CHAPTER XV. 179 



good results with it after haematoxylin of DEL AFIELD. 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. 



306. Congo-Corinth. Also an acid dye. HEIDENHAIN (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 haemotoxylin, the stain of 

 which it does not cause to fade. 



307. Benzopurpurin. According to GRIESBACH (loc. cit., 305), 

 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. 

 Deltapurpurin 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. 



308. Neutral Red (Neutralroth) (EHRLICH, 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 (cf. ROSIN, in Deutsche med. 

 Wochenschr., xxiv, 1898, p. 615 ; Zeit. wiss. MiL, 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 solu- 

 tion of 1 : 10,000 or 100,000 absorb so considerable a quantity of 

 the colour that all their tissues appear of a dark red. The stain is 

 limited to cytoplasmic granules (EHRLICH), and to the contents of 

 mucus cells (GALEOTTI). 



According to EHRLICH and LAZARUS (Spec. Paihol. und Therapie, 

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

 xv, 3, 1899, p. 338) it may be used for intra-vitam staining of tissues 

 in the same way as methylen blue, by injection or immersion with 

 contact of air. It is especially a granule stain. Similar results are 

 recorded by ARNOLD (Anat. Am., xvi, 1899, p. 568, and xxi, 1902, 

 p. 418). See also EHRLICH and LAZARUS, Ancemie, i, 1898, p. 85 ; 

 LOISEL (Journ. de I' Anat. et de la Phijsiol, 1898, pp. 197, 210, 217) 

 (intra-vitam staining of sponges) ; and PROWAZEK (Zeit. iviss. Zool., 

 Ixii, 1897, p. 187) (intra-vitam staining of Protozoa). I myself have 

 had very good results with it as an intra-vitam stain. 



According to GOLOVINE (Zeit. wiss. Mik., xix, 1902, p. 176), the 



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