124 Biological Stains 



gressed fast, both because of the small number of biologists who 

 employ it and because of the expense to manufacture; but it is 

 hoped that eventually it will be as well standardized as the more 

 commonly used stains. 



k40 new blue R C. I. NO. 909 



Synonyms: Naphthol blue R. Fast blue 3R. Phenylene blue. 

 Meldola's blue. Indin blue 2RD, 



I I CH3 



\/\_N_/\ / 

 1 I I UN-CH3 



\/~o-\/ \ 



CI 

 C18H15N2OCI; Mol. Wt. 310.773 

 {A basic dye; absorption maxima about \622\, 573y \53S]) 



Occasional reference has been made to this dye in the biological 

 literature, under the name of naphthol blue R, most recently by 

 Lewis (1938) in staining fat drops in bacteria. 



k45 RESAZURIN 



O 



H0~\/~"0"^/=0 

 C12H7NO4; Mol. Wt. 229.184 



This is not a dye, but a colored compound that has interesting 

 properties as an oxidation-reduction indicator. It is blue in its 

 completely oxidized state, and upon reduction becomes pink and 

 then colorless according to the following reaction : 



H 



-\/""0^/=0 YiO~\/-~0~\/=0 HO"~\/~0-X/~OH 

 Resazurin Resorufin Hydroresorufin 



(blue) (pink) (colorless) 



Various shades between blue and light pink can occur. 



A spectral curve of resazurin is included in Fig. 13, p. 118 

 (graph 3). 



It was first suggested by Ramsdell et al. (1935) that it might be 

 more valuable than methylene blue as an indicator of reduction in 

 milk, partly because of its greater speed in showing reduction and 



