EXTRACTS are medicinal preparations of vegetable principles, obtained in various ways. Sometimes they are merely the juices ex pressed from the fresh plants, brought by careful evaporation to the consistence of honey, and then more properly denominated inspissated juices; at other times they consist of certain principles of the fresh or dried plant extracted by some menstruum in which they are soluble, such as water, proof spirit, or vinegar, and afterwards evaporated, as in the former case. According to the nature of the menstruum employed the extract is called aqueous, alcoholic, or acetous.
The preparation of extracts requires the greatest care. The plants must be in every respect of the best quality, as regards the place of their growth, season when collected, &c.; and the evaporation must be conducted rapidly, yet at a low temperature. Extracts are simple or compound, according as they are prepared from one plant or from several dif ferent kinds.
A well-prepared extract should possess in a great degree the odour, and especially the taste, of the plant from which it is obtained ; it should not have either an erapyreurnatic smell or taste, and it should have a proper and uniform consistence. It is necessary to preserve extracts in a dry situation. To assist in keeping aqueous extracts, it is customary to sprinkle a little alcohol over the surface before covering them up; but such extracts, if made with cold water and with due care, rarely require this precaution. It is proper to examine the condition of all extracts very fre quently, both during very warm and very wet weather : any portion which seems spoiled should be immediately thrown out.