594 THE URINE [CH. XXXIX. 



nuclease is given to the whole group, and a dozen or more have 

 been isolated which deal with different steps in the cleavage of the 

 nucleic acid complex. They are classified into nucleinases which 

 resolve the molecule into mononucleotidases, i.e., compounds of carbo- 

 hydrate, phosphoric acid, and one base; nucleotidases which liberate 

 phosphoric acid, leaving the carbohydrate still united to the base ; 

 nucleosidases which hydrolytically cleave the base and carbohydrate 

 apart; deamidases which remove the amino-group from the purine 

 bases so set free ; one of these, called adenase, converts adenine into 

 hypoxanthine, and another, called guanase, converts guanine into 

 xanthine. Finally, oxidases step in, which convert hypoxanthine 

 into xanthine, and xanthine into uric acid. But even that does not 

 bring the list to a conclusion, for in some organs (especially the liver) 

 there is a capacity to destroy uric acid after it is formed, and so we 

 are protected from a too great accumulation of this substance. 

 What -exactly happens to the uric acid is not certain, although it is 

 clear that the products of its breakdown (probably allantoin and 

 urea) are not so harmful as uric acid itself. The enzyme responsible 

 for uric acid destruction is called the uricolytic enzyme. The uric 

 acid which ultimately escapes as urates (normally) in the urine is 

 the undestroyed residue. 



In gout and allied disorders there may be increased formation of 

 uric acid, or a smaller amount of that formed may be destroyed; 

 the excess may pass into the urine, partly as free uric acid or excess 

 of urates, and so there is a liability to concretions (calculi, gravel, 

 etc.), forming in the kidney or bladder. There is also a tendency 

 to the deposition of urates in certain parts, and the joint cartilages 

 in particular are liable to these concretions. The uric acid diathesis 

 is, however, much too large a subject to treat in a physiological text- 

 book, and medical students, when they come to the study of 

 pathology, will discover that many views are held in relation to it. 



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 the urine 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 fi H, 



C 6 H 6 .COOH +| . = | + H 2 Q 



COOH COOH 



[Benzoic acid.] [Glycine.] [Hippuric acid.] [Water.] 



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



