170 CHAPTER XIV. 



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 Methylaniliii green, Griinpidver, Vert Lumihe, Llclitgriin; 

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

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

 1887, p. 625)j it went by the 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'Eus'ehe), 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 

 Mayeb, Mitth. Zool. Stat. Neapel, xii, 1896, p. 312, and 

 FisCHEK, Fixirung, Fdrbunq, 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 i or 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). The solutions must ahcays he 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 (Bueckhaedt, La Celhde, 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 he acidulated. 



