CAKBOHYDEATES 141 



2. Examine the washings of the liver in the beakers a, 6, and c for sugar. 

 This may be done in a rough quantitative manner as follows : — Take equal 

 quantities of a, b, and c in three test-tubes ; to each add an equal amoimt of 

 Fehling's solution, and boU : a will give a heavy precipitate, 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 parafi&n. If parafl&n 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 radicles 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- 

 granunes of sodium acetate, and heat on the water-bath for half an hour. 

 On cooling, if not before, a crj'stalline 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 (CigH^oN^O^), 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 dififers 

 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 (Co^HogN^Oy). It crystallises readily 

 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.,,H3.,N^0y). 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. 



Isomaltose is a sugar formed at the same time as maltose by the action of 

 diastase, ptyalin, and amylopsin on starch. It is also an intermediate 

 product in the formation of dextrose by mineral acids from starch. An 

 amylolytic ferment in blood serum, capable of forming dextrose from starch, 

 acts similarly. It is readily soluble in water, is very sweet, and ferments 

 very slowly with yeast. Its formula and general characters are like 

 those of maltose, but its osazone forms fine yellow needles, which melt at 

 150° C. 



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

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

 used : — 



