COMPOSITION OF THE URINE. 437 



for example, showing distinct differences in the extent to which 

 they are individually converted into uric acid in the body. 



" Finally, we see that there is no causal relationship whatever 

 between the daily urea and uric acid output. They come from 

 totally different lines of metabolism ; they stand for totally dis- 

 tinct chemico-physiologic processes ; and hence any attempt to 

 emphasize the so-called ratio of urea to uric acid in the urine is 

 misleading, and shows, furthermore, a lack of understanding of 

 the true genesis of these two excretory products. Between uric 

 acid and ordinary proteid metabolism there is no connection what- 

 ever. With a purely non-nitrogenous diet, on the one hand, and 

 a diet rich in eggs, milk, and cheese, on the other, with perhaps a 

 maximum amount of contained proteid, the output of uric acid 

 remains practically unchanged. The genesis of uric acid is to be 

 found solely in metabolism of the tissue nucleins (endogenous) and 

 in the transformation of the nucleins and free purin bases of the 

 ingested foods (exogenous)." 



In discussing this subject, J. Walker Hall, in his book, " The 

 Purin Bodies of Food stuffs," etc., says : " As ' endogenous ' purins 

 are practically waste-products on their way to excretion, so when 

 they become ' exogenous ' to another organism, they have little nu- 

 tritive value and demand early and rapid elimination. This is 

 generally effected by the oxidation of the oxy-purins, hypoxanthin 

 and xanthin, to uric acid, and then the purin ring or chain in 

 the uric acid is in the liver partially split off and a portion of 

 the uric acid excreted as urea." It would appear from this 

 statement that there is a certain relationship between uric acid 

 and urea, but this is quite different from the old idea that a cer- 

 tain definite ratio exists between the output of urea and uric 

 acid on the assumption that both come from the ordinary proteid 

 katabolism. 



There is evidence looking toward the synthetic production of 

 uric acid in the liver, but this is not yet proven. The influence 

 of alcohol and alcoholic fluids in the excretion of uric acid is dis- 

 cussed elsewhere (p. 161). 



Xanthin Bases. The urine contains besides xanthin, the follow- 

 ing members of this group : Heteroxanthin, paraxanthin, hypo- 

 xanthin, guanin, adenin, and carnin* They are related to uric 

 acid, as is shown by the formulae given on page 435, and these bases 

 and uric acid are called by Kriiger and Wulff alloxuric substances, 

 because of their relation to alloxan and urea. The amount of the 

 xanthin bases daily excreted in the urine is about 0.1 gram. They 

 are increased after taking green vegetables and on a diet contain- 

 ing much nucleins, and also in some form of leukemia, 



Hippuric Acid (C 9 H 9 NO 3 ). Although present in herbivora in 

 considerable amount 2 per cent, in cattle hippuric acid occurs 

 in human urine on an ordinary diet to the amount of but about 



