PJ.ASII.V STAINS WITH COAL-TAIl DVHS. 101 



304. Bordeaux R, Th.ion.in, and Methyl G-ree-i (G-iti-Bnaa, Zsit. 

 wi6s. Mile, xiii, 4, 1836, p. 460). 



305. Coago Rad (Congoroth) (see G-RiBiiiACH, in Zeit. iciss. 

 ilik., u\, 1866, p. 379). — Au "acid" colour. Its solution 

 becomes blue in presence oi: the least trace o£ 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 Siiurefuchsin. 

 It is useful for staining some objects during life (see ante, § 

 208). Carnoy {La Cellule, xii, 1897, p. 216) has had very 

 good results with it after hoematoxylin of Delapiisld. He 

 used 0'5 per cent, solution in water. Note that this colour 

 is. not to be confounded with other Gongos, as Congo yellow, 

 or brilliant Congo. It is one of the azo dyes. 



306. Congo-Corinth. — Also an acid dye. Hbidenhain {Zeit. wiss. 

 Mile, XX, 1903, p. 179) recommends Oongo-Oorinth G (or the allied 

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

 mada alkaline before staining, by treating tliem with very weak sal 

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

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

 which it does not cause to fade. 



307. Benzopurpurin.— According to Geiesbach (loc. cit., § 305), 

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

 also ZscHOKKE {ibid., v, 1888, p. 486), 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. 

 Deltapurpurin may be used in the same way. 



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

 hain states is necessary with all dyes of this group. 



308. Blauschwarz B and Brillantschwarz 3 B (Heidenhain, ojj. 

 cit., § 306, p. 183). — Acid azo dyes. To be used in 1 per cent, solution 

 with sections of sublimate material, staining for five to ten minutes. 

 Then stain is a basic dye, such as tolmdin blue or safranin. 



309. Neutral Bed (Neutralroth) (Bhelicii, Allg. med. Zeit., 

 1894, pp. 2, 20; Zeit. wiss. 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 (c/. Rosin, in Deutsche med. Wochenschr., xxiv, 1898, 

 p. 615; Zeit. Unas. Mik., xvi, 2, 1899, p. 238). Up to the 



