This substance is what is generally termed a gum-resin; that is, a compound consisting of gum, resin, and volatile oil: late researches however seem to shew that these bodies are compounds of a peculiar character, consisting of a volatile substance, something between essential oil and a constituent which possesses the properties of extractive rather than those of gum.
True Elemi has a fragrant aromatic odour, not unlike that of fennel-seeds, but more potent. Sp. gr. 1·0182. When powdered it mixes with any unguent; it also combines with balsams and oils, and by the aid of heat, with turpentine. Uses. It is only employed for forming the mild digestive ointment which bears its name, viz. Unguent: Elemi comp: L.D.
EMPLASTRA. L.E.D. Plasters.
The principles upon which this form of preparation is to be constructed are fully detailed at p. 207.
Emplastrum Ammoniaci. L. Ammoniacum reduced to a suitable consistence by distilled vinegar. It adheres to the skin without irritating it, and without being attended with any unpleasant smell.[[494]] There is a peculiar disease of the knee, to which servant maids, who scour floors upon their knees, are liable, and for which this plaster is a specific. I have also found it particularly eligible in cases of delicate women with irritable skins.
Emplastrum Ammoniaci cum Hydrargyro. L.D. The mercury in this plaster is in the state of oxidation ad minimum. It is discutient and resolvent, and is applicable to indurated glands, and venereal nodes, and for removing indurations of the periosteum, remaining after a course of mercury; the addition of the ammoniacum increases the stimulating and discutient powers of the mercury, which gives this plaster a superiority over the Emplastrum Hydrargyri. It is also powerfully adhesive.
Emplastrum Assafœtidæ. E. Emplast. Plumbi and Assafœtida, of each two parts, galbanum and yellow wax, of each one part. I have seen it useful in flatulent cholic, when applied over the umbilical region.
Emplastrum Cantharidis. L. Emplast: Cantharidis vesicatoriæ. E.D. A variety of substances has in different times been employed for producing vesication, but no one has been found to answer with so much certainty and mildness as the Lyttæ. All the others are apt to leave ill conditioned ulcers: true it is, that the emplastrum lyttæ will occasionally fail, but this is generally attributable to some inattention, or want of caution on the part of the person who prepares it; in spreading it, the spatula should never be heated beyond the degree of boiling water; the plaster also should be sufficiently secured on the part by slips of adhesive plaster, but it ought not to be bound on too tight; where the cuticle is thick, the application of a poultice for an hour, previous to that of the blister, will be useful, or the part may be washed with vinegar. In consequence of the absorption of the active principle of the Lyttæ, blisters are apt to occasion strangury and bloody urine; it has been a problem therefore of some importance to discover a plan by which such an absorption may be obviated, for this purpose, camphor has been recommended to be mixed with the blistering composition, and a piece of thin gauze has been interposed between the plaster and the skin; but it has been lately found, that ebullition in water deprives the Cantharides of all power of thus acting on the kidneys, without in the least diminishing their vesicatory properties: the ordinary time required for the full action of a blister is ten or twelve hours, but if it be applied to the head, double that period will be necessary. Children, owing to delicacy of skin, are more speedily blistered, the epispastic may therefore be removed earlier. In some cases the blistered parts, instead of healing kindly, become a spreading sore; whenever this occurs, poultices are the best applications; it may arise from a peculiar irritability of the constitution, although I apprehend that it not unfrequently depends upon the sophistication of the plaster with euphorbium. In cases where it is desirable to keep up the local irritation, it is still a question with some practitioners whether it be more advisable to encourage a discharge from the vesicated part by some appropriate stimulant, or to renew the vesication at short intervals by repeated blisters; the latter mode is perhaps to be preferred, as being more effectual, and certainly less troublesome to the patient: it has moreover been stated,[[495]] that by a repeated application of this nature, the influence excited appears to extend much deeper, so as to derive a greater quantity of blood from the immediate neighbourhood of the vessels, or from the vessels themselves which are in a state of disease, than the influence excited by an application less stimulating upon the surface of a part already abraded. The character of the discharge would likewise appear essentially different; it being in the latter cast a purulent secretion from the superficial exhalants of the surface only; in the former, a copious effusion of serum, mixed with a large portion of lymph, produced from a deeper order of vessels.
Emplastrum Ceræ. L. Emplast: Simplex. E. This is the Emplast: Ceræ of P.L. 1787, the Emplast: Attrahens of 1745, so called because it was formerly employed to keep up a discharge from a blistered surface, and the Emplastrum de melilolo simplex of 1720.
Emplastrum Cumini. L. A valuable combination of warm and stimulant ingredients.