GLYCOGEN. 371 



all the glycogen in the liver occurs as such or whether it is in part 

 combined with protein (PFLUGER-NERKING). The investigations of 

 LOESCHCKE l 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 purification, 

 as suggested by BRUCKE, it is better, for quantitative determinations of 

 glycogen, to precipitate it directly from the alkaline solution by alcohol 



(PFLUGER 2 ). 



The quantitative estimation is best performed according to PFLUGER'S 

 method, which is as follows: The finely divided organ is heated on 

 the water-bath for 2-3 hours in the presence of 30-per cent KOH; 

 after diluting with water and filtering, the glycogen is precipitated 

 with alcohol, and the redissolved glycogen estimated in part by the polar- 

 iscope and in part as sugar after inversion. One part by weight of sugar 

 equals 0.927 part glycogen. As in the estimation the prescribed direc- 

 tions must be exactly followed, we must refer to the original work of 

 PFLUGER for the details of the method. Other methods of estimating 

 glycogen, such as those of BRUCKE-KULZ, PAVY, and AUSTIN, are described 

 in PFLUGER' s Archiv. 96. Also compare the recent works of PFLUGER 3 

 and BANG. 4 



Numerous investigators have endeavored to determine the origin 

 of glycogen in the animal body. It is positively established by the 

 unanimous observations of many investigators 5 that the varieties of 

 sugars and their anhydrides, dextrins and starches, have the property of 



iger's Arch., 102. 



also the method suggested by Gautier, Compt. rend., 129. 

 Pfliiger's Arch., 103, 104, 121. 



4 Hammarsten's Festschr., 1906. 



5 In reference to the literature on this subject, see E. Kiilz, Pfluger's Arch., 24, 

 and Luclwig, Festschrift, 1891 ; also the cited works of Pfliiger and Cremer, foot-note 

 1, p. 3C9. 



