162 ESSENTIALS OF CHEMICAL PHYSIOLOGY 



HIPPURIC ACID 



Hippuric acid (C 9 H 9 N0 3 ), combined with bases to form hip- 

 purates, is present in small quantities in human urine, but in large 

 quantities in that of herbivora. This is due to the food of herbivora 

 containing substances belonging to the aromatic group the benzoic 

 acid series. If benzoic acid is given to a man, it unites with glycine 

 with the elimination of a molecule of water, and is excreted as 

 hippuric acid 



CH 2 NH 2 CH 2 NH.CO.C 6 H 5 



C 6 H 5 COOH + = | +H 2 



COOH COOH 



[benzoic acid] [glycine] [hippuric acid] [water] 



This is a well-marked instance of synthesis carried out in the 

 animal body, and experimental investigation shows that it is accom- 

 plished by the living cells of the kidney itself ; for if a mixture of 

 glycine, benzoic acid, and defibrinated blood is injected through the 

 kidney (or mixed with a minced kidney just removed from the body of 

 an animal), their place is found to have been taken by hippuric acid. 



It may be crystallised from horse's urine by evaporating to a syrup and 

 saturating with HC1. The crystals are dissolved in boiling water, filtered, 

 and on cooling the acid again crystallises out. It melts at 186 C., and on 

 further heating gives rise to the odour of bitter almond oil. 



URINARY DEPOSITS 



The different substances that may occur in urinary deposits are 

 formed elements and chemical substances. 



The formed or histological elements may consist of blood 

 corpuscles, pus, mucus, epithelium cells, spermatozoa, casts of the 

 urinary tubules, fungi, and entozoa. All of these, with the exception 

 of a small quantity of mucus, which forms a flocculent cloud in the 

 urine, are pathological, and the microscope is chiefly employed in 

 their detection. 



The chemical substances are uric acid, urates, calcium oxalate, 

 calcium carbonate, and phosphates. Barer forms are leucine, tyro- 

 sine, xanthine, and cystin. We shall, however, here only consider 

 the commoner deposits, and for their identification the microscope 

 and chemical tests must both be employed. 



Deposit of Uric Acid. This is a sandy reddish deposit resembling 

 cayenne pepper. It may be recognised by its crystalline form (fig. 

 46, p. 157) and by the murexide reaction. The presence of these 

 crystals generally indicates an increased formation of uric acid, and, 



