296 THE URINE. 



unless biliary acids are present, can be directly referred to the 

 presence of sugar, and usually to glucose. Lsevorotation, however, 

 may be referable to other reducing substances besides Ia3vulose, 

 such as the conjugate glucuronates, /?-oxy butyric acid, and others. 

 If such substances, moreover, are present in larger amounts, traces 

 of dextrose may be overlooked. It is hence advisable to examine 

 the urine both before and after treatment with yeast, and in doubt- 

 ful cases to control the quantitative results, which are obtained by 

 the polarimeter, by some other method. For a detailed description 

 of this method I must refer the reader to special works. In every 

 case the urine must be perfectly clear and free from albumin. If 

 highly colored, it should be treated with lead acetate solution and 

 then filtered, in which case allowance must be made for the degree 

 of dilution if quantitative results are desired. 



Quantitative Estimation. KNAPP'S METHOD. The method is 

 based upon the observation that mercuric cyanide in alkaline solu- 

 tion is reduced by sugar to metallic mercury. If urine is then 

 added to a solution containing a known amount of the cyanide until 

 this is entirely reduced, the corresponding amount of sugar can be 

 directly ascertained. 



The solution which is generally employed for this purpose con- 

 tains 10 grammes of the chemically pure cyanide, and 100 c.c. of a 

 solution of sodium hydrate (sp. gr. 1.145) in the liter : 20 c.c. cor- 

 respond to 0.05 gramme of glucose. 



The urine must be free from albumin and should contain not 

 more than 0.5 to 1 per cent, of sugar. This should first be ascer- 

 tained by a preliminary test. If more is present, the urine should 

 be correspondingly diluted. 



Twenty c.c. of the reagent are diluted with 80 c.c. of distilled 

 water, or with less if a smaller amount of sugar than 0.5 per cent, 

 is present. The solution is heated to the boiling-point, and then 

 titrated with the diluted urine, boiling for one-half minute after the 

 addition of every 2 c.c. or less of the urine. As the end-reaction 

 is approached, the mercury together with the phosphates settles to 

 the bottom and the supernatant fluid becomes clear. The final point 

 is reached when a drop of the liquid, placed upon filter-paper, and 

 successively held over the mouth of a bottle containing fuming 

 hydrochloric acid and over that of one containing a strong solution 

 of hydrogen sulphide, is no longer colored yellow. The results are 

 then calculated on the basis outlined above. 



FEHLING'S METHOD. Two solutions are employed, which must 

 be kept in separate bottles ; the one contains 34.64 grammes of 

 crystallized cupric sulphate, dissolved in 500 c.c. of distilled water, 

 and the other 173 grammes of potassium and sodium tartrate and 

 125 grammes of potassium hydrate, dissolved in an equal volume of 

 water. This solution is of such strength that the copper contained 

 in 10 c.c. (5 c.c. of each) will be completely reduced by 0.05 gramme 

 of glucose. If then urine is carefully added to this quantity until 



