EXCITATORY POLAR EFFECTS OF CURRENTS 



193 



place during the variation of current, but not when the cur- 

 rent has attained a constant value ; and (c) that there is no 

 excitation at either kathode-break or anode-make or break. 



I next used a specimen oi BiopJiytum, the E.M.F. employed 

 being eight volts. The kathode was at first at the lower end of 

 the leaflets, the anode being on the main stem (fig. 89). At 

 make there was an excitatory wave at the kathode. This 

 travelled outwards and produced depression of four pairs of 

 leaflets. On reversing the current, the new anode did not 

 produce any effect at make, nor did 

 its break produce any excitation. It 

 will be shown presently that it is 

 necessary to have a certain moderate 

 intensity of current in order that the 

 anode-break may cause excitation. 



The effect on Biophytuvi of a 

 continuous current at the kathode is 

 to bring about a more or less pro- 

 longed 'contraction,' the period of 

 recovery being thereby much pro- 

 tracted. With the leaf-stalks of 

 Miiiiosa, however, the effect is not 

 so marked. With this plant, never- 

 theless, I have been able to observe certain antagonistic effects 

 of anodic and kathodic actions ; that is to say, while there is 

 slow recovery from kathodic contraction, on reversing the 

 current, there is often an impulse of relaxation, the recovery 

 being thereby suddenly hastened. But it must be under- 

 stood that these particular effects are liable to modification, 

 being dependent on the physiological condition of the tissue. 



I next repeated these experiments on the effect of feeble 

 E.M.F. producing excitation by means of condenser dis- 

 charge. The results obtained were .precisely the same as 

 with constant current. That is to say, with relatively feeble 

 charge, the excitation took place at the kathode at make, 

 and not at the anode. The great advantage of excitation 

 by the method of condenser discharge is, that the total 



O 



Fig. 89. Diagrammatic re- 

 presentation of Mono-polar 

 Excitation 



K was kathode, which at make 

 gave rise to excitatory 

 wave, causing depression 

 of four pairs of leaflets. 

 The electric connections 

 are always made with non- 

 polarisable electrodes. 



