THE QUANTITY AND COMPOSITION OF THE URINE 



Fig. 136.— Hippuric Acid 



named kreatin, which exists in considerable quantity in the muscles, and 

 from which urea can be artificially obtained in the laboratory. The kreatin 

 of the muscles, or possibly some intermediate substance as ammonium car- 

 bonate, is carried by the blood to the liver, and is there converted into 

 urea. This is taken up by the blood and carried to the kidneys, where it is 

 excreted by the cells of the urinary tubules and mixed with the water of 

 the urine. That urea is not formed at 

 or by the kidneys is demonstrated by 

 the fact that it accumulates in the blood 

 after the kidneys have been removed 

 from the body by operation. 



Hippuric Acid. — This acid, the 

 name of which (iV-to?, horse) is derived 

 from its abundance in the urine of the 

 horse, is closely connected with the 

 aromatic benzoic acid. It can, in fact, be made to appear in the urine of 

 man by the administration of benzoic acid with the food. Its chemical 

 formula is C 9 H 9 N0 3 , and it contains 7 - 8 per cent of nitrogen. When 

 separated from the urine it appears in the forms presented above (fig. 

 136), which represent large, white, four-sided prisms or elongated needles 

 easily soluble in hot water and in alcohol. 



The copious excretion of hippuric acid observed in animals fed on 

 meadow hay is due to the herbs mixed with the grass, 

 plants from which it is derived do not 

 appear to have been ascertained. It 

 appears in maximum quantities, 2 ozs. 

 per diem or more, in animals fed on 

 wheat and oat straw, but little is found 

 in the urine of those fed on oats or corn, 

 or on bean straw. It seems probable 

 that it is formed in the liver and in- 

 testines by the union of glycocine with 

 substances belonging to the benzoic acid series, or this may possibly 

 occur in the kidney itself. 



Hippuric acid, which sometimes constitutes as much as 2 per cent 

 of the urine of the horse, is usually combined with calcium and sodium, 

 forming hippurates of those metals. 



Uric Acid. — This acid, which has the composition represented by 

 the formula C' 6 rI 4 N 4 03, only presents itself as a trace in the normal urine 

 of the adult horse, though it is found in rather larger quantity in the 

 foal whilst it still lives on milk. 



but the precise 



Fig. 137.— Uric Acid 



