CHAPTER XII 



MELANINS 



THE melanins are dark, black or brown, even reddish-brown pig- 

 ments, occurring in hairs, the skin, the choroid coat of the eye, and in 

 pigmented new growths which start generally in connection with the 

 skin. As the melanins are built up qualitatively out of the same 

 radicals as are met with in albuminous substances, they are regarded 

 as derivatives of albumins, and are hence included in this book. 



It has already been mentioned that a number of the dissociation- 

 products of albumin, e.g. glucosamin, tyrosin, tryptophane, and lysin, 

 have a tendency to become converted into darkly coloured compounds 

 of unknown constitution forming the so-called 'humin substances' 

 when they are boiled with acids (Samuely). 1 



Schmiedeberg 2 has drawn attention to the fact that these bodies 

 have a considerable resemblance to the melanins both as regards 

 composition and reactions, and hence has called them melanoidins. 

 Schmiedeberg and Nencki 2 are of the opinion that melanins may be 

 derived from albumins over the humin substances, but especial attention 

 is drawn to the fact that our chemical knowledge regarding these 

 amorphous mixtures of substances is as yet very, limited, and that the 

 proof is still outstanding that humin substances and melanins are one 

 and the same. Spiegler, 3 on oxidising melanins with sulphuric acid 

 and potassium bichromate, has isolated a substance which he believes 

 to be methyl-dibutyl-acetic acid. 



Melanins differ considerably in their composition according to the 

 source they are derived from. They only agree in possessing a high 

 carbon and low hydrogen percentage. Some contain no sulphur, while 

 others may contain up to 7 and even 10 per cent. The iron-content 



1 Samuely, Hofmeisters Beitrage, 1. 229 (1902). 



2 0. Schmiedeberg, Arch-iv f. experiment. Pathol. und Pharm. 39. 1 (1897) (see 

 also the index). 



3 M. Nencki, Berichte d. deutsch. chem. Ges. 28. I. 560 (1895) ; C. Beitler, ibid, 

 31. II. 1604 (1898). 



4 E. Spiegler, Hofmeisters Beitrage, 4. 40 (1903). 



580 



