40 CELLULAR 



which Strikes the surface may penetrate provid- 

 ing there is no other hindrance except the elec- 

 trical forces. On this basis we should expect 

 undissociated molecules to enter more rapidly 

 than ions. 



In this connection it may be noted that the 

 work of Loeb, Harvey, Crozier, Haas, Jacobs, 

 M. M. Brooks, Smith, Clowes, and Beerman 

 (on various weak acids) indicates that undis- 

 sociated molecules penetrate, although the 

 methods employed do not enable us to decide 

 positively whether ions enter or not. Those who 

 have concluded that ions cannot penetrate have 

 done so on purely theoretical grounds or as the 

 result of indirect evidence. This also applies to 

 a large extent in cases where the opposite con- 

 clusion has been reached. 



If it should turn out to be generally true 

 that ions are unable to penetrate except very 

 slowly how shall we regard the evidence for the 

 contrary view? This evidence rests chiefly on 

 experiments with plasmolysis and electrical con- 

 ductivity. It is found that many cells recover 

 after plasmolysis when left in the plasmolyzing 



