Essence, or Essential Oil, as it is variously termed, in medicine, derotes the purest, most subtle, and balsamic part of a body, extracted by distillation.

There are a variety of essences drawn from flowers, fruits, etc. •which are used on account of their agreeable flavour by apothecaries, perfumers, and others : the principal of these are the essence of rosemary, of turpentine, of anise, of cloves, of cinnamon, and of lemons.

The essences sold by perfumers, chiefly consist of the oil of bitteralmonds, to which they impart the odour of jassamine, roses, cinnamon, and other flowers and spices. When essential oils have been distilled, they should be suffered to subside for some days, in vessels loosely covered with paper, till they have lost their disagreeable, ardent odour, and have become limpid ; they should be put into small bot-tles which ought to be completely filled, ciosely stopped, and ept in a cool place : by observing these precautions, they will retain their virtue for several years. But, if essential oils be carelessly managed, they gradually lose their flavour, and become thick : in this case, they should be put into a still, with fresh ingredients for distilling the same oil; by which means they will saturate them-selves with the odoriferous particles, and regain their former strength and purity.

Essential oils, medicinally considered, agree in the general qualities of pungency and heat: with respect to their particular virtues they vary as much as the vegetables from which they are extracted Thus, the carminative properties ofaromatc seeds, the diuretic efleefs of juniper-berries, the stomachic virtues of mint, and the antiscorbutic powers of scurvy-grass, are in a great measure concentrated in their oils.

These oils are never given in a pure state, on account of their extreme pungency, which in some is so great, that if a single drop be deposited on the tongue, it will occasion a gangrenous eschar, or scab. They are readily imbibed by pure, dry sugar, being the most convenient form in which they can be administered. The more mild and grateful oils are frequently used as ingredients with other medicines, to render them less nauseous. The more pungent ones are externally employed in paralytic complaints, numbness, colds, aches, and in other cases, where particular parts require to be heated or stimulated.