CHAPTER XVI. 



METHYLEN 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 impurity a 

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

 methylen red. This impurity is present from the beginning in 

 many brands of methylen blue, is frequently 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. Accord- 

 ing to NOCHT (Centralb. BakterioL, xxv, 1899, pp. 764769 ; Zeit. 

 wiss. Mik., 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 (Centralb. BakterioL, xxix, 1901, p. 763, and 

 xxx, 1901, p. 626 ; Zeit. wiss. Mik., xviii, 1902, p. 305, andxix, 1902, 

 p. 68) confirmed later by NOCHT, REUTER, and GIEMSA, this dye is 

 Methylenazur, 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 the metachromatic effects 

 of methylen blue solutions (methylen blue itself is not metachro- 

 matic). 



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 : A solution of 1 part of methylen blue and 

 1 of carbonate of potash in 20 of alcohol and 100 of water is evapo- 

 rated down to 100 parts. (It may be used at once, or after diluting 

 with an equal volume of anilin water, for sections, which after 

 staining may be differentiated with glycol, creosol, or Unna's 

 glycerin-ether mixture all of which, as well as the polychrome 

 methylen blue, can be obtained from Grubler & Hollborn.) MICH^ELIS 



