596 METABOLISM, NUTRITION AND DIETETICS 



excreted and about a half destroyed, being mainly changed into ure&. 

 Some of the exogenous moiety is also broken down. When uric acid 

 is heated in a sealed tube with strong hydrochloric acid, it is broken 

 up into glycin, carbon dioxide, and ammonia. There are grounds 

 for believing that a similar decomposition takes place in the body, 

 and that the products are then transformed to urea in the liver. 



The process of uricolysis, or destruction of uric acid, is usually 

 attributed to a ferment called the uricolytic ferment, and it has been 

 supposed that one of the factors in the production of gout may be 

 a diminution in the amount or activity of this ferment. In some 

 cases it is said to be entirely absent. It is doubtful, however, 

 whether in man and the anthropoid apes the oxidizing enzyme, 

 uricase or uricoxydase, which oxidizes uric acid to allantoin 

 (C,.H 6 N4C) 3 ), exists. In all other mammals hitherto investigated it 

 has been found in some of the tissues. In accordance with this, 

 only a trace of allantoin is present in human urine and in the urine 

 of the higher apes, while in the other mammals for example, in 

 the dog a large proportion of the purin excretion assumes this 

 form. It is probable that there is more than one way in which 

 uric acid may be decomposed in the body, and, if so, that there is 

 more than one ferment concerned in its transformation. It would 

 be well, therefore, not to speak of uricolysis as if it were synonymous 

 with the well-ascertained process by which allantoin is formed 

 from uric acid, and not to identify all enzymes which may take 

 part in uricolysis with uricoxydase. 



It is worthy of remark in this connection, as a further illustration 

 of the differences which may exist in the purin metabolism in 

 different kinds of animals, that in man and the anthropoid apes the 

 quantity of purin bases in the urine is small in proportion to the 

 quantity of uric acid. In the pig, which is included among the 

 animals that form allantoin from uric acid, the purin bases exceed 

 the uric acid in amount, whereas in the dog, which likewise excretes 

 allantoin, the purin bases exist in very small amount compared 

 with the uric acid. 



In concluding our consideration of the metabolism of the nucleic 

 acids, the question may be raised whether it is related to the metabo- 

 lism of the other substances carbo-hydrates, fats, and proteins 

 in such a way that derivatives of nucleic acid can contribute to the 

 formation of any of these, or derivatives of carbo-hydrates, fats, or 

 proteins contribute to the formation of any of the components of 

 nucleic acid. It has been already mentioned that the phosphoric 

 acid can aid in the synthesis of phosphatides, and that the carbo- 

 hydrate groups probably take their place in the ordinary carbo- 

 hydrate metabolism. There is no evidence that the purin bases can 

 take part or can yield products capable of taking part in the forma- 

 tion of any of the other substances. The purin metabolism, so far 



