FROM PROTEID SUBSTANCES. 363 



These results seemingly show that the sulphur and nitrogen 

 content of the melanin is not materially affected by the 

 character of the alkali used to dissolve it, i. e. a fixed alkali, 

 when dilute, causes no marked withdrawal of sulphur or 

 nitrogen. Natural pigment from hair or epidermis when 

 treated with 10 per cent solution of potassium hydroxide, and 

 then reprecipitated by acid is liable to lose both nitrogen 

 and sulphur,* but whether this is due to a change in the pig- 

 ment itself produced by the strong alkali, or whether due to 

 the withdrawal of contaminating substances derived from the 

 original pigmentary granules, is uncertain. 



Let us compare now the composition of our artificial melanins 

 with that of the antialbumid from which they were derived. 



Antialbumid. Melanin. Melanin. Antialbumid. t 



79 Hours' Boiling. 110 Hours' Boiling. 



C 63.52 54.26 68.05 64.70 



H 6.84 6.94 7.39 7.02 



N 13.65 12.00 11.92 13.79 



S 2.22 7.70 4.35 2.64 



The results seemingly justify the conclusion that these 

 melanins formed from antialbumid originate not by simple 

 hydrolysis, but by a process of hydrolytic cleavage, the pig- 

 ment holding the position of a cleavage residue, the exact 

 composition of which depends upon the extent or intensity of 

 the cleavage process. Further, it is evident that this melanin- 

 like residue, i. e. the true pigment, is either contaminated by 

 some substance or substances, which accounts for the marked 

 variation in composition, or else that under the term melanins 

 we have a class of related bodies more or less alike in their 

 physical properties but unlike in chemical composition. Cer- 

 tainly, our knowledge regarding the composition of the 

 natural melanins lends favor to the latter view, for it is a 

 well-known fact that certain melanins are exceedingly rich 



* See Abel and Davis, Journal of Experimental Medicine, 1896, i, p. 391. 

 Also, M. Nencki and N. Sieber, Archiv f. exper. Pathol. u. Pharmakol., 1887* 

 xxiv, p. 17. 



t After 38 hours' heating with 3 per cent sulphuric acid. 



