Amylum, B.P. Starch.
Starch is obtained from wheat, Triticum sativum, Lam., rice, Oryza sativa, Linn., and maize, Zea Mays, Linn. (N.O. Gramineae); but, in addition to these official varieties, potato and maranta starches are also used. Amylum, U.S.P., is the starch obtained from Zea Mays. The starch is obtained from the grain, etc., by grinding, freeing from glutin by washing and allowing the suspended starch to settle. It occurs as a fine, white, inodorous powder, or in irregular and columnar masses which are readily powdered. Starch is a carbohydrate with a very complex molecule, its formula being a multiple of C6H11O5. Its identity and freedom from admixture with other starches may be determined by means of the microscope. Air-dried starch usually loses from 12 to 16 per cent. of moisture on drying in a water oven. Wheat starch consists principally of large grains, about 30 to 40μ in diameter, mixed with small grains 2 to 8μ in diameter. The former are lenticular in shape, and seldom exhibit well-marked striations or a definite hilum. Maize starch grains are more uniform in size, measuring 10 to 25μ in diameter. The majority are polygonal in shape, but some are more or less rounded; the hilum is usually fissured or stellate, central, and conspicuous; concentric striations are not visible. Rice starch grains range mostly from 4 to 6μ in diameter; they are angular and seldom exhibit a definite hilum.
Potato starch grains from the tubers of Solanum tuberosum (N.O. Solanaceae) have an oval or ovate outline; the hilum is a point and generally situated near the narrow end of the grain; the striations are numerous and distinct. Large grains measure 75 to 110μ in length, those of medium size, 45 to 65μ. Maranta starch (arrowroot) from Maranta arundinacea (N.O. Marantaceae) resembles potato starch, but the grains are usually smaller (30 to 60μ, rarely 70μ); the hilum is often linear or stellate, and situated at the broad end of the grain.
Insoluble in water, to which it should not impart either an acid or alkaline reaction; but wheat starch is frequently slightly acid, maize and rice starch slightly alkaline to litmus. On boiling with water it forms a gelatinous mixture which, when cooled, gives a deep blue colour with solution of iodine.
Action and Uses.—Starch soaks up secretions and helps to render injured parts less liable to bacterial infection. As a dusting powder for application to chafings and excoriations, it is used either alone or mixed with zinc oxide, boric acid and other similar substances. It also forms the basis of violet powder. Boiled with water it may be employed as an emollient for the skin. As a protective application in skin diseases and for chilblains it may be used in the form of Glycerinum Amyli. Mucilage of starch is the basis for many enemata, and is the best antidote for poisoning by iodine; it should be freshly prepared as required. Boiled with sufficient water to form a stiff paste, starch forms an excellent poultice, which may be rendered antiseptic by the addition of 6 per cent. of boric acid. For determining the diastatic value of malt extract dried potato starch is used.
- Amylum Iodisatum, B.P.C.—IODISED STARCH. Syn.—Amylum Iodatum. 1 in 20.
- Iodised starch contains iodine in very weak combination. It is administered internally in syphilis and other cachexias, and may be given in milk, water, gruel, or arrowroot. Externally, it is used as a dry dressing, being a good substitute for iodoform. Dose.—2 to 5 grammes (30 to 75 grains).
- Cataplasma Amyli, B.P.C.—STARCH POULTICE. 1 in 10.
- Used as a substitute for the domestic bread poultice for application to small superficial ulcerations.
- Cataplasma Amyli et Acidi Borici, B.P.C.—STARCH AND BORIC ACID POULTICE.
- Starch, 10; boric acid, 6; water, 100. An antiseptic poultice for application to ulcerated wounds.
- Glycerinum Amyli, B.P.—GLYCERIN OF STARCH.
- Starch, 2; distilled water, 3; glycerin, 13. Heat the starch with the glycerin and distilled water on a sand bath, with constant stirring, until a clear jelly is obtained. Glycerin of starch is a soothing and emollient application for the skin, and is used for chapped hands and chilblains. It is much improved by the addition of a small proportion of tragacanth.
- Glyceritum Amyli, U.S.P.—GLYCERITE OF STARCH.
- Starch, 10; water, 10; glycerin, by weight, 80.
- Mucilago Amyli, B.P.C.—MUCILAGE OF STARCH. 1 in 40.
- This mucilage is used as a basis for enemata.