THE AROMATIC CONSTITUENTS OF THE URINE. 271 



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

 likewise originate within the tissues of the body. 



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 9,nd 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. 



On boiling with dilute mineral acids or alkalies hippuric acid is 

 decomposed into its components. The same result is reached if 

 ammoniacal decomposition is allowed to occur, and in such urines 

 benzoic acid only is found. In traces, benzoic acid is said to occur 

 in every urine together with hippuric acid, and it is thought that its 

 presence under normal conditions may be due to the action of a 

 ferment, the so-called histenzyme of Schmiedeberg, which has been 

 found in the kidneys, and which is known to be capable of effecting 

 the decomposition of hippuric acid as outlined. 



On heating hippuric acid in a dry test-tube it melts, and is then 

 decomposed with the formation of benzoic acid, which sublimes in 

 the upper portion of the tube. The liquid mass at the same time 

 assumes a red color, and develops an odor which at first is suggestive 

 of hay, but subsequently resembles that of hydrocyanic acid. This 

 reaction, together with the form of the crystals and their insolubility 

 in petroleum-ether, serves to distinguish hippuric acid from benzoic 

 acid. But like this, it develops a marked odor of bitter almonds 

 when it is evaporated with nitric acid and the residue is then 

 heated. The reaction is due to the formation of nitrobenzol. 

 In the urine hippuric acid is, of course, not present in the free 

 state, but in combination with alkalies, and notably potassium and 

 sodium. 



Synthesis of Hippuric Acid. Hippuric acid can be formed syn- 

 thetically in vitro also from benzoic acid and glycocoll by heating 

 the two substances together at a temperature of 160 C. in a sealed 

 tube. In a similar manner it is obtained from benzamide and 

 monochlor-acetic acid. The reactions which take place may be 

 represented by the equations : 



