THE PERMEABILITY OF CELLS 521 



fatty substances and fat solvents. It must not be forgotten that, 

 as Mathews ('98) showed, the basic stains yield colored precipi- 

 tates with proteids only in alkaline solution, the acid only in acid 

 solutions. The same was found to be true of the staining of coag- 

 ulated proteids as egg albumen. We should expect therefore 

 that the lecithalbumen platelets of the frog's egg would show the 

 same staining relations that Mathews found for coagulated albu- 

 men, even from very dilute solutions. It is probable that the acid 

 or alkali affects the lecithalbumen as w^ell as the dye. 



We might draw the conclusion from this that a dye only enters 

 a cell when it combines with the surface membrane.^ Yet I have 

 never noticed that the plasma membrane of any cell becomes 

 stained in dilute solutions of basic dyes. The most conspicuous 

 fact connected with the staining of plant cells is that the stain 

 passes through the cell protoplasm without affecting it in the 

 least and collects in the vacuole. 



My studies on dyes have not been extensive enough to warrant 

 generalizations as to the classes of dyestuffs for which cells are 

 permeable nor as to the nature of the cell surface. It appears to 

 be true^ — as a general rule, to which there are exceptions — that 

 the substances (including alkaloids, alkalies, dyes, anaesthetics, 

 etc.) more soluble in fat solvents or fatty substances than in 

 water, penetrate cells with practically no resistance, while those 

 compounds insoluble in ether and fats meet a marked resistance 

 at the cell boundary as Overton has postulated. But whether 

 we are to conclude from this that the boundary is lipoid in nature 

 is quite another question. The evidence on this point is far from 

 conclusive. Indeed, Traube has shown that the lipoid soluble 

 substances, the easily permeating substances, are those having the 

 greatest tendency to lower the surface tension of water in air, and, 

 according to his theory of osmosis to pass into the phase of greater 

 surface tension (into the cell). No lipoid membrane separating 

 the two phases is required. 



* Mathews ('10) has recently concluded that the dyes penetrate by "combination 

 with substances in the peripheral layer such as lecithin and the electro-negative 

 proteins, soaps and possible other substances." (p. 218). He regards the taking 

 up of basic dyes by lipoid solvents, which act as weak acids, as a chemical com- 

 bination. 



