468 PATHOLOGICAL PIGMENTATION 



bearing upon the question as to whether the melanin is derived from 

 hemoglobin or not, and the results obtained by the best methods indi- 

 cate that the amount of iron present is usually extremely small, and 

 often it is entirely absent; furthermore, the presence of iron is no 

 proof that the pigment is derived from hemoglobin, since other iron- 

 protein compounds undoubtedly exist, — especially nucleoproteins, and 

 chemical examination shows that melanin does not contain hemopyr- 

 role groups.* 



Composition of Melanin. — The elementary composition of differ- 

 ent specimens of melanin examined by various observers has been 

 found to vary greatly. This probably depends on three factors: 

 First, it is extremely difficult to obtain melanin in a pure condition; 

 second, the process of purification requires the action of strong acids 

 and alkalies, which undoubtedly modify the composition of the mel- 

 anin; thirdly, melanin is probably not a single substance of definite 

 composition, but includes several related but different bodies. The 

 values found vary for carbon from 48.95 to 60.02 per cent. ; for hy- 

 drogen from 3.05 to 7.57 per cent. ; for nitrogen, 8.1 to 13.77 per 

 cent. Hofmeister gives, as a characteristic of melanins, that their 

 elementary molecular composition is always nearlv in the proportions 

 N : H : C = 1 : 5 : 5. 



Gortner's ^ studies have led him to accept the general principle that 

 melanin is formed through the action of an oxidase on an oxidizable 

 chromogen, but that in keratinous structures there exist at least two 

 types of melanins, one, a ''melano-protein," soluble in dilute acids 

 and existing dissolved in the keratins; the other, insoluble in dilute 

 acids, exists as pigment granules and is of unknown nature. Piettre '^ 

 believes that melanin from sarcoma of the horse consists of a protein 

 united to a pigment. Those whose studies of melanin formation have 

 been made with the microscope, state that the nucleus is active in the 

 process," and some find the melanin so closely related to the lipoids 

 that they consider it a lipochrome.^ 



A particularly prominent constituent of some melanins is sulphur, 

 which has been found in as high proportions as 10 per cent, in mel- 

 anin from sarcomas, and even 12 per cent, in sepia from the squid ; 

 in melanin from hair the sulphur is usually about 2-4 per cent.; but 

 in choroid melanin, and in some other forms, sulphur seems to be ab- 

 sent. The proportions of sulphur obtained from the same specimen 

 purified by different methods show wide variations, and hence v. 



4 Spioprlcr, TTofmoistor's Beitr., 1007 (10), 253. 



•'". Biofhom. Bulletin. liHl (1), 207: rr'suni^. 



oConipt. Bend. Acad. Sci., 1011 (I'l:^), 782; also sec Ri'priiil frnm 1st Intor- 

 nat. ronfr. Compar. Pathol., Paris, 1912. 



T StanVi, Vcrli. Df'iit. Path. Ges., 1007 (11), 130; Schultz, Jour. Mod. Rca.. 

 1912 (20), 05. 



sDvaon, Jour. Path, and Bact., 1011 (15), 298; KriMbieii. Wien. klin. Woi'h., 

 ion "(24), 117. 



