Pharmacologia / Fourth American, from the Seventh London Edition

by John Ayrton Paris

DECOCTA. L.E.D. Decoctions.

These are solutions of the active principles of vegetables obtained by boiling them in water. To decide upon the expediency of this form of preparation, in each particular case, requires a knowledge of the chemical composition of the substance in question. In conducting the operation, the following rules must be observed.

1. Those substances only should be decocted, whose medicinal powers reside in principles which are soluble in water.

2. If the active principle be volatile, decoction must be an injurious process; and, if it consist of extractive matter, long boiling, by favouring its oxidizement, will render it insipid, insoluble, and inert.

3. The substances to be decocted should be previously bruised, or sliced, so as to expose an extended surface to the action of the water.

4. The substances should be completely covered with water, and the vessel slightly closed, in order to prevent, as much as possible, the access of air: the boiling should be continued without interruption, and gently.

5. In compound decoctions, it is sometimes convenient not to put in all the ingredients from the beginning, but in succession, according to their hardness, and the difficulty with which their virtues are extracted; and if any aromatic, or other substances containing volatile principles, or oxidizable matter, enter into the composition, the boiling decoction should be simply poured upon them, and covered up until cold.

6. The relative proportions of different vegetable substances to the water, must be regulated by their nature; the following general rule may be admitted; of roots, barks, or dried woods, from ʒij to ʒvj to every pint of water; of herbs, leaves, or flowers, half that quantity will suffice.

7. The decoction ought to be filtered through linen, while hot, as important portions of the dissolved matter are frequently deposited on cooling; care must be also taken that the filtre is not too fine, for it frequently happens, that the virtues of a decoction depend upon the presence of particles which are suspended in a minutely divided state.

8. A decoction should be prepared in small quantities only, and never employed, especially in summer, forty-eight hours after it has been made. It should be considered as an extemporaneous preparation, but introduced into the pharmacopœia for the purpose of convenience, and for the sake of abridging the labour of the physician.