98 GLYCOGEN. 



The hydrolytic products obtained by the action of enzymes and 

 dilute boiling acids on glycogen have not been as fully studied as 

 they have in the case of starch, but the general course of the de- 

 composition is the same in both cases. Thus when treated with 

 dilute mineral acids at 100C., the opalescence disappears, some, 

 dextrin is formed en passant, and finally the solution contains 

 only dextrose. 1 On the addition of saliva or pancreatic juice to 

 a solution of glycogen at 40, the first change observed is an im- 

 mediate disappearance of the opalescence, followed by a rapid con- 

 version into some form of dextrin and a considerable proportion 

 of a sugar which is apparently identical with maltose. 2 Some 

 trace of dextrose may perhaps at the same time be formed. 



The change which glycogen in the liver undergoes post-mortem 

 and presumably also during life is strikingly different from that 

 which has been described above. Whereas by ordinary enzyinic 

 hydrolysis, maltose is the chief final product obtained, there is 

 now no doubt that in the liver little if any maltose is formed, the 

 so-called liver-sugar being apparently identical with true dex- 

 trose. This fact throws considerable light on the mode of con- 

 version of glycogen into sugar by the liver. It has been most 

 usually taught that this conversion is due to some fermentative 

 action ; if this were so then the enzyme which is the active agent 

 must be possessed of powers differing from those of most other 

 enzymes since it forms dextrose and not maltose. But as a mat- 

 ter of fact it does not appear possible to extract any appreciable 

 quantity of enzyme from the liver, and if a trace is obtained it is 

 of one whose action on starch and glycogen yields chiefly maltose 

 and not dextrose. It is hence a legitimate conclusion that the 

 conversion of glycogen into sugar by the liver is the outcome of 

 the specific metabolic activity of the hepatic cells, and not of any 

 enzymic action. 3 It is also significantly probable, from what has 

 been already said (see above, p. 59), that the liver receives its 

 carbohydrates supplied in the form of dextrose, and there is no 

 doubt that diabetic sugar is closely related to, if not identical 

 with, true dextrose. 



The dextrin which some observers have obtained from muscles is 

 not to be regarded as a specific constituent, but as formed from their 

 glycogen by some post-mortem change. Horse-flesh is peculiarly rich 

 in glycogen, and it was chiefly from this source that dextrin was ob- 

 tained in large amount. 4 



1 Maydl, Zt. f. physiol. Chem. Bd. HI. (1879), S. 194. Kiilz u. Borntrager, 

 Pfluger's Arch. Bd. xxiv. (1881), S. 28. Seegen, Ibid. Bd. xix. (1879), S. 106. 



2 Musculus u. v. Mering, Zt. f. physiol. Chem. Bd. u. (1878), S. 403. Seegen, 

 loc. cit. Kiilz, Pfluger's Arch. Bd. xxiv. (1881), S. 81. 



3 Eves. JL of Physiol. Vol. v. (1884), p. 342 (contains lit. to date). See more 

 recently Langendorff, Arch. f. Physiol. 1886. Suppl.-Bd. S. 277. Panormow, Klin. 

 Wochenb. 1887, No. 27. Dastre, Arch, de Physiol (4) T. i. (1888), p. 69. 



* Limpricht, Liebig's Ann. Bd. cxxxm. (1865), S. 293. 



