URINE. 309 



a test-tube add about 4 c.c. of water, and boil. This is done to 

 determine whether the solution will of itself cause the formation 

 of a precipitate of brownish-red cuprous oxide. If such a pre- 

 cipitate forms, the Fehling's solution must not be used. Add 

 urine to the warm Fehling's solution, a jew drops at a time, and 

 heat the mixture after each addition. The production of yellow 

 cuprous hydroxide or brownish-red cuprous oxide indicates that 

 reduction has taken place. The yellow precipitate is more likely 

 to occur if the urine is added rapidly and in large amount, whereas 

 with a less rapid addition of smaller amounts of urine the brownish- 

 red precipitate is generally formed. 



This is a much more satisfactory test than Trommer's, but even 

 this test is not entirely reliable when used to detect sugar in the 

 urine. Such bodies as conjugate glycuronates, uric acid, nucleo- 

 protein and homogentisic acid, when present in sufficient amount, 

 may produce a result similar to that produced by sugar. Phosphates 

 of the alkaline earths may be precipitated by the alkali of the Feh- 

 ling's solution and iii appearance may be mistaken for the cuprous 

 hydroxide. Cupric hydroxide may also be reduced to cuprous 

 oxide and this in turn be dissolved by creatinine, a normal urinary 

 constituent. This will give the urine under examination a greenish 

 tinge and may obscure the sugar reaction even when a considerable 

 amount of sugar is present. 



(c) Benedict's Modifications of Fehling's Test. First Modifi- 

 cation. To 2 c.c. of Benedict's solution 1 in a test-tube add 6 c.c. 

 of distilled water and 7-9 drops (not more) of the urine under 

 examination. Boil the mixture vigorously for about ' 1 5-30 sec- 

 onds and permit it to cool to room temperature spontaneously. (If 

 desired this process may be repeated, although it is ordinarily un- 

 necessary.) If sugar is present in the solution a precipitate will 

 form which is often bluish- green or green at first, especially if the 



These solutions should be preserved separately in rubber-stoppered bottles and 

 mixed in equal volumes when needed for use. This is done to prevent de- 

 terioration. 



1 Benedict's modified Periling solution consists of two definite solutions a 

 cupric sulphate solution and an alkaline tartrate solution, which may be pre- 

 pared as follows : 



Cupric sulphate solution 34.65 grams of cupric sulphate dissolved in water 

 and made up to 500 c.c. 



Alkaline tartrate solution = 100 grams of anhydrous sodium carbonate and 

 173 grams of Rochelle salt dissolved in water and made up to 500 c.c. 



These solutions should be preserved separately in rubber-stoppered bottles 

 and mixed in equal volumes when needed for use. This is done to prevent 

 deterioration. 



