DEXTRINS. 229 



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 glu- 

 cose, 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, 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 

 formed, until finally we have sugar and a dextrin, maltodextrin, which 

 refuses to split further, as final products. The views are rather contra- 

 dictory in regard to the number of dextrins which occur as intermediate 

 steps. The sugar formed is maltose (or in first place isomaltose), and 

 only very little glucose is produced. Another view is that first several 

 dextrins are formed consecutively in the successive splittings, by hydra- 

 tion, and then finally the sugar is formed by the splitting of the last 

 dextrin. According to MOREAU, in the first stages of saccharification 

 amylodextrin, erythrodextrin, achroodextrin and sugar are formed sim- 

 ultaneously. Other investigators, especially SYNIEWSKI, have recently 

 suggested other views on the subject. 1 



This question has taken another direction by the investigations of 



1 In regard to the various views on the theories of the saccharification of starch; 

 see Musculus and Gruber, Zeitschr. f. physiol. Chem., 2; Lintner and Dull, Ber. d. d. 

 chem. Gesellsch., 26 and 28; Brown and Heron, Journ. of Chem. Soc., 1879; Brown 

 and Morris, ibid., 1885 and 1889; Moreau, Biochem. Centralbl., 3, 648; Syniewski, 

 Annal. d. Chem. u. Pharm., 309, and Chem. Centralbl., 1902, 2. 



