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DtCOCHONS.

PAKT III.

" Take of starch, three drachms ; water, a pint. Rub thestarch, gradually adding the water to it; then boil till a muci-lage be produced."

Starch thus treated forms a strong, insipid, inodorous, opa-line-coloured, gelatinous mucilage. In cases ofphthisis, hecticfever, and abrasions of the stomach, it is given as a demulcentby the mouth ; but it is more generally, and more advantage-ously exhibited in the form of enema in diarrhoea, dysentery,and abrasions of the rectum. It is the common vehicle forhibiting opium in the form of enema.

ex-

DECOCTA.

Decoctions.

These are aqueous solutions of the active principles of ve-getables obtained by boiling. They arc intended to affordmore powerful remedies than can be obtained by the sim-ple infusion of the same substances in cold or even in boilingwater; but although by the operation of boiling the solventpower of the water is increased, and a greater quantity ofthe soluble parts of any vegetable body is consequentlytaken up by it, yet it does not always follow, that the me-dicinal virtues of decoctions are greater than those of infu-sions. On the contrary, if the active principles of a plant bevolatile, or if they consist chiefly of extractive matter, thisform of preparation often renders the remedy altogether in-ert, either by dissipating the volatile matters, or by favour-ing the oxidizement of the extractive, which in a continuedtemperature of 212° attracts the oxygen of the atmosphere sorapidly, that it is soon converted into a soluble insipid inertmatter, and precipitated in the fluid. This is the case withsome substances, which are nevertheless ordered to be pre-pared in this form by the Colleges, and which we shall par-ticularly notice in treating of the individual decoctions.

For making decoctions, the substances employed must bedivided, if in the dry state, by pulverization, or, if fresh,by slicing, so as to expose an extended surface* to the ac-tion of the water; which is thus enabled to take up their so-luble principles in a shorter space of time, a circumstance,for the reasons already stated, of much importance in the pre-paration of decoctions. By covering the vessel in whichthey are made, the action of the air is prevented from af-