METABOLIC GRADIENTS IN AMOEBA 81 



like protoplasm, the assumption of the spumoid structure must 

 be accompanied by a loss of fluid properties, and a marked acqui- 

 sition of solid characteristics, such as compressibility, elasticity, 

 contractility, etc. 13 Hence, Rhumbler's whole argument, the 

 essentials of which are quoted above, that the discrepancies 

 between the behavior of living protoplasm and of fluids offer two 

 alternative explanations, i.e., the presence of a solid membrane, 

 or the existence of the spumoid structure, really leaves him no 

 alternative but leads on both sides to the conclusion that the 

 surfaces of free cells do not behave like fluids but like solids. And 

 from this it follows that amoeboid movement cannot be caused 

 by alterations in the surface tension since surface tension phe- 

 nomena as commonly understood are phenomena of fluids and 

 the exposed surface of protoplasm behaves like a solid, and is in 

 all probability a colloidal gel. 



I now wish to present certain other lines of evidence which in- 

 dicate conclusively that the surfaces of free cells, and particu- 

 larly of ameoboid organisms are altogether too stiff and firm to 

 obey the laws derived from the behavior of simple fluids. Ref- 

 erence may first be made to the micro-dissections of Kite ('13) 

 and Chambers ('15, '17). Chambers states that with proper 

 precautions no alteration of the physical condition of the proto- 

 plasm occurs as a result of the dissection. Kite found that the 

 ectoplasm of the amoeba is a " quite concentrated gel while the 

 interior is dilute," and that the " outer surface of Amoeba pro- 

 teus is a semi-rigid solid of from 5 to 12 or more microns in thick- 

 ness." The ectoplasm could easily be cut into pieces of all 

 sizes. Chambers has confirmed these results and finds that free 

 cells in general, such as egg cells and Protozoa consist of gel 

 surfaces and sol interiors. The surface gel is contractile and ex- 

 tensile and if ruptured allows the cytoplasm to escape. A much 

 more extensive rupture is required in the case of Amoeba than 

 in the case of Paramaecium before the endoplasm will escape, 



13 Perhaps the most beautiful example of alveolar protoplasm is the protoplasm 

 of the Heliozoa. I have found that the heliozoan Actinosphaerium Eichhornii 

 can be cut into pieces with a needle exactly as if it were solid, that is, the pieces 

 show no tendency to minimize their surfaces. Obviously, the alveolar structure 

 has conferred upon the protoplasm solid properties. 



