160 NUCLEAR STAINS WITH COAL-TAR DYES. 



name of Vert en cristaux. It is commonly met with in commerce 

 under the name of more costly greens, especially under that of 

 iodine green. It is important not to confuse it with the latter, nor 

 with aldehyde green (Vert d'Eusebe), nor with the phenylated 

 rosanilins, Paris green, and Vert d'Alcali, or Veridine. 



Methyl green is the chloromethylate of zinc and penta-methyl 

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

 methyl violet. The commercial dye always contains unconverted 

 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 nona-methyl-para-leukanilin. See BENEDIKT and 

 KNECHT'S Chemistry of the Coal-tar Colours. For tests for purity 

 see MAYER, Mititi. ZooL Stat. Neapel, xii, 1896, p. 312, and FISCHER, 

 Fixirung, Fdrbung, u. Bau des Protoplasmas, p. 89. 



Methyl green is extremely sensitive to alkalies. It is therefore 

 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 important 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 solution containing 

 a little acetic acid (about 1 per cent, in general). Tlte solutions 

 must always 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 in- 

 variably stained of a bright green (with the exception 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 meta- 

 chromatic reaction is probably due to the methyl-violet impurity, 

 and is not obtained with a chemically pure methyl green. 



