The substances belonging to this division are less demulcent than the preceding; but are occasionally used for this effect, and very much for nutritive purposes. They require attention, therefore; and I do not know where better to place them.

It will be most convenient, under this general head, to notice a few of the characteristic properties of starch, as a peculiar proximate principle, which the physician must be acquainted with, in order to employ the amylaceous substances intelligently. We shall thus spare ourselves useless repetition in treating of the several preparations distinctly. Starch, when pure and unchanged, is white, in the form of a powder or of pulverulent lumps, inodorous and nearly tasteless, insoluble in cold water and in alcohol, but readily dissolved by boiling water, which retains a small proportion on cooling. if the boiling water has taken up more than can be held in solution upon cooling, the liquid assumes a soft, semifluid, gelatinous character. The starch that has thus been dissolved, continues afterwards, on being obtained in the dried state, soluble in cold water. Exposed to dry heat, starch undergoes a change which renders it partially soluble in cold water; and the same effect is produced in some degree by rubbing. These peculiarities are explained by the organic constitution of starch discovered by the microscope. it consists of minute granules, made up of concentric layers, the outer of which are insoluble in water, the inner soluble; so that, when exposed to heat, moist or dry, the outer coating is ruptured, and water, being enabled to penetrate the interior, comes into contact with the soluble portion, and dissolves it. Starch is characterized by forming a deep-blue compound with free iodine. Like sugar and gum, it consists of carbon combined with hydrogen and oxygen in the proportion in which these principles unite to form water. The different kinds of starch have granules of a peculiar and characteristic formation, by which the varieties may be distinguished.