HIPPURIC ACID 



ammonium or sodium urate. When deposited in crystals, it is most fre- 

 quently in rhombic or diamond-shaped laminae, but other forms are not 

 uncommon, figure 295. When deposited from urine, the crystals are gener- 

 ally more or less deeply colored, from being combined with the coloring 

 principles of the urine. 



Hippuric Acid. This compound, C 9 H 9 NO 3 , has long been known 

 to exist in the urine of herbivorous animals in combination with soda. It 

 also exists naturally in the urine of man, in a quantity equal to or rather ex- 



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



ceeding 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 or 

 from some allied substance. The benzoic acid unites with glycin, and hip- 

 puric 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 one substance which has been clearly demonstrated 

 to be formed by the kidney itself. 



Kreatinin. This substance is present in urine in a remarkably 

 constant quantity, as shown recently by Folin's analyses. Its daily excre- 

 tion quantity is from i to 15 grams according to the amount of active tissue 

 in the individual. It is of especial importance as a measure of the metab- 

 olism of muscle protoplasm. 



Ammonia. A considerable daily quantity of ammonia in com- 

 bination is found in the urine, showing that this is an important method of 

 nitrogen elimination. 



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

 chrome, 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 



