DECOMPOSITION OF THE URINE. 393 



Pus. When pus is contained in the urine it subsides on standing, 

 and forms at the bottom a dense, homogeneous-looking, creamy-white 

 layer. It is perfectly fluid in consistency and may be easily dissemi- 

 nated by agitation. Microscopic examination shows it to be composed 

 exclusively of colorless, granular, nucleated " pus-globules," identical 

 in appearance with the white globules of the blood, but distinguishable 

 from those belonging to a deposit of blood by their much greater 

 abundance and by the absence of red globules. If the supernatant fluid 

 be poured off, and a few drops of a solution of caustic alkali added to 

 the purulent deposit, it loses its white color and opacity, owing to the 

 solution of its granular cells, and swells up into a transparent, colorless 

 substance of gelatinous consistency, which can no longer be poured 

 out of the vessel in drops, but slides out in a single semi-solid mass. 

 This character alone will serve to distinguish a deposit of pus from 

 any other liable to occur in the urine. The supernatant fluid, when 

 carefully filtered, is found to contain a small quantity of albumen, the 

 interstitial fluid of pus being itself albuminous. 



Decomposition of the Urine. 



After its discharge from the body, the urine undergoes spontaneous 

 changes, by w r hich its ingredients are altered and finally disappear. This 

 process of spontaneous decomposition is closely dependent upon the 

 small quantity of mucus contained in the urine, since it is very much 

 retarded if the mucus be separated by immediate filtration, and is hast- 

 ened in a corresponding degree when the mucus is abnormally abundant. 

 It is characterized by two different stages, which are distinguished from 

 each other by the successive development of an acid and an alkaline 

 reaction. They are known accordingly as the acid and the alkaline 

 fermentations. 



Acid Fermentation of the Urine. This process, which is the first to 

 show itself in the urine, takes place for the most part within the first 

 twelve, twenty-four, or forty-eight hours after the discharge of the urine, 

 according to the elevation of the surrounding temperature. It consists 

 in the production of a free acid, usually lactic acid, from some of the 

 undetermined organic ingredients of the excretion. The urine when 

 fresh contains no free acid substance, its reaction to test-paper being 

 due to the presence of its sodium biphosphate. But lactic acid has, 

 notwithstanding, been so often found in nearly fresh urine as to be 

 sometimes regarded as one of its normal constituents. Observation has 

 shown, however, that urine, although entirely 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, although not 

 constant, appears to be sufficiently frequent to be regarded as a normal 

 process. 



During the period of the acid fermentation, there is reason to believe 

 that oxalic acid is also sometimes produced in a similar manner. It is 

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