Its solution is colorless, but it becomes red on exposure to tlje air, 

 as it is then oxidized into the dye brazilein, which probably has the 

 formula : 



HO 



HO O 



With alum it is used as a nuclear stain (known as brazalum) by 

 Mayer. It is also used by Hickson for similar purposes following 

 treatment with iron alum as a mordant. 



HAEMATOXYLIN 



C. I. NO. 1246 



Haematoxylin is a homolog of brazilin, having one more hy- 

 droxyl group, the generally accepted formula being: 



OH 



HO 



O CH 



CH 



C— OH 

 CH. 



<z> 



HO HO 



Like brazilin it is not a dye, but its color develops in solution upon 

 standing, due to the oxidation into haematein, which is homologous 

 to brazilein and probably has the formula: 



OH 

 HO_/\_0_CH. 



C— OH 

 CH. 



V 



HO O 



Haematoxylin is without question one of the most important 

 biological stains. It is as valuable to the cytologist and histologist 

 as methylene blue is to the bacteriologist; and probably is second 



96 



