218 Biological Stains 



It required the second World War, however, with its interrup- 

 tion of trade and resulting cutting off of the supply of litmus, to 

 stimulate bacteriologists to investigate combinations of indicators 

 to replace litmus. Ulrich (1944) proposed a mixture of methylene 

 blue (to indicate reduction) with chlor phenol red (for pH) which 

 seemed, for some kinds of bacteria at least, to be preferable to 

 litmus as an indicator in milk. This combination, however, 

 shows no sign of replacing litmus for the purpose. 



Brazilin and Hematoxylin 



The two natural dyes, hematoxylin and brazilin, are closely 

 related chemically and upon decomposition yield the two com- 

 pounds, pyrocatechol 



OH 



OH 

 and pyrogallol 



OH 



I OH 



OH 



Both dyes are obtained by extraction of the bark of certain trees, 

 hematoxylin from logwood and brazilin from brazil wood (red 

 wood). Both trees are legumes and belong to the family Cesal- 

 piniaceae; they are found only in the tropics. Hematoxylin comes 

 from a single species ; while brazil wood is a term applied to various 

 different species all yielding brazilin. 



U40 BRAZILIN C. I. NO. 1143 



The composition of this substance is supposed to be: 



HO /\ O CH2 



C— OH 



CH \ 

 CH2 



HO OH 



