CHAPTER XVI. 



MBTHYLBN BLUE. 



337. Methylen Blue is a " basic " dye, being the chloride or 

 the zinc chloride double salt of tetramethylthionin. It 

 appears that some persons have confounded it with the 

 " acid " dye methyl blue, to which it has not, histologically, 

 any resemblance. 



Commercial methylen blue sometimes contains as an im- 

 purity a small quantity of a reddish dye, which used to be 

 taken to be methylen red. This impurity is present from 

 the beginnning in many brands of methylen blue, is 

 fi-equently developed in solutions of the dye that have been 

 long kept (so-called "ripened" solutions), and is still more 

 frequently found in kept alkaline solutions. According to 

 NocHT {Gentralh. Bakteriol., xxv, 1899, pp. 764-769; Zeit. 

 iviss. Mih., xvi, 1899, p. 225) it is not methylen red, nor 

 methylen violet either, but a new colour, for which Nocht 

 proposes the name " Roth aus Methylenblau." 



According to Mich^lis (Gentralh. Bakteriol., xxix, 1901, 

 p. 763, and xxx, 1901, p. 626; Zeit. wins. Mik., xviii, 1902, 

 p. 305, and xix, 1902, p. 68) confirmed later by Nocht, Reuter, 

 and GiEMSA, this dye is Ilethylenazur, an oxidation-product 

 of methylen blue, already described by Bernthsen in 1885. 

 It is an energetic dye, of markedly metachromatic action, 

 and to it are due tlie metachromatic effects of methylen blue 

 solutions (methylen blue itself is not metachromatic). 



The presence of this dye as an impurity in methylen blue 

 is not always an undesirable factor; on the contrary, it 

 sometimes affords differentiations of elements of tissues or of 

 cells that cannot be produced by any other means. Methylen 

 blue that contains it is known as polychrome methylen blue, 

 and is employed for staining certain cell-granules. Unna 

 [Zeit. wiss. Mik., viii, 1892, p. 483) makes this as follows : 



