602 THE URINE [CH. XXXIX. 



(c) Quantitative Determination of Sugar in Urine. Fehling's solution is pre- 

 pared as follows:- 34*639 grammes of copper sulphate are dissolved in about 200 

 c.c. of distilled water; 173 grammes of Rochelle salt are dissolved in 600 c.c. of a 

 14 per cent, solution of caustic soda. The two solutions are mixed and diluted to a 

 litre. Ten c.c. of this solution are equivalent to 0'05 gramme of dextrose. Dilute 

 10 c.c. of this solution with about 40 c.c. of water, and boil it in a porcelain basin. 

 Run into this from a burette the urine (which should be previously diluted with nine 

 times its volume of distilled water) until the blue colour of the copper solution 

 disappears that is, till all the cupric hydrate is reduced. The mixture in the basin 

 should be boiled after every addition. The quantity of diluted urine used from the 

 burette contains 0'05 gramme of sugar. Calculate the percentage from this, 

 remembering that the urine has been diluted to ten times its original volume. 



Pavy's modification of Fehling's solution is often used. Here ammonia 

 holds the copper in solution, and no precipitate forms on boiling with sugar, as 

 ammonia holds the cuprous oxide in solution. The reduction is complete when the 

 blue colour disappears; 10 c.c. of Pavy's solution = 1 c.c. of Fehling's solution = 

 0'005 gramme of dextrose. 



There are several other modifications of the original Fehling method which 

 have been introduced with the purpose of making the end-point clearer. Allihn's 

 method is the most accurate ; the cuprous oxide is collected, and finally reduced to 

 metallic copper, which is then weighed. 



Fehling's test is not absolutely trustworthy. Often a normal urine will 

 decolorise Fehling's solution, though seldom a red precipitate is formed. This is 

 due to excess of urates and creatinine. Another substance called glycuronic acid 

 (C 6 H 10 O 7 ) is, however, very likely to be confused with sugar by Fehling's test ; the 

 cause of its appearance is sometimes the administration of drugs (chloral, camphor, 

 etc.) ; but sometimes it appears independently of drug treatment. 



In the rare and hereditary condition called alcaptonuria, confusion may also 

 arise. Alcapton is a * substance which originates from tyrosine by an unusual 

 form of metabolism. It gives the urine a brown tint, which darkens on exposure 

 to the air. It is an aromatic substance, which Baumann and Wolkow and later 

 Garrod identified with homogentisic acid (C 6 H 3 .(OH),CH 2 .COOH). 



(d) A good confirmatory test for sugar is the fermentation test, which is per- 

 formed as follows : 



Half fill a test-tube with the urine and add a little German yeast. Fill up the 

 tube with mercury ; invert it in a basin of mercury, and leave it in a warm place 

 for twenty-four hours. The sugar will undergo fermentation : carbonic acid gas 

 accumulates in the tube, and the liquid no longer gives the tests for sugar, or only 

 faintly, but gives those for alcohol instead. The specific gravity falls. 



(e) The phenylhydrazine test (p. 412) may also be applied. 



Another hereditary abnormality of metabolism is pentosuria ; this is apt to be 

 mistaken for diabetes, for pentose reduces Fehling's solution, but it will not ferment 

 with yeast. It is a rare condition, but does not appear to do any harm. The source 

 of the pentose is not the food, for pentosuria continues in these cases when the food 

 contains no pentose. The pentose of the urine, moreover, is a different one from 

 that found in the nucleic acids of the body. Neuberg thinks it arises in some way 

 from galactose, and that it originates from the galactosides of the body. 



Bile. This occurs in jaundice. The urine is dark-brown, 

 greenish, or in extreme cases almost black in colour. The most 

 readily applied test is Gmelin's test for the bile pigments. Excess 

 of urobilin should not be mistaken for bile pigment. Pettenkofer's 

 test for the bile acids seldom succeeds in urine if the test is done in 

 the ordinary way. The best method is to warm a thin film of urine 

 and cane sugar solution in a flat porcelain dish. Then dip a glass rod 

 in strong sulphuric acid, and draw it across the film. Its track is 

 marked by a purplish line. Hay's sulphur test is a good one for bile 



