DEXTRIN, GLYCOGEN 107 



powder which is shghtly soluble in cold water, but readily in 

 hot. It is strongly dextro-rotatory («„ = + 196"), does not re- 

 duce Fehling's solution, and gives a blue colour with iodine. 



Erythro-dextrin. — This is a solid which dissolves readily in 

 water, and has a rotatory power of ud = + 196°; it reduces 

 Fehling's solution, and with iodine produces a red-brown 

 colour. 



The existence of erythro-dextrin as a chemical entity is, 

 however, disputed by Ost, who says that it is a mixture of 

 achroo-dextrin with starch ; an artificial mixture of achroo- 

 dextrin with a half per cent of starch also produces a red 

 colour with iodine. 



Achroo-dextrin. — This substance is optically active, and 

 has the value a^ = + 192°. It reduces Fehling's solution, 

 gives no colour with iodine, and has a sweetish taste. 



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 cereviseae, 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 possibly in certain Algae 

 and 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. 



