CARBOHYDRATES 177 



quantities of #, 6, and c in three test-tubes ; to each add an equal amount of 

 Fehling's solution, and boil : a will give a heavy precipitate of cuprous 

 oxide, b one not so heavy, and c least of all, or none at all. 



3. Micro-chemical detection of Glycogen, A thin piece of the same liver is 

 hardened in 90 per cent, alcohol. Sections are cut by the free hand, or after 

 embedding in paraffin. If paraffin is used, this is got rid of by means of 

 turpentine ; and the sections prepared by either method are treated with 

 chloroform in which iodine is dissolved, and mounted in chloroform balsam 

 containing some iodine. The glycogen is stained brown, and is most abundant 

 in the cells around the radicals of the hepatic vein. 



4. Phenyl-Hydrazine Test for Sugars. To 5 c.c. of the suspected fluid (e.g. 

 diabetic urine) add 1 decigramme of phenyl-hydrazine hydrochloride, 2 deci- 

 grammes of sodium acetate, and heat on the water-bath at 100 C. for 30 to 

 60 minutes. On cooling, if not before, a crystalline or amorphous precipitate 

 separates out. If amorphous, dissolve it in hot alcohol ; dilute the solution 

 with water, and boil to expel the alcohol, whereupon the osazone separates 

 out in yellow crystals. Examine the crystals with the microscope (see 

 accompanying plate). 



Dextrose gives a precipitate of phenyl-glucosazone C 6 H 10 4 (N 3 H.C 6 H 3 ) i , 

 which crystallises in yellow needles (melting-point 205 C.). 



Levulose yields an osazone identical with this. 



Galactose yields a very similar osazone (phenyl-galactosazone). It differs 

 from phenyl-glucosazone by melting at 190-193, and in being optically in- 

 active when dissolved in glacial acetic acid. 



Cane sugar does not form a compound with phenyl-hydrazine. 



Lactose yields phenyl-lactosazone C ]3 H. 20 O d (N 3 H.C H 5 ), r It crystallises 

 in needles, usually in clusters (melting-point 200 C.). It is soluble in 

 80-90 parts of boiling water. Lactose in urine does not give this test 

 readily. 



Maltose yields phenyl-maltosazone (C 24 H 32 N 4 O y ). It crystallises in yellow 

 needles much wider than those yielded by glucose or lactose (melting-point 

 206 ^ C.). Unlike phenyl-glucosazone, it dissolves in 75 parts of boiling water, 

 and is still more soluble in hot alcohol. 



The chemistry of the. phenyl-hydrazine reaction is represented in the 

 following equations, dextrose being taken as an example of the sugar used : 



I. CH 3 OH[CH(OH)] 3 CH(OH)COH + H,N.NH(C 6 H 5 ) 



[dextrose] [phenyl-hydrazine] 



CH,OH[CH(OH)] 3 CH(OH)CH 



II + H. 2 



N-NH(C 6 H,) 



[hydrazone] [water] 



II. CH. 2 OH[CH(OH)] S CH(OH)CH 



|| +C 6 H,.NH-NH,, 



N-NH(C 6 H 5 ) 



[hydrazone] [phenyl-hydrazine] 



CHoOH [CH(OH)] 3 C - CH 



II || + a, + H O O 



C 6 H 5 .NH-N N-NH.C (i H, 



[osazone] [hydrogen] [water] 



N 



