318 MOTOR RESPONSES 



negative ions, SO^, PO^, NO3, and others. In a structure like the plas- 

 magel, the movement of ions is undoubtedly hindered. Nevertheless, 

 the positive ions may move farther from their initial positions toward 

 the pole than do the negative ions. It may be assumed that the nega- 

 tive ions tend to remain in the plasmagel, whereas the positive ions 

 tend to leave it and return again as the direction of the current reverses. 

 If the return movement of the positive ions is inhibited, there may be 

 a momentary preponderance of negative ions within the plasmagel, 

 and of positive ions in the adjoining substances, i.e., in the plasmasol, 

 the hyaline layer, and the plasmalemma. If the movement of the posi- 

 tive ions away from the negative ions is extensive enough, the negative 

 ions remaining in the plasmagel will unite with the hydrogen ions of the 

 water surrounding them, to form acids. The hydroxyl ions thus lib- 

 erated will, owing to the fact that they pass rapidly and freely through 

 tissues, move out and unite with the positive ions, to form bases in the 

 substance adjoining the plasmagel. It is possible that this union retards 

 the return movement of the positive ions during the next reversal in the 

 direction of the current. Consequently the effect would be cumulative, 

 gradually increasing the acidity within the plasmagel and the alkalinity 

 of the substance on either side. 



The increase in acidity in the plasmagel would produce gelation in this 

 layer and probably also in closely applied plasmasol. This would in- 

 crease the thickness and elastic strength of the plasmagel. Contraction 

 would be the result. If the accumulation of negative ions were great 

 enough, the increase in acidity in the plasmagel would cause irreversible 

 coagulation (death), accompanied by violent contraction and dehydra- 

 tion, thus making the coagulated plasmagel so brittle that it would break 

 readily. The increased alkalinity in the plasmasol and plasmalemma 

 would tend to make the former more fluid, and it would tend to break 

 up the latter. The postulated action of the current is precisely in accord 

 with the observations. It also accounts for the fact that no response was 

 observed in pseudopods which contained no plasmagel. According to the 

 explanation offered, an accumulation of ions occurs in or near the plas- 

 magel; there could be no action in structures which have none. 



Moreover, on the basis of this hypothesis, it is possible to account 

 for the well-known fact that in many organisms the effect of a current 

 varies inversely with the frequency of reversal. It is necessary only to as- 



