FROM PROTE1D SUBSTANCES. 369 



tion of melanin resulting from 79 hours' boiling of the proteid 

 with sulphuric acid contained 54 per cent of carbon, while the 

 second preparation resulting from 110 hours' boiling contained 

 58 per cent of carbon. Further, in the content of sulphur the 

 differences were still more striking. The table on page 368, 

 showing the composition of melanins from various sources, 

 affords evidence of the extent to which these black pigments 

 may differ from each other in chemical composition as well as 

 indicating the extent to which the artificial melanins resemble 

 the natural pigments. 



These figures, which are fairly typical of the composition of 

 the various melanins hitherto studied, show quite clearly how 

 widely these bodies may vary in composition; yet throughout the 

 entire list, as well as hi many other preparations not tabulated, 

 there is to be found almost invariably a relatively high content 

 of carbon and a low content of nitrogen. Further, in all but the 

 choroidal pigment, sulphur is very conspicuous. These facts, 

 coupled with the inappreciable amounts of iron usually found, 

 strengthen belief in the theory that these pigments, whether 

 formed normally or as a result of pathological conditions, have 

 their origin not in the hsematin molecule but in proteid matter. 

 Further, we see in the experiments of Schmiedeberg, as well 

 as in our own results, evidence that serum-albumin, proteoses, 

 antialbumid, and hemipeptone may all yield melanin-like sub- 

 stances by simple hydrolytic cleavage, pigments which in 

 composition and reaction differ from the natural pigments no 

 more widely than the latter differ from each other. No two 

 melanins are exactly alike in composition, and the artificial 

 bodies, certainly, are exceedingly prone to vary in composition 

 with variations in the method of preparation; especially, 

 variations in the extent and intensity of the hydrolytic cleavage. 

 In the hydrolytic cleavage induced by boiling acids, proteid 

 substances tend to lose nitrogen, partially as ammonia and 

 partially in the form of amido-acids and nitrogenous bases, 

 while the artificial melanins simultaneously formed appear to 

 have their origin in the carbon-rich residue left after the 

 splitting off of these nitrogenous radicals. For this reason, 



24 



