. URINE 417 



PIGMENTS 



There are at least three pigments normally present in human urine. 

 These pigments are urochrome, urobilin, and uroerythrin. 



A. UROCHROME 



This is the principal pigment of normal urine and imparts the char- 

 acteristic yellow color to that fluid. It is apparently closely related to 

 its associated pigment urobilin since the latter may be readily converted 

 into urochrome through evaporation of its aqueous-ether solution. Uro- 

 chrome may be obtained in the form of a brown, amorphous powder 

 which is readily soluble in water and 95 per cent alcohol. It is less 

 soluble in absolute alcohol, acetone, amyl alcohol and acetic ether, and 

 insoluble in benzene, chloroform, and ether. Urochrome is said to be a 

 nitrogenous body (4.2 per cent nkrogen), free from iron. Urochrome 

 is believed to be identical with the yellow.pigment, lactochrome, of 

 milk whey. 1 The chromogen of urochrome, i.e., urochromogen is present 

 in the urine in pulmonary tuberculosis. Its presence is said to be of 

 prognostic value (see page 467). 



B. UROBILIN 



Urobilin, which was at one time considered to be the principal pig- 

 ment of urine, in reality contributes little toward the pigmentation of 

 this fluid. It is claimed that no urobilin is present in freshly voided nor- 

 mal urine but that its precursor, a chromogen called urobilinogew, is 

 present and gives rise to urobilin upon decomposition through the in- 

 fluence of light. It is claimed by some investigators that there are 

 various forms of urobilin, e.g., normal, febrile, physiological, and patho- 

 logical. Urobilin is said to be very similar to, if not absolutely iden- 

 tical with, hydrobilirubin (see page 225). It may be determined 

 quantitatively. 2 



Urobilin may be obtained as an amorphous powder which varies 

 in color from brown to reddish-brown, red and reddish-yellow, depend- 

 ing upon the way in which it is prepared. It is easily soluble in ethyl 

 alcohol, amyl alcohol, and chloroform, and slightly soluble in ether, 

 acetic ether, and in water. Its solutions show characteristic absorption 

 bands (see Absorption Spectra, Plate II). Under normal conditions 

 urobilin is derived from the bile pigments in the intestine. 



Urobilin is increased in most acute infectious diseases such as ery- 



1 Palmer and Cooledge: Jour. Biol. Chem., 17, 251, 1914. 

 Pelkan: Jour. Biol. Chem., 43, 237, 1920. 



2 Marcussen and Hansen: Jour. Biol. Chem., 36, 381, 1918. 



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