We therefore find that the
operations above described only go to this, that the watery particles in
the common juice should be evaporated, as being a part necessary to be
got rid of; and the proper juice being of a volatile nature, the less
time the plants are exposed for that purpose, the less of this precious
material will be lost: and as those parts are flying off continually
from all dried vegetables, there should be one general rule made with
regard to their peparation; for, if we instance mint, balm, pennyroyal,
&c., the longer these are kept in the open air, the weaker are they
found to be in their several parts.
From hence we may naturally infer, that the usual mode in which the
generality of herbs are dried, is not so good for the purpose, as one
would be if contrived on similar principles, as, during the length of
time necessary for the purpose, a great deal of the principal parts of
the plants must of course be evaporated and lost; for little else is
regarded than to dry them so as to prevent putrefaction. Although the
generality of herbs met with are prepared as above described, yet in
such articles as Digitalis, Hyoscyamus, Conium, Toxicodendron, &c.,
where the quantity necessary for a dose is so small, and so much depends
on its action, practitioners are often obliged to prepare it themselves.
I shall therefore relate the following mode as the best adapted to that
purpose.
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