THE PERMEABILITY OF PROTOPLASM 111 



Evidently the remarkable result produced by the mix- 

 ture is brought about by a mutual hindrance of each salt 

 upon the entrance of the other into the cells. The an- 

 tagonistic action of various metallic ions has been studied 

 in detail by Loeb (1906), who has summarized many of his 

 researches in " Dynamics of Living Matter." The experi- 

 ment just described shows that the toxic action of each 

 salt upon the protoplasm is diminished by the presence of 

 the other because their rate of penetration into the proto- 

 plasm is greatly reduced. 



This conclusion is supported by the fact that recovery 

 from plasmolysis is very slow in a balanced solution of the 

 chlorides of sodium and calcium as compared with a solu- 

 tion of the sodium salt only. Thus in one species of Spiro- 

 gyra recovery requires ten hours when in a solution of 

 the two chlorides in which the molecular proportion of 

 sodium to calcium is a hundred to one, whereas when in 

 pure sodium chloride half an hour is sufficient. 



It is highly probable that the outer surface of the proto- 

 plasm is not the only one at which the sodium and calcium 

 ions exert a retarding influence, but that at all the other 

 surfaces, down to those which are ultramicroscopic, a similar 

 delay in penetration is occasioned. It is not clear why, 

 since the salts ultimately penetrate the protoplasm through 

 and through, a retardation in the rate of entry should be 

 so important. However, there are several instances in 

 colloid chemistry of the influence which the rate of addition 

 of an electrolyte has upon the ultimate condition of the 

 system. 



Osterhout summarizes the results of these researches as 

 follows : 



1. Overton's hypothesis is untenable, since it requires 

 that only those salts which are soluble in lipoid should be 

 able to penetrate. 



