174 INTERMEDIATE METABOLISM 



variations also occur according to age and species. It is 

 worthy of notice here that gastric and pancreatic juice 

 have no action upon nucleic acid, and that intestinal juice 

 only converts it into the mononucleotide form. Nucleic 

 acid is therefore absorbed practically unchanged. The 

 conversion of nucleic acid into uric acid occurs almost 

 entirely in the Uver and spleen. It does not occur in the 

 kidney. 



The Formation of Uric Acid from Muscle Hypoxanthine 



Hypoxanthine exists in muscle combined with hexose 

 and phosphoric acid, forming inosinic acid. It is not 

 derived from adenine, for muscle contains no adenase. 

 The oxidation of muscle hypoxanthine to uric acid, sup- 

 posing this to occur, must have its seat in the liver, for 

 this is the only organ which contains xanthoxidase. 



Factors Influencing the Formation of Endogenous Uric Acid 



1. Muscular Activity: — The relation between the degree 

 of muscular activity and the amount of uric acid excreted 

 is not yet understood. An increase in purine excretion 

 does not always follow muscular exercise. Some have 

 found it to occur only when the exercise has been severe, 

 or when the form of the exercise is unusual. It is said 

 to follow involuntary muscular activity such as shivering 

 rather than voluntary exercise, and tonic rather than 

 repeated contraction. It has also been observed that the 

 increase of uric acid excretion occurs not immediately 

 but two or three days after exercise. The hypoxanthine 

 content of muscle is said to be increased after activity. 

 All we can say definitely is that muscular activity is not 

 necessarily associated with a contemporaneous liberation 

 of muscle purine. 



2. Fevers. — The increased uric acid excretion which 

 invariably accompanies fevers is to be ascribed to the 

 abnormal breakdown of tissue, particularly of muscle. 



