THE CARBOHYDRATES AND FATS 



15 



Fig. 4. -Section of pea sliowing starch 

 and aleurone grains embediled in the 

 protoplasm of the cells : a, aleurone 

 jrrains ; st, starch grains ; i, inter- 

 cellular spaces. (Yeo, after Sachs.) 



By the action of diastatic ferments, maltose is the chief end product. 

 In both cases dextrin is an intermediate stage in the process. 



Before the formation of dextrin the starch solution loses its opal- 

 escence, a substance called soluble starch or amidulin being formed. 

 This, like native starch, gives a blue colour with iodine. Although the 

 molecular weight of starch is unknown, 

 the formula for soluble starch is probably 

 (C6H,o05)2oo- Equations that represent 

 the formation of sugars and dextrins 

 from this are very complex, and are at 

 present hypothetical. 



Dextrin is the name given to the 

 intermediate products in the hydration 

 of starch, and two chief varieties are 

 distinguished — erythro-dcxtrin, which 

 gives a reddish-brown colour with 

 iodine ; and achroo-dextrin, which does 

 not. 



It is readily soluble in water, but 

 insoluble in alcohol and ether. It is 

 gummy and amorphous. It does not 

 does it ferment with yeast. It is dextro-rotatory, 

 agencies it is converted into glucose. 



Glycogen, or animal starch, is found in liver, muscle, and colour- 

 less blood corpuscles. It is also abundant in all embryonic 

 tissues. 



Glycogen is a white tasteless powder, soluble in water, but it 

 forms, like starch, an opalescent solution. It is insoluble in alcohol 

 and ether. It is dextro-rotatory. With Trommer's test it gives a 

 blue solution, but no reduction occurs on boiling. 



With iodine it gives a reddish or port-wine colour, very similar to 

 that given by erythro-dextrin. Dextrin may be distinguished from 

 glycogen by (1) the fact that it gives a clear, not an opalescent, 

 solution with water; and (2) it is not precipitated by basic lead 

 acetate as glycogen is. It is, however, precipitated by basic lead 

 acetate and ammonia. (3) Glycogen is precipitated by 55 per cent, 

 of alcohol ; the dextrins requu-e 85 per cent, or more. 



Cellulose. — This is the colourless material of which the cell-walls 

 and woody fibres of plants are composed. By treatment with 

 strong mineral acids it is, like starch, converted into glucose, but 

 with much greater difficulty. The various digestive ferments have 

 little or no action on cellulose ; hence the necessity of boiling starch 



give 



Trommer's test, nor 

 By hydrating 



