CARBOHYDRATES 77 



gives no color. This is the achroodextrin stage (Greek word 

 means "no color"). Beyond this stage maltose is formed, 

 which then breaks up into glucose. The appearance of reducing 

 sugars may be recognized, since the mixture will reduce Feh- 

 ling's solution. 



Starch is an enormously important food substance, and is 

 widely used in the arts. In stiffening linen, the starch is broken 

 down into dextrins by the heat of the iron. These dextrins 

 give the fabric its stiffness and glossy appearance. 



Dextrins. Little need be said of the dextrins in addition to 

 the fact that they are intermediate stages formed in the hydrol- 

 ysis of starch to glucose. There probably are many members 

 of the group, but so far, little is known of the different individ- 

 ual dextrins. Dextrins themselves probably do not reduce Feh- 

 ling's solution, or only slightly, but commercial dextrin, which 

 is prepared by the partial hydrolysis of starch, usually reduces 

 Fehling's solution slightly, probably because the mixture con- 

 tains maltose or glucose as the result of complete hydrolysis of 

 some of the material. Dextrin solutions do not ferment, and 

 give a red color (erythrodextrin) or no color (achroodextrin) 

 with iodine according to the extent of the hydrolysis. Dex- 

 trins are readily soluble in water, but are precipitated by the 

 addition of alcohol. The aqueous solution is dextrorotatory. 



Inulin. Inulin occurs in the sap of various plants and is 

 found to the extent of 10-12% in the tubers of the dahlia. It 

 is soluble in hot water, and gives a yellow or brownish color 

 with iodine. It is interesting chiefly because on hydrolysis it 

 yields levulose instead of glucose. It does not reduce Fehling's 

 solution, and its solution is levorotatory. 



Gums and Mucilages. The gums and mucilages are widely 

 distributed and on hydrolysis yield various pentoses and hex- 

 oses, and other substances. They vary greatly in their solubil- 

 ities. 



Cellulose. Cellulose is chiefly important in forming a large 

 part of the structural framework of plants. The plant cell walls 

 are made up of cellulose mixed with lignin and other sub- 



