SELECTIVE PERMEABILITY 347 



believes that they diffuse through the water which is held, as 

 he claims to have shown, in solution in the plasma-membrane. 

 Any dye soluble in water regardless of its solubility or insolubil- 

 ity in lipoids will, according, to him diffuse into the cell. Over- 

 ton's observations with reference to the pei'meability of the cell 

 to dyes concern themselves, according to him as well as accord- 

 ing to Ruhland" only with the accumulation of these dyes in the 

 cell. The water-soluble dyes which are classed among those to 

 which the cell is impermeable, in reality enter the cell but do 

 not accumulate. The fact that only basic dyes were found by 

 Overton to penetrate into the cell lends, according to him, s^ up- 

 port to his view, as the basic dyes form compounds with the 

 organic acids found in the cell sap and precipitate out. With 

 reference to the few acid dyes which were definitely found by 

 Pfeffer to be incapable of entering the cell, he found that they 

 form distinctly colloidal solutions which pass with difficulty 

 through the cell wall and with still more difficulty through the 

 protoplasm even after the cell is killed by heating. 



As a proof against Nathanson's view that the aniline dyes 

 enter the cell through the lipoids, Lepeshkin considers the fact 

 that, (as was shown by him) aniline dyes which are more soluble 

 in water than in certain narcotics enter the cell with more diffi- 

 culty in the presence of these narcotics. This would, according 

 to him, tend to show that all substances to which a cell is per- 

 meable enter through the same way and that there are no differ- 

 ent passage ways for aniline dyes and mineral salts, for instance. ^^ 



This argument as well as Lepeshkin's opposition to Nathan- 

 son's conception of the plasma-membrane in general is somewhat 

 inconsistent. The principal point in Nathanson's modification 

 of 0\'erton's lipoid-hjqDothesis is that the lipoids do not form a 

 continuous layer in the plasma-membrane. Lepeshkin holds 

 the same view. As to the existence of different passage ways in 

 the plasma-membrane for different substances Lepeshkin recog- 

 nizes the same principle, having assmned that the narcotics 

 sparingly soluble in water enter through the lipoid components 



" L.c, Jahrb. f. Wiss. Bot. 46. 



38 L.c, Ber. d. d. Bot. Ges. 29: 247-261. 1911. 



THE PLAXT WORLD, VOL. 19, NO. 11 



