OUTPUT OF WASTE MATTER 135 



may appear in various crystalline forms in 

 the urine, and when this habitually occurs, 

 various symptoms of illness may appear 

 which are spoken of as gouty or rheumatic. 

 There can be no doubt that uric acid is derived 

 from the breaking down, not of cell-substance, 

 but from the oxidation of nuclein, one of the 

 chief chemical substances in the nuclei of 

 cells. This shows that even nuclei, on which 

 the activity of cell-life so much depends, are 

 the seat of metabolic changes, and that 

 there are processes of breaking down. It is 

 known that nuclein yields, during certain 

 chemical reactions, a chain of nitrogenous 

 bodies, all more or less closely related, known 

 as the purine bases. These are purine, 

 hypoxanthin, xanthin, adenin, guanin, and 

 uric acid. They sometimes appear in the 

 urine and they abound in such tissues as 

 are the seat of active metabolism. Certain 

 foods, such as liver and sweetbread, contain 

 these substances. These bases may thus be 

 formed exogenously from food stuffs or endo- 

 genously by the metabolism of tissue. Any 

 increased activity in nuclei, implying tear 



