86 LIBBIE H. HYMAN 



the same conclusion that we have reached from other lines of 

 evidence. 



Finally I may mentioned the observations of Mast and Root 

 ('16) on the feeding of Amoeba on Paramecium. They fre- 

 quently saw an amoeba partially inclose a Paramecium with 

 food cup, and then cut the Paramecium in two by bringing 

 the edges of the cup together. They calculated that the force 

 necessary to sever a Paramecium in this way is very much 

 greater than any which could possibly be developed through 

 differences between the surface tension of the rim of the food cup 

 and the surface tension elsewhere. The argument is obviously 

 open to the criticism that the amoeba may extrude something 

 which softens the surface gel of the Paramaecium but this ap- 

 pears to be ruled out by the rapidity with which the process 

 occurs — 10 seconds — as well as by the consideration that such 

 softening would probably cause visible changes in the Para- 

 maecium which could scarcely have been overlooked by the 

 observers. 



Probably a great many more facts of experiment and observa- 

 tion could be brought forward as evidences against the surface 

 tension theory. I have not attempted a thorough search through 

 the literature. I believe that the facts which I have already 

 presented are quite sufficient to convince one that the ectoplasm 

 of the amoeba is solidified to a degree which makes it highly 

 improbable if not impossible that surface tension can play any 

 important role in amoeboid movement, and further that the 

 behavior of amoeba in general is incompatible with such an 

 idea. 



We may therefore come to the following conclusions regarding 

 the physical state of the protoplasm of the amoeba and probably 

 many other Rhizopods. The ectoplasm is an emulsoid gel, 

 semi-rigid and more or less solidified. Like all such emulsoid 

 gels, it possesses many properties of solids, such as high elasticity, 

 contractility, extreme viscosity, compressibility (cf. Freundlich 

 '09, pp. 474 ff.). These properties are in all probability due to 

 the structure of such gels; they are probably made up of poly- 

 gonal cells, the thin walls of which consist of the colloidal ma- 



