ELECTROTONUS 



233 



FlG. 99. Effect of Anode as Block. 

 a, Anode ; k, Kathode 



The progressive wave of excitation, 

 initiated at x , stopped by anode, 

 one pair of leaflets to its left. 



either with greater velocity or to a greater distance ; but if 

 conductivity be in any way diminished, the distance to which 

 the excitatory disturbance will be transmitted, will be corre- 

 spondingly reduced. 



The anodic block. — In order to demonstrate the de- 

 pressing action of the anode, I took a leaf of Biophytiim, and 

 sent a current through portions of it, entering at A, the anode, 

 and leaving at K, or kathode 

 (fig. 99). The E.M.F. used was 

 two volts, and was thus insuffi- 

 cient to cause responsive action. 

 In this and the following expe- 

 riments, it will be understood, 

 unless the contrary is stated, 

 that the intensity of the elec- 

 trotonic currents was not such 

 as to create any direct action at the kathode. Thermal 

 stimulus was now applied at x, and the excitatory wave was 

 found to be stopped at a distance of one pair of leaflets to 

 the left of A. This shows that the depressing effect of the 

 anode acts as a block to the passage of stimulus, and that 

 such depressing action extends to some distance beyond the 

 anode itself. 



Experiments showing differences of anode and 

 kathode.— In order to show that the kathode acts differently 

 from the anode, not offering 

 a block, but rather facili- 

 tating the passage of stimu- 

 lation, I performed another 

 experimenton a leaf similar 

 to the last. In that case, 

 the anode was near the 

 point of application of 

 stimulus. I now made the 

 nearer electrode kathode. 



On next applying the usual stimulus, the excitatory wave 

 passed on through the kathodic area, producing successive 



1 



M< 



*0wmmi 



FlG. 100. Experiment showing the 

 Transmission of Excitatory Wave 

 through Kathodic Area, and its Stop- 

 page by the Anode 



Stimulus was applied at x . 



