( 374 ) 



stress almost only on the total quantity of nitrogen excreted, in 

 relation to the (luantily lakeii up in tiie food, and not enough 

 attention has been paid to the (piantifies of each of the different 

 nitrogenous products of metabolism which are excreted with the urine. 

 Wiien tiie quantity of proteid in the food is enlarged or diminished 

 then the secretion of nitrogen increases or decreases till after a short 

 time a condition of equilibrium has been again obtained when intake 

 and output of nitrogen are alike. The variability of the metabolism of 

 proteids does not manifest itself in connection with all nitrogenous 

 substances but for the greater part with connection to the urea. 

 The secretion of creatinin on the contrary and also in a less degree 

 that of uric acid is apparently independent of the richness of the 

 food in proteid. We must distinguish a desintegration of proteid 

 variable under the intluence of tlie food, on whicli depends in the 

 first place the forming of urea and which according to Folin's 

 conception takes place for the greater part if not wholly in the 

 digestive organs — in the cavity and in the mucosa of the intestine 

 and in the liver — and beside a much less xariable desintegration 

 of proteid in the different organs which does not immediately depend 

 on the food but on the function of the tissues. In the tissues there 

 arise undoubtedly nitrogenous products of desintegrating of different 

 composition. To them belongs as has been stated by Nencki, Salaskin 

 and their collaborators ammonia, which is changed into the harmless 

 urea by the liver. Moreover urea is formed in the organism in 

 other places than the liver. This product of metabolism proceeds thus 

 for a part, as Folin expresses it "endogenously" in consequence of 

 the rather regular metabolism of proteid in the tissues and for another 

 part "exogenously" in larger or smaller quantities, as more or less 

 proteid is taken up in the digestive canal. It is however not possible 

 to distinguish these two parts from each other in the urine. 



But on the contrary the secretion of creatinin, on which the digestion 

 of the food when it contains no creatin has no direct influence, 

 gives an indication about the intensity of the desintegration of 

 proteid in the tissues. In this respect the muscular tissue, must be 

 thought of in the first place, but not exclusively, as creatin is formed 

 undoubtedly in other tissues too. 



It does not seem necessary to accept that all the creatin which 

 is formed in the tissues is excreted as creatinin. The observations 

 of Meissner give already rise to the supposition that creatin must 

 be considered as an "intermediate" product of metabolism, as has been 

 stated by Bum an and Schur for the uric acid. Meissner at least 

 could not quite retrace in the urine the creatinin brought into the 



