206 



PEACTICAL PHYSIOLOGY 



would at once suggest that urea is derived from creatine, but all experi- 

 ments to prove that such a relationship actually exists have proved 

 entirely futile. 



A. 



FIG. 147. Crystals obtained from meat extract, mostly creatine, a few sodium chloride. 



The other nitrogenous extractives, alloxuric bodies, are scarcely less 

 interesting. 1 They are members of a large group of bodies containing 

 as their basis of construction the so-called purin ring, which consists of 

 two urea radicles linked together by a central chain of carbon atoms. 



The most familiar member of this group is uric acid 2 which has 

 the formula 



/NH- C -N 

 fl -NH' 



\ 



NH-CO 



urea radicle, urea radicle. 



J They are precipitated from the creatin-free extract by ammoniacal silver 

 nitrate (see p. 441). 



8 Uric acid does not, however, occur in a muscle extract 



