THE CARBOHYDRATES 23 



when malted grain is "mashed" with warm water in brewing. 

 On hydrolysis with dilute acids it is split up into two molecules 

 of dextrose. This change is not produced by any further 

 action of diastase, and as yeast converts it into alcohol it was 

 thought that maltose was directly fermentable. It is not 

 improbable, however, that yeast contains an enzyme capable 

 of hydrolysing the maltose, and that such a change actually 

 occurs before fermentation. The specific rotatory power 



[4> = + i37. 



Maltose reduces Fehling's solution. It is considered 

 probable, therefore, that it contains an aldose group, and that 

 the molecular structure is similar to that of lactose. 



Amyloses or Polysaccharides. This group includes all 

 carbohydrates of definite composition corresponding to the 

 empirical formula C 6 H 10 O 5 . They are frequently called 

 polysaccharides because they are all resolved ultimately into 

 hexoses on treatment with hydrolytic agents. 



C 6 H 10 5 + H 2 = C 6 H 12 6 



They cannot, however, be regarded as simple anhydro- 

 aggregates like the bioses and trioses. They are quite unlike 

 the sugars in general characteristics, and one type at least, 

 cellulose, is believed to be a ring compound. Nothing is 

 known of the molecular weights except that it is a multiple of 

 162 and the formula can only be written (C 6 H 10 O 5 ) rt . 



The most important members of the group are: (i) starch 

 and cellulose, which are insoluble and exhibit an organised 

 structure characteristic of the particular plants from which 

 they are derived; (2) dextrine, inulin, and glycogen, which are 

 amorphous and soluble in water. 



Starch. Starch occurs in the leaves and green parts of 

 nearly all plants. It is rapidly formed in bright sunlight when 

 the plant is in a state of active growth, and is one of the first 

 visible products of metabolism. In many cases it is stored up 

 in seeds and in stems, roots, tubers, etc. It is obtained by 

 disintegrating the cellular tissues and washing with water on 

 a fine sieve through the meshes of which the starch escapes 

 The water is then poured off and the starch is dried (p. 282). 



