(From coquo, to boil). Boiling; and metaphorically preparing. Also decoctio and apozema. The effect of boiling differs greatly from that of infusion. In the heat of boiling water the essential oils of vegetables, in which their virtue generally resides, are dissipated; and when the medicine to be obtained is to consist of the more volatile parts of the ingredients, infusion is obviously preferable to decoction. The grosser parts of many substances are only extracted by boiling. The infusions of animal substances are of much lighter digestion than the decoctions; and boiling water extracts, for instance, the rougher and more disagreeable portions of camomile flowers, and the carduus benedic-tus: cold water, the milder and more aromatic.

In decoctions, those ingredients should be boiled first from which their virtues are most difficultly extracted; and those which more readily impart them may be reserved until a later period. Volatile ones may be added when the decoction is removed from the fire; they may stand closely covered until the liquor is cool.

Agglutinants, astringents, and emollients, are the chief subjects of this operation, and such other materials as require some force to separate their parts. See Decocta.

By decoction the tendency to fermentation in fermentable liquors is lessened. See Dict. Chem. 4to.

By the coctions of humours is meant the digestion of the aliment into chyle; the reduction of the chyle into blood; and the separation of the juices from the blood, by means of the glands. These are styled the first, second, and third coction.