THE NITROGENOUS EXCRETION. URINE. 365 



to illustrate their relations by the structural formulas worked 

 out or confirmed by Fischer. Starting with the assumed 

 purine nucleus we have these formulas, with the nucleus atoms 

 numbered, as suggested by Fischer : 



HX CO N=C NH. HN CO 



II II II 



OC C NH HC C N HC C NH 



CO 



ii i 



/CH 



>H 



HN C NH N C N H N C N 



Uric acid, C 6 H 4 N 4 O 3 Adenine, C 6 H 6 N 5 Hypoxanthine, C S H 4 N 4 O 



Employing the Fischer nomenclature these bodies have the 

 following names : 



Adenine 6-aminopurine 



Hypoxanthine 6-oxypurine 



Xanthine 2, 6-dioxypurine 



Uric acid 2, 6, 8-trioxypurine 



Guanine 2-amino-6-oxypurine 



As their relations have been shown by various syntheses and 

 other transformations, and as further, the xanthihe and hypo- 

 xanthine, adenine and guanine have been directly derived from 

 the nucleinic acids, the relation of uric acid to the latter bodies 

 is not far to seek. 



Xot all of the nucleinic acid destroyed can be assumed to 

 come from body cell structures ; many of our foods contain nu- 

 cleins and these must give rise to the same derivatives on oxi- 

 dation without passing through, becoming part of, the cells of 

 the glandular organs of the body. Accordingly we distinguish 

 between endogenous and exogenous purines and uric acid. 

 With the food nucleins eliminated as far as possible it has been 

 found that the uric acid excreted becomes nearly constant and 

 bears a more uniform relation to the urea. This indicates that 



