CHAPTER XVII. 



METHYLEN BLUE. 



321. Methylen Blue is the chloride or the zinc chloride 

 double salt of tetrametbylthioniii, 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 methyleii blue sometimes contains as an im- 

 purity a small quantity of a red dye, which used to be taken to 

 be methyleii red. This impurity is present from the beginning 

 in many brands of methyleii 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. J/-/A-., xvi, 2, 1899, p. 225) it is not 

 methyleii 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 methyleii 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. Methyleii 

 blue that contains it is known as polychromatic methylen l)lne, 

 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, 011 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 methyleii 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, 



