460 



THE URINE. 



Fig. 121* 



the portion of urine containing the sediment ; this dissolves 

 urate of. ammonia and soda, while the comparatively in- 

 soluble crystals of uric acid subside to the bottom. 



The most common form in which uric acid is deposited 

 in urine, is that of a brownish or yellowish powdery sub- 

 stance, consisting of granules of urate of ammonia or soda. 

 When deposited in crystals, it is most frequently in 

 rhombic or diamond- shaped laminae, but other forms are 

 not uncommon (fig. 120). When deposited from urine, 

 the crystals are generally more or less deeply coloured, 

 by being combined with the colouring principles of the 

 urine. 



Hippuric Acid has long 

 been known to exist in the 

 urine of herbivorous animals 

 in combination with soda. 

 Liebig has shown that it also 

 exists naturally in the urine 

 of man, in quantity equal to 

 the uric acid, and Weismann's 

 observations agree with this. 

 It is a nitrogenous compound 

 with the formula CgHgNOg. 

 It is closely allied to benzoic 

 acid; and this substance when introduced into the system, 

 is excreted by the kidneys as hippuric acid (Ure). Its 

 source is not satisfactorily determined : in part it is pro- 

 bably derived from some constituents of vegetable diet, 

 though man has no hippuric acid in his food, nor, com- 

 monly, any benzoic acid that might be converted into it ; 

 in part from the natural disintegration of tissues, inde- 

 pendent of vegetable food, for Weismann constantly found 

 an appreciable quantity, even when living on an exclu- 

 sively animal ,diet. 



Fig. 121. Crystals of hippuric acid. 



