These consist of alcohol, proof spirit, or spirit of greater or less
density, holding in solution one or more of those proximate principles
of vegetable or animal matter which are soluble in that menstruum, viz;
_Sugar_, _resin_, _extractive_, _tannin_, _cinchonia_, _camphor_,
_volatile oils_, _morphia_, _emetin_, _conein_, _elatin_, _tiglin_, and
_several acids_. The proper solvent of those bodies, termed gum-resins,
appears to be proof spirit. The compilers of the _Codex Medicamentarius_
of Paris, have defined the different degrees of spirituous strength
requisite for the full and perfect extraction of the active elements of
different bodies with great truth and nicety; thus they direct for these
purposes a spirit of three different standards, viz. 36 (_Sp._ _gr._
·837,) 32 (·856) 22, (·915) of Beaumé’s hydrometer; with the first are
prepared the _resinous_ tinctures; with the second those wherein the
_resinous_, _extractive_, or _gummy_ elements, hold nearly an equal
place; and with the third those in which the latter predominate. We are
moreover indebted to this committee for having set at rest a question
which has been long doubtful, whether the addition of alkaline agents
increases the extractive powers of the spirit? They have indeed
ascertained by experiment, that the reverse not frequently obtains; for
instance, they found that a smaller proportion of _guaiacum_ was
dissolved by the spirit of ammonia, than by alcohol of the same
strength, and that the quantity of matter dissolved from the _root of
Valerian_ was the same in both cases. Very active substances, soluble in
alcohol, are those which are particularly adapted for tinctures, since
they furnish preparations which are efficient in small doses, and very
manageable in extemporaneous prescription, such are the tinctures of
_Opium_, _Digitalis_, _Hyoscyamus_, _Scilla_, _&c._ and from the
chemical analysis of _Elaterium_, there can be no doubt but that a very
active and useful tincture of that substance might be introduced into
practice; while Dr. Nimmo has very clearly proved that the active matter
of the _Croton Tiglium_ may be thus concentrated, see _Tiglii Oleum_. On
the contrary, substances of little activity, except in large doses, are
the least adapted for this form of exhibition, as in such cases the
solvent will act more powerfully on the living system, than the
principles which it may hold in solution, and when continued for any
length of time, will lay the foundation of the pernicious custom of dram
drinking; such tinctures, however, are not without their value in
combination; they sometimes increase the efficacy, and often correct the
operation or disguise the flavour, of the medicines with which they may
be united; for example, the cathartic tinctures in _Formula 70_, augment
the purgative powers of the combination, at the same time that they
correct its unpleasant operation; many other illustrations are presented
in the different formulæ, for the explanation of which I must refer the
student to the _Key Letters_. The addition of a tincture has likewise
the effect of preserving decoctions and infusions from spontaneous
decomposition, the _compound tincture of Cardamoms_ answers such an
object in the _compound decoction of Aloes_. Tinctures are sometimes
made with æther, but they are generally more strongly characterised by
the nature of the menstruum than by that of the substance dissolved in
it; indeed, æther is used in these cases, not to dissolve substances
which would resist the action of alcohol and water, but for the sake of
its own direct action on the body; thus the Edinburgh pharmacopœia
directs an _Æthereal Tincture of Aloes_, which is more penetrating and
stimulant than the alcoholic tinctures; the London College, with the
exception of the _Aromatic Spirit of Æther_, does not recognise any
preparation of this nature: I have already alluded to the _Æthereal
Tincture of Digitalis_ of the French Codex, than which nothing can be
more injudicious, for the digitalis does not amount to more than 1⁄70th
part of the tincture, and must therefore be entirely counteracted by the
stimulant effects of the menstruum. The same objection cannot be urged
against the æthereal tinctures of _Castor_, _Musk_, and _Amber_, since
in these cases, the subject and the menstruum concur in their mode of
operation.
Tinctures derive their names from the substances which impart activity
to them, and as the medicinal history of each substance is detailed
under its proper head, it will be unnecessary to dwell at any length
upon the individual virtues of these tinctures.