120 LABORATORY WORK IN PHYSIOLOGICAL CHEMISTRY. 



Method: 10 c.c. of quantitative Fehling's. solution are 

 placed in an evaporating-dish and diluted with 40 c.c. of 

 water. The solution is brought to boiling and kept so while 

 the urine (usually diluted ten times) is run in slowly from 

 a burette, until the blue color of the copper solution has. 

 entirely disappeared. An accurate determination of the end 

 point of the reaction requires considerable experience. 



Since 10 c.c. of Fehling's solution are completely reduced 

 by 0.05 grm. of dextrose, the quantity of urine required 

 to produce the end reaction must contain that quantity of 

 dextrose. From this can be easily calculated the total 

 amount of dextrose in the 24-hour urine. 



2. The possible simultaneous appearance in the urine 

 of laBvogyrate bodies (e.g. glycuronates, /?-oxybutyric acid) 

 renders the application of methods of this type of doubtful 

 value. Even when substances of this kind are apparently 

 absent, comparative values obtained by polarization and 

 reduction methods seldom agree within wide limits. When- 

 ever polarization determinations are made, they must be- 

 followed by a second estimation after fermentation. 



The urine may be decolorized by the addition of a crystal 

 or two of lead acetate and subsequent stirring and filtration 

 (see Polarization, p. 5). 



3. For rough approximations this method, using Einhorn's 

 saccharometer, serves the purpose better than any other.. 

 The procedure is described under Monosaccharides, p. 5. 

 A method of this type has also been suggested, based upon 

 the difference of the specific gravity of urine observed before 

 and after fermentation. 



