THE URINE. [CH. xxxvii. 



acid, and may contain or yield on distillation acetone, and ethyl- 

 diacetic acid. The methods usually adopted for detecting and 

 estimating the sugar are as follows : 



(a) The urine has generally a high specific gravity. 



(*) The presence of sugar is shown by the reduction (yellow precipitate 

 of cuprous oxide) that occurs on boiling with Fehltng's solution. Fehling's 

 solution is an alkaline solution of copper sulphate to which Rochelle salt 

 has been added. The Rochelle salt (double tartrate of potash and soda) 

 holds the cupric hydrate in solution. Fehling's solution should always be 

 freshly prepared, as, on standing, racemic acid is formed from the taftaric 

 acid, and this substance itself reduces the cupric to cuprous oxide. Fehling's 

 solution should, therefore, always be tested by boiling before it is used. If 

 it remains clear on boiling, it is in good condition. 



(c) Picric Acid Test. The work of Sir George Johnson and G. S. Johnson 

 has shown the value of this reagent in detecting both albumin and sugar in 

 the urine. The same reagent may be employed for the detection of" both 

 substances. The method of testing for albumin has been already studied 

 with Esbach's tube. To test for sugar do the following experiment. Take 

 a drachm (about 4 c.c.) of diabetic urine ; add to it an equal volume of 

 saturated aqueous solution of picric acid, and half the volume (i.e.. 2 c.c.) of 

 the liquor potassae of the British Pharmacopoeia. Boil the mixture for about 

 a minute, and it becomes so intensely dark red as to be opaque. Now do 

 the same experiment with normal urine. An orange-red colour appears 

 even in the cold, and is deepened by boiling, but it never becomes opaque, 

 and so the urine for clinical purposes may be considered free from sugar. 

 This reduction of picric acid by normal urine is due to creatinine (see 



P- 559)- 



(<f) Quantitative Determination of Sugar in Urine. Fehling's solution 

 is prepared as follows : 34-639 grammes of copper sulphate are dissolved in 

 about 200 c.c. of distilled water ; 1 73 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 grammes 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 sometimes used. Here am- 

 monia 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 = i c.c. 

 of Fehling's solution ^ o'oot; grammes 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 tl.e 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 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, &c.) ; but sometimes it appears independently 



