THE POLYSACCHARIDES. 61 



achroodextrin appears later, and from this isomaltose, maltose, and 

 glucose are finally obtained. It appears, however, that during the 

 decomposition of achroodextrin at least still other dextrins of lower 

 molecular weight are simultaneously formed, which in turn yield 

 maltose and glucose. But finally one dextrin is obtained which 

 undergoes no further change, and which is termed maltodextrin. 



Most characteristic is the behavior of starch toward iodine, with 

 which it gives an intense blue color that disappears on heating, but 

 reappears on cooling. In a solution of sodium or potassium hydrate 

 starch swells up and forms a paste. 



Inulin and lichenin, which also belong to the starches, and which 

 occur in the roots of various composites and in lichens, respectively, 

 are insignificant as food-stuffs and need not be considered. 



Glycogen, which likewise belongs to this class, and is known also 

 as animal starch, is largely formed in the animal body and represents 

 one of its most important constituents. It will be considered in 

 detail in a subsequent chapter. 



Dextrins. -The dextrins, as has been shown, are formed from 

 starch during its hydrolytic decomposition by means of ferments or 

 on boiling with dilute mineral acids. To a certain extent they 

 result also when starch is heated to a temperature of from 200 

 to 210 C. Through continued decomposition they give rise to 

 maltose and isomaltose, and finally to glucose. 



As a class the dextrins are easily soluble in water and turn the 

 plane of polarization to the right. From the other polysaccharides 

 they differ in their ability to dissolve cupric hydroxide in alkaline 

 solution. With erythrodextrin iodine strikes a red color, while 

 achroodextrin is unaffected. 



The so-called vegetable gums and vegetable mucins will not be 

 considered, as they are of no importance as food-stuffs. To this 

 class belong the so-called gum Arabic, wood gum, cherry gum, etc., 

 as also the various pectins. 



Celluloses. As food-stuffs the celluloses are likewise of second- 

 ary importance. They are considered, however, at this place owing 

 to their wide distribution in the vegetable world, where they form 

 the greater portion of all cell-envelopes. In the animal world 

 they are likewise encountered, and enter largely into the composi- 

 tion of the external skeleton of the tunicates, the arthropods, and 

 some of the cephalopods. They are characterized by their extreme 

 resistance to the most divers solvents, and are indeed soluble only in 

 a solution of cupric hydroxide in strong ammonia the so-called 

 Schweitzer's reagent. From this solution the substance can be 

 obtained in amorphous form on precipitation with acids. Moder- 

 ately concentrated sulphuric acid transforms cellulose into vegetable 

 amyloid, which is colored blue by iodine. With concentrated nitric 

 acid, or with a mixture of nitric acid and concentrated sulphuric 

 acid, it yields the highly explosive nitrocelluloses. 



Wood (lignin) and cork are derivatives of cellulose. On hydro- 



