562 VETERINARY PHYSIOLOGY 



4. Hippuric Acid. — This is benzoyl-amino-acetic acid — 



CeH, 



O 



— c- 



H H O 



i I II 

 .N—C-C— O— H 



1 

 H 



It is formed from benzoic acid taken in the food by linking 

 it to giycin — amino-acetic acid. This synthesis appears to 

 take place in the kidneys, for it has been found that hippuric 

 acid is not formed when these organs are excised, and that, when 

 blood containing benzoates is circulated through them, hippuric 

 acid is produced. Its chief interest is in the fact that it is one 

 of the first organic compounds which were demonstrated to be 

 formed synthetically in the animal body. Normally it is present 

 in human urine in very small quantities, but in the urine of 

 herbivora the amount is considerable, from the presence of 

 benzoic acid in the fodder, and is most abundant on a diet of 

 grass or hay, less so upon one of oats. The acid itself is 

 insoluble, and it occurs as the soluble sodium salt. 



5, Mon-amino Acids are always present in traces in the urine, 

 and any interference with the activity of the liver, the organ 

 chiefly concerned in changing them to urea, leads to their 

 appearance in increased amounts (p. 360). 



6. Undetermined Nitrogen. — A small quantity of the nitrogen 

 in the urine exists in substances the chemical nature of which 

 has not been determined. The amount of these varies con- 

 siderably. 



The proportions of the total nitrogen of the urine in these 

 various compounds varies with the kind of food taken. Folin 

 gives the following table for the human subject, which shows 

 this very clearly : — 



Per cent, of Total Nitrogen 

 Protein-rich Diet. 



Total Nitrogen 



Urea ,, 



NH3 



Creatinin Nitrogen 



Uric Acid Nitrogen 



Undetermined Nitrogen 



14-8 to 18-2 grms. 

 86-3 ,, 89"2 per cent. 



S'S ,, o'l ,, 



3-2 „ 4-5 



0-5 „ 10 „ 



2-7 



5-3 



Protein-poor Diet. 



4-S to 8'0 grni.s. 



62-0 ,, 80-4 per cent. 



4-2 ,, 11-7 



5-5 „ 111 



1-2 „ 2-4 



4-8 „ 14-6 



