306 MOTOR RESPONSES 



tions on rhizopods in a direct current, maintains that immediately after 

 the circuit is closed, there is marked contraction at the anodal side and 

 then movement toward the cathode, and that if the current is strong 

 enough, disintegration begins on the anodal surface of the organism. 



Greeley (1904), in referring to Amoeba, says that "on the anodal 

 side of the cells the protoplasm is coagulated . . . and on the cathode side 

 it is liquefied." Bayliss (1920) maintains, however, that the current 

 causes only gelation. According to the careful observations of Luce 

 ( 1926) , hyaline blisters appear on pseudopods oriented with their longi- 

 tudinal axis perpendicular to the direction of the current. With the aid 

 of superior optical apparatus, he observed the transformation of these 

 blisters into pseudopodia. Since there was no indication of gelation, the 

 phenomenon must have been due to a liquefaction of the plasmagel at 

 the cathodal surface. 



More details concerning response of rhizopods to electricity were ob- 

 tained by Mast (1931b) in observations on A. proteus in direct and 

 alternating currents of various intensities. The results obtained are as fol- 

 lows. 



Direct current. — In direct current of low density, movement continues 

 no matter how the amoebae are oriented in the field, but the formation 

 of pseudopods is inhibited on the anodal side, resulting in gradual turn- 

 ing toward the cathode. In stronger currents movement ceases imme- 

 diately after the circuit is closed, then in a few moments one or more 

 pseudopods appear on the cathodal side and movement continues directly 

 toward the cathode. In still stronger currents there is marked contraction 

 on the anodal side immediately after the circuit is closed. This is soon 

 followed by disintegration which begins at this side. 



If the anterior end of the amoeba faces the cathode when the current 

 is made, there is, in the lowest density that produces an observable effect, 

 merely a slight momentary increase in the rate of flow in the plasmasol 

 immediately back of the hyaline cap. No change in the rate of flow is 

 seen elsewhere. If the current is stronger, this increase extends back 

 farther, the hyaline cap disappears, the plasmasol extends to the tip, the 

 anterior end becomes distinctly broader, and the plasmagel becomes very 

 thin (Fig. 111). If the current is strong enough, this is followed by 

 violent contraction at the posterior end, slight contraction at the an- 



