732 CARBOHYDRATES. [APP. 



in water, but is precipitated by alcohol. It does not undergo alcoholic 

 fermentation until after it has been changed into dextrose, nor can it 

 reduce metallic salts. It yields a reddish port-wine colour with iodine, 

 which disappears on warming and does not return on cooling. Further 

 action of acids or of ferments converts dextrin into dextrose. Dextrin 

 is present in the contents of the alimentary canal after a meal containing 

 starch, and has also been found in the blood. 



There is not the least doubt that several modifications of dextrin 

 exist and may be obtained by the action of acids and ferments on starch. 

 Of these two of the best known are those described by Briickei under 

 the name of erythrodextrin and achroodextrin, the former giving a red 

 colour with iodine, the latter not yielding any colour at all. Erythro- 

 dextrin may be readily converted into a sugar by the action of ferments, 

 and thus is not found as a product of the complete action of ptyalin on 

 starch. Achroodextrin on the other hand is not thus converted by 

 ferments, and therefore remains in solution, together with the sugar 

 formed by the action of ptyalin on starch. Achroodextrin may be con- 

 verted into dextrose by boiling with dilute hydrochloric acid. 



6. Glycogen. C 6 H 10 O 5 . 



Belongs to the starch division of carbohydrates. Discovered by 

 Bernard in the liver and other organs (see p. 416). 



Glycogen is, when pure, an amorphous powder, colourless, and taste- 

 less, readily soluble in water, insoluble in alcohol and sether. Its 

 aqueous solution is generally though not always strongly opalescent, but 

 contains no particles visible microscopically ; the opalescence is much 

 reduced by the presence of free alkalis. The same solution possesses, 

 according to Hoppe-Seyler, a very strong dextro-rotatory power, about 

 three times as great as that of dextrose 8 ; it dissolves hydrated cupric 

 oxide ; but this is not reduced on boiling. 



By the action of dilute mineral acids (except nitric) it is partially 

 converted into a form of sugar very closely resembling, though probably 

 differing somewhat from true dextrose, and the same conversion is also 

 readily effected by the action of amylolytic ferments. The sugar into 

 which the glycogen of the liver is naturally converted after death (see 

 p. 424), appears to be true dextrose 3 ; so also the sugar of diabetes. 

 The result of the action of diastase, or salivary or pancreatic ferment, 

 upon glycogen is however according to Musculus and v. Mering 4 a 



1 Sitzber. d. Wien. AJcad. 1872, in. AUli. Also Vorlesungen 2. Aufi. 1875, Bd. i. 

 S. 224. 



2 See Kiilz, Pfliiger's Arch. Bd. xxiv. (1881), S. 85. 



s Pfliiger's Arch. Bd. xix. (1879), S. 106, and xxn. (1880), S. 206. Also Kiilz, 

 Ibid. Bd. xxiv. (1881), S. 52. 



* Zeitschr. f. physiol. CJiem. Bd. n. (1878), S. 403. 



