URINE 447 



fructose may be inferred when the percentage of sugar, as determined 

 by the titration method, is greater than the percentage indicated by 

 the polariscopic examination. 



EXPERIMENTS 



1. Borchardt's Reaction. To about 5 c.c. of urine in a test-tube add an equal 

 volume of 25 per cent hydrochloric acid and a few crystals of resorcinol. Heat to 

 boiling and after the production of a red color, cool the tube under running water 

 and transfer to an evaporating dish or beaker. Make the mixture slightly alka- 

 line with solid potassium hydroxide, return it to a test-tube, add 2-3 c.c. of 

 acetic ether, and shake the tube vigorously. In the presence of fructose the 

 acetic ether is colored yellow. 



The only urinary constituents which interfere with the test are 

 nitrites and indican and these interfere only when they are simul- 

 taneously present. Under these conditions, the urine should be acidified 

 with acetic acid and heated to boiling for one minute to remove the 

 nitrites. In case the indican content is very large, it will impart a blue 

 color to the acetic ether, thus masking the yellow color due to fructose. 

 When such urines are to be examined, the indican should first be re- 

 moved by Obermayer's test (see page 388). The chloroform should 

 then be discarded, the acid-urine mixture diluted with one-third its 

 volume of water, and the test applied as described above. The urine 

 of patients who have ingested santonin or rhubarb responds to the test. 

 The test will serve to detect fructose when present in a dilution of 

 i 12000, i.e., 0.05 per cent. 



2. Resorcinol-Hydrochtoric Acid Reaction (Seliwanoff). To 5 c.c. of Seliwa- 

 noff s reagent 1 hi a test-tube add a few drops of the urine under examination 

 and heat the mixture to boiling. The presence of fructose is indicated by the 

 production of a red color and the separation of a red precipitate. The latter 

 may be dissolved in alcohol to which it will impart a striking red color. 



If the boiling be prolonged a similar reaction may be obtained with 

 urines containing glucose. This has been explained 2 in the case of 

 glucose as due to the transformation of the glucose into fructose by 

 the catalytic action of the hydrochloric acid. The precautions neces- 

 sary for a positive test for fructose are as follows : The concentration of 

 the hydrochloric acid must not be 'more than 12 per cent. The reac- 

 tion (red color) and the precipitate must be observed after not more than 

 20-30 seconds of boiling. Glucose must not be present in amounts 

 exceeding 2 per cent. The precipitate must be soluble in alcohol with 

 a bright red color. 



1 Seliwanoff 's reagent may be prepared by dissolving 0.05 gram of resorcinol in 100 c.c. 

 of dilute (i : 2) hydrochloric acid. 



2 Koenigsfeld: Bioch. Zeit. 38, 311, 1912. 



