60 



A TEXTBOOK OF PHYSIOLOGY 



from the variety known as insoluble starch into soluble starch. The 

 solution yields a characteristic blue colour with iodine solution, which, 

 if sufficient starch be present, disappears on heating, and reappears 

 on cooling. 2-5 to 4-6 per cent.. solutions exhibit a rotatory power of 

 about + 202. Starch gives neither Moore's nor Trommer's test, and 

 none of the other reduction tests. 'It does not ferment with yeast. 

 Upon boiling with dilute acid, or under the action of the group of 

 enzymes known as diastases, it is split first into dextrins and then 

 into sugars, maltose being formed as the result of enzyme action, 

 dextrose by the action of the acids. Starches are " salted out " by 

 half -saturation with ammonium sulphate. They are also precipitated 

 from their solutions by 50 to 55 per cent, alcohol. In some plants, 

 such as the tubers of the dahlia, a special variety of starch known 

 as inulin occurs. It forms an amorphous white powder, differing 

 from ordinary starch in giving a yellow colour with iodine solution, 

 and yielding levulose on hydrolysis with acid. Diastatic enzymes have 

 little or no effect on this body. 



Glycogen, or animal starch, found chiefly in the liver of animals, is 

 obtained as a white amorphous powder soluble to an opalescent solu- 

 tion in water. It gives a mahogany brown colour with iodine, is pre- 

 cipitated from solution by 60 per cent, alcohol and basic lead acetate. 



CHARACTERISTIC REACTIONS OF POLYSACCHARIDES. 



Dextrins (C 6 H 10 5 )w. These are the first products of the hydro- 

 fysis of starches produced by the action of weak acids or of starch- 



