20 PHYSIOLOGICAL CHEMISTRY 



IV. Polysaccharides, (C 6 Hi 5 ) x . 



1. Gum and Vegetable Mucilage Group. 



(a) Dextrin. 



(6) Vegetable Gums. 



2. Starch Group. 



(a) Starch. 



(b) Inulin. 



(c) Glycogen. 



(d) Lichenin. 



3. Cellulose Group. 



(a) Cellulose. 



(b) Hemicelluloses. 



(1) Pentosans. 



Gum Arabic. 



(2) Hexosans. 



Gal ac tans. 

 Agar-agar. 



Each member of the above carbohydrate classes, except the members 

 of the pentose group, may be supposed to contain the group CeHioC^, 

 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 HioO 5 ) x = polysaccharide, (C 6 Hi O 5 )2 + H 2 disacchar- 

 ide, CeHioOs + H 2 > monosaccharide. In a general way the solu- 

 bility of the carbohydrates 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 mono- 

 saccharides (hexoses) are the most soluble and the polysaccharides 

 (starches and cellulose) are the least soluble. 



MONOSACCHARIDES 



Hexoses, C 6 Hi 2 O 6 



The hexoses are monosaccharides containing six oxygen atoms in a 

 molecule. They are the most important of the simple sugars, and two 

 of the principal hexoses, glucose and fructose, occur widely distributed 

 in plants and fruits. Of these two hexoses, glucose results from the 

 hydrolysis of starch, whereas both glucose and fructose are formed in 

 the hydrolysis of sucrose. Galactose, which with glucose results from 

 the hydrolysis of lactose, is also an important hexose. These three 

 hexoses are fermentable by yeast, and yield levulinic acid upon heating 



