MUSCULAR TISSUE 361 



r61e of the liver in creatine and creatinine metabolism. In this con- 

 nection it is important to note that there is no normal excretion of 

 endogenous (see page 395) creatine, a statement proven by the fact that 

 if no creatine be ingested none will be excreted. Folin 1 has shown that 

 the main bulk of ingested creatine is retained in the body, unless the diet 

 contains a large amount of protein material. In fasting the urine 

 contains considerable creatine, i.e., 120 mg. or more per day. Under 

 certain pathological conditions, e.g., fevers, the urine may contain 

 endogenous creatine which is probably derived from the catabolism 

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

 Benedict and Osterberg 2 believe we may have a high creatine elimina- 

 tion which has no relation to the catabolism of muscle. 



McCrudden 3 reports creatine in the urine in cases of infantilism, 

 achondroplasia and cretinism the amount present being increased 

 when the carbohydrate ingestion was increased. 



It has been stated that creatine does not occur in non-striated 

 muscle. It has, however, been found in the ribn-striated muscles of 

 the lamprey the lowest form of vertebrates. 4 



Amberg and Morrill, 5 Sedgwick, 6 Rose 7 and Folin 8 have shown that 

 creatine is a normal constituent of the urine of infants and children 

 (10-15 m g- P er day). Folin explains this phenomenon on the basis of 

 the relatively high protein intake, whereas Rose believes it is due to a 

 peculiar carbohydrate metabolism. 



Besides being a normal constituent of muscle, xan thine has been 

 found in the brain, spleen, pancreas, thy'mus, kidneys, testicles, liver, 

 and in the urine. It may be obtained in crystalline form (Fig. 116, 

 p. 362), but ordinarily it is amorphous. Xanthine is easily soluble in 

 alkalis, less soluble in water and dilute acids, and entirely insoluble in 

 alcohol and ether. 



Hypoxanthine occurs ordinarily in those tissues and fluids which 

 contain xanthine. It has been found, unaccompanied by xanthine, in 

 bone marVow and in milk. Unlike xanthine it may be easily crystallized 

 in the form of small, colorless needles. It is readily soluble in alkalis, 

 acids, and boiling water, less soluble in cold water and practically in- 

 soluble in alcohol and ether. 

 ^ The predominating inorganic salt of muscle is potassium phosphate 



1 Folin: Hammarsten Festschrift, p. 15. 



2 Benedict and Osterberg: Jour. Biol. Chem., 18, 195, 1914. 



3 Me Crudden: Jour. Expt. Med., 15, 457, 1912. 



4 Mellanby: Jour, of PhysioL, 36, 472, 1908. Wilson: Jour. Biol. Chem., 18, 17, 1914. 

 6 Amberg and Morrill: Jour. Biol. Chem., 3, 311, 1907. 



6 Sedgwick: Jour. Am. Med. Ass'n, 55, 1178, 1910. 



7 Rose: Jour. Biol. Chem., 10, 265, 1911. 



8 Folin: Ibid., n, 253, 1912. 



