268 J. F. McClendon 



portions that were attached to the substratum. I found from a 

 large number of observations that an Amoeba stimulated in the 

 center of a large flat area over an attachment to the substratum, 

 by introducing into the ectosarc a copper needle, showed a tem- 

 porary stoppage of the extension of pseudopodia in the most 

 remote parts. The interval of time was in half the cases less than 

 that calculated for the movement of hydrogen ions in aqueous 

 solution (.03 mm. per second). The reaction time in Amoeba 

 is considerable (though apparently very variable) and allowing 

 for it, it is probable that in all cases the stimulus traveled at a speed 

 greater than .03 mm. per second. Lest there be an electrostatic 

 action at a distance I "grounded" the copper needle and repeated 

 the experiment many times but with the same results. In order 

 to facilitate observation I selected large Amoebae moving along 

 without dorsal or lateral pseudopodia. These gave the same 

 results. 



The Food Taking of the Amceha 



From the above results, and observations on food taking I pro- 

 pose the following hypothesis to account for the latter process : 

 Chemical and physical influences of the medium cause a har- 

 dening and shrinkage (by loss of water) of the ectosarc (Rhum- 

 blers "Geletinisirungsdruck"). Chemical processes within prevent 

 this hardening from extending to the endosarc, and dissolve 

 portions of the ectosarc that are displaced inward. The medium 

 affects difi^erent portions of the surface to different degrees, causing 

 regional differences in degree of hardening and shrinking, thus 

 producing amoeboid movements. A food body being protoplasmic 

 and therefore similar to the substance of the Amoeba might, in 

 lying near an Amoeba, protect it from these outside influences. 

 The protected region would become more fluid, and shrinkage of 

 other regions of the surface would press it out toward the food until 

 it touched it. The food would be pushed along and sometimes 

 rolled over and would rub on the surface of the pseudopod pro- 

 ducing mechanical stimuli of sufficient frequency to cause a local 

 shrinkage of the ectosarc. This stimulus would spread through 

 the protoplasm but being very weak and rapidly growing weaker 



