CARBOHYDRATES, ACIDS, FATS, OILS 77 



mainly obtained from corn and potatoes. Special forms of 

 starch used in cookery are sago, tapioca, and arrowroot. 

 It is used as human food, as a source of dextrin, and in 

 other ways. By treatment with an acid, corn starch is 

 converted into the glucose of our markets, dextrin and 

 maltose being intermediate products. 



103. Glycogen. — ^This is the only uncombined carbo- 

 hydrate found in the animal body in appreciable quan-. 

 tity outside the forms that are in the blood circulation. 

 It is sometimes called animal starch. It is a white pow- 

 der, soluble in water, and may be extracted in small 

 amounts from the muscles and liver. It is formed out of 

 the sugars that are taken into the circulation from the 

 digestive tract, and, as we shall see, is held a reserve store 

 of fuel for the maintenance of muscular energy, and in 

 this way it performs a very important office in nourishing 

 the animal body. (See Par. 214.) It was formerly believed 

 that another carbohydrate exists in muscle called inosUe, 

 but it is now known that this substance belongs to a 

 different class of compounds. 



104. The pentosans. — ^These bodies are very widely 

 distributed in nature, being found in the leaves, stem, 

 roots, and seeds of a great variety of plants, in algse and 

 in beets and turnips. Certain pentosans are known as 

 gums, such as gum arable, gum tragacanth, and cherry 

 gum. Pentosans, on hydrolysis, yield pentose sugars, 

 among which are arabinose and zylose. These gum-like 

 substances exist in beets and turnips and probably in all 

 herbaceous plants that serve as cattle foods. 



105. Galactans, mannans, levulans, dextrans. — These 

 are compounds of some importance that are more or less 

 associated in the framework of a great variety of plants 

 or parts of plants, including seeds, beets and turnips. 



