45 2 PHYSIOLOGICAL CHEMISTRY 



melanotic growth. In many instances, without doubt, urines rich in 

 indican have been wrongly taken as diagnostic proof of melanuria. 

 The pigment melanin is sometimes mistaken for indigo and melanogen 

 for indican. It is comparatively easy to differentiate between indigo 

 and melanin through the solubility of the former in chloroform. 



In rare cases melanin is found in urinary sediment in the form of fine 

 amorphous granules. 



EXPERIMENTS 



1. Ferric Chloride Reaction (von Jaksch-Pollak). Add a few drops of 

 ferric chloride solution to 10 c.c. of urine in a test-tube and note the formation of 

 a gray color. Upon the further addition of the chloride a dark precipitate forms, 

 consisting of phosphates and adhering melanin. An excess of ferric chloride 

 causes the precipitate to dissolve. 



This is the most satisfactory test for the indentification of melanin in the 

 urine. 



2. Bromine Test (Zeller). To 50 c.c. of urine in a small beaker add an equal 

 volume of bromine water. In the presence of melanin a yellow precipitate will 

 form and will gradually darken in color, ultimately becoming black. 



UROROSEIN 



This is a pigment which is not present in normal urine but may 

 be detected in the urine in various diseases, such as pulmonary tuber- 

 culosis, typhoid fever, nephritis, and stomach disorders. Urorosein, 

 in common with various other pigments, does not occur preformed in 

 the urine, but is present in the form of a chromogen, which is trans- 

 formed into the pigment upon treatment with a mineral acid. Herter 1 

 showed this chromogen to be indole acetic acid, 



H 



I 

 ,C-C-COOH 



I 

 H 



Normal urine responds to the urorosein reaction (see below) if nitrites 

 are present. 



EXPERIMENTS 



i. Nitrite-Hydrochloric Acid Test (Urorosein Reaction). To 10 c.c. of urine 

 in a test-tube add 2 c.c. of concentrated hydrochloric acid and a few drops of a 

 i per cent solution of potassium nitrite. A rose-red color indicates urorosein. 



The chromogen (indole acetic acid) has been changed into urorosein 

 by oxidation. 



1 Herter: Jour. Biol. Chern., 4, 253, 1908. 



