MOTOR RESPONSES 317 



situation is quite different. There is an equal movement of all substances 

 in opposite directions. Consequently there can be no accumulation of 

 different substances in different parts of the organism, unless there is 

 some process which makes the movement in one direction greater than 

 that in the other. 



The essential phenomena observed in Amoeba as a consequence of 

 exposure to alternating current may be summarized in the order of their 

 appearance. A mild contraction begins first at the tips of extended pseudo- 

 podia. This is followed by violent contraction on the two surfaces fac- 

 ing the poles (blisters appear on these surfaces). Then highly fluid 

 pseudopods form between these two surfaces. Finally, the surfaces di- 

 rected toward the poles rupture and the organism disintegrates. 



Numerous observations with the best lens system obtainable were 

 made on the movement of microscopic particles, both in the field of the 

 alternating current and in the amoebae in this field. There was no indi- 

 cation of a drift of these particles nor of their accumulation in any part of 

 the organisms. It therefore is evident that cataphoresis and electroendos- 

 mosis cannot be involved in the observed contraction. It seems necessary, 

 then, to conclude that the phenomenon of contraction is associated with 

 the movement of the ions produced by the electric current; and, further, 

 that ion movements are accompanied by processes which result in the 

 accumulation of ions in certain regions of the organism. 



Dixon and Bennet-Clark (1927) and others maintain that alternat- 

 ing current causes increase in the permeability of the plasmamembrane 

 in cells. If so, then may not the contraction observed in the plasmagel be 

 due to the action of substances which enter from the surrounding medium, 

 since localized accumulation of ions at the surface of the amoeba in- 

 creases its permeability owing to the action of the current? 



Two facts suggest that the contraction of Amoeba during exposure to 

 alternating current cannot be due to the entrance of substances from the 

 outside. In the first place, the contractions are known to occur in both 

 alkaline and acid solutions. Secondly, alkaline solutions tend to produce 

 solation in the plasmagel, thus decreasing its elastic strength. Possibly 

 the accumulation of ions in or near the plasmagel causes the contrac- 

 tion. 



It is well known that the positive ions, Na, K, Ca, and others ordi- 

 narily pass through membranes more readily and more rapidly than the 



