48. Starch is one of the most important of all vegetable foods. It does not contain any albumenoid substances and cannot therefore supply the materials of which our bodies are formed; taken by itself, it would not long support life, nor enable a young animal to grow; but it is the source of the warmth of our bodies and of the strength we exert, in this respect resembling fat and the other oleaginous foods with which it is classed.
As obtained in a pure state, it consists of very minute grains, each covered with an outer skin which is perfectly insoluble in and unchanged by water; hence pure starch is unaffected by moisture, and may be washed without change.
In boiling water these grains crack, and the interior of each dissolves in the water, forming a thick, gummy solution. A similar change takes place if starch is baked, when it becomes soluble and forms what is called British Gum, which is used in stiffening muslins and cementing postage stamps, &c. Several nearly pure starches are largely used as food. Tapioca is a very pure starch, which is slightly heated during its preparation, and rendered partially soluble in cold water.
Sago is a starch obtained from the interior of the stem of a palm tree. It also is heated in its preparation.
Arrowroot is a very pure starch, obtained in the form of a white powder. Potatoe-starch may be easily prepared by grating well washed large potatoes into water and allowing time for the starch to settle at the bottom, when the water with the vegetable fibre may be poured away, fresh water being added, and