THE CARBOHYDRATES 33 



that dextrine is digestible and that it has much the same 

 nutritive value as other carbohydrates. 



Dextrine may be obtained by diastatic fermentation of 

 starch at 62 C. for about 15 minutes ; the solution, after being 

 filtered and concentrated by evaporation, is precipitated by 

 alcohol. The commercial product, prepared by moistening 

 starch with dilute (2 per cent.) nitric acid, allowing it to dry 

 in the air and then heating to 110 C., is used as a substitute 

 for gum. 



Glycogen. Glycogen is a white amorphous powder, 

 soluble in water but insoluble in alcohol. It is optically 

 active, [a] D = 203-220. It gives a bright red colour with 

 iodine, but does not reduce Fehling's solution. Diastase 

 converts it into maltose, boiling with dilute acids converts it 

 into dextrose. Glycogen is one of the few carbohydrates 

 produced by animals, and its presence only marks a stage in 

 the transformation of other compounds. It is found in the 

 blood and muscles, especially in embryonic tissues, and in larger 

 quantities in the liver of animals which have recently partaken 

 of food. The liver ferments convert it rapidly into dextrose. 



Inulin. Inulin resembles starch in many respects, and 

 appears to replace it in certain plants chiefly belonging to 

 the order composite. It is readily soluble in hot water, but 

 practically insoluble in cold. It separates from hot aqueous 

 solutions on cooling and is. precipitated also by addition of 

 alcohol. It is most readily obtained from the milky juice 

 expressed from dahlia tubers and dandelion roots from which 

 it separates in the form of minute white grains on standing. 

 It may be purified by re-solution and precipitation. Inulin 

 does not reduce Fehling's solution, and it gives no coloration 

 with iodine. On prolonged boiling with water, or more rapidly 

 in the presence of acids, it is completely hydrolysed to 

 fructose (laevulose). 



Gums. The true gums, as distinct from dextrine, exude 

 from the stems and twigs of certain trees, or are extracted 

 from the same by means of solvents. They are all amorphous, 

 transparent substances, insoluble in alcohol, but are soluble 

 or become gelatinous when mixed with cold or hot water 



D 



