222 THE CARBOHYDRATES. 



of the Dahlia, the varieties of Helianthus, etc. It is ordinarily obtained 

 from the tubers of the Dahlia. 



Inulin forms a white powder similar to starch, consisting of spheroid 

 crystals which are readily soluble in warm water without forming a paste. 

 It separates slowly on cooling, but more rapidly on freezing. Its solu- 

 tions are levogyrate and are precipitated by alcohol, and are colored 

 only yellow with iodine. Inulin is converted into the levogyrate mono- 

 saccharide aMevulose on boiling with dilute sulphuric acid. Diastatic 

 enzymes have no, or only a very slight, action on inulin. 1 



According to DEAN 2 inulin occurs in combination with other substances, 

 levulins, which are more soluble and have less rotation. He suggests that we 

 limit the name inulin to that carbohydrate (or mixture of carbohydrates), 

 which is readily precipitable by 60-per cent alcohol and shows a specific rota- 

 tion of ()D= -38-40. 



Lichenin (MOSS-STARCH) occurs in many lichens, especially in Iceland moss. 

 It is not soluble in cold water, but swells up into a jelly. It is soluble in hot 

 water, forming a jelly on allowing the concentrated solution to cool. It is colored 

 yellow by iodine and yields glucose on boiling with dilute acids. Lichenin is 

 not changed by diastatic enzymes such as ptyalin or amylopsin (NiLSON 3 ) . 



Glycogen. This carbohydrate, which stands to a certain extent 

 between starch and dextrin, is principally found in the animal kingdom, 

 hence it will be considered in a subsequent chapter (on the liver) . 



Dextrins and Gums. 



The dextrins stand in close relation to the starches, and are formed 

 therefrom as intermediate products by the action of acids or diastatic 

 enzymes. They yield as final products only hexoses, indeed only dex- 

 trose, on complete hydrolysis. The vegetable gums, the vegetable 

 mucilages and the pectin bodies, which all stand close to the hemicellu- 

 loses, yield, on the contrary, abundance of pentose and, among the hex- 

 oses, a galactose is very often found. 



Dextrin (starch-gum, British gum) is produced on heating starch to 

 200-210 C., or by heating starch, which has previously been moistened 

 with water containing a little nitric acid, to 100-110 C. Dextrins are 

 also produced by the action of dilute acids and diastatic enzymes on 

 starch. There have been numerous investigations as to the steps 

 involved in the last-mentioned process, but they have led to conflicting 

 views. One of these, which used to be generally accepted, is as follows: 

 The first product, which gives a blue color with iodine, is soluble starch 

 or amylodextrin, which on -further hydrolytic cleavage yields sugar and 

 erythrodextrin, which is colored red by iodine. On further cleavage of 

 this erythrodextrin more sugar and a dextrin, achroodextrin, which is 

 not colored by iodine, is formed. From this achroodextrin after suc- 

 cessive splittings we have sugar and dextrins of lower molecular weights 



Pollen's Handbuch, 208. 2 Amer. Chem. Journ., 32. 8 Upsala Lakaref. Forh., 28. 



