46 APPLIED PHYSIOLOGY 



of glycin and possibly of oxalic acid and allantoin, and 

 only a fraction appears in the urine. Of oxypurins 

 (hypoxanthin), about one-half ; of amino-purins (e.g., 

 those derived from nuclein), three-fourths ; and of 

 methyl purins (caffeine), two-thirds, are destroyed in 

 this way. Whether gouty individuals have less capacity 

 for destroying purin than others has not been definitely 

 determined, but in any case the attempt to lessen the 

 amount of uric acid in the blood by feeding an individual 

 on a purin-free diet is undoubtedly rational therapeutics. 

 A diet of milk and vegetables was recommended to the 

 gouty so long ago as 1729 by Dr. George Cheyne, and 

 has since, under the title of a purin-free diet, been 

 widely advocated in this country by Dr. Haig. 



2. Uric acid is also produced by the breaking down of 

 body tissues ivliich contain amino-purins (e.g., adenin and 

 guanin) and oxypurins (e.g., xanthin and hypoxanthin). 

 The two former are most abundant in nuclein, the two 

 latter in muscle. The uric acid so derived is spoken of 

 as * endogenous ' uric acid. It was at first supposed that 

 the destruction of leucocytes supplied the nuclein from 

 which most of the endogenous uric acid arose, and this 

 opinion gained confirmation from the large excretion of 

 uric acid in cases of leukaemia. It is now known, how- 

 ever, that there is no constant relation between the 

 number of leucocytes and the excretion of uric acid, and 

 present physiological opinion is more in favour of re- 

 garding the muscles as the chief source of endogenous 

 uric acid. 



The amount of endogenous uric acid varies consider- 

 ably in different individuals, but is singularly constant 



