METABOLIC GRADIENTS IN AMOEBA 75 



The shock reaction is readily capable of a purely niechanistic 

 explanation. Since there exists in the moving amoeba a tempo- 

 rary metabolic gradient — and in other organisms a permanent 

 gradient — a strong stimulus applied with equal intensity to all 

 parts of the animal, and therefore not in itself differential, must 

 nevertheless produce a differential effect, owing to the internal 

 gradient. The most active end of the organism will be most 

 affected by the stimulus and most inhibited, while the least 

 active part is least altered and hence more capable of carrying 

 out the normal activity. The anterior half is literally prevented 

 from giving rise to pseudopodia. 



These observations serve, I think, to remove any doubts as to 

 the correctness of my interpretation of the initial rupture of the 

 ectoplasm which occurs in normal cyanide. • When the amoeba 

 is exposed to cyanide of this strength, it gives the shock reaction. 

 The contraction of the anterior end does not occur — this is prob- 

 able impossible in the cyanide — but pseudopodium formation is 

 initiated at the posterior end in the manner typical of the shock 

 reaction. Whether pseudopodia actually appear or not depends 

 upon the concentration of cyanide employed but in either event, 

 the same internal change, increased susceptibility, takes place. 

 From this it follows that this change, which I have interpreted as 

 a metabolic change, is the direct cause of the formation of pseudo- 

 podia, and if long enough continued, of the pseudopodial gradient. 

 The fact, then, that increased susceptibility, increased metabolic 

 rate, precede pseudopodium formation constitutes a basis for 

 certain suggestions regarding the nature of amoeboid movement. 



IV. EXPLANATION OF AMOEBOID MOVEMENT 



I wish to state at the outset that it is with considerable diffi- 

 dence and a conviction of inadequacy that I enter upon a dis- 

 cussion of this difficult problem. I feel, however, that it is in- 

 cumbent upon me to present the line of argument which naturally 

 follows from my observations. 



Anyone who writes upon the subject of amoeboid movement 

 must give serious consideration to the surface tension theory be- 

 cause of the careful analysis to which this theory has been sub- 



