1896.J MICROSCOPICAL JOURNAL. 351 



only the decolorization with acids demonstrates the mast- 

 cells with certainty and in an easy manner in over- stained 

 sections. I therefore consider it more probable that the 

 acids in the nuclei of the mast-cells fix an acid-coloring 

 component (here methylene red) which, on its part, fixes 

 the basic, chief coloring constituent (here methylene 

 blue) ; and these acids, on this account, decolorize the re- 

 maining color constituents because they have not at the 

 same time attracted the (acid) coloring constituents, such 

 as methylene redo 



While I have found the violet in methylene blue a 

 valuable coloring material I have obtained as a by-pro- 

 duct in some solutions, methylene red and my polychrome 

 methylene blue solution (Griibler) present through this 

 the most diff'erent varieties of protoplasm and, at the 

 same time, the nuclei of mast-cells with a specific red 

 color. This secondary eff'ect of the polychrome methylene 

 blue solution proves its value because it made the dif- 

 ferential diagnosis of mast-cells (red) and plasma-cells 

 (blue) a very easy matter. Both kinds of cells are usually 

 easy to distinguish by other characteristics ; but there 

 are isolated ones in which the differential diagnosis can- 

 not be easily made without this differential stain. 



Wherein then is the advantage of this differential 

 staining of mast-cells over that of the metachromatic 

 methods which have been used heretofore ? In the 

 purity and absorption of color, so that no one can doubt 

 whether a given nucleus belongs to a mast-cell or not. 

 Only in the staining have we saturated red alongside of 

 a saturated blue, while by methods of metachromasia 

 heretofore used they were seen only occasionally, and 

 accordingly well pronounced the stronger the entire sec- 

 tion was stained. We have here, in each individual case, 

 an intense and clear stain of mast-cell nuclei (red) with 

 just as deep a staining of all the remaining tissues (partly 



