GLYCOGEN 167 



COMMERCIAL DEXTRIN. 



Commercial dextrin is prepared by heating starch to about 

 230-260° ; it is a yellowish-brown powder, while that prepared 

 by acid hydrolysis of starch is an almost colourless solid with 

 a choncoidal fracture, or else a white powder resembling 

 starch. It is composed chiefly of achroo-dextrin mixed with 

 varying quantities of erythro-dextrin and glucose. It dissolves 

 in an equal volume of water to give a neutral sticky solution 

 with a faint sweet taste ; the solution is strongly dextro- 

 rotatory. Dextrin is insoluble in alcohol and ether. 



GLYCOGEN. 



This substance, although one of the most important and 

 widely distributed reserve foods in the animal kingdom, has 

 a restricted distribution in plants. It occurs abundantly in 

 certain Fungi, especially in Saccharomyces cerevisece, where it 

 may sometimes form as much as 30 per cent of the dry weight. 

 It has also been described as forming part of the cell-contents 

 in Myxomycetes, Flagellates, and in certain Algae including 

 the Cyanophyceae. In the yeast plant the glycogen varies in 

 amount according to the physiological phase of the organism, 

 and, it appears, accumulates and disappears often with great 

 rapidity. 



The glycogen appears in the cells of Saccharomyces during 

 the early stages of fermentation as minute refractive granules 

 scattered through the protoplasm ; after a few hours these 

 granules give place to small vacuoles, which in turn are re- 

 placed by one large vacuole, which may occupy the greater 

 space in the cell.* 



Wager and Peniston,t have shown that the amount of 

 glycogen present is correlated with the periodical fluctuations 

 in the fermentative activity. 



When yeast is placed in a nutrient fluid, e.g. Pasteur's 

 solution, fermentation may start at once, in which case it was 

 found that the cells float and contain very little glycogen, 

 while the cells which contain much glycogen sink to the 



* Harden and Rowland : " J. Chem. Soc, Lond.," 1901. 79, 1234. 

 t Wager and Peniston : " Ann. Bot.," 1910, 24, 45. 



