THE URINE. 



339 



lactic acid, from some undetermined organic ingredients of the excretion. 

 The urine when fresh contains no free acid, its reaction being due to the 

 presence of sodium biphosphate. But lactic acid has so often been found 

 in urine as to be sometimes regarded as one of its normal constituents. 

 Observation, however, has shown that urine, though free from lactic acid 

 when first passed, may present distinct traces of this substance after 

 some hours of exposure to the air. Its production in this way, though 

 not constant, appears sufficiently frequent to be regarded as a normal 

 process. 



There is reason to believe that oxalic acid is sometimes produced in a 

 similar manner. A deposit of lime oxalate is frequently present in the 

 urine a day or two after its discharge, without the existence of any per- 

 ceptible morbid symptom. Whenever oxalic acid is formed in the urine 

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

 is consequently deposited under the form of lime oxalate, which is 

 quite insoluble in urine, even at the boiling point. In these cases, the 

 lime oxalate crystals gradually appear in the light cloud of mucus at 

 the bottom of the vessel. They are of minute size, for the most part 

 just visible to the naked eye, scanty in amount, transparent, and color- 

 less. They have the form of regular octohedra, or double quadrangular 

 pyramids, united base to base. They usually show themselves about 

 the second day, the urine continuing clear and retaining its acid reac- 

 tion ; and they frequently appear as a deposit when no substance con- 

 taining oxalic acid or oxalates has been taken with the food. The precise 

 source of the oxalic acid, under 

 these circumstances, has not 

 been determined, but it is prob- 

 ably derived from a partial meta- 

 morphosis of the uric acid. If 

 uric acid be boiled in two parts 

 of water with lead peroxide, it 

 is decomposed, with the produc- 

 tion, among other substances, 

 of oxalic acid ; and it is supposed 

 that some similar change may 

 take place in the urine, causing 

 the appearance of oxalic acid in 

 minute quantity. This decom- 

 poses a portion of the lime salts, 

 and consequently appears as a 



Crystalline deposit of lime OX- CRYSTALS OP LIME OXALATE, deposited from healthy 

 j , urine, during the acid fermentation. 



Alkaline Fermentation of the Urine. After a few days the changes 

 above described come to an end, and are succeeded by the transformation 

 of urea into ammonium carbonate. This change, which may be artifi- 

 cially produced in a watery solution of urea by continued boiling, takes 

 place in the urine slowly at low temperatures, more rapidly during warm 



FIG. 83. 



