212 Biological Stains 



factured are largely species of the genus known as Indigofera, al- 

 though some indigo-bearing plants are recognized by botanists as 

 belonging to different genera. In these plants is a glucoside, 

 indican, which is converted by fermentation into the dye indigo. 

 Various formulae have been given for indigo; the one favored at 

 present is based upon its method of artificial manufacture: 



rY 



CO CO 



c=c I I 



\ / \ /\/ 



NH NH 



C16H10N2O2; Mol. Wt. 262.256 



In this formula the exact chromophore group is uncertain; but 

 the ketone group (CO) in a closed ring occurs so often in dyes that 

 it is regarded as probably having chromophoric properties; the 

 same is true of the C = C linkage. 



ul2 INDIGO-CARMINE C. I. NO. I180 



Synonym: Indigotine la. 

 This is the sodium salt of indigo disulfonic acid: 

 NaS03 CO CO SOsNa 



Ci6H8N208S2Na2; Mol Wt. 466.354 



Indigo carmine is a blue dye of acid properties, which is sometimes 

 used as a plasma stain in contrast to some red dye such as carmine 

 or basic fuchsin (see Shumway, 1926), sometimes hematoxylin. 

 A few special applications of the stain can be mentioned: by 

 Petragnani (1928), mixed with acid fuchsin, as a stain for Negri 

 bodies; by Cuyler (1932), mixed with eosin Y, as a counterstain to 

 hematoxylin for staining vaginal smears; by Brozek (see Hruby, 

 1933) in plant cytology where it is used in picric acid solution in 

 contrast to basic fuchsin; by Kempton, Bott and Richards (1937) 

 for uretral injection in studies of glomerular excretion. 



For use in Fraenkel's method for elastic tissue, see Staining Procedures, p.IBs-lT. 

 ul5 BeRBERINE C. I. NO. 1137 



Berberine was originally obtained from barberry and is some- 

 times called barberry extract. It is found in other plants, how- 

 ever, and can also be prepared synthetically. It has the following 

 formula: 



