ELEMENTARY PHYSIOLOGICAL CHEMISTRY 261 



Chemically, hippuric acid consists of a combination of benzoic acid and 

 glycocine, and can be prepared artificially by heating these two bodies 

 together in a closed tube. 



CH 9 -NH 2 CH 2 -NH-CO-C 6 H 5 + H 2 0. 



+ C 6 H 5 COOH= | 

 COOH COOH 



Glytin. Benzoic add. Hippuric acid. 



The explanation of its presence in the urine of herbivora is, that they 

 take aromatic bodies in their food ; these are oxidised to benzoic acid in 

 the tissues, and this then combines with glycin to form hippuric acid. 

 In man, etc., there is very little aromatic body in the food, and conse- 

 quently, most of the glycin combines with cholalic acid to form one of 

 the bile salts (see p. 233). The synthesis of hippuric acid takes place in 

 the kidney, as has been shown by perfusing the excised kidney with 

 defibrinated blood containing the two precursors. A similar experi- 

 ment with any other organ yields no hippuric acid. 



Creatinin. It will be remembered in connection with creatin 

 (see p. 205) that one of its reactions is that, by standing in acid solution, 

 it loses a molecule of water, and changes into creatinin. 



NH 2 N 



C(NH) H 2 0=C(NH) 



\ CH 3 \ CH 3 



N< N< 



CH 2 COOH CH 2 CO 



Creatin Creatinin 



(methyl guanidin acetic acid). (anhydride of creatin). 



When, from any cause, the urine reacts alkaline, creatin is excreted 

 instead of creatinin. It is, therefore, the reaction of the urine which 

 determines in what form this base will be excreted. It can be 

 detected by the following test : 



EXPERIMENT VII. Weyl's Reaction. To five c.c. of urine are added 

 four or five drops of a very dilute solution of sodium nitroprusside, so 

 that the original colour of the urine remains unchanged. If a weak 

 solution of caustic potash be now added drop by drop a ruby-red 

 colour results, quickly changing to yellow. If an excess of acetic acid 

 be added and the solution boiled, a greenish to blue colour results, 

 and after standing some time a blue sediment (Prussian blue) settles to 

 the bottom of the tube. 



Aceton gives a similar colour with the nitroprusside and alkali, 

 which, however, does not become yellow on standing, or even after 

 adding acetic acid. 



