PLASMA STAINS 171 



1 per cent, solution, and stained for twelve to twenty-four hours. 

 The stain is sufficiently fast. 



Solubility at 26° C, in water 518 per cent., in alcohol 112 per cent. 



331. Bordeaux R, Thionin, and Methyl Green (Graberg, Zeit. wiss. 

 Mik., xiii, 4, 189G, p. 460). 



332. Congo Red (Congoroth) (see Griesbach, in Zeit. wiss. 

 Mik., iii, 1866, p. 379). An " acid " colour. Its solution 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 the papers quoted loc. cit.). A stain much of the 

 same nature as Saurefuchsin. It is useful for staining some 

 objects during life. Carxoy {La Cellule, xii, 1897, p. 216) has 

 had very good results with it after hsematoxylin of Delafield. 

 He used 0-5 per cent, solution in water. Note that this colour is 

 not to be confounded with other Congos, as Congo yellow, or 

 brilliant Congo. It is one of the azo dyes. 



333. Congo-Corinth. Also an acid dye. Heidknhain {Zeit. wiss. 

 Mik., XX, 1903, p. 179) recommends Congo-Corinth G (or the allied 

 colour Benzopurpurin 6 B) (Elberfelder Farbwerke). Sections must be 

 made alkaline before staining, by treating them with very weak sal 

 ammoniac or caustic soda, in alcohol. After staining, pass through 

 absolute alcohol into xylol. Used after alum haematoxylin, the stain of 

 which it does not cause to fade. 



334. Benzopurpurin. According to Griesbach {loc. cit., § 332), 

 another " acid " colour very similar in its results to Congo red. See 

 also ZscHOKKE {ibid., v. 1888, p. 466), who recommends Benzopurpurin 

 B, and says that weak aqueous solutions should be used for staining, 

 which is effected in a few minutes, and alcohol for washing out. Delta- 

 purpurin may be used in the same way. 



See last § as to the necessity of alkalising the sections, which Heiden- 

 hain states is necessary with all dyes of this group. 



335. Neutral Red (Neutralroth) (Ehrlich, Allg. med. Zeit., 

 1894, pp. 2, 20 ; Zeit. zviss. Mik., xi, 1894, p. 250 ; Galeotti, 

 ibid., p. 193). A " basic " dye. The term " neutral " refers to 

 the hue of its solution. Its neutral red tint is turned bright red 

 by acids, yellow by alkalies. The stain in tissues is in general 

 metachromatic, nuclei being red, cell-bodies yellow {cf. Rosin, 

 in Deutsche med. Wochenschr., xxiv, 1898, p. 615 ; Zeit. iviss. 

 Mik., xvi, 2, 1899, p. 238). Up to the present this colour has 

 chiefly been employed for intra-vitam staining. Tadpoles kept 

 for a day or two in a solution of 1 : 10,000 or 100,000 absorb so 

 considerable a quantity of the colour that they appear a dark 

 red. The stain is limited to cytoplasmic granules (Ehrlich), 

 and to the contents of mucus cells (Galeotti). See also §§ 680, 

 and 766. 



Solubility at 26° C, in water 5-64 per cent., in alcohol 2-45 per cent. 



According to Ehrlich and Lazarus {Spec. Pathol, und Therapie, 

 herausgeg. von Nothnagel, viii, 1, 1898, p. 1 ; Zeit.f. wiss Mik., 



