CHAPTER XIV. 



NUCLEAR STAINS WITH COAL-TAR DYES. 



275. Introduction. Very few coal-tar dyes give a precise nuclear 

 or chromatin stain by the progressive method ( 209). Two of them 

 methyl green and Bismarck brown rare pre-eminently progressive 

 chromatin 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 ( 209) 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 

 haematoxylin 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. 



I 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. 



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

 the " anilin " greens. It appears to go by the synonyms of Meihyl- 

 anilin green, Griinpulver, 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 



