographic Record of Response anode, and owing to 

 under the Arrangements given in Fig>. 351, 



352 in Nerve of Fern increased conductivity 



a, Balanced record before .passage of polarising 



current. 



l>, Resultant response downwards when polar- 

 ising current is from left to right, as shown 



by arrow ->. This shows excitability of 



E' and conductivity in direction SE' to be 



relatively enhanced. 

 c, Resultant response upwards when polarising 



current is from right to left <-. This 



shows excitability of E and conductivity in 



direction SE to be relatively enhanced. 



in that direction the 

 excitation is better con- 

 ducted than in the case 

 of the second wave, 

 which is proceeding 

 electrically downhill to- 

 wards the kathode at 



E. It must also be 

 remembered that not only is the intensity of excitation 

 which reaches E' greater than that which reaches E, but also 

 that the point E' is itself rendered more excitable by the 



