394 



THE URINE. 



Fig. 132. 



certain that a deposit of lime oxalate is frequently present in perfectly 

 normal urine after a day or two of exposure to the atmosphere, and may 

 be observed, under these circumstances, without the existence of any 

 morbid symptom. Whenever oxalic acid is formed in the urine it must 

 unite with the lime in preference to any other of the bases present, and 

 is consequently deposited under the form of lime oxalate ; a salt which 

 is quite insoluble both in water and in the urine, even when heated to 

 the boiling point. In these cases, the lime oxalate crystals gradually 

 appear in the light cloud of mucus collected at the bottom of the vessel, 



while the supernatant fluid re- 

 main s clear. They are of minute 

 size, for the most part just 

 visible to the naked eye, rather 

 scanty in amount, transparent, 

 and colorless. They have the 

 form of regular octohedra, or 

 double quadrangular pyramids, 

 united base to base. They make 

 their appearance usually about 

 the commencement of the sec- 

 ond day, the urine at the same 

 time continuing clear and re- 

 taining its acid reaction. They 

 frequently appear as a deposit 

 when no substance containing 

 oxalic acid or oxalates has been 

 taken with the food. The pre- 

 cise source from which the oxalic acid, under these circumstances, is 

 derived has not been fully determined, but it is most probably produced 

 from a metamorphosis of a small portion of the uric acid of the urine. 

 If uric acid be boiled in two parts of water with lead peroxide, it is de- 

 composed, with the production, among other substances, of urea and 

 oxalic acid ; and it is supposed that some similar change may take place 

 in the urine, causing the appearance of a minute quantity of oxalic acid, 

 which decomposes a portion of the lime salts and thus appears as a 

 crystalline deposit of lime oxalate. 



Alkaline Fermentation of the Urine. At the end of a few days the 

 changes above described come to an end, and are Succeeded by a different 

 process, which consists essentially in the decomposition of the urea of 

 the urine and its transformation into ammonium carbonate. This 

 change, which may be produced artificially in a watery solution of urea 

 by continued boiling, takes place in the urine slowly at low tempera- 

 tures, more rapidly during warm weather. The elements of two 

 molecules of water unite with those of the urea undergoing decomposi- 

 tion, to produce ammonium carbonate, as follows : 



Urea. Ammonium carbonate. 



CH 4 N 2 + H 4 0, = (NH 4 ).C0 3 . 



CRYSTALS OF IJIME OXALATE, deposited 

 from healthy urine, during the acid fermentation. 



