CHAPTER XVII. 



METHYLEN BLUE. 



321. Methylen Blue is the chloride or the zinc chloride 

 double salt of tetramethylthionin, and is a " basic " colour in 

 EHRLICH'S sense. It appears that some persons have con- 

 founded it with methyl blue, to which it has not, histologi- 

 cally, any resembance. 



Commercial methylen blue sometimes contains as an im- 

 purity a small quantity of a red 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. It is a reddish-violet dye, and ac- 

 cording to NOCHT (Centralb. f. Bacterial., xxv, 1899, pp. 

 764769 ; Zeit. f. wiss. Mik., xvi, 2, 1899, p. 225) it is not 

 methylen red, nor methylen violet either, but a new colour, 

 for which NOCHT proposes the name " Roth aus Methylen- 

 blau." The presence of this impurity in methylen blue is 

 not always an undesirable factor ; .on the contrary, it some- 

 times 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 polychromatic methylen blue, 

 and is employed for staining certain cell-granules. It can 

 be obtained from Griibler & Hollborn. (See also UNNA'S 

 method of producing it, in Part II.) 



The colour to be employed for intra-vitam nerve staining 

 should, on the contrary, be as pure as possible. APATHY has 

 a note in Zeit. f. wiss. Mik., ix, 4, 1893, p. 466, to the effect 

 that the best methylen blue for impregnation in fact, the 

 only one that will give exactly the results described by him 

 (see 327) is that obtained from E. MERCK, of Darmstadt, 



