METABOLIC GEADIENTS IN AMOEBA 89 



characteristic of fluids. At some local spot in this gel, a chemi- 

 cal change occurs, an increase in metabolic rate or an alteration 

 of some kind of metabolism. As a result of this, substances or 

 ions are set free or removed which alter the colloidal state of the 

 ectoplasm, and cause it to become more liquid, that is, to go 

 over into the sol state. If emulsoid gels have an alveolar 

 structure, 18 this would involve dissolution of the walls of the 

 alveoli and a reversal of phase such as Clowes has suggested. 

 These reversals are easily and rapidly brought about by the 

 addition of the proper ions. At the region where the liquefaction 

 has occurred, the protoplasm must necessarily flow out owing to 

 the tension exerted by the ectoplasm. As soon, however, as the 

 pseudopodium extends out into the water, its surface gelatinizes 

 because of contact with the water. It is necessary therefore for 

 the continuous production of a pseudopodium, that the metabolic 

 change which is the cause of the liquefaction should continue to 

 occur at the pseudopodial tip. There is thus produced the meta- 

 bolic gradient along the pseudopodium which I have described 

 in the earlier part of this paper The pseudopodium thus co- 

 agulates as it goes so that it may readily curve or bend or assume 

 and maintain any of the irregular forms often seen, and further 

 it is sufficiently stiff to support the amoeba in the way that 

 Dellinger discovered. 



While I have based the idea that pseudopod formation is 

 the result of liquefaction mainly on logical grounds, direct ob- 

 servational evidence to the same effect is not wanting. Thus 

 many observers have noted that the newest pseudopodia are 

 much more fluid than the older ones, and that pseudopodia 

 which have been long in contact with the water are quite stiff 

 and rigid and are dragged about by the amoeba like inert masses 

 (for instance, Gruber, '11). Observation of the amplitude of the 

 Brownian movement of the endoplasmic granules confirms these 

 statements. While it is indeed somewhat difficult to compare 

 the Brownian movements of the granules in various parts of the 

 amoeba with any degree of certainty, yet I am reasonably sure 



18 The existence of the alveolar structure is not of course in the least neces- 

 sary for the theory presented here. 



