COLORING MATTERS OF URINE. 401 



glycin, and forming a conjugated acid, a molecule of water being 

 formed at the same time, thus : 



Benzoic acid. Glycin. Hippuric acid. Water. 



C 7 H 6 2 + C 2 H 5 N0 2 = C 9 H 9 N0 3 + H 2 O. 



The amount of hippuric acid increases with increased consump- 

 tion of vegetable food, in the cellulose of which the materials 

 exist that are required for its formation. It is in the liver that 

 the union between the glycin and the benzoic acid takes place, as 

 is proved by the removal of that organ, when benzoic acid in- 

 jected into the portal vein appears unchanged in the urine. 



Oxalic acid (C 2 H 2 O 4 ) occurs often, but not constantly, in the 

 urine. It is generally united with lime. It is said to appear in 

 greater quantity, together with an excess of uric acid, after meals, 

 and therefore to be related to the production of the latter in the 

 body ; but it probably is chiefly derived from oxalates being con- 

 tained in some material taken with the food. 



COLORING MATTERS. 



It appears probable that the color of the urine depends on the 

 presence of small quantities of distinct substances which have 

 different origins in the body. Three such have been described, 

 and may be taken provisionally to represent our knowledge of 

 the subject : 



1. Urobilin, which is an outcome of the coloring matter of the 

 bile, and therefore a remote derivative of the coloring matter of 

 the blood, is frequently present in the urine. It is probably the 

 same as hydrobilirubin, some of which is occasionally absorbed 

 from the intestinal tract and eliminated by the kidneys. 



2. Urochrom is said to be the special pigment of the urine. It 

 oxidizes on exposure, forming a reddish substance that gives the 

 dark color to some urinary sediments ( Uroerythriii). 



3. A certain material (Indican) capable of producing Indigo, 

 is commonly present in the urine of man, and in greater quantity 

 in that of some animals, particularly the horse. It is supposed 

 to be formed from the indol that arises from the putrefactive 



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