84 THE PHYSIOLOGY OF URIC ACID 



other products, certain purin bodies, called guanin 

 and adenin. 



The uric acid and other purin bodies in the urine 

 (xanthin, etc.) are derived from two sources, referred 

 to as exogenous and endogenous. By exogenous 

 origin we mean that substances capable of yielding 

 purin bodies taken as food are broken down by the 

 digestive juices, the purin bodies are then liberated 

 and absorbed by the blood, carried, with or without 

 alteration, to the kidneys, and by them excreted in 

 the urine. These have never been built up into the 

 protoplasm of the living cells of the body. By 

 endogenous origin we mean that purin bodies are 

 end products of the breaking down of certain of the 

 constituents of the living protoplasm of the indi- 

 vidual. In other words, the purin bodies of the urine 

 may be derived from the food, or from the living 

 tissues of the body. The normal man on an ordinary 

 diet excretes exogenous and endogenous purin in 

 about equal quantities. 



Variations in the amount of uric acid excreted 

 may be affected, then, by variations in the food, or 

 by variations in the breaking down of the tissues. 



Considering first the effect of diet, it is found that 

 on a purin-free diet the uric acid and the purin bodies 

 in the urine drop to about half the ordinary amount. 

 Feeding on meat, broths, coffee, etc., increases the 

 excretion of the uric acid and other purin bodies, and 

 the same effect may be obtained by feeding with 

 hypoxanthin itself. Again, any tissue rich in nucleo- 

 protein, that is to say rich in cell-nuclei, will, if given 

 by the mouth, increase the output of uric acid and 



