238 PHYSIOLOGICAL CHEMISTRY. 



may be crystallized and forms colorless rhombic prisms (Fig. 77, 

 below) which are soluble in warm water and practically insoluble 



FIG. 77. 



in alcohol and ether. Upon boiling a solution of creatine with 

 dilute hydrochloric acid it is dehydrolyzed and its anhydride crea- 

 tinine is formed. The theory that the creatine of ingested meat is 

 transformed into creatinine and excreted in the urine has been 

 proven untenable through the recent researches of Folin, Klercker, 

 and Wolf and Shaffer. It is now known that the ingestion of 

 creatine in no way influences the excretion of creatinine. In this 

 connection it is important to note that there is no normal excretion 

 of endogenous (see p. 272) creatine, a statement proven by the 

 fact that if no creatine be ingested none will be excreted. Folin 

 has shown that the main bulk of ingested creatine is retained in the 

 body, unless the diet contains a large amount of protein material. 

 Under pathological conditions the urine contains endogenous crea- 

 tine which is probably derived from the catabolism of muscular 

 tissue, as Benedict, Mellanby, and Shaffer have suggested. 



Besides being a normal constituent of muscle, xanthine has been 

 found in the brain, spleen, pancreas, thymus, kidneys, testicles, 

 liver, and in the urine. It may be obtained in crystalline form 

 (Fig. 78, p. 239) but ordinarily it is amorphous. Xanthine is easily 

 soluble in alkalis, less easily soluble in water and dilute acids, and 

 entirely insoluble in alcohol and ether. 



Hypoxanthine occurs ordinarily in those tissues and fluids which 



