514 EDMUND NEWTON HARVEY 



to determine changes in function associated with the entrance of 

 a given quantity. 



Most of the present experiments were performed in the Zoolog- 

 ical Laboratory of Columbia University. The study of marine 

 eggs was made possible by a visit to the Tortugas Laboratory of 

 the Carnegie Institution and the Marine Biological Laboratory at 

 Woods Hole. I wish to express my indebtedness to Dr. Mayer 

 for the many special opportunities for research offered me at the 

 former station and to Dr. Morgan for permission to use a Colum- 

 bia table at Woods Hole as well as for many helpful suggestions. 



THE PENETRATION OF ANILINE DYES 



1 . Mechanism of staining plant cells 



In studying permeability for alkalies, to be discussed below, 

 penetration was indicated by the change in color of neutral red 

 in which the cells had been stained. In order to determine under 

 what conditions neutral red exists in the cell and the nature of 

 the dye compounds which the alkali must decompose on enter- 

 ing, I have conducted a few experiments on certain dyes with 

 the above points in mind. The most interesting fact obtained 

 is that basic dyes as a rule cannot enter cells in the presence of 

 a trace of acid in the medium whereas certain acid dyes do not 

 enter cells in neutral or weakly alkaline solution but readily 

 stain and kill the cell in weakly acid solution. We should natur- 

 ally suppose the explanation of the above results to be in the 

 effect of the acid or alkah on the dissociation of the dye molecules. 



a. Overton's hypothesis: — Overton had at one time supposed 

 that only the free dye base of basic dyes might enter cells. Since 

 basic dyes are combination of weak bases with strong acids we 

 should expect them to be hydrolytically dissociated in water, 

 thus : 



RCl + HoO = ROH + HCl 



Only the ROH and not the RCl might enter. Overton ('00) 

 later abandoned this idea since he was unable to show that the 

 dye acetates entered the cell more readily than the dye chlorides. 



