44^ PHYSIOLOGICAL CHEMISTRY 



GALACTOSE 



Galactose has. occasionally been detected in the urine, and in par- 

 ticular in that of nursing infants afflicted with a deranged digestive 

 function. Lactose and galactose may be differentiated from other 

 reducing sugars which may be present in the urine by means of the 

 mucic acid test. This test simply consists in the production of mucic 

 acid through oxidation of the sugar with nitric acid. 



EXPERIMENTS 



1. Mucic Acid Test Treat 100 c.c. of the urine under examination with 

 20 c.c. 1 of concentrated nitric acid and evaporate the mixture in a broad, shallow 

 glass vessel, upon a boiling water-bath, until the volume of the solution is only 

 20 c.c. At this point the fluid should be clear and a fine, white precipitate of 

 mucic acid should separate. 



If the percentage of galactose present in the urine is low it may be 

 necessary to cool the solution and permit it to stand for some time 

 before the precipitate will form. It is impossible to differentiate 

 between galactose and lactose by means of this test, but the reaction 

 does serve to differentiate these two sugars from all other reducing 

 sugars. A satisfactory differentiation between galactose and lactose 

 may be made by the Phloroglucinol-Hydrochloric Acid Test of Tollens, 

 below. 



2. Phloroglucinol-Hydrochloric Acid Reaction (Tollens). To equal volumes of 

 the urine and hydrochloric acid (sp. gr. 1.09) add a little phloroglucinol and heat 

 the mixture on a boiling water-bath. Galactose, pentose, and glycuronic acid will 

 be indicated by the appearance of a red color. Galactose may be differentiated 

 from the two latter substances in that its solutions exhibit no absorption bands 

 upon spectroscopical examination. 



FRUCTOSE 



Diabetic urine frequently possesses the power of rotating the plane of 

 polarized light to the left, thus indicating the presence of a levorotatory 

 substance. The levorotation is sometimes due to the presence of 

 fructose, although not necessarily confined to this carbohydrate, since 

 conjugate glycuronates and /3-hydroxybutyric acid, two other levo- 

 rotatory bodies, are frequently found in the urine of diabetics. Fructose 

 is invariably accompanied by glucose in diabetic urine, but fruc- 

 tosuria has been observed as a separate anomaly. The presence of 



1 If the specific gravity of the urine is 1020 or over it is necessary to use 25-35 c.c. of 

 nitric acid. Under these conditions the mixture should be evaporated until the remaining 

 volume is approximately equivalent to that of the nitric acid added. 



