URINE 417 



Such bodies as conjugate glycuronates, uric acid, nucleo protein, and homo- 

 gentisic 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 Fehling's solution and in appear- 

 ance 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. According to Laird 1 

 even small amounts of creatinine will retard the reaction -velocity of re- 

 ducing sugars with Fehling's solution. 



Conjugate glycuronates are formed after the ingestion of such sub- 

 stances as chloral hydrate, camphor, menthol, thymol, antipyrin, 

 phenol, etc. The chloral hydrate is excreted in the urine as trichlor- 

 ethylglycuronic acid, C2C1 3 H 2 .C6H907. This compound reduces Fehl- 

 ing's solution and is /CT0rotatory, whereas glucose also reduces but is 

 dextrorotatory. Therefore by means of a polariscopic test we may dif- 

 ferentiate between a "chloral urine " and a " sugar urine." 



In testing urine preserved by chloroform a positive test may be ob- 

 tained in the absence of sugar. This is due to the fact that the hot 

 alkali produces for mic acid (a reducing fatty acid) from the chloroform. 



Ammonium salts also interfere with Fehling's test. If present in 

 excess the urine should be made alkaline and boiled in order to decom- 

 pose the ammonium salts. 



(c) Benedict's Modifications of Fehling's Test. First Modification. To 2 

 c.c. of Benedict's solution 2 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 15-30 seconds and permit it to cool to room temperature spontaneously. 

 (If desired this process may be repeated, although it is ordinarily unnecessary.) 

 If sugar is present in the solution a precipitate will form which is often bluish- 

 green or green at first, especially if the percentage of sugar is low, and which 

 usually becomes yellowish upon standing. If the sugar present exceeds 0.06 

 per cent this precipitate generally forms at or below the boiling-point, whereas if 

 less than 0.06 per cent of sugar is present the precipitate forms more slowly and 

 generally only after the solution has cooled. The greenish precipitate obtained 

 with urines containing small amounts of sugar may be a compound of copper with 

 the sugar or a compound of some constituent of the urine with reduced copper 



1 Laird: Journ. Path, and Bact., 16, 398 1912. 



2 Benedict's modified Fehling solution consists of ^ two definite solutions a copper 

 sulphate solution and an alkaline tartrate solution, which may be prepared as follows: 



Copper sulphate solution = 34.65 grams of copper sulphate dissolved m water and made 

 up to 500 c.c. 



Alkaline tartrale 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. 



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