92 Biological Stains 



d22 BISMARCK BROWN R C. I. NO. 332. 



Synonyms: Bismarck brown GOOO 53 A or 53B. Brown R, AT, 

 C or N. Manchester brown EE. Vesuvin NR, B, R. 



Basic brown BR or BXN. 



C21H26N8CI2; Mol. Wt. 461.396 

 {A basic dye. . Solubility at 26° C: in water 1.10%, in alcohol 0.98%) 



This dye has not ordinarily been employed as a biological stain. 

 One sample was submitted by a stain company by mistake, and 

 it appeared to be a satisfactory substitute for Bismarck brown Y. 

 Lillie (1945) specifies it as a good counterstain to oil blue NA. 



d26 CONGO RED C. I. NO. 37O 



Synonyms: Congo. Cotton red B or C. Direct red, C, R or Y. 



I 

 NaSOi NaSOj 



C32H22N606S2Na2; Mol. Wt. 696.658 



(An acid dye; absorption maximum about 4-97) 



Solubility at 26°C: in alcohol 0.19%) 



This dye is best known to the biologist as an indicator. The 

 dye acid is blue, but its sodium salt is red. The red color of the 

 salt is readily changed by weak acids into blue. Besides serving 

 as an indicator, Congo red has certain histological uses, as for axis 

 cylinders (Griesbach, 1886), for embryo sections (Schaffer, 1888), 

 for staining elastic tissue (Matsuura, 1925), plant mucin, as a 

 stain for Uredineae (Blackman, 1905), and as a general background 

 stain in contrast to hematoxylin and other nuclear dyes. It has 

 been used by Klebs (1886) as a reagent for cellulose. It proves 



