766 URINE. 



then 0.2 cc., and lastly 0.1 cc. After each addition let it boil minute. When 

 the end-reaction is approaching, the liquid begins to clarify and the mercury 

 separates with the phosphates. The end-reaction is determined by taking a 

 drop of the upper layer of the liquid into a capillary tube and then blowing it out 

 on pure white filter-paper. The moist spot is first held over a bottle containing 

 fuming hydrochloric acid and then over strong sulphuretted hydrogen. The 

 presence of a minimum quantity of mercury salt in the liquid is shown by the 

 spot becoming yellowish, which is best seen when it is compared with a second 

 spot that has not been exposed to the gas. The end-reaction is still clearer when 

 a small part of the liquid is filtered, acidified with acetic acid, and tested with 

 sulphuretted hydrogen (Orro *). The calculations are just as simple as for the 

 previous method. 



This titration, unlike the previous one, may be performed equally well by 

 daylight and by artificial light. KNAPP'S method has the following advantages 

 over FEHLING'S method: It is applicable even when the quantity of sugar in 

 the urine is very small and that of the other urinary constituents is normal. It 

 is more easily performed, and the titration liquids may be kept without decom- 

 posing for a long time (WoRM-MuLLER and his pupils 2 ) . There is diversity of 

 opinion, nevertheless, among investigators on the value of this titration method. 



ESTIMATION OF THE QUANTITY OF SUGAR BY FERMENTATION. This 

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

 time sufficiently exact for ordinary cases, is that of ROBERTS. This 

 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. ROBERTS found that a decrease of 0.001 in 

 the specific gravity corresponded to 0.23 per cent sugar, and this has been 

 substantiated since by several other investigators (WoRM-MuLLER and 

 others). If the urine, for example, has a specific gravity of 1.030 before 

 fermentation and 1 .008 after, then the quantity of sugar contained therein 

 was 22X0.23 ==5.06 per cent. 



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 hydro- 

 chloric acid or sulphuric acid. The activity of the yeast must, when 

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

 in a 400 cc. flask, add a piece of compressed yeast the size of a pea, and 

 subdivide the yeast through the liquid by shaking; close the flask with 

 a stopper provided with a finely-drawn-out glass tube, and allow the test 

 to stand at the temperature of the room or, still better, at 30-35 C. 

 After hours the fermentation is ordinarily ended, but this must be 

 verified by the bismuth test. After complete fermentation filter through 

 a dry niter, bring the filtrate to the proper [temperature, and determine 

 the specific gravity. 



If the specific gravity be determined with a good pyknometer sup- 

 plied with a thermometer and an expansion-tube, this method, when the 

 quantity of sugar is not less than 4-5 p. m., gives, according to WORM- 

 SB, very exact results, but this has been disputed by BUDDED 



1 Journal f. prakt. Chem., 26. 



1 Pfliiger's Arch., 16 and 23. 



3 Roberts, Edinburgh Med. Joijrn, 1861, and The Lancet, 1, 1862; Worm-Muller r 



