242 THE URINE. 



and its solubility in hydrochloric acid. Its amount normally varies 

 between 0.02 and 0.05 gramme. Oxaluric acid, on the other hand, 

 exists in the urine as an ammonium salt and is not found in sedi- 

 ments. Its amount is even smaller than that of oxalic acid 



As many articles of food, such as asparagus, spinach, grapes, 

 apples, etc., contain oxalic acid in not inconsiderable amounts, it is 

 supposed that a certain fraction of the oxalic acid of the urine is 

 referable to this source. We find, as a matter of fact, that in the 

 asparagus season larger amounts are eliminated than at any other 

 time of the year. But it has also been noted that oxalic acid does 

 not disappear from the urine when the diet consists exclusively of 

 albumins and fats, and that during starvation also oxalic acid can 

 still be found. We are consequently forced to the conclusion that 

 a certain amount of the substance must originate in the tissues of 

 the body, and there is a growing belief that the albumins are here 

 its ultimate source. We know indeed that oxaluric acid is closely 

 related to uric acid, and it in turn can be decomposed into urea and 

 oxalic acid, as is shown by the equations : 



CO NH, 



(1) C 5 H 4 N,O 3 + O + H 2 O = CO \CO + CO(NH 2 ) 2 



CO NH/ 



Alloxan. 



CO NH X 



CO - NH. 



(2) CO >CO + O >CO + C0 2 



CO NH X 



CO NH/ Parabanic acid. 



Alloxan. 



CO NH, CO NH\ 



(3) | >CO + H 2 O ^/CO 

 CO NH X COOH - NH/ 



Parabanic acid. Oxaluric acid. 



CO NH^ CO OH /NH 2 



(4) I ^>CO + H 2 = | + C0< 



COOH NH/ CO OH \NH 2 



Oxaluric acid. Oxalic acid. Urea. 



As oxalic acid on further oxidation is decomposed into water and 

 carbon dioxide, it would thus appear that both oxaluric acid and 

 oxalic acid may be regarded as complete oxidation-products of uric 

 acid. We find, as a matter of fact, that oxalic acid is increased in 

 various diseases in which the oxidation-processes are manifestly 

 impaired, such as diabetes mellitus, various diseases of the circulatory 

 apparatus when associated with deficient oxygenation of the blood, 

 in obesity, etc. I have frequently observed, moreover, that an 

 increased elimination of oxalic acid is associated with an increased 

 excretion of uric acid in young, more or less anemic individuals of 

 a neurotic typo. Whether or not oxalic acid may further be derived 

 from carbohydrates is as yet unknown, but is rather improbable. 



