408 PHYSIOLOGICAL CHEMISTRY 



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. 130, page 406. 



The chemistry of the synthesis is represented thus: 



CH 2 -NH 2 COC1 OC-NH-CH 2 -COOH. 



+ HC1. 



1 



:OOH 



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. When ingested it is eliminated, at least in part, unchanged, there- 

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

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

 acid (oxalates) it seems probable that the ingested food supplies a por- 

 tion 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 

 carbohydrates, especially under certain abnormal conditions. Patho- 

 logically, 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. 140, page 476). 



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 a'cid 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. 140, page 476. 



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

 ammonium hydroxide and filtering off the precipitate of phosphates. 



