POLAR EFFECTS OF ELECTRICAL CURRENT 199 



excitation with a feeble current is initiated only at the 

 kathode at ' make,' this excitation being then conducted 

 along the nerve to cause the contraction of the terminal 

 muscle. 



It has been ascertained that this particular type of effect 

 is by no means universal. In working on the polar effects of 

 currents on Protozoa, it was found by Kiihne, Verworn, 

 and others that the phenomena there displayed are more 

 or less the opposite. Hence it has been assumed by some 

 that the law of polar reaction in unfibrillated protoplasm 

 is entirely different from that which holds good in animal 

 tissues in general. 



I shall, however, be able to show that the reactions in the 

 undifferentiated protoplasm of the plant body are identical 

 with those of highly differentiated animal tissues. Experi- 

 ments with plants, moreover, led me to the discovery that 

 what is known as Pfliiger's Law is not a complete statement 

 of the polar reactions that take place in living tissues. For 

 it will be shown that under high electromotive forces a new 

 class of phenomena comes into prominence, culminating in 

 a more or less complete reversal of the normal reactions. 

 From a consideration of these it would appear as if 

 the effects on Protozoa were perhaps to be regarded as less 

 anomalous than has hitherto been supposed. 



In studying the polar effects of an electrical current on 

 the plant, I shall first take a simple case and employ the 

 pulvinus of Mimosa as the contractile organ by which the 

 excitatory action is to be detected. A straight form non- 

 polarising electrode is employed for making the necessary 

 electrical connections. This consists of a glass tube the 

 lower half of which is filled with kaolin paste moistened 

 with normal saHne. A wet thread hangs down from the 

 kaolin and makes contact with the plant. The upper half 

 of the tube, above the kaolin paste, is filled with a saturated 

 solution of zinc sulphate ; an amalgamated thin rod of zinc 

 dips into the zinc sulphate and serves as the electrode. In 

 the Mono-polar method of experiment one contact is now 



