104 



CHEMICAL PHYSIOLOGY. 



6. Hippuric Acid, C 9 H 9 NO 3 . This substance is so called be- 

 cause it occurs in large quantity in the urine of the horse and 

 many herbivora, chiefly in the form of alkaline hippurates. 



Quantity in man -5 to 1 gramme daily. It is a conjugate 

 acid, which, when boiled with alkalies and acids, takes up water 

 and splits into benzoic acid and glycocin. It occurs in colourless 

 four-sided prisms, usually with two or four bevelled surfaces at 

 their ends. It has a bitter taste. Benzoic acid, oil of bitter 

 almonds, benzamid, cinnamic acid, and toluol reappear in the 

 urine as hippuric acid. The benzoic acid unites with the ele- 

 ments of glycocoll (glycin), and is excreted as hippuric acid in the 

 urine. 



Benzoic acid. 



C 7 H 6 2 



Glvcocoll. 



C 2 H 5 N0 2 = 



Hippuric acid. 



C 9 H 9 N0 3 



Water. 



H O. 



The amount is increased by eating pears, apples with their 

 skins, cranberries, and plums. Nothing is known of its clinical 

 significance. It seems to be formed chiefly from the husks or 

 cuticular structures. 



Tests and Reactions. 



(a.) Heat some crystals in a dry tube. Oily red drops are 

 deposited in the tube, while a sublimate of benzoic acid and 



Fig. 28. Hippuric Acid. 



