388 THE METABOLISM OF THE PURltf BODIES 



In studying the metabolism of the purin bodies, as in other 

 studies" in metabolism, it is necessary that we possess a clear 

 understanding of their chemistry : i.e. of their relationship to one 

 another, of their methods of synthesis, and of their decomposi- 

 tion products in the laboratory. On this account, it may not 

 be out of place to describe briefly some of these points at this 

 stage. 



Let us first of all consider the decomposition products of uric 

 acid, for it is only after learning what these are that we can 

 hope to understand the synthesis of this complex organic sub- 

 stance. The empirical formula for uric acid is C 5 H 4 N 4 3 . 

 By treating uric acid with nitric acid a double process of de- 

 composition and oxidation ensues : with cold nitric acid alloxan and 

 urea are produced, and by further oxidising alloxan (as by 

 treating it with warm nitric acid), parabanic acid and carbon 

 dioxide gas are formed. By causing parabanic acid to take 

 up a molecule of water (by heating it with alkalies), oxaluric 

 acid is produced, and this can be still further hydrolysed (by 

 prolonged boiling with water) when it yields urea and oxalic 

 acid. From this we see that uric acid must contain two 

 urea molecules (one easily liberated, the other liberated only 

 by vigorous treatment), linked together by a chain of carbon 

 atoms which is represented in the decomposition products by 

 oxalic acid. 



To explain, by structural formulae, the chemical reactions 

 involved in this process, it will be necessary to consider the con- 

 stitutional formula of uric acid, although by so doing we are of 

 course anticipating the deductions from its other reactions, for the 

 structural formula of any substance is simply a diagrammatic ex- 

 pression of all its chemical reactions, and can be set forth only 

 after all these have been considered. Medicus and Emil Fischer 

 have shown this structural formula to be : 



NH-CO 



I I 

 CO C-NH 



I II \CO. 



NH- C-NH/ 



The reactions described above can then be easily demon- 

 strated : 



