102 Biological Stains 



following are occasionally mentioned, however, in connection with 

 histology: 



h5 BINDSCHEDLEr's GREEN C. I. NO. 819 



CH3 CH3 



\ / 



N_/~\_N=/~V=N— CH3 



/ \_/ \_/ \ 



CHj CI 



C16H20N3CI; MoL Wt. 289.801 



{A basic dye; typically of the above formulay but sometimes sold as 



the zinc double salt) 



Bindschedler's green has occasional employment as an indicator 

 of oxidation reduction. It is reduced to the colorless pp'-tetra- 

 methyldiamino-diphenylamine. Elliott and Baker (1935) have re- 

 cently employed it for this purpose in studying the metabolism of 

 tumor tissue. 



HlO TOLUYLENE BLUE C. I. NO. 8iO 



NH, CHj 



/ / 



H2N_/"~\_N=/~\^N— C H3 



\_/ \_/ \ 



/ CI 



CH3 



C15H19N4CI; MoL Wt. 290.791 



{A basic dye) 



Like its homolog, Bindschedler's green, toluylene blue is readily 

 reduced to a substituted diphenylamine; and accordingly it has 

 similar indicator properties. 



2. THE INDOPHENOLS 



Closely related to the indamines is a small group of colored com- 

 pounds known as indophenols, which do not readily form salts 

 with mineral acids. The simplest compound of this group is 

 indophenol (sometimes called benzenoneindophenol) and has the 

 following structural formula. 



0_/~\_N /~\ OH 



Various halogen substitution products of indophenol are known, 

 and all have indicator value, showing an acid-base color change 

 and a disappearance of color on reduction. The best known in- 

 dicator of this series is: 



