732 PHYSIOLOGICAL CHEMISTRY. 



tity of sugar present. In case but a slight change takes place in 

 color, it is well to compare it with that of an unchanged specimen 

 of the urine. 



5. Fermentation test. This is based upon the decomposition of 

 dextrose by yeast with the generation of carbon dioxide. A piece 

 of yeast about the size of a pea is ground up in urine and the mixture 

 used to fill a fermentation tube. The tube is then kept for twenty- 

 four hours at a fairly constant temperature of 22 to 28 C. If dex- 

 trose be present, fermentation will commence within twelve hours 

 and will manifest itself by the formation of carbon dioxide gas, which 

 will collect at the upper end of the long arm of the tube. 



The urine and the fermentation apparatus should be sterilized by heat to 

 destroy any gas-producing bacteria present. For a control of the test, two 

 more fermentation tubes should be prepared, one with a mixture of a glucose 

 solution and yeast (to determine that the yeast is efficient),, and another with 

 sterilized water and yeast (to show that the yeast itself does not generate 



The disadvantages of this process are the length of time required for its per- 

 formance, the unreliability of the ferment, and the fact that small quantities 

 of sugar (less than 0.5 per cent.) evolve so little carbon dioxide that a doubt 

 may be felt as to the presence of sugar at all. 



6. The pTienyl-Tiydrazine test. To 10 c.c. of urine in a test-tube, 

 add phenyl-hydrazine hydrochloride, 0.4 gramme and sodium ace- 

 tate, 1 gramme, warm until dissolved, adding water, if necessary, and 

 keep in a boiling water-bath for half an hour. Filter while hot, and 

 allow to cool slowly. The presence of dextrose will be shown by the 

 deposition of yellow crystals, which are seen with the microscope to 

 be needles arranged in sheaves. This precipitate is an osazone 

 (phenyl-dextrosazone) and melts at 205 C. Pentoses and maltose 

 give similar osazones, as do lactose and glycuronic acid. The latter 

 are rarely present in sufficient amount to give a positive test with the 

 urine directly. The melting-points are of value in recognizing the 

 different osazones. 



7. Polariscopic test. Before urine can be examined by the polari- 

 scope it should be freed from proteins and from the greater part of 

 coloring-matters by precipitation with neutral lead acetate. The 

 sensitiveness of the test depends on the construction of the instru- 

 ment, but even the best polarimeters do not show traces of sugar, 

 for which reason it is generally useless to apply the test unless sugar 

 has been indicated bv other tests. 



