410 EXCRETION 



posited in crystals, uric acid is most frequently obtained in rhombic or dia- 

 mond-shaped laminae, but other forms are not uncommon, figure 295. 

 When deposited from urine, the crystals are generally more or less deeply 

 colored, from being combined with the coloring principles of the urine. 



Hippuric Acid. This compound, C 6 H 5 .CO.NH.CH 2 COOH, has long 

 been known to exist in the urine of herbivorous animals in combination with 

 sodium. It also exists naturally in the urine of man, in a quantity equal to 



FIG. 295. Various Forms of Uric Acid Crystals. FIG. 296. Crystals of Hippuric Acid. 



or rather exceeding, that of the uric acid. The quantity excreted is increased 

 by a vegetable diet. 



Hippuric acid appears to be formed in the body from benzoic acid. The 

 benzoic acid unites with glycocoll, and hippuric acid and water are formed 

 thus: 



C 6 H 5 .COOH +CH 2 .NH 2 .COOH = C 6 H 5 .CO.NH.CH 2 .COOH + H 2 O. 



Benzoic acid Glycin Hippuric acid 



Hippuric acid is the first substance which was demonstrated to be synthet- 

 ized in the body. 



Kreatinin. This substance, which is the anhydride of kreatin, is pres- 

 ent in urine in a remarkably constant quantity, as shown recently by Folin's 

 analyses. Its daily excretion quantity is from i to 1.5 grams according to 

 the amount of active tissue in the individual. It is of especial importance 

 as a measure of the metabolism of muscle protoplasm. 



Ammonia. A considerable daily quantity of ammonia (about o . 7 gram) 

 in combination, as chloride, phosphate, or sulphate, is found in the normal 

 urine, showing that this is an important method of nitrogen elimination. 



Pigments. The pigments of the urine are the following: i. Urochrome, 

 a yellow coloring matter, giving no absorption band; of which but little is 

 known. Urine owes its yellow color mainly to the presence of this body. 

 2. Urobilin, an orange pigment, of which traces may be found in nearly all 

 urines, and which is especially abundant in the urines passed by febrile 

 patients. It is characterized by a well-marked spectroscopic absorption 



