418 PHYSIOLOGICAL CHEM18THY. 



the following advantages over FEELING'S method. It is applicable 

 even when the quantity of sugar in the urine is very small and the 

 amount of the other urinary constituents is normal. It is more 

 easily performed, and the titration liquids may be kept without 

 decomposing for a long time (WORM MULLER and his pupils). The 

 views of different investigators on the value of this titration method 

 are still somewhat contradictory. 



ESTIMATION OF THE QUANTITY OF SUGAR BY FERMENTATION. 

 This may be done in various ways ; the simplest, and at the same 

 time sufficiently exact for ordinary cases, is ROBERTS' method. 

 This method consists in determining the specific gravity of the 

 urine before and after fermentation. In the fermentation of sugar, 

 carbon dioxide and alcohol are formed as chief products and the 

 specific gravity is lowered, partly on account of the disappearance 

 of the sugar and partly on account of the production of alcohol. 

 EGBERTS found, and this has been substantiated later by several 

 other investigators (WORM MULLER and others), that a decrease of 

 0.001 in the specific gravity corresponded to 0.23$ sugar. If the 

 urine, for example, had a specific gravity of 1.030 before fermenta- 

 tion and 1.008 after, then the quantity of sugar contained therein 

 was 22 x 0.23 = 5.06$. 



In performing this test the specific gravity must be taken at the 

 same temperature before and after the fermentation. The urine 

 must be faintly acid, and when necessary it should be acidified with 

 a little tartaric-acid solution. The activity of th'e yeast must, when 

 necessary, be controlled by a special test. Place 200 c. c. of the 

 urine in a 400-c. c. flask and add a piece of compressed yeast the 

 size of a pea, and subdivide the yeast through the liquid by shak- 

 ing, close the flask with a stopper provided with a finely drawn-out 

 open glass tube, and allow the test to stand at the temperature of 

 the room, or still better at + 20-25 C. After 24-48 hours the 

 fermentation is. ordinarily ended, but this must be verified by the 

 bismuth test. After complete fermentation filter through a dry 

 filter, bring the filtrate to the proper temperature, and determine 

 the specific gravity. 



If the specific gravity be determined with a good pyknometer 

 supplied with a thermometer and an expansion-tube, this method, 

 when the quantity of sugar is not less than 4-5 p. m., gives, accord- 

 ing to WORM MULLER, very exact results, but this has been disputed 

 by BUDDE. For the physician this method in this form is not 

 serviceable. Even if the specific gravity is determined by a delicate 

 urinometer which can give the density to the fourth decimal, we 

 do not obtain quite exact results because of the principal errors 

 of the method (BUDDE) ; but the error is usually smaller than 

 those which occur in ti'trations made by unpractised hands. Among 

 the methods proposed and closely tested for the quantitative esti- 



