(“_Jucunde._”)
These elements however are not all necessarily present in every
scientific formula, for many medicines do not require any addition to
promote their operation, and the mild and tractable nature of others
renders the addition of any corrective unnecessary; whilst many again
are in themselves sufficiently manageable, and do not therefore require
the _intermede_ of any _vehicle_ or _constituent_. It also frequently
occurs that one element is capable of fulfilling two or more of the
objects required; the ADJUVANS for instance, may at the same time act as
the CORRIGENS, or CONSTITUENS; thus the addition of _Soap_ to _Aloes_,
or _Extract of Jalap_, mitigates their acrimony, and at the same time
quickens their operation (80.) So again _Neutral Salts_ both quicken and
correct the griping which attends the operation of resinous purgatives.
The disposition of the key letters placed opposite to the elements of
the following _Formulæ_, will furnish the practitioner with a farther
elucidation of these principles, viz. 70, 71, 76, 77, 101, 102, 105,
135, &c. This coincidence, if possible, should be always attained, for
it simplifies the formula, and by decreasing the bulk of the remedy,
renders it less nauseous and more elegant.[276]
This division also affords the best general rule for placing the
ingredients of a formula in proper order, for the order should
correspond with that of the arrangement; and those elements intended to
act in unity should be marshalled together. The chemical and mechanical
nature however of a medicinal substance will occasionally offer
exceptions to any general rule; thus the volatile ingredients should be
those last added, and the constituent or _vehicle_ should be placed next
the particular element to which it is intended to impart convenience or
efficacy of form, or a capability of mixing with the other ingredients,
as may be seen in Formulæ 69, 71, 127, 136, &c. This consideration
induced the Committee, appointed to revise the late Pharmacopœia, to
alter the order of the ingredients in the “_Mistura Ferri composita_,”
and to place the “_Spiritus Myristicæ_” next in succession to the
“_Potassæ Sub-carbonas_” and _Myrrh_. If any substance require decoction
or infusion, a question then arises, determinable only by a knowledge of
its chemical composition, whether the remaining ingredients should be
added previous to, during, or subsequent to, that operation; _Formula
40_, which is recommended by Pringle as a remedy for Typhus fever, may
serve to exemplify this principle. The preparation of the ingredients is
resolved into three distinct stages, and it is easy to discover that by
any other arrangement their several virtues could not be fully obtained,
and secured from change. The _Cinchona_, for instance, yields its full
powers only by decoction, a process which would necessarily impair those
of _Serpentaria_, connected as they are with an essential oil; whilst
the addition of the acid at any other stage of the process than that
directed, would produce decompositions in the vegetable substances; and
it is evident that were the _Spirit of Cinnamon_ added previously, it
would be entirely lost by vaporization. So in making the _Compound
Decoction of Sarsaparilla_, the _Sassafras_ should be added after the
other ingredients have undergone boiling. The Decoctions of _Lichen
Islandicus_ and _Sarsaparilla_ constitute a popular remedy on the
Continent, in certain forms of Phthisis; now it is evident that as the
former plant loses its virtues by long coction, and the latter requires
a protracted ebullition for the extraction of its virtues, they ought
not to be included under the same general directions; each decoction
should be separately performed, and the results subsequently mixed.
COMPOUND MEDICINES have been divided into two Classes, _viz_.