22 PHYSIOLOGICAL CHEMISTRY. 



III. Trisaccharides, C 18 H 32 O 1G . 



i. Raffinose. 



IV. Polysaccharides, (C 6 H 10 O 5 ) X . 



1. Starch Group. 



(a) Starch. 



(b) Inulin. 



(c) Glycogen. 



(d) Lichenin. 



2. Gum and Vegetable Mucilage Group. 



(a) Dextrin. 



(b) Vegetable Gums. 



3. Cellulose Group. 



(a) Cellulose. 



(b) Hemi-Cellulose. 



Each member of the above carbohydrate classes, except the mem- 

 bers of the pentose group, may be supposed to contain the group 

 C 6 H 10 O 5 called the saccharide group. The polysaccharides consist 

 of this group alone taken a large number of times, whereas the 

 disaccharides may be supposed to contain two such groups plus a 

 molecule of water, and the monosaccharides to contain one such 

 group plus a molecule of water. Thus, (C 6 H 10 O 5 ) x = polysac- 

 charide, ( C 6 H 10 O 5 ) 2 + H 2 O == disaccharide, C 6 H 10 O 5 + H 2 O 

 = monosaccharide. In a general way the solubility of the carbo- 

 hydrates varies with the number of saccharide groups present, the 

 substances containing the largest number of these groups being 

 the least soluble. This means simply that, as a class, the monosac- 

 charides (hexoses) are the most soluble and the polysaccharides 

 (starches and cellulose) are the least soluble. 



MONOSACCHARIDES. 



Hexoses, C 6 H 12 6 . 



The hexoses are monosaccharides containing six oxygen atoms 

 in the molecule. They are the most important of the simple sugars, 

 and two of the principal hexoses, dextrose and laevulose, occur 

 widely distributed in plants and fruits. Of these two hexoses, 

 dextrose results from the hydrolysis of starch whereas both dextrose 

 and laevulose are formed in the hydrolysis of sucrose. Galactose, 

 which with dextrose results from the hydrolysis of lactose, is also 



