THE NUCLEOPROTEIDS. 291 



nate the amount of uric acid eliminated with a diet free from purine bases 

 as endogenous uric acid, and contrast this part of the total uric acid elimina- 

 tion during an ordinary diet with that obtained from the purines in the 

 food. The amount of the latter, which they designate as exogenous uric 

 acid, naturally varies, and is dependent upon the quantity of purine 

 bases ingested and absorbed. The amount of endogenous uric acid 

 remains constant, even from a diet rich in purine bases. The uric acid 

 arising from the purine bases is added to that of endogenous origin. 

 Burian states that the amount of endogenous uric acid excreted daily by 

 a normal adult ranges between 0.3-0.6 gram. The endogenous uric 

 acid value is a direct expression of the extent of cell activity, which, as we 

 know from various observations, is very carefully regulated and adjusted 

 for each individual. 



Although we may look upon this conception of endogenous and exoge- 

 nous uric acid, in the sense suggested by Burian and Schur, as a distinct 

 advance in our knowledge of the course of cell-metabolism, we must, 

 nevertheless, emphasize the fact that this separation between the two 

 sources is merely a superficial one. In no case are we justified in con- 

 cluding that the total purine metabolism is sharply divided into two 

 phases; i.e., that the purines in the food are immediately converted into 

 uric acid, nor that cell-metabolism, in the narrowest sense of the word, 

 takes place independently. We have no doubt that the purine bases, 

 and the other components of nucleic acid, replace continually material 

 used in the building up of cells, and particularly their nuclei, and thus 

 take part in the formation of endogenous uric acid, of a later period. 

 Although we know that the total nitrogen of the food, as a rule, soon re- 

 appears in the urine, we nevertheless assume that the albumins, at least 

 to some extent, participate in cell-metabolism, and in the construction of 

 cells partly supplying material, and partly acting as a source of energy. 

 Similarly, the purine bases in the food undoubtedly participate in cell- 

 metabolism. The endogenous purine value may perhaps be compared, 

 within certain limits, with that amount of albumin which the cells require 

 even during starvation. We do not mean to represent that this compari- 

 son is an absolute one. It merely suggests the similarity between the 

 metabolism of albumin and purine both are very closely related to 

 cellular metabolism. We must be especially cautious not to differentiate 

 sharply the endogenous and exogenous uric acid with regard to the total 

 purine metabolism of the cells. 



The question arises, What sources have we to assume in particular for 

 the endogenous uric acid? In general it may be said that the endogenous 

 uric acid may be traced primarily to the decomposed nuclear material, 

 and also to the cells which have been completely destroyed. R. Burian l 



1 Z. physiol. Chem. 43, 494 (1905). 



