METABOLIC GKADIENTS IN AMOEBA 69 



permeability, or of colloidal state, or what-not, it must be ac- 

 counted for, and accounted for on the basis of some internal 

 change in the amoeba. It might be said that the tips of the 

 pseudopodia are more freely exposed to the cyanide than other 

 parts, and that therefore the cyanide penetrates them more rap- 

 idly. This objection is invalid, not only because experience 

 indicates that the cyanides penetrate readily into protoplasm 

 but for the reasons that susceptibility differences exist between 

 pseudopodia which are equally exposed to the solution and that 

 the most susceptible places are not the pseudopodia but those 

 places in the central mass where the pseudopodia are about to 

 appear. It might further be said that differences in permea- 

 bility or in physical state along the axis of the pseudopodium 

 would account for the differential disintegration. I believe such 

 differences do and must exist; in fact I think that amoeboid 

 movement is directly due to alterations of the colloidal state but 

 I am unable to account for such alterations except as the result 

 of internal metabolic changes. 



Criticism may be made of my explanation that the initial rup- 

 ture of the ectoplasm in normal cyanide is due to an attempt at 

 pseudopod formation, because if the cyanide is diluted slightly, 

 an actual outflow of protoplasm precedes the rupture. It might 

 be said that this outflow is not a pseudopodium but merely a 

 stage in the bursting of the ectoplasm. In support of this con- 

 tention one might maintain that the amoeba does not ordinarily 

 put out pseudopodia at its posterior end, where this rupture of 

 the ectoplasm generally takes place. It is well known to all 

 observers of amoeba that the animal tends to continue in the same 

 direction for long periods of time, pursuing a somewhat zigzag 

 course, the pseudopodia advancing first on one side and then on 

 the other side of the anterior end. It retains the same anterior 

 end as long as undisturbed and is not ordinarily observed to 

 stop suddenly in its course and put forth a pseudopodium at its 

 posterior end. These considerations have impelled me to per- 

 form some experiments on the behavior of amoeba. 



Jennings ('04, '06) has described the reactions of amoeba to 

 various stimuli. His general conception of the avoiding reaction 



THE JOURNAL OF EXPERIMENTAL ZOOLOGY, VOL. 24, NO. 1 



