220 



Biological Stains 



facturers introduced the process of bleaching with sulfur dioxide. 

 It was subsequently found that this bleaching injured the staining 

 qualities, and the manufacturers changed their method and began 

 turning out a darker colored but more satisfactory stain. About 

 1926 another change in process of manufacture was made and the 

 staining properties seemed thereby to be improved. Until re- 

 cently there has been only one American manufacturer of hema- 

 toxylin whose product could qualify as a biological stain; but the 

 great demand caused by the second World War has resulted in 

 other companies entering the field and developing cheaper pro- 

 cesses of manufacture. These cheaper methods of production 

 yield a darker colored and presumably less pure product; it is not, 

 however, to be compared with the crude material put on the 

 American market during the first World War, as it seems to be a 

 satisfactory stain in spite of impurities that may be present. 



Hematoxylin is similar to brazilin, but has one more hydroxyl 

 group, the generally accepted formula being: 



OH 



HO 



O CH 



CH 



C— OH 



■ \ 

 CH2 



HO HO 



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

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

 to brazilein and probably has the formula: 



OH 



HO 



.0_CH2 



C 



C— OH 



X 

 CH, 





HO O 



Hematein is available commercially in dry form. Less atten- 

 tion has been given to its production than to that of hematoxylin. 

 Hence it frequently results that a hematein sold by some company 

 is more crude than their hematoxylin, although theoretically 

 hematein is a derivative of hematoxylin. 



