AN-UREIDE ACIDS. 131 



the demonstration, we may provisionally, as I have said, regard 

 the dialuric and uric acids as tartron-ureide and tartron-diureide 

 respectively. 



(138.) The several bodies I have just mentioned are typical of 

 three well-defined classes of compounds, to one or other of which 

 the immense number of uric acid products are, with but very few 

 exceptions, assignable. We have first the class of simple non- 

 nitrogenous acids, or an-ureides, like the tartronic and mes- 

 oxalic acids. Then we have the class of bodies containing a 

 residue of the acid plus one residue of urea, or the mon-ureides, 

 such as dialuric acid and alloxan ; and lastly, we have the class 

 of bodies containing a residue of the acid plus two residues of 

 urea, orthedi-ureides, such as uric acid itself. Confining our 

 present attention to the an-ureides, let us consider briefly their 

 derivation and mutual relationship. Mesoxalic acid, then, the 

 most complex non-nitrogenous product obtainable directly from 

 uric acid, constitutes the third term in the following series : 



An-ureides 



C H a 3 Carbonic. 

 C 3 H Z 4 Oxalic. 

 C 3 H 3 S Mesoxalic. 



Oxalic acid, you observe, differs in composition from carbonic 

 acid by one atom of carbonic oxide CO, in excess ; while mes- 

 oxalic acid differs in composition from oxalic acid by a further 

 atom of carbonic oxide CO, in excess. Now, when mesoxalic 

 acid is acted upon by nascent oxygen O, its excess of carbonic 

 oxide CO, is removed in the form of carb-anhydride C0 2 , so as 

 to leave oxalic acid, thus; 



Mesoxalio Oxygen Carb-anhyd. Oxalic 



C 3 H,0 5 + = CO, + C a H 2 4 . 



Hence when uric acid is subjected to a more active oxidation 

 than suffices to produce mesoxalic acid we obtain oxalic acid, 

 which may occur in its simple an-ureide state, or conjugated with 

 one atom of urea to form a mon-ureide such as parabanic acid, 



K 2 



