FOOD AND DIGESTION 331 



By the polymerisation of two monosaccharid molecules with 

 the loss of water, disaeeharids, or double sugars, are formed. 

 Thus, two glucose molecules polymerise to form one maltose 

 molecule. 



C a H 12 O e + C fl H ls O e =2 (C 6 H 12 6 )-H 2 



= C 12 H 2-211 



Maltose is the sugar formed by the action of malt and other 

 vegetable and animal zymins upon starch. By the action 

 of dilute acids and other agents it can be split into two 

 dextrose molecules. Like the rnonosaccharids, it ferments 

 with yeast. 



Lactose, the sugar of milk, is a disaccharid composed of a 

 molecule of dextrose united to a molecule of galactose with 

 dehydration. It readily splits into these two rnonosaccharids, 

 but does not ferment with yeast. 



Dextrose, polymerising with l^evulose, yields cane sugar, 

 and this sugar, so largely used as an article of food, can 

 be split into dextrose and Isevulose. It does not reduce 

 Fehling's solution, and does not ferment with yeast. Under the 

 action of mineral acids it breaks down into its component 

 sugars. 



By further polymerisation of monosaccharids with the loss 

 of water, molecules of greater size are produced and form the 

 set of substances known as the polysaeeharids. Among the 

 simplest of these are the dextrins. 



Closely allied to dextrins are the inulins. But while dextrin 

 is formed of dextrose molecules, inulin contains laevulose 

 molecules. Both are formed from the splitting of the more 

 complex starches. The molecule of soluble starch is built up 

 of no less than thirty dehydrated monosaccharid molecules, 

 and has a molecular weight of 9000. Ordinary starch seems 

 to have a molecular weight of 20,000 or 30,000, and hence 

 must be of still greater complexity. 



These polysaeeharids are distinguished from the sugars by 

 being precipitated from their solutions by the addition of 

 alcohol. They are not oxidised when boiled with caustic 

 potash, nor do they change to alcohol and carbon dioxide 



