URINE 549 



The availability of the fermentation procedure as a quantitative 

 aid has been appreciably lowered through the important findings of 

 Neuberg and Associates. 1 They show that yeast has the property of 

 splitting off carbon dioxide from the carboxyl group of amino- and other 

 aliphatic acids. The active agent in this "sugar-free fermentation" is 

 an enzyme called carboxylase. Inasmuch as amino-acids are always 

 present in the urine, the error from this source is apparent. 



9. Polariscopic Examination. Before subjecting urine to a polariscopic ex- 

 amination the slightly acid fluid should be decolorized as thoroughly as possible 

 by the addition of a little basic lead acetate. The urine should be well stirred 

 and then filtered through a filter paper which has not been previously moistened. 

 In this way a perfectly clear and almost colorless liquid is obtained. 



In determining dextrose by means of the polariscope it should be borne hi 

 mind that this carbohydrate is often accompanied by other optically active sub- 

 stances, such as proteins, fructose, /3-hydroxybutyric acid, and conjugate gly- 

 curonates which may introduce an error into the polariscopic reading ; the method 

 is, however, sufficiently accurate for practical purposes. 



For directions as to the manipulation of the polariscope see page 31. 



Below are given the specific rotations of some physiologically important sugars 

 as well as of certain other optically active substances the possible presence of 

 which must be borne in mind hi determining glucose polarimetrically in urine. 



Specific Rotation Specific Rotation 



Glucose +52.49 Fructose 92.25 



Maltose +136.5 /3-Hydroxybutyric 24.12 



Isomaltose +68.0 acid. 



Lactose t +52.53 Conjugated Gly- Levorotatory in 



Pentose (i-ara- o.o curonic Acids. varying degrees, 



binose). 



10. Benedict's Method for Sugar in Normal Urine. 2 Principle. The red color 

 obtained by heating a glucose solution with picric acid and sodium carbonate is 

 employed as the basis of the colorimetric determination. Acetone is used to 

 eliminate color due to creatinine. 



Procedure. To 12-15 c.c. of urine (sp. gr. not over 1.030) in a large test tube 

 or small Erlenmeyer flask add about i gm. of special bone black 3 shake 1-2 minutes, 

 let stand 10 minutes, and filter through a small dry filter paper. 



From i to 3 c.c. of the filtrate (if less than 3 c.c. are used, make up with dis- 

 tilled water to 3 c.c.) are measured into a graduated test tube (the tube employed 

 for the blood sugar estimation is satisfactory, see p. 287) and i c.c. of half saturated 

 picric acid and 0.5 c.c. of 5 per cent sodium hydroxide added. 



1 Neuberg and Associates: Biochem. Zeitschr., vol. 31 and 36, 1911. 



2 Private communication from the author. 



3 The special bone black may be prepared by treating 250 gm. of bone black with 1.5 

 liters of dilute hydrochloric acid (i part of acid to 5 parts of water) and boiling for 30 

 minutes. The bone black is now filtered on a large Buchner funnel and washed with 

 hot water until the nitrate is free from acid. 



