572 THE URINE [CH. XXXVII. 



(d) 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 O'Oo 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. 



In some cases of diabetic urine where there is excess of ammonio-magnesic 

 phosphate, the full reduction is not obtained with Fehling's solution, and when the 

 quantity of sugar is small it may be missed. In such a case excess of soda or 

 potash should be first added, the precipitated phosphates filtered off, and the filtrate 

 after it has been well boiled may then be titrated with Fehling's solution. 



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. (See p. 517.) 



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 homogentisinic acid (C fi H 3 .(OH). 2 CH. 2 .COOH). 



(e) 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. A control 

 experiment should be made with yeast and water in another test-tube, as a small 

 yield of carbonic acid is sometimes obtained from impurities in the yeast. 



(/) The phenylhydrazine test (p. 391) may also be applied. 



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. Petten- 

 kofer'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. Excess of urobilin should not 

 be mistaken for bile pigment. 



Blood. When haemorrhage occurs in any part of the urinary 

 tract, blood appears in the urine. It is found in the acute stage of 

 Bright's disease. If a large quantity is present, the urine is deep 



