466 PHYSIOLOGICAL CHEMISTRY 



and a little calcium chloride solution to the moist residue and evaporate the mixture 

 to dryness. In the presence of inositol (o.ooi gram) a bright red color is obtained. 

 For a more satisfactory test, which is also more time-consuming, see Salkowski's 1 

 modification of Scherer's test. 



LAIOSE 



This substance is occasionally found in the urine in severe cases of 

 diabetes mellitus. By some investigators laiose is classed with the 

 sugars. It resembles fructose in that it has the property of reducing 

 certain metallic oxides and is levorotatory, but differs from fructose 

 in being amorphous, non-fermentable, and in not possessing a sweet 

 taste. 



MELANINS 



These pigments never occur normally in the urine, but are present 

 under certain pathological conditions, their presence being especially 

 associated with melanotic tumors. Ordinarily the freshly passed urine 

 is clear, but upon exposure to the air the color deepens and may at 

 last be very dark brown or black in color. The pigment is probably 

 present in the form of a chromogen or melanogen and upon coming 

 into contact with the air oxidation occurs, causing the transforma- 

 tion of the melanogen into melanin and consequently the darkening 

 of the urine. 



It is claimed that melanuria is proof of the formation of a visceral 

 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 identification 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. 



1 Salkowski: Zeit. physiol. chem., 69, 478, 1910. 



