126 CREATIN AND CREATININ 



It is apparent from this that (just as we are accustomed 

 to recognize an endogenous and an exogenous fraction of 

 the purin bodies in the urine) we are in position to make 

 an analogous differentiation in case of the creatin-creatinin 

 excretion. The possibility of increasing the proportion of 

 creatin and creatinin in the urine by free intake of creatin in 

 meat food or Liebig's meat extract has been repeatedly 

 observed. This exogenous part can readily be excluded by 

 starvation or by exhibition of food which does not contain 

 creatin. In this connection the interesting fact has been 

 developed that under such circumstances individual vari- 

 ations may be observed and these may remain constant for 

 a given normal individual for as long a time as a year, 13 

 reminding one of the observations of Burian and Schur, who 

 were able to establish a similar individual constancy in case 

 of the endogenous purins. 



Taking up next the question as to how far we are justified 

 in assuming a relation between the disintegration of tissue 

 protein and creatin formation in metabolism, it may be 

 assumed, as indicated in the above schema, that neither the 

 food protein nor the readily mobilizable " circulating " 

 protein forms a source of creatin and its anhydride, 

 creatinin. This is directly apparent from the fact that the 

 excretion of creatin-creatinin does not proceed in precisely 

 parallel lines with the total protein exchange, 14 and more- 

 over seems to be fairly independent of the intake of proteid 

 food. 



Relation of Creatin-Creatinm Excretion to Decomposi- 

 tion of Tissue Protein. However, an increase in the excre- 

 tion of creatin and creatinin is to be observed in those condi- 

 tions where (and here probably is the kernel of the whole 

 problem) there is extensive decomposition of the tissue 



33 O. Folin (Waverley), Amer. Jour, of Physiol., 13, 84, 1905; C. J. C. Van 

 Hoogenhuyze and H. Verploegh (Physiol. Lab., Utrecht), Zeitschr. f. physiol. 

 Chem., 57, 161, 1908; 59, 101, 1909. 



14 J. Forschbach and S. Weber (Minkowski's Clinic, Greifswald), Centralbl. 

 f. Physiol. u. Pathol. d. Stoffw., 1906, 569. 



