704 PHYSIOLOGICAL CHEMISTRY. 



crystals of acid urates, or uric acid, are deposited. In this condition 

 the urine may often continue unchanged for several weeks, provided 

 the temperature be low. If, however, the temperature be above the 

 mean, decomposition speedily takes place. The urine is then found 

 to be covered with a thin, shining, and frequently iridescent mem- 

 brane, fragments of which sink gradually to the bottom. The urine 

 then becomes turbid, acquires a pale color, its reaction becomes alka- 

 line, and it begins to develop a nauseous ammoniacal odor, due to the 

 products formed by the decomposing action of certain microorganisms 

 (chiefly bacterium ureaB and micrococcus urea?) upon urea, which is 

 converted into ammonium carbonate and ammonium carbamate. The 

 change from an acid to an alkaline urine causes the precipitation of 

 earthy phosphates, ammonium-magnesium phosphate, ammonium 

 urate, etc. 



Points to be considered in the analysis of urine. They are : 



1. Color, odor, general appearance whether clear, smoky, cloudy, 

 turbid, etc. 



2. Reaction whether acid, neutral, or alkaline to test-paper. 



3. Specific gravity, and amount for twenty-four hours. 



4. Examination of sediments, microscopically and chemically. 



5. Chemical examination for the various normal and abnormal 

 constituents. 



Samples of urine should always be drawn from the well-mixed and 

 exactly measured quantity of the total urine discharged in twenty- 

 four hours. 



If the specimen cannot be examined promptly it should be pre- 

 served in a stoppered bottle by the addition of a very small amount 

 of chloroform (3 to 5 c.c. to one liter of urine). 



Color. Normal urine is generally pale yellow or reddish yellow, 

 but it may be as colorless as water, or as dark brownish-black as 

 porter ; a reddish and smoky tint generally indicates the presence of 

 blood, and a brownish-green suggests the presence of the coloring- 

 matter of bile. 



The nature of the normal coloring-matters of urine is as yet 

 doubtful ; the existence of three separate pigments has been demon- 

 strated ; they have been named urobilin, urochrome, and uroerythrin, 

 and, most likely, are products of the decomposition of biliary mat- 

 ters. Numerous other substances, such as indican, occur occasionally 

 in the urine, and produce various colors, especially when the urine is 

 exposed to air and light, or when acted on by reagents. 



