518 EDMUND NEWTON HARVEY 



show that the conditions determining absorption of neutral red 

 are equally true of other classes of dye stuffs (table 1). 



Besides Pfeffer's original monograph, the most important com- 

 parative studies of permeability for the aniline dyes have been 

 made by Overton, Ruhland, and Hoeber and Robertson. 



Overton ('00) studied the permeability of both plant and 

 animal cells in neutral solution for many different dyes and the 

 solubility of the same dyes in olive oil and mixtures of lipoids. 

 He came to the conclusion that the lipoid-soluble dyes enter liv- 

 ing cells and the lipoid-insoluble do not. It has since been 

 found that there are certain exceptions to Overton's conclusion. 



Ruhland ('08) pointed out that there are some dyes which are 

 lipoid soluble and fail to enter living cells, others are lipoid in- 

 soluble yet enter readily and still others which may enter, yet 

 show no relation between rate of entrance and solubility in lipoids. 



Hoeber's ('09) recent study of the same question gave a similar 

 result to that of Ruhland with respect to certain dyes. He con- 

 cludes that the facts correspond better with the 'Satz' that basic 

 dye stuffs are intra vitam stains and acid dye stuffs are not. 



Robertson ('08) has attacked Overton's original position by a 

 study of the partition coefficient of various analine dyes in ethyl- 

 acetate, ethylbenzoate, triacetin and triolein. He came to the 

 conclusion that the solution of an acid dye in fatty substances 

 is increased by the addition of acid, the basic by the addition 

 of an alkali. In other words the free color acids or bases are more 

 soluble in lipoids than their salts. Robertson also studied the 

 stainability of fat cells, connective tisue cells, and red blood 

 corpuscles (fixed on a slide) in acid and alkaline solution. But 

 the HCl and NaOH used were so strong {rm) that they must have 

 killed the cells and no conclusions as to the permeability of living 

 cells can be drawn from his experiments. 



I have observed also the stainability of the yolk platelets of 

 the frog's egg in dilute solution of analine dyes in the acid and 

 alkaline condition. These bodies are likewise more readily 

 stainable by the free color acids and bases than their salts. I 

 will discuss this matter later. 



