60 THE TROPISMS 



inserted in the two sides of a drop of water containing 

 Paramcecia the infusorians will soon all collect around the 

 negative pole. In solutions of sodium chloride and certain 

 other salts Paramcecium frequently swims backward 

 toward the anode, and Bancroft has found that true anodal 

 electrotaxis, in which the infusorians swim forward toward 

 the anode, may occur for a short time in solutions of sodium 

 chloride, sodium carbonate and other salts if the Para- 

 mcecia are washed in distilled water before being placed in 

 the solutions. 



Electrotaxis has been observed in ccelenterates, worms, 

 mollusks, Crustacea, the larvae of insects and in fishes, tad- 

 poles and salamanders. In general the reaction of worms 

 andTmollusks is negative and the reaction of Crustacea 

 positive. In tadpoles which orient their bodies parallel 

 with the direction of the current the direction of orientation 

 is dependent upon the strength of the current. 



Orientation to the electric current is apparently brought 

 about by the polar effect of the current upon the tissues of 

 the body. In Paramcecium there is a direct orientation pro- 

 duced by the unequal beat of the cilia on the two sides. In 

 cathodal orientation the forward phase of the stroke of the 

 cilia is accentuated where the current leaves the body so that 

 there may be a reversal of the effective stroke; where the 

 current enters, the backward stroke continues so the organism 

 naturally swings into line with the current. In higher organ- 

 isms there is a distinctly evident polar effect upon the 

 musculature of the body which can be seen to produce the 

 orientation of the organism. The effect of the electric 

 current on animals generally is to produce movements 

 which are in a certain sense "forced/' and the orientation 

 so brought about affords an excellent example of a typical 

 tropism as conceived by Dr. Loeb. 



