402 



HIPPURIC ACID. 



a, 



b, octa- 



Fig. 258. 

 Oxalate of lime. 

 hedra; c, compound forms; 

 d, dumb-bells. 



creased iu amount. Perhaps, in the first instance, there is an increased formation of uric acid, 



from which oxalic acid, urea, and C0 2 may be formed. The amount of oxalic acid is increased 



after the use of wine and sodic bicarbonate. 



Hippuric Acid = C () H 9 N0 3 (Benzoylamidoacetic acid) occurs in large amount in 



the urine of herbivora, and in them is the chief end-product of the metabolism of 



nitrogenous substances ; in human urine the daily quantity is small, 0*3 to 3*8 

 grms. (5 to 50 grains). It is an odourless monobasic 

 acid with a bitter taste, crystallising in colourless four- 

 sided prisms (fig. 259). Readily soluble in alcohol, and 

 soluble in 600 parts of water. 



[Crystals of hippuric acid when heated in a test-tube are decom- 

 posed, and a sublimate of benzoic acid and amnionic benzoate 

 condenses on the upper cool part of the tube, while there is an 

 odour of new hay, and oily drops remain in the tube.] 



It is a conjugated acid, and is formed in the body from 

 benzoic acid, or some nearly related chemical body, such 

 as the cuticular substance of plants, or from oil of bitter 

 almonds, cinnamic or chinic acid, which easily pass by 



reduction (chinic acid) or by oxidation (cinnamic acid) into benzoic acid ; glycin 



uniting with it, with the formation of water 



C 7 H 6 2 +C 2 H 5 N0 2 = C 9 H 9 N0 3 +H 2 



Benzoic acid + Glycin = Hippuric acid + Water. 



[Formation. When benzoic acid is introduced into the alimentary canal of an 

 animal (rabbit or dog), it appears in the urine as hippuric acid j while nitro-benzoic 



acid appears as nitro-hippuric acid. 

 As the benzoic acid passes through 

 the body, it becomes conjugated with 

 glycin or glycocin, chiefly in the kid- 

 neys. The hippuric acid in the urine 

 of herbivora is chiefly derived from 

 some substance with a benzoic acid 

 residue present in the cuticular cover- 

 ings of the food. That hippuric acid, 

 in part at least, is formed in the 

 kidneys is shown by the following 

 considerations : If arterialised blood, 

 containing benzoic acid and glycin, or 

 even benzoic acid alone, be passed 

 through the blood-vessels of a fresh, 

 living, excised kidney, hippuric acid 

 is found in the blood after it is per- 

 fused. Even after forty-eight hours, 

 if the kidney be kept cool, the syn- 

 thesis takes place. If the kidney be 

 kept too long, the conjugation does 

 not take place. If the fresh kidney be chopped up, and kept at the temperature of 

 the body with benzoic acid and glycin, hippuric acid is formed. Oxygen seems to 

 be necessary for the process, for, if blood or serum containing carbonic oxide be used, 

 there is no formation of hippuric acid.] 



According to this view, it is derived chiefly from the food of herbivorous animals, and hence 

 it is absent from the urine of sucking calves, as well as after feeding with grain devoid of husk. 

 But it is also formed in the body from the proteids. In the dog, the formation of hippuric acid 

 occurs in the kidney {Schmiedcbcrg a?ul Bungc), and in the frog also outside the kidney. Kuhne 

 and Hallwachs thought it was formed in the liver, and Jaarsveld and Stockvis in the kidney, 

 liver, and intestine. The observation of Salomon that, after excision of the kidneys in rabbits, 



Fig. 259. 

 Hippuric Acid. 



