314 MOTOR RESPONSES 



the structure of the pseudopods which form at this time. The evidence 

 presented above shows that the described changes are brought about by 

 the action of the current. 



Alsup (1939) measured the time required in alternating current and 

 in Hght respectively to cause cessation in streaming (reaction time) and 

 that required for recovery after this response (recovery period). He 

 found in both that the reaction increased as the recovery period decreased. 

 This indicates that after the plasmasol has gelated, owing to the action 

 of electricity or light, and then solated, owing to the recovery processes, 

 it no longer gelates so readily as it did. 



Alsup also found that subminimum exposure to an alternating cur- 

 rent followed by a subminimum exposure to light, or vice versa, may 

 induce a response, indicating that the effects of these two agents are 

 additive. 



In order to account for the essential phenomena observed in amoebae 

 when subjected to the action of an alternating current, it is then neces- 

 sary to explain reversible gelation of the plasmasol adjoining the plasma- 

 gel on the sides of the organisms facing the poles. It should be noted 

 that the gelation of the plasmasol is followed by changes in the plasmagel 

 in the adjoining regions — changes which result in violent contraction, 

 loss of fluid, decrease in elasticity, and rupture, and by increase in the 

 fluidity of the plasmasol. 



Mechanics of response. — In rhizopods all of the responses to direct 

 current appear to be due primarily to solation at the cathodal surface, 

 followed by gelation at the anodal surface. The question then arises as 

 to what causes this. 



If an electric current is passed through a culture solution containing 

 amoebae, the negative ions in the solution and in the amoebae move to- 

 ward the anode, whereas the positive ions migrate toward the cathode. 

 If the surface layers of the amoebae are semipermeable, as they un- 

 doubtedly are, there will be an accumulation of positive ions (e.g., Na) 

 on the inside, and negative ions (e.g., CI) on the outside of the surface 

 of the amoebae directed toward the cathode. Positive ions will accumulate 

 on the outside and negative ions on the inside of the surface directed 

 toward the anode (Ostwald, 1890). The positive ions will, however, 

 unite with the hydroxyl ions of the water, forming bases (e.g., NaOH) ; 

 and the negative ions will unite with the hydrogen ions of the water, 



