CHAPTER X\ II 

 NUCLEAR STAINS WITH COAL-TAR DYES * 



362. Introduction. Very few coal-tar dyes give a precise 

 nuclear or chromatin stain by the progressive method (§ 241). 

 Two of them — methyl green and Bismarck brown — are pre- 

 eminently progressive cliromatin stains. Many of the others — 

 for instance, safranin, gentian, and especially dahlia — may be 

 made to give a progressive nuclear stain with fresh tissues by 

 combining them with acetic acid ; but in general are not so 

 suitable for this kind of work as the two colours first named. 



Again, very few coal-tar dyes give a pure plasmatic stain (one 

 leaving nuclei unaffected). The majority give a diffuse stain, 

 which in some few cases becomes by the application of the regressive 

 method (§ 241) a most precise and splendid chromatin stain. 



But plasma staining is generally done by the progressive method. 



The basic anilin dyes were at one time greatly in vogue for the 

 staining of chromatin in researches on the structure of nuclei. 

 They have been little used for that purpose since the working 

 out of the iron haematoxylin process, which gives a more energetic 

 stain. But they may still be useful as a means of controlling the 

 iron hfematoxylin process, which frequently stains all sorts of 

 things besides chromatin, which does not occur with the best tar 

 colour stains. 



The acid and neutral anilin dyes afford some of our best plasma 

 stains. 



We recommend — for staining nuclei of fresh tissues, methyl 

 green ; for staining nuclei of fixed tissues by the regressive method, 

 safranin for a red stain, and gentian violet or Thionin for a blue 

 one ; as a plasma stain for sections, Saurefuchsin ; for entire 

 objects, picric acid. 



A. PROGRESSIVE STAINS 



363. Methyl Green. This is the most common in commerce of 

 the " anilin " greens. It is a basic dye. It appears to go by the 

 synonyms of Methyl-anilin green, GriXnpulver, Vert Lumiere, 

 Lichtgrun ; these two last are in reality the name of another colour. 

 When first studied by Calberla, in 1874 {Morphol. Jahrb., iii, 

 1887, p. 625), it went by the name of Vert en cristaux. It is com- 

 monly met with in commerce under the name of more costly 

 * For further details, see Conn, op. cit. 



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