THE AROMATIC CONSTITUENTS OF THE URINE. 257 



process of intestinal putrefaction, are in part absorbed in the intestinal 

 tract, and are eliminated in the urine in combination with glycocoll 

 as hippuric acid and phenaceturic acid, respectively. But while 

 phenyl-acetic acid unites with glycocoll directly, phenyl-propionic 

 acid is usually first oxidized to benzoic acid (see page 97). 



Hippuric Acid. While a certain amount of the benzoic acid 

 which enters into the construction of the hippuric acid molecule is 

 derived from the phenyl-propionic acid which results during the 

 process of intestinal putrefaction, another portion is ingested as 

 such, or in the form of other aromatic substances which can be 

 transformed into benzoic acid in the animal body. We can thus 

 understand why larger amounts of hippuric acid are encountered 

 in the urine of herbivorous animals than in that of the carnivora, as 

 the food of the former always contains very considerable amounts of 

 toluol, cinnamic acid, quinic acid, etc., all of which may give rise to 

 benzoic acid. In man the daily elimination corresponds to about 

 0.7 gramme, but may be increased by the ingestion of such articles 

 of food as cranberries, prunes, reine-claudes, etc. 



In a few instances the substance has been found in urinary 

 sediments. 



While the source of the aromatic component of hippuric acid 

 is thus quite well understood, we know but little of the origin of 

 glycocoll. To a certain extent this may also be formed during the 

 process of albuminous putrefaction, as we know that all albumins 

 contain a glycocoll radicle, but there is reason to believe that it 

 may likewise originate within the tissues of the body. It mani- 

 festly plays an important role in the process of metabolism, for we 

 have seen that to a certain extent, no doubt, it is concerned in the 

 formation of urea, and it has also been noted that in man and in 

 other animals a very considerable proportion of cholalic acid is elimi- 

 nated from the body in combination with glycocoll. 



Through the interesting researches of Schmiedeberg we know that 

 the synthesis of glycocoll and benzoic acid is in dogs effected in the 

 kidneys exclusively. In other animals, however, this process may 

 occur in other organs as well, for it has been shown that after 

 removal of the kidneys hippuric acid can be isolated from the liver 

 and the muscles, at least, if benzoic acid has been previously 

 administered. 



Properties. Hippuric acid crystallizes in long rhombic prisms 

 when allowed to separate from its solutions slowly, while when 

 rapidly formed, and especially if the amount is small, it occurs in 

 long needles which are frequently grouped in stars and rosettes. 

 The melting-point of the substance is 187.5 C. It is soluble with 

 great difficulty in cold water and ether, while in hot water and 

 alcohol it dissolves with comparative ease. In aqueous solutions of 

 the alkaline hydrates and carbonates it dissolves with the formation 

 of the corresponding salts, from which the free acid may again be 

 obtained by acidifying with a mineral acid. 



17 



