88 LIBBIE H. HYMAN 



• Without then any intention of denying that amoebae with 

 fluid surfaces exist, I much nevertheless insist on the basis of the 

 facts presented above that in the great majority of the Rhizo- 

 poda, the ectoplasm has undergone gelation; indeed, this would 

 seem to be the necessary consequence of the exposure of such a 

 colloidal solution as protoplasm to the water. Thus it has fre- 

 quently been demonstrated that isolated portions of cells quickly 

 form the same sort of surface 'membrane' as was present on the 

 original cell. It is unnecessary to point out that fluid proto- 

 plasm in the absence of such a surface layer would quickly dif- 

 fuse out into the water, as happens in the amoeba when the ecto- 

 plasm is destroyed. 



I may now state an explanation of amoeboid movement based 

 on the foregoing facts. Since the ectoplasm is a more or less 

 rigid gel, the direct cause of pseudopod formation must be a 

 local liquefaction, and the direct cause of the withdrawal and 

 contraction of pseudopodia must be coagulation. Thus gelation 

 and solation 17 are the essential processes in amoeboid motion. 

 The metabolic change which I have shown with the cyanide 

 method to precede pseudopod formation is undoubtedly the 

 cause of the solation or liquefaction; the cause of the gelation is 

 not so clear, but it must be a reversal of the changes which bring 

 about liquefaction. 



According to this idea, an amoeba moves in the following way. 

 The ectoplasm is an elastic tensile gel which exerts a tension 

 upon the more fluid endoplasm. This elastic tension — the ' gela- 

 tinierungsdruck' of Rhumbler — is characteristic of colloidal gels 

 and appears to be very much greater than the surface tension 



17 I have used the terms gelation and solation in preference to the more awk- 

 ward but perhaps more familiar words gelatinization and peptonization. By 

 gelation I mean an increase in size of the colloidal particles due to aggregation, 

 resulting in a great increase in viscosity, and by solation, a decrease in size of 

 the particles, a finer state of dispersion, with decrease in viscosity. I have 

 avoided a discussion of the relation between viscosity and colloidal state be- 

 cause this subject is in a very unsatisfactory state at the present time. I have 

 also avoided a discussion of the energy changes involved in such alterations of the 

 colloidal state but obviously they must be very great. I prefer not to use the 

 term coagulation because this generally implies a separation out of the colloidal 

 material, an occurrence which seems to be incompatible with life. 



