6 ESSENTIALS OF PHYSIOLOGY. 



and Benedict. Dextrose has also the power of reducing acid solutions 

 of cupric salts, differing in this respect from reducing sugars which 

 belong to the class of disaccharides. On being heated with phenyl- 

 hydrazine and acetic acid, dextrose forms a compound, phenylglucosazone, 

 which crystallises in yellow needles, generally arranged in loose sheaves. 

 Solutions of dextrose are decomposed by the action of yeast into carbonic 

 acid and alcohol. Further, dextrose is dextro-rotatory, that is, its 

 solutions rotate the plane of polarised light to the right. 



Lsevulose (fructose) and galactose occur in the body in smaller 

 quantity. The former is Isevo-, the latter dexto-rotatory. Like dextrose, 

 they have the property of reducing alkaline solutions of cupric salts, 

 and they also form osazones. 



Dextrose and galactose are aldehydes and are known as aldoses, 

 while leevulose is a ketone and belongs to the group of ketoses. 



CHO CH 2 OH CHO 



H.C.OH CO H.C.OH 



I I I 



HO.C.H HO.C.H HO.C.H 



I I ! 



H.C.OH H.C.OH HO.C.H 



I I 



H.C.OH H.C.OH H.C.OH 



CH 2 OH CH 2 OH CH 2 OH 



Dextrose Lsevulose Galactose 



The only disaccharide which occurs in the body is lactose, the sugar 

 of milk. Two other disaccharides, cane sugar and maltose, are of 

 physiological importance, the former being an important food-stuff, 

 the latter an intermediate stage in the digestion of starch. Lactose 

 and maltose are reducing sugars and form characteristic osazones. 

 Each of the three, when boiled with dilute mineral acid, undergoes 

 hydrolysis, the molecule taking up water and being split into two 

 molecules of a monosaccharide. 



The polysaccharide, glycogen or animal starch, occurs chiefly in the 

 liver and muscles as a storage product. Its solution in water differs 

 from that of vegetable starch, which is also a polysaccharide (1) in 

 that it is more markedly opalescent than that of the latter, and (2) 

 in giving a reddish brown colour with iodine, whereas vegetable starch 

 gives a blue colour. The polysaccharides do not reduce alkaline solu- 

 tions of cupric salts. They undergo hydrolysis when boiled with dilute 

 mineral acid or as the result of ferment action, yielding first poly- 



