84 BIOLOGICAL CHEMISTRY 



pass into the cell when present in the surrounding medium are 

 soluble in the cell contents when passed directly into the cell.* 



The experimental evidence indicates that in many ways the 

 cells react as if they were surrounded by semi-permeable 

 membranes but that some cells at least do not possess a 

 limiting membrane. 



Amoeboid movement is better explicable on the assumption 

 that the cell is a fluid immiscible with its surroundings. The 

 surface condensation of fatty materials produced by the 

 influence of surface tension does not explain the ease or 

 difficulty with which some substances enter the cells because 

 there are fat soluble substances that do not enter cells and 

 there are substances not soluble in fat that do enter the cells. 



The ingestion of solid particles by one liquid suspended in 



A B 



FIG. 15. Diagram to illustrate formation of a pseudopodium. 

 With even surface tension a spherical form exists. (A) By the action of some substance 

 outside the cell a local decrease in surface tension causes a projection as shown at B. It 

 is possible that the same result may be brought about by some local change inside the cell ; 

 this is indicated by the second sphere of influence. Ihe internal change may be either a 

 rise in osmotic pressure or a decrease in surface tension, probably the latter. 



another depends on the relative surface tensions between 

 the object and the two solutions. A drop of chloroform in 

 water will absorb a piece of glass coated with shellac and 

 extrude it after the shellac has been dissolved from the surface 

 of the glass. f 



Destruction of cells by substances which decrease the surface 

 tension indicates that the cells behave like immiscible fluids, 

 sp that when the surface tension is decreased the two fluids mix. 



Czapek has shown that when the air water surface tension is 

 reduced to o'68 to 0*69 of that of pure water, the cell contents 



escape. J 



When a phenol-water mixture is warmed to 68-4 C. the 

 constituents mix in all proportions. Red blood corpuscles 

 haemolyse when warmed, but unlike the phenol-water mixture 

 separation does not occur again when the solution is cooled. 



* G. L. Kite, Biol. Bull., 1913, vol. 25, p. i. 



f Rhumbler, Ergeb. d. Physiol., 1914, vol. 14, p. 474. 



I F. Czapek, Ber. d. d. bot. GeselL, 1910, vol. 28, p. 480. 



