THE URINE. 357 



mended for clinical purposes. For exact determinations it is not 

 quite reliable, because the amount of silver in the precipitate of 

 'silver urate is not constant (SALKOWSKI). Since the value of this 

 method has been the subject of much adverse criticism, we will not 

 give further particulars. 



OXALURIC ACID, C 3 H 4 N 2 O4=(CON a H3).CO.COOH. This acid, whose 

 relation to uric acid and urea has been spoken of above, occurs only as traces 

 in the urine as ammonium salts. This salt is not directly precipitated by CaCl s 

 and NH S , but after boiling, when it is decomposed into urea and oxalate. In 

 preparing oxaluric acid from urine the latter is filtered through animal char- 

 coal. The oxalurate retained by the charcoal may be obtained by boiling 

 with alcohol. 



POOTT 

 Oxalic Acid, C 8 H 8 4 , or QQQTT> occurs under physiological 



conditions in very small amounts in the urine, about 0.02 grm. in 

 24 hours (FuRB RINGER). According to the generally-received 

 opinion it is found in the urine as calcium oxalate, which is kept 

 in solution by the acid phosphates present. Calcium oxalate is a 

 frequent constituent of the urinary sediments, and occurs also in 

 certain urinary calculi. 



The origin of the oxalic acid in the urine is not well known. 

 Oxalic acid, when administered, is eliminated by the urine un- 

 changed, and as many vegetables and fruits, such as cabbage, spin- 

 ach, asparagus, sorrel, apples, grapes, etc., contain oxalic acid, it is 

 possible that a part of the oxalic acid of the urine originates directly 

 from the food. Another part is certainly formed in the body from 

 the proteids and fat or by the incomplete combustion of the car- 

 bohydrates. The formation of oxalic acid from proteids (or fat) is 

 inferred from the fact that oxalic acid is eliminated by the urine 

 after food consisting entirely of flesh and fat, as also in starvation. 

 It has also been considered, but without sufficient reason, that the 

 oxalic acid of the urine is an oxidation product of uric acid. 



An increased elimination of oxalic acid may occur in diabetes. 

 The question whether it may occur as an independent disease 

 (oxaluria, oxalic-acid diathesis) has not been positively decided. 



The properties and reactions of oxalic acid and calcium oxalate 

 are well known. The calcium oxalate as a constituent of urinary 

 sediments will be described later. 



Defection and quantitative estimation of oxalic acid in urine. 

 The presence of oxalic acid in solution in urine is determined 



