CARBOHYDRATES. 45 



to stand for twenty-four hours, a considerable quantity of sugar will then 

 be found present. This suggested to Bernard that a substance must be 

 present in liver which is difficultly soluble in water, but yielded sugar by 

 the action of the liver substance, and this must be " living," as the fol- 

 lowing experiment showed. After thoroughly washing the liver, half of 

 it was boiled, and from this it was not possible to obtain any more sugar, 

 whereas sugar was slowly formed in the other piece. Bernard not only 

 assumed the presence of a complicated substance in the liver from which 

 the sugar was formed, but he actually succeeded in isolating such a sub- 

 stance. 1 The method employed by him for the preparation of glycogen 

 is essentially the same as that of to-day. It depends upon the fact that 

 alcohol precipitates glycogen from an alkaline solution of the organ. By 

 dissolving it again in caustic potash and reprecipitating by alcohol, it is 

 easy to purify the crude glycogen. In this way August Kekule 2 succeeded 

 in preparing glycogen free from nitrogen and ash. 



We shall later find that this skillful investigator, Bernard, not only dis- 

 covered glycogen, but to him is also due the credit of clearly recognizing 

 its biological significance. 



Glycogen is closely related to starch not alone by acting as a reserve 

 carbohydrate, but also as regards its formation. It is, however, not iden- 

 tical with starch, but sharply distinct from it. In common with the other 

 members of this complicated group of carbohydrates, its empirical formula 

 is represented by (CeHioOs)^ It is a fine, white, amorphous powder. 

 We know absolutely nothing concerning its molecular weight. 3 It swells 

 in cold water and apparently dissolves, although the solution shows a 

 distinct opalescence. That an actual solution is not formed is shown by 

 the fact that the glycogen will not diffuse through a parchment membrane. 

 Furthermore, Gatin-Gruzewska 4 has recently shown that glycogen in 

 water behaves exactly like a colloid, migrating towards the anode. Gly- 

 cogen is dextrorotary. Its solutions are colored by iodine yellowish- 

 brown, reddish-brown to deep red according to the concentration. An 

 alkaline solution of copper oxide dissolves it, but the solvent is not 

 reduced. 5 



Quite like the other polysaccharides, glycogen is decomposed by 

 boiling with dilute mineral acids into its simplest component, which in 

 this case is exclusively grape-sugar. The breaking down of the complex 



1 Claude Bernard: Leons sur la Physiologie et la Pathologie du Systeme nerveux, 

 vol. i, p. 467 (1857). See also Gazette medicale, 28, III (1857). 



2 Pharm. Zentrb. p. 300 (1858). 



3 Z. Gatin-Gruzewska : Wanderung des Glykogens unter dem Einfluss des elektrischen 

 Stromes. Pfliiger's Arch. 103, 287 (1904). 



4 Pfliiger's Arch. 103, 282 (1904). 



5 Concerning its quantitative estimation, see E. F. W. Pfliiger, loc. cit. pp. 61 

 and 67, et seq. 



