CHAPTER XIV. 



NUCLEAR STAINS WITH COAL-TAB 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 are 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 hasmatoxylin 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. 



