780 PHYSIOLOGY OF DIGESTION AND SECRETION. 



derived mainly from a metabolism of the muscular substance 

 whereby hypoxanthin is produced. This substance is then oxidized 

 to uric acid and a part of the uric acid is further changed to urea.* 



Origin and Significance of the Creatinin. Creatinin 

 (C 4 H 7 N 3 O) occurs in the urine and it has been assumed that 

 it is derived from the creatin (C 4 H 9 N 3 O 2 ) found in muscle. Its 



/NH CO 

 structural formula is given as NHC/ I and its chemical re- 



X N(CH 3 )CH 2 



lations are indicated by the fact that it may be prepared synthetically 

 from methyl-glycocoll and cyanamid, that is, the union of these 

 two substances gives creatin, from which in turn creatinin may be 

 obtained. 



N=C-NH, + NH(CH,)CH,COOH == 



Cyanamid. Methyl-glycocoll. Creatin. 



Creatinin occurs in the urine constantly and in amounts equal to 

 1 to 2 gms. per day. Next to the urea and the ammonia com- 

 pounds it forms the most important nitrogenous constituent of the 

 urine. Its physiological history, is imperfectly known. Under 

 constant conditions of life the amount of creatinin is independent 

 of the quantity of protein eaten, and this fact indicates (Folin) that 

 it represents an end-product of the metabolism of living or organized 

 protein tissue rather than one of the results of the metabolism of the 

 food protein. Everything would indicate also that this substance 

 originates in the muscular tissue. Creatin is a constant and consid- 

 erable constituent of muscle, and a fair inference, therefore, is that 

 it originates in this tissue from the catabolism of the muscle sub- 

 stance, and is subsequently given to the blood and excreted as crea- 

 tinin. A difficulty in regard to this last hypothesis is found in the 

 fact that the mass of muscular tissue in the body contains a relatively 

 large amount of creatin (90 gms.) and yet only 1 to 2 gms. are 

 excreted in the urine during the day. On account of this dis- 

 proportion it has been suggested that some of the creatin may 

 be converted to urea, but no proof has been furnished as yet that 

 the body can accomplish this transformation. Creatin given in 

 the food is, according to some observers, eliminated as creatinin. 

 Folin, however, finds that when creatin in not too large amounts is 

 given to an individual living on a low protein diet none of it appears 

 in the urine as creatinin. On the contrary, when creatinin is fed 

 most of it may be recovered as creatinin in the urine. This observer 

 finds that the conversion of creatin to creatinin is a matter of 

 some difficulty. According to his experiments this conversion is 



* For a review of the extensive literature see Block, "Biochemisches 

 Centralblatt, " 1906, v., Nos. 12-14. 



