328 PHYSIOLOGICAL CHEMISTRY 



microscope and note the diagonally crossed crystals of calcium 

 oxalate. 



25. Urinary Indican. Indican is usually, but not always, 

 found in the urine. It is formed from the products of protein 

 putrefaction in the intestine. To 15-20 c.c. urine in a test tube 

 add 2 c.c. copper sulphate solution, 15 or 20 c.c. cone. HC1 and 

 5 c.c. chloroform. Close the mouth of the tube with the thumb 

 and shake cautiously (over the sink). Continue the shaking for 

 several minutes. The ' ' indican ' ' is oxidized to indigo, which dis- 

 solves in the chloroform, giving it a blue color. The depth of 

 color developed in the chloroform indicates roughly the amount 

 of indican present. 



PIGMENTS. Urochrome and uroerythrin are the most im- 

 portant urinary pigments. 



Urochrome is a substance which gives the yellow color to urine. 



Uroerythrin. This red pigment gives the deep reddish color 

 to sediments of uric acid and urates. 



In addition to the above constituents the urine contains small 

 and varying amounts of various substances, e. g., hippuric acid, 

 allantoin, aromatic oxyacids, compounds containing sulphur and 

 many other substances. 



Collection and Preservation of a Specimen for Quantitative 

 Analysis General Properties 



As the composition of the urine voided at different times of 

 the day varies considerably, it is customary to use for metabolism 

 studies either a 3-hour or a complete 24-hour sample. This may 

 be obtained as follows: On rising in the morning empty the 

 bladder and discard the urine voided. Then collect all urine 

 voided during the day, and the first voiding on rising the fol- 

 lowing morning. This constitutes a complete 24-hour specimen. 

 For the observations in this section and the quantitative anal- 

 ysis in the section following, a complete 24-hour specimen should 

 be used, and all determinations made on the same specimen. 



As some urinary constituents decompose on standing, it is 

 necessary to add a preservative to the urine. In collecting a 24 



