CARBOHYDRATES ^^ 



bring about the partial hydrolysis of the starch. "British Gum" is one 

 of the important commercial dextrins. Dextrins are widely used as 

 adhesives on postage stamps, envelopes, and textiles. Mucilage and 

 other industrial pastes are composed largely of dextrin. Tn the manu- 

 facture of cotton clotli. the material is sized with dextrin to make possible 

 the printing of the pattern. The candy industry uses large quantities of 

 dextrin to give a smooth texture to the product. 



The starch-splitting enzymes, ptyalin, amylopsin, and diastase, act also 

 on dextrins and form the same end product as from starch, namely, 

 maltose. Since dextrins include a number of degradation products of 

 starch, it is not surprising that they differ in their response to the iodine 

 test. Some are colored blue-violet, others red-brown, and yet others are 

 not colored at all by iodine. 



Glycogen 



Glycogen, or as it is sometimes called, animal starch, is tlie chief form 

 in which carbohydrates are stored in the animal body. It is found most 

 abundantly in the liver and muscles, but has also been isolated from bone, 

 blood, skin, and many other tissues. It seems to be present in all animal 

 cells. The amount fluctuates within wide limits. Hunger and severe 

 muscular work greatly deplete the supply of glycogen, whereas liberal 

 feeding with carbohydrate foods greatly increases it. By feeding, the 

 glycogen content of the rabbit's liver has been raised to 27 per cent of 

 the total weight of the liver. In the dog, under the same conditions, a 

 17 per cent glycogen content of the liver has been found. In man it is 

 estimated to reach as high as 10 per cent on a high carbohydrate diet. 

 Under usual conditions the liver of an animal contains from 1.5-4.0 per 

 cent. Other animal tissues have been found to contain the following 

 percentages of glycogen: muscle, 0.5-0.9; skin, 0.1-1.7; bone, 0.2-1.9; 

 blood, 0.007-0.016. The percentage of glycogen varies in the same kind 

 of tissue of different animals, in the different muscles of t'he same animal, 

 and in the different parts of the same muscle. 



Like amylopectin, glycogen is believed to consist of branched chains 

 that form a macromolecule containing about 2400 glucose residues. Such 

 a molecule would have a molecular weight of about 400,000. The length 

 of the individual chains in glycogen appears to be shorter than in starch 

 and is thought to contain from 12 to 18 glucose units instead of 24 to 30 

 units as reported for starch. 



A so-called plant glycogen has been found in several plants, molds, 

 yeasts, etc., which possesses many of the chemical properties of animal 

 glycogen, for example, iodine reaction, but is unlike it in certain other 

 aspects, such as oj^tical activity. 



Glycogen is a snow-wliitc powder readily soluble in water, with which 



