178 The Mechanistic Conception of Life 



that only water but no salt can diffuse through the cell-wall; 

 since otherwise salt should gradually diffuse from the solution 

 into the cell, and through this increase in the osmotic pressure 

 of the cell the water should finally diffuse back into the cell and 

 restitute the normal volume of the cell. According to Overton 

 this does not happen. 



Osterhout has recently shown that Overton's observations 

 were incomplete in a very essential point and that in reality 

 the plasmolysis, which occurs in this case when the cell is put 

 into the h^q^ertonic solution, disappears again in a time which 

 varies wdth the nature of the salt in solution. This stage of 

 reversion of plasmolysis had been overlooked by Overton. If 

 the cell, however, remains permanently in the h^^jertonic 

 sodium chloride solution, a shrinking of the contents of the 

 cell takes place again, which superficially resembles plasmolysis, 

 but which in reality has nothing to do with plasmolysis, but 

 is a phenomenon of death. That this second ''false plas- 

 molysis," as Osterhout calls it, has nothing to do with the hyper- 

 tonic character of the solution was proved by the fact that 

 hypotonic solutions of toxic substances may produce the same 

 phenomenon. 



In one experiment which Osterhout describes, 



a portion of a Spirogyra filament was plasmolyzed in .2 m CaCl2, 

 but not in . 195 m CaClo. A .29 m NaCl solution has approximately 

 the same osmotic pressure as a .2m CaClo solution. But on placing 

 another portion of the same Spirogyra filament in a . 29 m NaCl solu- 

 tion the expected plasmolysis does not occur and it is impossible to 

 plasmolyze the cells until they are placed in . 4 m NaCl. 



Osterhout explains this difference in the concentration of the 

 two salts required for plasmolysis by the assumption that NaCl 

 diffuses more rapidly into the cell than CaCl.,, a conclusion which 

 I reached also on the basis of my earlier experiments on animals. 

 Osterhout's experiments also show that the antagonism of 

 NaCl and CaClg depends partly on the facts that the two salts 



