URINE. 323 



properly performed. Buckmaster has recently suggested the use 

 of guaiaconic acid instead of the solution of guaiac. See discussion 

 on page 192 and test on page 196. 



7. Schumm's Modification of the Guaiac Test. To about 5 

 c.c. of urine 1 in a test-tube add about 10 drops of a freshly prepared 

 alcoholic solution of guaiac. Agitate the tube gently, add about 20 

 drops of old turpentine, subject the tube to a thorough shaking and 

 permit it to stand for about 2-3 minutes. A blue color indicates 

 the presence of blood in the solution under examination. In case 

 there is insufficient blood to yield a blue color under these con- 

 ditions, a few c.c. of alcohol should be added and the tube gently 

 shaken, whereupon a blue coloration will appear in the upper al- 

 cohol-turpentine layer. 



A control test should always be made using water in place of 

 urine. In the detection of very minute traces of blood only 3-5 

 drops of the guaiac solution should be employed. 



8. Adler's Benzidine Reaction. This is one of the most deli- 

 cate of the reactions for the detection of blood. Different benzidine 

 preparations vary greatly in their sensitiveness, ho.wever. Inas- 

 much as benzidine solutions change readily upon contact with light, 

 it is essential that they be kept in a dark place. The test is per- 

 formed as follows : To a saturated solution of benzidine in alcohol 

 or glacial acetic acid add an equal volume of 3 per cent hydrogen 

 peroxide and one c.c. of the urine under examination. If the mix- 

 ture is not already acid, render it so with acetic acid, and note the 

 'appearance of a green or blue color. A control test should be made 

 substituting water for the urine. 



Often when urines containing a small amount of blood are tested 

 by this reaction, the mixture is rendered so turbid as to make it 

 difficult to decide as to the presence of a faint green color. Such 

 urines should be extracted with an ether-acetic acid solution and 

 the resulting extract washed with water before the test is applied 

 to it. The sensitiveness of the benzidine reaction is greater when 

 applied to aqueous solutions than when applied to the urine. 



9. Spectroscopic Examination. Submit the urine to a spectro- 

 scopic examination according to the directions given on page 203 

 looking especially for the absorption-bands of oxyhsemoglobin and 

 methsemoglobin (see Absorption Spectra, Plate I.). 



Alkaline urine should be made slightly acid with acetic acid as the blue end- 

 reaction is very sensitive to alkali. 



