METABOLIC GRADIENTS IN AMOEBA 61 



it ceases to move and remains motionless, neither extending nor 

 withdrawing its pseudopodia. The first change that occurs is 

 one that was totally unexpected and for a time seemed inexplic- 

 able. A few seconds after the cyanide has been applied, the 

 ectoplasm at some spot on the surface dissolves away, and the 

 fluid endoplasm instantly bursts out and mingles indistinguishably 

 with the surrounding water. The point in the ectoplasm where 

 this occurs bears no relation to any of the pseudopodia but it is 

 almost invariably at the 'posterior' end of the amoeba, i.e., the 

 end opposite the direction of locomotion; it does, however, occa- 

 sionally take place on the side of one of the larger pseudopodia. 

 As a result of the loss of some of the endoplasm, the amoeba 

 shrinks considerably, and changes its form to some extent but 

 not sufficiently to interfere with the identification of the 

 pseudopodia. 



This entire initial behavior of the amoeba to strong cyanide 

 unavoidably suggests that the ectoplasm is a firm elastic layer 

 inclosing a fluid, the endoplasm. Since the ectoplasm is in a 

 state of tension, the endoplasm bursts forth immediately when the 

 ectoplasm is locally ruptured. The explanation of the local rup- 

 ture of the ectoplasm is deferred until the next section where 

 the action of slightly weaker solutions of cyanide is described. 



Shortly after the ectoplasm breaks disintegration sets in. Dis- 

 integration invariably begins at the tips of the pseudopodia, and 

 proceeds rapidly down each of them to the posterior end of the 

 amoeba in the case of elongated forms, or to the central part in 

 the case of radiate forms. In general, where several pseudopodia 

 are present, the most recent or most recent vigorous pseudopo- 

 dium disintegrates first and the others follow in the reverse order 

 of their formation. In the process of disintegration the ecto- 

 plasm appears to dissolve away so that there is no longer any 

 boundary between the endoplasm and the water, and the endo- 

 plasm then bursts forth, and spreads into the water. All that 

 remains visible of the amoeba is a scattered collection of the 



alkali increases permeability. Thus Child has found that addition of alkali to 

 the cyanide (in dilutions of cyanide too weak to be in themselves alkaline) greatly 

 increases the susceptibility of Planaria while addition of acid decreases it. 



