268 



DYEING 



itself are present in the polychromed dye. It will be convenient to 

 represent the various thiazines by shortened formulae. The 



H^ 

 H^ 



H 



-.N- 



Thionine (cation) 





:n- 





Shortened formula for 

 thionine {cation) 



simplest is thionine. The four hydrogens shown in the shortened 

 formula can be replaced one by one by methyl, till the tetramethyl 



H3C\ 



N— 



H^ 





H3C\ 



N- 



H^ 



+ yC3H 



Monomethyl thionine 

 {azure C) 



H«Cn 



3- \ 



N- 



=N' 



H 



H,C' 



\ 



H 



Asymmetrical dimethyl 

 thionine (azure A) 



HgCX +/CH3 



)n- ^nC' 



H3C/ ^CHa 



Tetramethyl thionine 

 (methylene blue) 



Symmetrical dimethyl 

 thionine {azure IV) 



H3C\ +/CH3 



>N- =Nr 



Trimethyl thionine (azure B, 

 main component of azure I) 



)n— =0 



H3C/ 



Dimethyl thionolin 

 {Bernthsen's methylene violet) 



compound, methylene blue, is reached. In methylene violet an 

 oxygen atom replaces one of the substituted amino-groups of 

 methylene blue. 



Our understanding of the composition of polychrome methylene 

 blue is due to the researches of Bernthsen ^^ and Kehrmann.^^^ 

 The former isolated methylene violet from the oxidation products 

 of methylene blue, and announced the presence of yet another dye, 

 which he called Methylenazur; the latter proved that Bernthsen's 

 Methylenazur was a mixture of what are now called azure B and 

 azure A. The other thionines shown above are not present in 

 polychrome methylene blue. Apart from thionine itself, they have 

 no important uses in microtechnique. 



More than to any other man w^e are indebted to Giemsa for the 

 placing of Romanow^sky dyeing on a scientific basis. It was his 

 purpose to avoid methylene blue that had been polychromed at 

 random, and to use instead known quantities of known dyes. 

 Throughout the 22 years during which he published papers on 

 this subject, he remained an assistant in Nocht's institute. 



Giemsa made use of a dye that he called methylene azure or 



