112 THE CARBOHYDRATES 



or none, the fact that in the spores of species of Miicor and in 

 sclerotia glycogen does not appear until growth has com- 

 menced, points to the conclusion that in these plants, at any 

 rate, it is not primarily a storage product. Kohl considers 

 that since it is more abundant in Saccharomyces during active 

 gemmation, it is not exclusively a reserve substance, but an 

 intermediate product in the formation of alcohol from the 

 sugar. 



In the animal kingdom, according to Hoppe-Se}'ler, gly- 

 cogen is an invariable constituent of almost all developing 

 cells ; it is found also in the muscles and blood, and chiefly in 

 the liver, where it is stored in larger quantities. 



It may be remarked that there is little doubt that the 

 glycogen obtained from animal and plant sources are identical. 



Preparation. 



The following method of obtaining glycogen was devised 

 by Pfliiger.* Fresh finely-cut liver is stirred up with water 

 and 60 per cent caustic potash, and heated for two hours ; the 

 filtered solution, containing 15 per cent of potash, is then 

 mixed with an equal volume of 96 per cent alcohol, and the 

 precipitated glycogen is collected and washed wuth a mixture 

 of one part of 1 5 per cent potash with two parts of 96 per cent 

 alcohol ; if necessary, the substance may be redissolved and 

 purified in the same way. 



Glycogen may also be prepared from yeast, but not in a 

 particularly pure state, in the following manner : A quantity 

 of bakers' yeast, which has been previously w^ell washed with 

 water, is mixed with fine well-cleaned sand and ground very 

 thoroughly in order to rupture the cells. The mixture is then 

 placed in a vessel with about thrice its volume of water and 

 heated for some time, being constantly stirred. The liquid is 

 then filtered off, cooled, and strong alcohol added to the filtrate 

 in order to precipitate the glycogen, which is filtered off. 

 The glycogen so obtained may be purified by redissolving it 

 in water, adding a little acetic acid, and boiling in order to 

 remove any proteins which may not have been removed by 

 the initial heating, filtering, and precipitating with alcohol. 



* Pfliiger : " Pfliiger's .\rchiv f. Phys.," 1902, 91, 119, and 1903, 93, 163. 



