350 THE AMERICAN MONTHLY [Oct. 



cell nuclei are themselves more intensely charged with 

 the coloring matter, and the cells themselves contained 

 therein, and they appear isolated therefrom by their 

 weakly-colored surroundings, it is then proven that, as 

 the mast-cell nuclei are stained a clear reddish color, 

 just in this proportion will the surrounding parts retain 

 their color. Certainly this contributes much to make the 

 mast-cells quickly and easily recognized under difficult 

 circumstances. It is therefore not to be wondered at 

 that those colors liave been preferred which tend to pro- 

 duce metachromasia, especially methylene blue (red mast- 

 cells) and saffronin (orange colored mast-cells.) 



Thus the staining of the mast-cell nuclei takes place 

 gradually by means of a metachromatic stain. Our en- 

 tire energies are bent, however, in the production of the 

 most available staining mixtures which render possible a 

 differential staining of the tissues ; and these staining 

 mixtures, which have been given us by nature, are those 

 which have usually been considered as simple colors ; 

 but those which; through the metachromasia of indi- 

 vidual tissue elements show that they are actually color 

 mixtures and contain valuable by-products, are mostly 

 overlooked. Indeed it has appeared probable to me, 

 through long use of the polychrome methylene blue so- 

 lution, that this last contains by-products which produce 

 the metachromasia (here methylene red). At the same 

 time the colors more easily taken up bring fortli the same 

 elements, since their chief coloring matter (here methy- 

 lene blue) is strengthened and are also necessary for the 

 quantitative effect. If, for example, the cause of the 

 stronger staining of the mast-cells with basic aniline 

 coloring resided only in the attraction of the nuclei for 

 basic stains, so would this necessarily appear in the de- 

 colorization of over-stained sections with various simple 

 solutions (alcohol, glycerine). But it is well known that 



