470 PATHOLOGICAL PIGMENTATION 



quite insoluble in all ordinary reagents except alkalies, in which some 

 melanins dissolve easily, and some with difficulty. Strong boiling 

 hydrochloric acid scarcely affects non-i)rotein melanins. By the 

 action of sunlight or oxidizing agents on melanin-containing sections 

 the pigment can be bleached out. The chief decomposition-products 

 formed on fusing with alkalies are indole, skatole, and "melanic 

 acid"; no cystine, leucine, tyrosine, or other amino-acids can be iso- 

 lated. ]\rost authors, therefore, consider the melanins as heterocyclic 

 compounds standing in some relation to the indole nucleus. 



If melanin is injected subcutaneously into animals (rabbits and 

 guinea-pigs), there appears in the urine a substance which turns dark 

 brown after the urine has stood for some time (Kobert, Helman). 

 The pigment is apparently reduced, particularly by the liver, to a 

 colorless melanogen, which is eliminated in the urine. The same 

 process occurs when melanin is produced in excess and enters the 

 blood, as in the case of melanosarcoma, a colorless melanogen being 

 formed which is excreted in the urine, constituting "melanuria." 

 Occasionally the urine is dark when first passed, because of the pres- 

 ence of melanin, but usually it must be subjected to oxidizing agen- 

 cies (bromine water, nitric acid, hypochlorites, etc.), or exposed to 

 air to bring out the brown color. Helman ^^ says that true melano- 

 gen may be considered to' be present in urine : ( 1 ) If the careful 

 addition of ferric chloride causes the development of a black precipi- 

 tate. (2) If this precipitate dissolves in sodium carbonate, forming 

 a black solution. (3) If from this solution mineral acids precipitate 

 a black or brownish-black powder. All three reactions must be 

 obtained, for substances other than melanin may give the first 

 two. 



The coloring power of melanin is very great, for urine containing 

 but 0.1 per cent, of melanin has the color of dark beer (Hensen and 

 Nfilke), and the entire skin of a negro contains only about 1 gram 

 of melanin (Abel and Davis). ^- Excessive quantities of melanin ma.y 

 be in part deposited in the lymph-glands and skin, causing diffuse 

 pigmentation ; it may be deposited in the endothelium lining the 

 blood-vessels, hi a pigmented colon Al)derhalden ^-'' found melanin- 

 like substances which seemed to be derived from tryptophane. Nik- 

 las,'-'' however, Ijelieves t3a'osinase activity to be responsible for this 

 type of intestinal melanosis. Kobert injected melanin into albino 

 ra])l)its, but did not succeed in getting any dejiosition in the choroid 



(Amor. Xatiiralist, 1010 (44), 407) boliovos this to bo a docDmiKisif imi ])ro(liiot 

 of koratin, iinrolalod to incdanin. 



iiCViit. f. inn. Mod., 1002 (2:5), 1017: Aroh. iiiloniat. riianiial<odviiaiii.. 100.3 

 (12), 271. 



12 Jour. Faj). Mod., IHOG (1), .Sfil. 



i2aZoit. phvsiol. Choni.. 101.3 (S.5). 02. 



i2b]\liinoli. inod. W(m-Ii.. 1014 (61), 13:52. 8oo also llattori, :\litt. Mod. Cosollscli. 

 Tokio, 1010 (.30), No. 6. 



