Corn-starch, treated with weak sulfuric acid, changes the starch into glucose. The ordinary glucose or corn-sirup is not all changed by this process, into pure glucose, but contains some maltose and other gummy compounds; hence it will not crystallize or granulate into pure sugar. After the acid has changed the starch into glucose it (the acid) is neutralized with an alkali. A crude compound is thus formed, which settles to the bottom of the tank, and from which the glucose can be easily separated. Commercial glucose is now very extensively used in the manufacture of various food products, especially confectionery. Pure glucose is a wholesome food, but there is some danger that the commercial product may (due to carelessness in manufacturing, or to the use of cheap and impure acid) contain various mineral poisons. Government testing of glucose and similar manufactured products is, in the writer's opinion, fully as essential as the government inspection of packing-house products. [Sidenote: How starch is changed into maltose] Just as glucose may be manufactured from starch treated with dilute acids, so maltose may be made by treating starch with malt. The brewing of beer depends upon the chemical changes induced in starch by malt. Barley is ordinarily used for this purpose. The barley is sprouted in a warm, damp room, and a process of starch digestion begins, which is necessary in order that the young barley sprouts may grow. This changes the starch into maltose. The digestive principle developed in the barley-malt may be utilized to malt other grains by mixing them with the sprouted barley. [Sidenote: Maltose in foods] If this process of malting is stopped at the proper time, and the sugar dissolved, and extracted, a product is formed consisting chiefly of the sugar maltose. This is the basis of malt extract, malt honey, and many similar foods put on the market, which are claimed by the manufacturers to have wonderful dietetic and curative values. 2 GLYCOGEN [Sidenote: Glycogen--how formed and where stored] Glycogen is commonly called animal-starch. It exists in the liver in small quantities. All carbohydrates are digested in the alimentary canal and absorbed into the blood in the form of simple sugars of the glucose group. When these sugars reach the liver they are again built up into a complex carbohydrate very similar to starch in composition. This glycogen or animal-starch is stored in the liver until the body has need of it, when it is changed into glucose and given back to the body in the form of energy. (See "Metabolism of Carbohydrates," Lesson VI, p. 202). 3 CELLULOSE [Sidenote: Cellulose--its purpose, source, and importance]