Quinone-imine Dyes 117 



This dye has practically never been called for in microscopical 

 work. The most interesting fact concerning it which has come to 

 light relates to the Van Wijhe technic as applied by Louise Smith 

 (1920) for staining the cartilage of frogs. The latter specified 

 methylene blue, but the results could not be duplicated with any 

 domestic or foreign methylene blue subsequently obtained. When 

 furnished through the Commission with samples of various stains 

 to try, she found that her earlier results could be duplicated with 

 new methylene blue — a fact which not only implies mislabeling of 

 her original supply of methylene blue, but suggests that new 

 methylene blue may have some value in histological work. 



4. THE OXAZINS 



This group is like the thiazins in chemical formula except that 

 the sulfur atom is replaced by an oxygen atom. Only a few of the 

 dyes find use in microscopic technic, and they are not stains having 

 very general application. 



Ko BRILLIANT CRESYL BLUE C. I. NO. 877 



Synonyms: Cresyl blue 2RN or BBS. Brilliant blue C. 



CHj'CHz 



\ 



N 

 / \/X_0_/\_NH. 

 CH3-CH, I I I \ 



1 I 1 CI 



CH3/\/-N==\/ 

 C17H20N3OCI; Mol. Wt. 317.811 



{A basic dye; absorption maxima about 62Jf.-6£8) 



This dye is expensive to manufacture, and as it is not at present 

 employed in any line of commercial dyeing, it must be prepared 

 specially for the biologist. Its manufacturers, although willing to 

 cooperate to any reasonable extent, were naturally reluctant to 

 carry on much experimental work with this dye unless they were 

 sure the results would justify the outlay. This fact caused some 

 delay in bringing about its complete standardization. 



The spectral curve of a typical sample of brilliant cresyl blue is 

 given in Fig. 13, p. 118, where it is compared with curves for resa- 

 zurin and Nile blue sulfate. 



The dye has been employed to some extent in vital staining, 

 Irwin (1927), for instance, having found it the most favorable dye 

 available for investigating penetration into living cells; in vital 



