474 PATHOLOGICAL PIGMENTATION 



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 ad- 

 dition 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. 

 Especially to be distinguished are alkaptonuria, chronic intoxication 

 with phenols, and some cases of extreme indicanuria.^* In support of 

 the view that tryptophane is the mother substance of melanin is the 

 fact that feeding tryptophane to melanurics increases the melanin 

 excretion (Eppinger). 



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 

 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 be deposited in the endothelium lining the 

 blood-vessels. Koberfc injected melanin into albino rabbits, but 

 did not succeed in getting 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 

 possibly due to the alkali rather than to the melanin. 



Melanotic Tumors.^" — Tumor melanin does not differ from mel- 

 anin produced by normal cells in any essential respect. Usually it con- 

 tains 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 mel- 

 anins. Iron is frequently found microscopicallj'- in the pigment in 

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

 coming from extravasations of blood. The peculiar fact that melano- 

 sarcoma is very common in white or gray horses, but very seldom 



" Cent. f. inn. Med., 1902 (23), 1017; Arch, internat. Pharmakodynam., 1903 

 (12), 271. 



^8 Melanuria fully discussed by Feigl and Querner, Deut. Arch. klin. Med., 

 1917(123), 107. 



" Jour. Exp. Med.. 189G (1), 3G1. 



2" Under the title Acanthosis Nigi'icans (see PoUitzer, Jour. Amer. Med. Assoc, 

 1909 (53), 1369) is included a group of cases of widespread cutaneous pigmentation 

 with papillary hypertrophy, commonly associated with cancer, most often ab- 

 dominal. While ascribed to action of the sympathetic nervous system injured 

 by the cancer, this explanation is far from satisfactory, and the possibility of 

 metabolic pigmentary disturbance must be considered. 



