URINE 161 



directed to the nuclei of leucocytes because they can be readily 

 examined during life, it must be remembered that nuclein meta- 

 bolism of all cells may contribute to uric acid formation. 



A study of uric acid formation forms a useful occasion on which 

 to allude to ferment actions in metabolism generally. Ferments of 

 a digestive kind are not confined to the interior of the alimentary 

 canal ; but most of the body cells are provided with ferments to 

 assist them either in utilising the nutrient materials brought to them 

 by the blood-stream, or in breaking them down previously to expel- 

 ling them as waste substances. The ferment which enables the liver 

 cells to turn glycogen into sugar is the one which has been known 

 longest. The ferment called arginase (see p. 150), which leads to 

 the hydrolysis of arginine into urea and ornithine, is one of the most 

 recently discovered. Other examples which may be mentioned are 

 proteolytic enzym.es (tissue erepsin, &c.) found in many organs. 



The formation of uric acid from nuclein is perhaps the best 

 instance of all, for here we have to deal with numerous ferments 

 acting one after another. The first to come into play is called 

 nuclease ; this liberates purine bases such as adenine and gua- 

 nine from the nuclein ; the next ferments that act remove the 

 amino-group from the purine bases just mentioned ; in this way 

 adenine (0 A H 3 N 4 .NHo) is converted into hypoxanthine 5 H 4 N 4 O ; 

 and guanine (C 5 H 3 N 4 O.NH 2 ) into xanthine C 5 H 4 N 4 2 . These two 

 ferments are respectively called adenase and guanase. Finally, oxi- 

 dising ferments, or oxidases, step in and oxidise hypoxanthine into 

 xanthine, and xanthine into uric acid. By examining extracts of 

 various organs, the distribution of these numerous ferments has been 

 determined, and in general terms the spleen and liver are the organs 

 where they are most abundant. But the examination of such extracts 

 has shown in addition that the list of ferments is not yet complete ; 

 for some extracts in part break up the uric acid, which is formed into 

 simpler substances ; the uric acid destroying ferment is called the 

 uricolytic ferment. We therefore learn that the uric acid discharged 

 in the urine is only the balance left over when the amount destroyed 

 is deducted from the amount originally formed. In other words, the 

 body possesses to some extent the power of protecting itself from an 

 excessive formation of uric acid, and so from the evils which would 

 result from an accumulation of this substance. 



