URINE 391 



with ether. The hippuric acid remains in the aqueous solution. Filter it off and 

 wash it with a small amount of cold water while still on the filter. Remove it to 

 a small, shallow vessel, dissolve it in a small amount of hot water and set it aside 

 for crystallization. Examine the crystals microscopically and compare them with 

 those in Fig. 125, page 389. 



The chemistry of the synthesis is represented thus : 



CH 2 -NH 2 COC1 OC-NH-CHVCOOH. 



+ ( I =/ I +HC1. 



COOH \/ 



Glycocoll. Benzoyl chloride. Hippuric acid. 



COOH 



OXALIC ACID, | 



COOH 



Oxalic acid is a constituent of normal urine, about 15-20 mg. being 

 eliminated in 24 hours. It is present in the urine as calcium oxalate 

 which is kept in solution through the medium of the acid phosphates. 

 The origin of the oxalic acid content of the urine is not well under- 

 stood. It is eliminated, at least in part, unchanged when ingested, there- 

 fore since many of the common articles of diet, e.g., asparagus, apples, 

 cabbage, grapes, lettuce, spinach, tomatoes, etc., contain oxalic acid 

 (oxalates) it seems probable that the ingested food supplies a portion of 

 the oxalic acid found in the urine. There is also experimental evidence 

 that part of the oxalic acid of the urine is formed within the organism 

 in the course of protein and fat metabolism. It has also been suggested 

 that oxalic acid may arise from an incomplete combustion of carbo- 

 hydrates, especially under certain abnormal conditions. Patholog- 

 ically, oxalic acid is found to be increased in amount in diabetes mellitus, 

 in organic diseases of the liver, and in various other conditions which are 

 accompanied by a derangement of the oxidation mechanism. An 

 abnormal increase of oxalic acid is termed oxaluria. A considerable 

 increase in the content of oxalic acid may be noted unaccompanied by 

 any other apparent symptom. Calcium oxalate crystallizes in at least 

 two distinct forms, dumb-bells and octahedra (Fig. 134, page 459). 



EXPERIMENTS 



Preparation of Calcium Oxalate. First Method. Place 200-250 c.c. of 

 urine in a beaker, add 5 c.c. of a saturated solution of calcium chloride, make the 

 urine slightly acid with acetic acid, and stand the beaker aside in a cool place for 

 24 hours. Examine the sediment under the microscope and compare the crystal- 

 line forms with those shown in Fig. 134, page 459. 



Second Method. Proceed as above, replacing the acetic acid by an excess of 

 ammonium hydroxide and filtering off the precipitate of phosphates. 



