COAL-TAE PLASMA STAINS. 219 



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two " acid " colours, methyl green being a strongly " basic 

 colour. The following is a recent formula of EHRLICH, com- 

 municated to REINBACH (quoted from Zeit. f. wiss. Mik., xi, 

 3, 1894, p. 259). 



Orange Gr, sol. sat. aq. . . . 120 



Saurefuchsin ,, . . .80 



Methyl green ,, ... 100 



Distilled water .... 300 



Absolute alcohol . . . .180 



Glycerin ..... 50 



Care must be taken that the solutions be absolutely satu- 



rated before mixing. The mixture must never be shaken, 



the quantity necessary for use at any time must be carefully 



taken off from the top of the stock by means of a pipette. 



With these precautions the mixture will keep for years. 



I have not made up this mixture, but have examined a 

 triacid solution procured from (rriibler & Hollborn. Its 

 qualities and defects appear to be very much those of the 

 Ehrlich-Biondi mixture. It appears to be a more powerful, 

 but perhaps less delicate stain, and the methyl green appears 

 to have more resistance to alcohol, so that it m;iy perhaps 

 give better results for ordinary work. 



292. Bordeaux R. A general stain taking effect both on 

 chromatin and cytoplasm, and, I consider, a very good plasma 

 stain. It is much used, on the recommendation of M. 

 HEIDENHAIN (Arch. mil:. Anal., xlii, 1894, p. 665), for stain- 

 ing sections before iron-haematoxylin, it being supposed that 

 this treatment affords a sharper stain of his " central cor- 

 puscles/' I use for chrom-osmium material a 1 per cent. 

 solution, and stain for twelve to twenty-four hours. The 

 stain resists alcohol well. 



293. Bordeaux R, Thionin, and Methyl Green (GRABERG, Zeit.f. 

 wiss. Mik., xiii, 4, 1896, p. 460). 



294. Congo Red (Congoroth) (see GRIESBACH, in Zeit.f. imss. Mik., iii. 

 3, 1866, p. 379). Also an " acid " colour in EHELICH'S sense. The aqueous 

 solution, however, has a neutral or alkaline reaction. It becomes blue in 

 presence of the least trace of free acid (hence Congo is a valuable reagent 

 for demonstrating the presence of free acid in tissues ; see tbe papers quoted, 

 loc. cit.}. A stain much of the same nature as Saurefuchsin, and like 



