212 On Melanin [Dec. 



snlphuric acid, readily soluble when moist in alkalis, but when dried 

 by heat, Solution in alkalis took place only slowly. 



The melanin which is soluble in dilute acids differs widely from 

 the other preparations, and I believe it to be the pigment in more 

 nearly the same form in which it occurs in the natural keratin. 

 When freshly precipitated, the pigment is very plastic and may be 

 moulded into compact balls. When heated on a water-bath, these 

 balls contract strongly, forcing out water, and a tough, elastic mass 

 results. When thoroughly dried, the product powders readily to a 

 dark brown dust. When dried by heat, the pigment is found to be 

 insoluble in dilute acids, and only incompletely soluble in alkaline 

 Solutions. After drying slowly, at room temperature, it completely 

 dissolves in n/20 HCl or 50 per cent. acetic acid forming dense 

 black Solutions. Boiling with alkali, of a strength exceeding 0.2 

 per cent. sodium hydroxide, decomposes the melanin yielding, to- 

 gether with volatile and soluble products, a colored substance which 

 is insoluble in acids. 



By hydrolysis with strong mineral acids the melanin is decom- 

 posed, yielding a series of cleavage products, among which I have 

 identified tyrosin, lysin, and arginin, and leaving a brownish black 

 residue equal to about 10 per cent. of the original material. The 

 nature of this " melano-humin " and the products of hydrolysis are 

 being further investigated. 



Judging from these data, it appears that this melanin is of a pro- 

 tein nature. I believe it to be of the same type as an alkali albumin, 

 but with a portion of the molecule so modified as to be deeply pig- 

 mented. I have proposed for this type of Compounds the name 

 melano-protein when they are discussed under the proteins, and 

 retain the name of melanin when they are treated under animal pig- 

 ments, with the distinction, however, that all melano-proteins are 

 melanins. while only a portion of the melanins are melano-proteins. 



In the isolation of melanin from other keratin structures, by 

 the method that was used in the case of the black wool, I have 

 found melano-proteins in auburn human hair, and both light and 

 dark brown horse hair. Brown human hair (three samples), 

 black feathers from domestic poultry, negro hair, black rabbit 

 hair, and crow feathers do not contain a melano-protein but give 



