INFU′SION

Syn. Infusum , Infusio , L. A liquid medicine, prepared by macerating vegetable or animal substances in water, at any temperature below that of ebullition. The mode of preparing infusions is, with most substances, precisely similar to that pursued for making the almost universal beverage— TEA . The ingredients are commonly placed in a stoneware pot or ve el (an ‘infusion pot’), previously made hot; boiling water is then poured over them, and the cover being placed on, the whole is allowed to digest together, at first, for a short time, in a warm situation, as on the hob or the fender, and afterwards (the ve el being removed from the heat) until the whole becomes cold. The liquid is then poured from the ingredients, and the latter, being slightly pre ed, if nece ary, the infusion is strained through a piece of clean linen or a hair sieve for use. During the digestion the ingredients should be occasionally stirred, an important matter often neglected, and not even referred to by most pharmaceutical writers. The substances employed for making infusions receive the same preliminary treatment as those intended for making DECOCTIONS . Shavings, leaves, and flowers require no previous preparation beyond being pulled asunder; but roots, woods, and other solid substances must be bruised or sliced, if in the green or recent state, or bruised or coarsely pulverised, if dry, for the purpose of exposing as large a surface as po ible to the action of the menstruum. The substances extracted by water from vegetables by infusion are chiefly gum, mucus extractive, tannin, certain vegetable acids, the bitter and narcotic principles, gum-resin, e ential oil, and alkaloids. Some of these substances are only sparingly soluble in water at ordinary temperatures; but more readily so in hot water, and freely soluble in boiling water. The temperature of the water should be therefore proportioned to the nature of the vegetable matter operated on. For mere ‘demulcent infusions,’ in which starch and gum are the chief substances sought to be di olved out, and when the active principle is scarcely soluble in water, unle at nearly the boiling temperature, boiling water alone should be employed; but when the medicinal virtues of vegetables are soluble in water at lower temperatures, it is better to employ hot water (165° to 175° Fahr.), and to allow a little longer period for the digestion. In many cases temperate water (from 60° to 70° Fahr.), or tepid water (from 80° to 90° Fahr.), may be used with advantage, especially in the preparation of ‘aromatic bitter infusions,’ and in most cases where it is wished that the product should contain as little inert matter as po ible; but when water at low temperatures is employed, the period of the maceration must be proportionately increased. By adopting the method of maceration in vacuo, or in an atmosphere of carbonic acid, the menstruum may be allowed to lay in contact with the vegetable matter for an unlimited period, without decomposition taking place. Infusions, like decoctions, are liable to undergo spontaneous decomposition by keeping, especially in warm weather, when a few hours are often sufficient for their pa age into a state of active fermentation; they should, therefore, when po ible, be prepared for use daily, as beyond twenty-four hours they cannot be depended on. The London College directs a pint only to be made at a time, thus very properly regarding them as extemporaneous preparations. Concentrated infusions , now so common in the shops, and, unfortunately, so generally used in dispensing, are either made by taking 8 times the quantity of the ingredients ordered in the pharma copœia, and then proceeding in the usual manner, or by the method of displacement; or, by carefully and rapidly concentrating the simple infusions, by evaporation in a steam or salt-water bath, until reduced to about 1-7th of the original quantity. In either case the liquid is put into a strong bottle, without being filtered, and 10 to 12% of rectified spirit added to it, whilst still hot. The cork is then put in and secured down, and the whole agitated for some minutes, after which it is set aside for a week, when the clear portion is carefully decanted from the sediment for sale. Another method, which answers well with the aromatic bitter vegetables, is to take 8 times the usual quantity of the ingredients, and to exhaust them with a mixture of rectified spirits, 1 part, and distilled water, 3 parts; by digestion, or, better still, by percolation. Concentrated infusions made in this way keep well, and deposit scarcely any sediment. Many houses that are remarkable for the ‘brilliancy’ and beauty of these preparations, employ 1 ⁄ 3 spirit of wine and 2 ⁄ 3 water as the menstruum. It may, however, be taken, as a general rule, that for vegetable substances that abound in woody fibre, and contain little extractive matter soluble in water (as qua ia, for instance), 1 ⁄ 6 to 1 ⁄ 5 part of spirit is sufficient for their preservation; whilst for those abounding in mucilage or fecula, or that readily soften and become pulpy and glutinous in weak spirit (as rhubarb), 1 ⁄ 5 to 1 ⁄ 3 is required. By adopting the method originally suggested by Mr Alsop, infusions may be preserved, uninjured, for a year or longer, without the addition of spirit or any other substance. The only precaution nece ary is to keep them in bottles, perfectly filled and hermetically sealed. [360] Our own plan is to put a few bruised cloves or seeds of black mustard into the bottles, which must be only 2-3rds filled, then completely fill them with a condensed atmosphere of carbonic acid gas; and, lastly, to stopper them and seal them over, so as to perfectly exclude the air. A pint of decoction of sarsaparilla and 1 ⁄ 2 pint of infusion of calumba, treated in this way, kept good for fully 9 years. By simply macerating in the infusion as much bruised mustard seed as can be added without flavouring the liquor, along with a little bruised cloves, we find that most vegetable infusions may be preserved in bottles which are occasionally uncorked, without either fermenting or becoming mouldy, by the use of very little spirit ( 1 ⁄ 9 or 1 ⁄ 10 ). [360] ‘Pharm. Journ.,’ i, 57. Before adding the spirit to infusions made with cold water, or with water which is only tepid, it is advisable to heat the liquid to about 185° Fahr., in a water bath, and after keeping it at that temperature for a few minutes, and allowing it again to become cold, to separate it from the precipitated matter, either by filtration or decantation. It is often very difficult to render vegetable infusions and decoctions perfectly transparent, a quality always expected in the concentrated preparations. Defecation by repose is always better than filtration, owing to the more or le viscidity of the suspended matter. When this is not sufficient, they may be clarified with white of egg (2 or 3 to the gall.), previously beaten up with 5 or 6 fl. oz. of water. Most of the vegetable infusions and decoctions will readily pa the filter, after a very small quantity of acetic, nitric, or sulphuric acid has been added to them. The most obstinate may be rendered ‘brilliant,’ or ‘candle bright,’ as the ‘cellarmen’ call it, by shaking them up, first with about a drachm of dilute sulphuric acid, and afterwards with the whites of 3 or 4 eggs, previously mixed with a few ounces of water, for each gallon of the liquid. This plan is, however, objectionable for many medicinal preparations. As many infusions which are occasionally employed in medicine must nece arily escape being separately noticed in this work, it may be as well to remark that the infusions of all vegetables that do not exert a very powerful action on the human frame as ordinary herbs and roots may be made by pouring 1 pint of boiling water on 1 oz. of the vegetable matter, and allowing it to macerate for 1 ⁄ 2 an hour to an hour. The decoctions of the same vegetables may be made by simply boiling the above ingredients, in the same proportions, for 10 or 15 minutes, instead of operating by mere infusion. With substances of somewhat greater activity, only half the above quantity should be taken; whilst, with the narcotic plants and those po e ing great activity, 1 to 2 dr. to water, 1 pint, will be the proper quantity. The ordinary dose of such infusions and decoctions is 1 ⁄ 2 to 1 wine-gla ful (1 to 2 fl. oz.), two, three, or four times a day, as the case may indicate. Infusion is preferred for all bodies of a delicate texture, which readily yield their active principles to water; and especially when these are either volatile or liable to be injured by the heat of ebullition. The simple infusions are now le frequently made by the druggist than formerly. In most cases he merely furnishes the ingredients, and the infusions are prepared by either the nurse or patient, by whom they are commonly called ‘ TEAS ,’ ⁂ The following list embraces most of the infusions used in prescribing or noticed in books. Where the proportions of the ingredients are not given, 1 oz. of the medicinal substance and 1 pint of boiling water are to be taken, and the dose is that referred to above.