Maltose is the second member of the disaccharid group, and is of the same composition as the other two. Maltose derives its name from malt. It is formed from the starch of grains by a process of digestion which may be performed in the animal body, or by the process of malting. Maltose, like cane-sugar, can be further digested into monosaccharid sugars, but upon such digestion, instead of forming two separate simple sugars, it is wholly converted into glucose. The reader will now understand the meaning of the terms _monosaccharid_, _disaccharid_, and _polysaccharid_. MONO, which means _one_, is the simplest form of carbohydrates. Disaccharids (DI, meaning _two_), split up to form two simple sugars. Polysaccharids (POLY, meaning _many_) are complex compounds which form many simple sugars. 3 LACTOSE (C₁₂H₂₂O₁₁) Lactose exists in milk and has the same formula as cane-sugar. Milk contains about five per cent of this sugar. When lactose is digested it combines with water as does cane-sugar, but instead of yielding glucose and levulose, it yields glucose and galactose. c POLYSACCHARIDS 1 STARCH The chemical formula of starch and other polysaccharids is written (C₆H₁₀O₅)n. This means that the proportion of the elements is according to the figures given, but the number of atoms that are supposed to be combined is many times greater than five, and is not accurately known. This is purely theoretical, and of no practical importance, except that it shows that the polysaccharid is capable of being digested or broken up into many simple carbohydrate compounds. [Sidenote: Sources of starch] Starch is the most abundant carbohydrate known. It is the chief constituent of all cereals, and is found in large quantities in green fruits and tuberous plants. Starch occurs in small granules, varying greatly in size in different foods. [Sidenote: Potato starch] Potatoes are composed chiefly of starch and water. The starch grains of potatoes can almost be distinguished with the naked eye. These starch granules are not atoms or molecules in the chemical sense, but are small receptacles in which starch has been deposited by the growing plant. When cooked or boiled in water these starch grains swell into a mushy, pasty or gelatinous mass; when cooked in dry heat until they begin to turn brown, they are changed into a compound related to the gum group, known as dextrin. [Sidenote: Solubility of starch] Starch does not dissolve in water as do sugars. If starch is treated with digestive fluids, such as saliva, or with certain acids, it goes through a complex process of digestion in which it is first turned into soluble starch, then into the various forms of dextrin or gums, and finally into maltose or malt-sugar. [Sidenote: How corn-starch is changed into glucose]