THE CARBOHYDRATES 73 



a glucoside of glucose, lactose as the ft galactoside of glucose. The 

 mode of combination of the two hexose groups to form these disac- 

 charides may be represented as follows : 



H H OH H 



CH 2 OH C C C C 



OH X H OH 



H 



C glucose rest 



HO H HO HO 



OHO C C C C CH 2 glucose rest 

 H OH H H 



maltose. 



H 

 CH 2 OH C C C - - C C galactose rest ) 



OH H H OH 







lactose. 



HO H HO HO 



OHC C C C C CH 2 glucose rest 

 H OH H H 



A very large number of glucosides occur as plant products. Among 

 these we may mention amygdalin, salicin, phloridzin, indican, &c. 



THE DISACCHARIDES 



The disaccharides are formed by the union of two molecules of 

 monosaccharides with the elimination of one molecule of water, and 

 can be regarded, according to the manner in which the molecules 

 are combined, as glucosides, galactosides, &c. On hydrolysis, e.g. 

 on heating with acids, they take up one molecule of water and are split 

 up into the corresponding monosaccharides. Thus, cane sugar gives 

 equal parts of glucose ani fructose, maltose gives equal parts of glucose 

 and glucose, while milk sugar or lactose gives equal parts of glucose 

 and galactose. 



CANE SUGAR, sometimes known as saccharose, is widely dis- 

 tributed throughout the vegetable kingdom, and forms an important 

 article of diet. It has no reducing power on Fehling's solution. It is 

 strongly dextro-rotatory and has a specific rotatory power of -f 66-5. 

 On hydrolysis it is converted into equal molecules of glucose and 



