METABOLIC GRADIENTS IN AMOEBA 67 



ceding case. Here, however, the pseudopodia are not fixed, but 

 continue to change slowly, new ones being formed, and old ones 

 retracted. The animal thus slowly alters its shape but does not 

 change its position. After this condition has persisted for several 

 hours, the pseudopodia are gradually completely withdrawn, 

 leaving the surface smooth and free from corrugations. In this 

 condition death occurs, generally by simultaneous rupture of the 

 entire surface. Sometimes a local rupture precedes the general 

 disintegration but in such cases it is impossible to relate this 

 occurrence to any preceding condition of the pseudopodia. 



In very dilute solutions, ^ molecular or above, the amoeba 

 moves about in the normal manner for many hours although 

 more slowly than usual. Eventually the movement ceases; the 

 animal contracts into a smooth sphere, entirely free from sur- 

 face irregularities. The amoeba remains in this state for hours, 

 bearing considerable resemblance to an encysted individual 

 except that a protecting membrane is lacking. I have not ob- 

 served the death of the animals in these dilutions but have found 

 the disintegrated remains. 



III. INTERPRETATION OF RESULTS; THE SHOCK AND AVOIDING 



REACTIONS 



These experiments demonstrate that a local region of increased 

 susceptibility exists before pseudopod formation; that a differ- 

 ential susceptibility exists along the axis of each pseudopodium 

 from its distal to its proximal end, the distal end being most sus- 

 ceptible; that the susceptibility of a pseudopodium depends 

 upon its age and vigor, the youngest and most vigorous being 

 most susceptible, while old non-functioning pseudopodia are 

 much less susceptible, although still exhibiting differential sus- 

 ceptibility. These are the results as they stand without inter- 

 pretation. The interpretation here of course must be the same 

 as that made for susceptibility to toxic agents in general. No 

 one will assume that the amoeba is different from other organ- 

 isms in this respect. Now as I have already pointed out in my 

 introductory remarks there is a clear relation between suscepti- 

 bility and metabolic rate, such that regions of high metabolic rate 



