280 THE URISE. 



iued microscopically. As we are generally only dealing with glu- 

 cose in the urine, a further examination is usually not necessary, 

 especially if the substance crystallizes out in large needles, which are 

 often collected in stars and sheaves. To identify these further, how- 

 ever, their melting-point must be determined. As has been stated, 

 this differs in the different osazons, with the exception of laevulose 

 and glucose, which have the same melting-point. Lsevulose, how- 

 ever, is found only under exceptional conditions. Its presence may 

 be established as shown below. The melting-points of the various 

 osazons which may be encountered are as follows : 



Glucose 204-20o C. 



Laevulose 204-205 C. 



Galactose 193 C. 



Maltose 206 C. 



IsoniMltose 150-~153 C. 



Lactose 200 C. 



Arabinose 159 C. 



Xylose 159 C. 



Glucuronic acid 114-115 C. 



The glucosazon is insoluble in water, but dissolves with ease in 

 hot alcohol, from which it can be precipitated on cooling in crystal- 

 line form, by diluting with water. The crystals are then collected 

 on a filter, dried over sulphuric acid, and further examined if 

 desired. 



POLARIMETRIC EXAMINATION. The polarimetric examination 

 for the presence of sugar should always be controlled by one or 

 more of the tests that have just been described. Dextro rotation, 

 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 laevulose, 

 such as the conjugate glucuronates, /9-oxy butyric acid, and others. 

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

 of dextrose may be overlookod. 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. DIFFERENTIAL DENSITY METHOD. 

 The methods available for the quantitative estimation of glucose 

 are, like the common tests, on the whole most unsatisfactory. The 

 least objectionable perhaps is that based upon the determination of 

 the difference in the specific gravity before and after fermentation. 

 It has been found that a diminution by 0.001 corresponds to the 

 previous presence of 0.230 per cent, of sugar. 



