344 J. DAVIDSON 



toplasm and lipoid insoluble dyes do not enter the cell at all 

 because the protoplasm is selectively impermeable to them. 



Nathanson's modification frees Overton's hypothesis from 

 intrinsic contradictions but deprives it of its universality by 

 relegating the lipoids to a position of secondary importance 

 among the factors which condition the diosmotic properties of 

 the cell. It does not meet the arguments brought against 

 Overton's conclusions with reference to the relation between 

 the lipoids of the plasma-membrane and the aniline dyes, does 

 not substantiate these conclusions by any new evidence, and 

 consequently does not eliminate their speculative character. 



Lepeshkin^i considers the plasma-membrane as a polyphasic 

 colloidal solution of various substances, as protein, lipoids, and 

 water, which in the inner layers passes over into an emulsion 

 or perhaps even into a colloidal suspension. The nature of the 

 dispersing phase is entirely unknown. The solution, according 

 to him, possesses only temporary fluid properties as it has a 

 tendency to solidify. The fluid condition of the plasma-mem- 

 brane is maintained only under normal conditions of metabohsm 

 because a prolonged plasmolysis which interferes with certain 

 physiological functions of the cell, causes solidification of the 

 protoplasm even in the absence of the agencies by which it is 

 generally caused. The permeability of the plasma-membrane 

 is conditioned, according to him, by solubility in the dispersing 

 agent. Water passes through very easily. The endosmosis of 

 other substances depends upon their specific solubility in the 

 dispersing agent of the plasma-membrane. Under the influence 

 of various factors the apparent homogeneousness of the limiting 

 plasma layer disappears. The remaining plasma mass also 

 becomes richer in granular protoplasm and the cell loses the 

 property of selective permeability. The process is, as Lepeshkin 

 is inclined to think, a phenomenon of coagulation. The parti- 

 cles of the dispersed phases in the colloidal solution representing 

 the protoplasm are drawn together. The continuity of the 

 plasma-membrane disappears, channels are formed and are 

 filled with the water which was held in colloidal solution in the 



31 L.c. Ber. d. deut. Bot. Ges., 1910. 



