380 BACTERIOLOGICAL CHEMISTRY 



Most of Miem gi\^e the lipocyan reac^tion, an intense ))lue 

 colour with concentrated sulphuric acid. 



{h) Quinone Pigments. — Substituted toluquinones, 



O 



II II 



CH /\ ■ "/X/N 



, naphthoquinones and anthra- 



II 

 







il 



quinones are found quite frequently as 





 pigments in bacteria and the lower fungi. 



(c) Melanins. — The melanins are black or brown pig- 

 ments which are very insoluble in nearly all solvents, 

 even hot concentrated hydrochloric acid. They are 

 soluble in warm concentrated sulphuric acid and are 

 reprecipitated on dilution of the solution with water. 

 They are formed as a result of the decomposition of 

 proteins, either by boiling concentrated acids or by the 

 action of the enzyme tyrosinase on the amino -acid 

 tyrosine. Tryptophane and hydroxy-phenylethylamine 

 are also sources of melanin pigments. They occur in the 

 black Torula yeasts, in the De7natiacece, fungi with dark 

 brown or black hyphse, and in the black varieties of 

 certain bacilli such as B. mesentericus 7iiger. 



The following is a classification of the pigments based 

 on solubility characteristics ; — 



