10 NUTRITION OF FARM ANIMALS 



Glucosids 



11. The monosaccharids not only occur in the free state but 

 also in combination with a great variety of substances in the 

 so-called glucosids. The glucosids readily undergo hydrolytic 

 cleavage into their two (or more) constituents, either by the 

 action of chemical reagents or of enzyms. For example, the 

 amygdalin of the bitter almond yields two molecules of dextrose, 

 one of benzaldehyd and one of hydrocyanic acid, and cerebron, 

 a constituent of the brain, splits up into cerebronic acid, sphin- 

 gosin and galactose. Among other more or less familiar glucosids 

 may be mentioned salicin, saponin, phloridzin and digitalin. 



Disaccharids 



12. The hexose group. The disaccharids may be regarded 

 as polymers or anhydrids of the monosaccharids, formed by the 

 union of two molecules of the latter with the elimination of one 

 molecule of water. The only disaccharids at present known be- 

 long to the hexose group and their formation may be repre- 

 sented by the equation C 6 Hi 2 O 6 + C 6 Hi 2 O 6 = Ci 2 H 22 On + H 2 O. 

 From another point of view they are termed by some writers 

 glucosids of the monosaccharids. 



Sucrose. Sucrose, or cane sugar, has probably been longest 

 known of the more familiar carbohydrates. It is found in the 

 juices of the sugar cane and sorghum, in the sugar beet and in 

 the sap of the maple, all of which are utilized as commercial 

 sources of sugar. In smaller amounts it is present in a large 

 number of plants. 



By the action of heat, aided by a dilute acid or alkali, or by 

 the action of certain enzyms, notably the invertase of yeast, 

 the reverse of the general reaction for the formation of the 

 disaccharids may be brought about, one molecule of sucrose 

 combining with one molecule of water to yield one molecule 

 each of dextrose and levulose. 



Ci 2 H 22 Oii + H 2 O = C 6 Hi20 6 + C 6 Hi 2 O 6 



Sucrose rotates the plane of polarized light to the right, 

 while, owing to the fact that the rotatory power of levulose is 

 greater than that of dextrose, the mixture of equal parts of the 

 two which is formed in the foregoing reaction rotates to the 



