Plasmae.—Plasmas.
History.—In 1858, G. F. Schacht proposed glycerin as a substitute for oils and fats in ointments, the glycerin being heated with starch, and the compounds thus formed being termed "Plasmas." This term we propose to employ here for all solid or semisolid preparations for external use, excepting glycerites, in which glycerin forms an important basis. These preparations are more costly than the ordinary fatty ointments, but there are certain cases in which the latter irritate the parts to which they are applied, and, consequently, aggravate the disorders for which they are used, which is not the case with the plasmas, the glycerin being comparatively unirritating, not possessed of any rancidity, nor of any irritating fatty acids, etc. In addition to these advantages, it can be removed at any time without the use of soap and friction, and its application does not involve soiling and greasing the garments or bed-clothing (see Glycerita). The formula of Mr. Schacht is to take powdered starch, 70 grains; glycerin, 1 fluid ounce; mix the ingredients and heat to 115.5° C. (240° F.), constantly stirring. If a large quantity (6 or 8 pounds) is to be prepared, he advises that the starch be triturated with one-twelfth of the glycerin, placing the remainder on the fire, heating it to 126.6° C. (260° F.), and then stirring it thoroughly into the mixture previously made. By this means much time is saved, as well as labor, in stirring the mass. He states that the plasma does not mold by keeping.
Other formulae besides that of Mr. Schacht's have, at various times, been offered to the profession, thus: Mr. H. Seymour has offered the following: (1) Take of Fuller's earth, ½ ounce; palm oil, 2 drachms. (2) Take of Fuller's earth, ½ ounce; oil of sweet almonds, 2 fluid drachms; water, 2 fluid drachms; glycerin, 1 fluid drachm. More recently, Mr. T. B. Groves has proposed a new basis for ointments, which he calls Glycelaeum. It is made by triturating together almond meal (from oil-cake, or decorticated pressed sweet almonds), ½ ounce; glycerin, 1 ounce; olive oil, 3 ounces. Mix by trituration in a mortar. It forms a soft, semi-gelatinous paste, which, when mixed gradually with water or a watery fluid, readily forms an emulsion. As it remains unaffected by the ordinary temperatures of the body, its softness is not an objection to its use, which, in fact, is an advantage, as it leaves plenty of room for powdery admixtures of every kind (Trans. Brit. Conf., 1867; Chem. and Drug., Sept. 14).
