396 PATHOLOGICAL PIGMENTATION 



addition of ferric chloride causes the development of a black 

 precipitate. (2) If this precipitate dissolves in sodium car- 

 bonate, forming a black solution. (3) If from this solution min- 

 eral 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 con- 

 taining but 0.1 per cent, of melanin has the color of dark beer 

 (Hensen and Nolke), and' the entire skin of a negro contains 

 only about 1 gram of melanin (Abel and Davis *). Excessive 

 quantities of melanin may be in part deposited in the lymph- 

 glands and skin, causing diffuse pigmentation ; it may also be 

 deposited in the endothelium lining the blood-vessels. Kobert 

 injected melanin into albino rabbits, but did not succeed in get- 

 ting any deposition in the choroid or skin. Helman found 

 some evidence of toxicity when large doses of melanin dissolved 

 in sodium carbonate are injected into animals, but this is pos- 

 sibly due to the alkali rather than to the melanin. 



Melanotic Tumors. Tumor melanin does not differ from 

 melanin produced by normal cells in any essential respect. 

 Usually it contains much sulphur, even as much as 10 per cent., 

 yet Helman in eight specimens found but four that contained 

 both sulphur and iron, in three only sulphur, in one only iron 

 and no sulphur; therefore, tumor melanins show the same 

 variations in composition as do normal melanins. Iron is fre- 

 quently found microscopically in the pigment in melanosar- 

 coma, but this is chiefly due to admixture of blood-pigment 

 coming from extravasations of blood. The peculiar fact that 

 melanosarcoma is very common in white or gray horses, but 

 very seldom occurs in dark -coated horses, has not been explained. 

 The frequent occurrence of melanuria and melanemia in patients 

 with melanosarcoma is not due to any peculiar property of 

 sarcoma melanin, but to the enormous quantity of melanin that 

 is produced by the tumor and set free in the degenerating por- 

 tions. Thus, while Abel and Davis 1 estimate that there is 

 only about 1 gram of melanin in the entire skin of a negro, 

 Nencki and Berdez have obtained from a sarcomatous liver 300 

 grams of melanin, and estimate that the entire body contained 

 500 grams. Helman 2 states that the melanin may constitute 

 7.3 per cent, by weight of the fresh substance of some melano- 

 sarcomas. According to Lubarsch and to Helman, melanotic 

 tumors rarely contain glycogen. 



1 Jour. Exp. Med., 1896 (1), 361. 



2 Arch, internal. Pharmakodynam. , 1903 (12), 271. 



