CH. XII.] AMMONIA AND HIPPURIC ACID. 3OI 



363. Weyl's test for creatinine. To 5 cc. of urine add a few 

 drops of a freshly prepared 5 per cent, solution of sodium nitro- 

 prusside. Add a 5 per cent, solution of sodium hydroxide, drop by 

 drop. A ruby-red colour appears. Boil. The solution turns 

 yellow. Acidify with strong acetic acid and heat. A green tint 

 appears and a blue precipitate of Prussian blue may separate on 

 standing. 



I. Ammonia. 



Ammonia is a constituent of normal urine, being 

 present to the extent of about 0*7 grams, per diem. There 

 is an increased excretion following the administration of 

 ammonium salts of inorganic acids, in certain cases of 

 hepatic disease, and as a result of acid poisoning. This 

 last condition ("acidosis") can be produced by the adminis- 

 tration of inorganic acids or by the excessive formation of 

 acids in the body, especially if this is not accompanied by 

 an increased intake of alkalies. Thus it is seen in severe 

 diabetes, in starvation, and in delayed chloroform poison- 

 ing, the acids formed being aceto-acetic and /3-oxy-butyric 

 acids. In certain forms of renal disease there is a decreased 

 excretion (see p. 275). 



For methods of estimation see Exs. 398 to 400. 



J. Hippuric Acid. 



Hipp uric acid is formed in the kidney by the con- 

 densation of benzoic acid with glycine. 



C 6 H 5 .COOH + HaN.CHjj.COOH = C 6 H 6 .CO.NH.CH 2 COOH + H 2 O 



Benzoic acid. Glycine. Hippuric acid. 



The amount excreted by a normal individual on a 

 mixed diet is about 0-7 grams, per diem. It is increased by a 

 vegetable diet, owing to the presence in most plant foods of 

 an aromatic complex that is oxidised to benzoic acid in the 

 body. 



Hippuric acid crystallises in 4-sided prisms, somewhat 

 resembling triple phosphate. It melts at 187-5 C. : above 



