PLANT CONSTITUENTS — CARBOHYDRATES 271 



ence is in the hexose monosaccharoses which they yield on 

 hydrolysis. Starch and dextrin each yield glucose or dextrose 

 and are, therefore, both termed dextrosans or glucosans. 

 Inulin, on the other hand, yields levulose and is termed a 

 levulosan. Similarly, the ftiannans or mannosans are starch- 

 like polysaccharoses which yield mannose and the galactosans 

 or galactans yield galactose. 



Dextrin. — The most important member of the group is 

 dextrin. It occurs in quantity only in a few plants, for it is a 

 transitory substance in the enzymatic hydrolysis of starch by 

 diastase. In the chapter on salivary digestion (Chapter XI), 

 the formation of dextrin in its several forms as an intermediate 

 substance in the hydrolysis of starch to maltose sugar by 

 ptyalin has been fully discussed. It differs from starch in 

 being soluble in cold water. As a food substance it has the 

 same value as starch. 



It may be prepared by the action of enzymes on starch or 

 by heating starch to 23o°-26o° C. In this latter way it is 

 made for industrial use. We spoke of the use of starch as a 

 sizing material for cloth and paper. Strictly speaking, except 

 in laundering, it is not starch, but dextrin, made as above, 

 which is generally used in this way. It is also used as an ad- 

 hesive gum or mucilage. 



Glycogen. — This compound may be referred to in this con- 

 nection, for it is also a glucosan. It does not occur in green 

 plants, but is found in some fungi, especially yeast, and in 

 some other cryptogamous plants. It is known as animal starch 

 and has been discussed in connection with the metabolism of 

 carbohydrates in animals (Chapter XII). 



Inulin. — This isomer of starch differs from it and from 

 dextrin in yielding only levulose on hydrolysis. Like starch it 

 is a reserve food in certain plants, especially the dahlia, where 

 it occurs in the tubers. It is also present in the artichoke 

 and in cherry roots. It is not hydrolyzed by diastase or ptyalin 

 and is, therefore, undigested by animals. The enzyme which 

 hydrolyzes it is known as inulase. 



