KIDNEY AND SKIN AS EXCRETORY ORGANS. 853 



sumed that it is derived from the creatin (C^gNsC^) found in 



/NH - CO 

 muscle. Its structural formula is given as NHC< I and its 



X N(CH 3 )CH 2 



chemical relations 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 by loss of a molecule of water. 



N =C_NH 2 + NH(CH3)C Hj COOH = 



Cyanamid. Methyl-glycocoll. Creatin. 



Creatinin occurs in the urine constantly and in amounts equal to 

 1 to 2 gins, per day, or, according to Shaffer,* there is an excretion 

 of from 7 to 11 mg. of creatinin nitrogen per kilogram of body- 

 weight. Next to the urea and the ammonia compounds it forms 

 the most important of the known nitrogenous constituent of the 

 urine. Its physiological history is imperfectly known. Under 

 constant conditions of life the amount of creatinin formed in the 

 body 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. This con- 

 clusion is strengthened by the fact that in fevers and other patho- 

 logical conditions in which there is an increased breaking down of 

 tissues the creatinin excretion is increased, f Creatinin is present 

 in small amounts in the blood, 1 to 2 mgms per 100 gms. of blood, 

 and in somewhat larger amount in the muscular tissue. Creatin, 

 on the other hand, is present in muscular tissue to a relatively large 

 per cent., 0.5 to 0.6 gm. per 100 gms. of muscle, although Folin 

 contends J that this large yield is due to postmortem changes and 

 that in the living muscle little or none is present in free condition. 

 Creatin occurs in the blood in small amounts, but in the urine it is 

 not normally present so far as the normal adult man is concerned. 

 In children, however, it is constantly present in the urine, and in 

 women it is said to occur after menstruation, during pregnancy, 

 and in the puerperium. So also in mankind the urine shows the 

 presence of creatin during starvation or in fevers. It has not been 

 found possible to interpret satisfactorily these various facts. 

 According to one view,|| the creatin and creatinin are related and 



* Consult Shaffer, "American Journal of Physiology," 33, 1, 1908. 



f Hoogenhuyze and Verploegh, "Zeitschrift f. physiol. Chemie," 57, 161, 

 1908. 



J Folin and Denis, "Journal of Biological Chemistry," 17, 493, 1914. 



Krause, "Quarterly Journal of Exp. Physiology," 7, 87, 1913. 



|| Mendel and Rose, "Journal of Biological Chemistry," 10, 213, 1911; also 

 Meyers and Fine, ibid., 15, 283, 1913. 



