140 



ELECTRICITY AND PROTOPLASM 



[CH. VI 



and Amoeba to a weak constant current. At first the pseudo- 

 podia on the anode side plainly retracted, but later ceased to 

 do so, and, finally, the current still passing, the retracted 

 pseudopodia began to extend again. The action of the current 

 so modified the protoplasm as to change the attunernent of the 

 organism. 



3. ELECTROTAXIS 



In studying the subject of aggregation with reference to the 

 electric current, we shall consider first the simplest case of this 

 phenomenon as it is exhibited in Amoeba ; then pass to the 

 more complex forms of Protista, especially the Ciliata, and after 



FIG. 32. Galvanotaxis of Amoeba diffluens. A, Amoeba creeping, unstimulated ; 

 B, after closing of the constant current. The arrow indicates the direction of 

 locomotion. (From VEBWOBN, '95.) 



that to the Metazoa. After dealing with the phenomena we 

 must attempt to explain them. 



When such an amoeba as that shown in Fig. 32, A, is sub- 

 jected in a drop of water to the action of a weak constant 

 current, as already indicated (p. 129), it contracts, especially 

 upon the face turned towards the anode. If the current is not 

 strong enough to produce disintegration at that pole, but only 

 repeated contraction, and if meanwhile the kathode pole retains 

 its power of throwing out pseudopodia, the amoeba must grad- 

 ually move from the anode (Fig. 32, jB), and if several Amoebae 

 are under the cover-glass, they will eventually aggregate about 

 the kathode. Here we have, then, in its simplest form, a case 

 of electrotaxis, and, since the organism moves toward the 

 negative electrode, we may call it negative electrotaxis. 



If now, instead of an amoeba, we watch a free swimming 

 flagellate Infusorian, Trachelomonas hispida (Fig. 33), we 



