254 Biological Chemistry. 



ference must be made to more advanced works and to 

 original memoirs.* The methods are to a large extent 

 due to the labours of Kossel and his pupils. 



The nucleic acids are substances of considerable biolo- 

 gical importance, as might be expected from their relation- 

 ship to the nuclei of cells. They possess also another 

 point of interest by virtue of the chemical relationship of 

 their nitrogenous hydrolysis products to uric acid, which 

 is the chief nitrogenous constituent of birds' urine, and a 

 constant, though quantitatively a subordinate constituent 

 of mammalian urine. Furthermore, under various patho- 

 logical conditions, such as those in certain cases of gout, 

 uric acid is excreted in abnormally large quantities. 



Uric acid has been obtained by several synthetical 

 methods. To it the following formula has been assigned : 



HN -- CO 

 00 C-NH 



HN 



J 



C NH 



This is derived from a parent substance, designated by 

 Emil Fischer, to whom the chief knowledge of the consti- 

 tution of the alloxuric bases is due, purine, which also; 

 contains two rings. This has the formula 

 N = CH 



HC NH 



I! II > 



N C N 



All the alloxuric bases have this ground structure, and are 

 consequently known also as the purine bases. 



* For complete literature, see Jones: "Nucleic Acids." (Longmans, 

 Green, & Co. 1914.) 



