392 THE LIVER. 



ammoniacal basic lead acetate. An aqueous solution of glycogen made 

 alkaline with caustic potash (15 per cent KOH) is completely precipitated 

 by an equal volume of 96 per cent alcohol. Tannic acid also precipitates 

 glycogen. It gives a white granular precipitate of benzoyl-glycogen 

 with benzoyl chloride and caustic soda. Glycogen is completely pre- 

 cipitated by saturating its solution at ordinary temperatures with magne- 

 sium or ammonium sulphate. It is not precipitated by sodium chloride, 

 or by half saturation with ammonium sulphate (NASSE, NEUMEISTER, 

 HALLIBURTON, YouNG 1 ). On boiling with dilute caustic potash (1-2 

 per cent) the gh r cogen may be more or less changed, especially if it has 

 been previously exposed to the action of acid or to BRUCKE'S reagent 

 (see below) (PFLUGER). On boiling with stronger caustic potash (even 

 of 36 per cent) it is not injured (PFLUGER). By diastatic enzymes 

 glycogen is converted into maltose or glucose, depending upon the nature 

 of the enzyme. It is transformed into glucose by dilute mineral acids. 

 According to TEBB 2 various dextrins appear as intermediary steps in 

 the saccharification of glycogen, depending on whether the hydrolysis 

 is caused by mineral acids or enzymes. The glycogen from various 

 animals and different organs is the same according to PFLUGER. 3 Nor has 

 it been decided whether all the glycogen in the liver occurs as such or 

 whether it is in part combined with protein (PFLUGER-NERKING) . The 

 investigations of LoESCHCKE 4 have shown that we have no positive 

 reasons for this assumption. 



The preparation of pure glycogen (most easily from the liver) is 

 generally performed by the method suggested by BRUCKE, of which the 

 main points are the following: Immediately after the death of the animal 

 the liver is thrown into boiling water, then finely divided and boiled 

 several times with fresh water. The filtered extract is now sufficiently 

 concentrated, allowed to cool, and the proteins removed by alternately 

 adding potassium-mercuric iodide and hydrochloric acid. The glycogen 

 is precipitated from the filtered liquid by the addition of alcohol until 

 the liquid contains 60 vols. per cent. By repeating this and precipitating 

 the glycogen several times from its alkaline and acetic-acid solution it 

 is purified on the filter by washing first with 60 per cent and then with 

 95 per cent alcohol, then treating with ether, and drying over sulphuric 

 acid. It is always contaminated with mineral substances. To be able 

 to extract the glycogen from the liver or, especially, from muscles and 

 other tissues completely, which is essential in a quantitative estimation, 

 these parts must first be warmed for two hours with strong caustic potash 

 (30 per cent) on the water-bath. As the glycogen changes in this purifica- 



1 Young, Journ. of Physiol., 22, citing the other investigators. 



2 Journ. of Physiol., 22. 

 1 Pfliiger's, Arch. 129. 



* Ibid., 102. 



