THE PHYSIOLOGY OF URIC ACID 83 



of protein metabolism in birds and snakes is uric 

 acid ; in mammals it is urea. It by no means 

 follows, therefore, that uric acid is formed in the 

 mammalian liver. We may say at once that urea 

 is formed in the mammalian liver. 



We now believe that uric acid in mammals is 

 derived partly from certain substances in the food, and 

 partly from the breaking down of cell nuclei, which 

 takes place in most organs in the body, notably in the 

 spleen. From these organs it is carried to the kidney, 

 and excreted thereby. As we shall see, however, 

 there is a curious complicating factor, in that any 

 uric acid which chances to reach the liver instead of 

 the kidney is changed into urea. The liver, like all 

 other glands, furnishes a little uric acid to the blood, 

 but it probably destroys more than it supplies. 



The researches of Fischer and his pupils have 

 demonstrated that uric acid belongs to a group of 

 bodies containing a hypothetical nucleus, the purin 

 ring. Other members of the group are xanthin 

 and hypoxanthin, which occur in muscle and meat 

 extracts ; caffeine, which occurs in coffee ; and 

 theobromine, in cocoa. Many food-stuffs contain 

 small quantities of these bodies ; amongst vegetables, 

 peas, beans, lentils, and asparagus may be mentioned 

 as yielding them ; there is also a small quantity in 

 beer. Milk, eggs, and most vegetables contain 

 practically no purin bodies. 



The nuclei of all cells in the animal body contain 

 a special form of protein called nucleoprotein, in 

 which the protein is combined with nucleic acid. 

 On ultimate analysis this substance yields, amongst 



