NUCLEAR STAINS, COAL TAR 179 



greens, especially under that of iodine green. It is important 

 not to confuse it with the latter, nor with aldehyde green ( Vert 

 d'Eusehc), nor with the phenylated rosanilins, Paris green, and 

 Vert d'Alcali, or Veridine. 



Methyl green is the chloromethylate of zinc and pentamethly 

 rosanilin-violet. It is obtained by the action of methyl chloride 

 on methyl violet. The commercial dye always contains incon- 

 verted methyl violet as a consequence of defective purification. 

 It is sometimes adulterated with anilin blue (soluble blue). It 

 is also sometimes adulterated with a green bye-product of the 

 manufacture — the chloride of mona-methyl-para-leukanilin. See 

 Benedikt and Knecht's Chemistry of the Coal-tar Colours. For 

 tests for purity see Mayer, Mitth. Zool. Stat. Neapel, xii, 1896, 

 p. 312, and Fischer, Fixirung, Fdrhung, u. Bau des Protojjlasmas, 

 p. 89. 



Methyl green is extremely sensitive to alkalies. It is there- 

 fore important to use it only in acidified solutions and to use 

 only acid, or at least perfectly neutral fluids, for washing and 

 mounting. 



This is an extremely imjyortant histological reagent. Its chief 

 use is as a chromatin stain for fresh, unfixed tissues. For this 

 purpose it should be used in the form of a strong aqueous solu- 

 tion containing a little acetic acid (about 1 per cent, in general). 

 The solutions must ahtays be acid. If the tissues have been 

 previously fixed with acetic acid you will not get a chromatin 

 stain. The same applies to fixation with acetic acid sublimate ; 

 whilst pure sublimate will allow of a chromatin stain 

 (BuRCKHARDT, La Cellule, xii, 1897, p. 364). You may wash 

 out with water (best acidulated) and mount in some acid aqueous 

 medium containing a little of the methyl green in solution. The 

 mounting medium, if aqueous, must be acidulated. 



Employed in this way, with, fresh unfixed tissues, methyl green 

 is a pure chromatin stain, in the sense of being a precise colour 

 reagent for chromatin. For in the nucleus it stains nothing but 

 chromosomes or chromatin elements ; it does not stain plasmatic 

 nucleoli (unless indeed these contain chromatin), nor caryoplasm, 

 nor achromatic filaments. Outside the nucleus it stains some 

 kinds of cytoplasm and some kinds of formed material, especially 

 glandular secretions (silk, for instance, and mucin). The chromatin 

 elements are invariably stained a bright green (with the excep- 

 tion of the nuclein of the head of some spermatozoa), whilst 

 extra-nuclear structures are in general stained in tones of blue or 

 violet. But this metachromatic reaction is probably due to the 

 methyl-violet impurity, and is not obtained with a chemically 

 pure methyl green. 



Staining is instantaneous ; overstaining never occurs. The 

 solution is very penetrating, kills cells instantly without swelling 



