DETERMINATION OF SUGAR. 763 



ethylate in the cold according to BAISCH'S method, 1 and the various carbohydrates 

 separated according to his suggestion. 



If small quantities of sugar are to be isolated from the urine, precipitate the 

 urine first with sugar of lead, filter, precipitate the filtrate with ammoniacal basic 

 lead acetate, wash this precipitate with water, decompose it with H 2 S when sus- 

 pended in water and use the filtrate for the special tests. SCHONDORFF 2 has 

 suggested a method for the detection and estimation of very small amounts of 

 sugar based upon the work of PATEIN and DUPAU. This method depends upon 

 precipitating the nitrogenous substances with mercuric nitrate. 



To the physician, who naturally wants simple and quick methods, 

 the bismuth test is especially to be recommended. If this test gives 

 negative results, the urine is to be considered as free from sugar in a clinical 

 sense. If it gives positive results, the presence of sugar must be con- 

 trolled by other tests, especially by the fermentation test. 



Other tests for sugar, as, for example, the reaction with orthonitrophenyl- 

 propiolic acid, picric acid, diazobenzene-sulphonic acid, are superfluous. The 

 reaction with a-naphthol, which is a reaction for carbohydrates in general, for 

 glucuronic acid and mucin, may, because of its extreme delicacy, give rise to 

 mistakes, and is therefore not to be recommended to physicians. Normal urines 

 give this test, and if the strongly diluted urine gives the reaction the presence 

 of great quantities of carbohydrates may be suspected. In these cases more 

 positive results are obtained by using other tests. This test requires great clean- 

 liness, and it has the inconvenience that sufficiently pure sulphuric acid is not 

 always readily procurable. Several investigators, such as v. UDRANSKY, LUTHER, 

 Roos and TREUPEL, S have investigated this test in regard to its applicability 

 as an approximate test for carbohydrates in the urine. 



Quantitative Determination of Sugar in the Urine. The quantity of 

 sugar can be determined by titration, by fermentation of the sugar, by 

 polarization, and also in other ways. 



The titration methods are based upon the property of the sugar to 

 reduce metallic oxides in alkaline solutions. As the titration liquids 

 (cupric oxide solution in the FEHLING-SOXHLET, PAVY, BANG methods 

 and mercuric oxide in KNAPP'S method) are also reduced by other urinary 

 constituents, these reduction methods always give too high results. 

 When large quantities of sugar are present, as in typical diabetic urine, 

 which generally contains a lower percentage of normal reducing con- 

 stituents, this is indeed of little account; but when small quantities of 

 sugar are present in an otherwise normal urine, the mistake may, on 

 the contrary, be important, as the reducing power of normal urine may 

 correspond to 5 p. m. dextrose (see page 711). In such cases the titra- 

 tion procedure must be employed in connection with the fermentation 

 method, which will be described later. 



Of the titration methods with copper solutions the method suggested 

 by BANG is the simplest, and at the same time seems to be more reliable 

 than any of the others. For this reason we will describe only this method 



1 Zeitschr. f. physiol. Chem., 19. 



z Pfliiger's Arch., 121, which cites the work of Patein and Dufau. 



3 See Roos and Treupel, Zeitschr. f . physiol. Chem., 15 and 16. 



