CHEMICAL RELATIONS OF NUCLEUS AND CYTOPLASM 335 



the bodies stained. The prevalent view that staining-reactions are 

 due to a chemical combination of the dye with the elements of the 

 cell has been attacked by Gierke ('85), Rawitz ('97), and Fischer 

 ('97, '99), all of whom have endeavoured to show that these reactions 

 are of no value as a chemical test, being only a result of surface- 

 attraction and absorption due to purely physical qualities of the 

 bodies stained. On the other hand, a long series of experiments, 

 beginning with Miescher's discovery ('74) that isolated nucleinic acid 

 forms green insoluble salts with methyl-green, and continued by 

 Lilienfeld, Heidenhain, Paul Mayer, and others, gives strong reason 

 to believe that beyond the physical imbibition of colour a true chemical 

 union takes place, which, with due precautions, gives us at least a 

 rough test of the chemical conditions existing in the cell. 1 



Second, similarity of staining-reaction is by no means always indica- 

 tive of chemical similarity, as is shown, for example, by the fact that 

 in cartilage both nuclei and inter-cellular matrix are intensely stained 

 by methyl-green, though chemically they differ very widely. 



Third, colour in itself gives no evidence of chemical nature ; for the 

 nucleus and other elements of the same cell may be stained red, 

 green, or blue, according to the dye employed, and to class them as 

 " erythrophilous," " cyanophilous," and the like, is therefore absurd. 



Fourth, the character of the staining-reaction is influenced and in 

 some cases determined by the fixation or other preliminary treatment, 

 a principle made use of practically in the operations of mordaunting, 

 but one which may give very misleading results unless carefully con- 

 trolled. Thus Rawitz ('95) shows that certain colours which ordinarily 

 stain especially the nucleus (saffranin, gentian-violet), can be made to 

 stain only the cytoplasm through preliminary treatment of object 

 with solutions of tannin, followed by tartar-emetic. In like manner 

 Mathews ('98) shows that many of the " nuclear " tar-colours (saffra- 

 nin, methyl-green, etc.) stain or do not stain the cytoplasm, according 

 as the material has been previously treated with alkaline or with acid 

 solutions. 



The results with which we now have to deal are based mainly 

 upon experiments with tar-colours ("aniline dyes"). Ehrlich ('79) 

 long since characterized these dyes as "acid" or "basic," according 

 as the colouring matter plays the part of an acid or a base in the com- 

 pound employed, showing further that, other things equal, the basic 

 dyes (methyl-green, saffranin, etc.) are especially "nuclear stains" 

 and the acid (rubin, eosin, orange, etc.) "plasma stains." Malfatti 

 ('91), and especially Lilienfeld ('^2, '93), following out Miescher's 

 earlier work ('74), found that albumin stains preeminently in the 

 acid stains, nucleinic acid only in the basic ; and, further, that artifi- 



1 Cf. Mayer, '91, '92, '97; Lilienfeld, '93; Mathews, '98. 



