Two things are essentially necessary to be observed, which are: - the proper methods of making decoctions and infusions. These require some knowledge of the nature and properties of vegetable matter.

The virtues of most plants are extracted by infusion, and this is generally the case with aromatic plants, and those whose properties depend on an essential oil; for, in boiling, the whole of the aroma of the plant is dispersed, and the syrup loses that delicate flavour for which it is prized.

Aromatic herbs, and the leaves of plants in general, yield their virtues most perfectly when moderately dried. Cold water extracts from these in a few hours, the lighter, more fragrant and agreeable parts, and then begins to take up the more ungrateful and grosser. By pouring the same liquor on fresh parcels of the herb, it becomes stronger, richer, thicker, and balsamic.

Those only should be decocted whose principles consist of mucilage, gum, or resin, and require boiling to extract them.

The compact resinous woods, roots and barks, yield their virtues most freely while fresh. Dry, they yield little to cold or moderately warm water, and require it to be boiling. By this process the grosser, more fixed saline and mucilaginous parts are dissolved, the resinous melted out, and the volatile dissipated.