Substances, whose continued administration gives strength and vigour to
the body.
It is very justly admitted, that a state of permanent tension in the
fibres of the body is necessary for the existence of life, and that any
undue departure from such a condition is followed by debility. Thus, Sir
Gilbert Blane observes, that no muscle, whether voluntary or
involuntary, can act unless its fibres are previously in such a state,
that if divided they would shrink by their own resiliency, leaving an
interval between the cut extremities; the same may be said of the
vascular system in all its ramifications, in order to give play to their
contraction in grasping and propelling their contained fluids. It
appears that there are certain medicinal bodies that have the power of
affecting this state of tension, and when their effects contribute to
its restoration, they are properly denominated _Tonics_. We are not,
however, to consider them as producing such a change by any mechanical
operation upon the matter of which the fibre is composed, but by a
direct action upon its living principle; it seems probable that certain
poisons may thus produce sudden death by their agency on the vital
principle, by which the tension of the heart and whole arterial system
is immediately relaxed. In this point of view, _Tonics_, like the other
remedies which we have described, may be _relative_ or _absolute_ in
their operation. Venesection, purgation, or whatever will, under certain
conditions of the body, occasion a salutary change in its vital powers,
may produce a corresponding alteration in the tension of its fibres, and
consequently fall under the denomination of a tonic remedy: but
independent of the state of the body, there would seem to be certain
substances that act as specific stimuli upon the living fibre, and are
in certain cases indispensable for the maintenance of its healthy tone;
such are vegetable bitters, which produce a powerful effect upon the
digestive organs, and by nervous sympathy, upon the rest of the system.
_Bitter Extractive_,[141] seems to be as essential to the digestion of
herbivorous, as salt is to that of carnivorous animals; it acts as a
natural stimulant, for it has been shewn by a variety of experiments
that it passes through the body without suffering any diminution in its
quantity, or change in its nature. No cattle will thrive upon grasses
which do not contain a portion of this vegetable principle; this fact
has been most satisfactorily proved by the late researches of Mr.
Sinclair, gardener to the Duke of Bedford, which are recorded in that
magnificent work, the “HORTUS GRAMINEUS WOBURNENSIS.” They shew, that if
sheep are fed on _Yellow Turnips_, which contain little or no bitter
principle, they instinctively seek for, and greedily devour any
provender which may contain it, and if they cannot so obtain it they
become diseased and die. We are ourselves conscious of the invigorating
effects of slight bitters upon our stomach; and their presence in malt
liquors not only tends to diminish the noxious effects of such
potations, by counteracting the indirect debility which they are liable
to occasion, but even to render them, when taken in moderation,
promoters of digestion. The custom of infusing bitter herbs in vinous
drinks is very ancient and universal; the _Poculum Absinthiatum_ was
regarded in remote ages as a wholesome beverage, and the Wormwood was
supposed to act as an antidote against drunkenness. The Swiss peasant
cheers himself amidst the frigid solitude of his glaciers, with a spirit
distilled from _Gentian_, the extreme bitterness of which is relished
with a glee that is quite unintelligible to a more cultivated taste.
With regard to the natural use of _Bitter Extractive_, it may be laid
down as a truth, that it stimulates the stomach,—corrects putrefying and
unwholesome nutriment,—promotes tardy digestion,—increases the nutritive
powers of those vegetable substances to which it is united,—and
furnishes a natural remedy for the deranged functions of the stomach in
particular, and through the sympathetic medium of that organ, for the
atony of remote parts in general; and I shall hereafter shew, that in
its medicinal applications it certainly imparts additional activity to
many remedies, while it renders the stomach and system more susceptible
of their salutary energies. As an essential ingredient in the provender
of herbivorous animals, it may I think be admitted as a fact, that its
importance is _in an inverse ratio_ with the nutritive powers[142] of
the food, and we accordingly find, in conformity with that universal
scheme of self-adjustment and compensation, which influences all the
operations of nature, that cultivation, which extends the nutritive
powers of vegetable bodies, generally diminishes their bitterness in the
same proportion; the natural history of the Potatoe offers a good
illustration of this fact, for the roots of this useful plant which have
been so greatly improved by culture, are in their wild state both small
and _bitter_.[143] Gummy matter, which seems to result from the first
change of the sap, is undoubtedly rendered more digestible and nutritive
by the presence of a _bitter_; pure gum is not very much disposed to
yield to the assimilative functions; “it frequently passes through the
bowels,” says Dr. Chapman,[144] “very little changed, as I have
witnessed a thousand times.” We see therefore the value of the bitter
principle, in the economy of the _Lichen Islandicus_, which is intended
as the food of animals in northern latitudes; we are told that boiled
linseed constituted the sole diet of the people of Zealand during a
scarcity of long continuance, on which occasion, symptoms of great
debility occurred, attended with those of dyspepsia; so again Professor
Fritze, in his Medical Annals, states that vegetable mucilage, when used
as a principal article of diet, relaxes the organs of digestion, and
produces a viscid slimy mucus, and a morbid action in the primæ viæ, an
effect which analogy shews might be obviated by the addition of bitter
extractive. For the same reason animals that feed in marshy lands, on
food containing but little nourishment, are best defended from the
diseases they are liable to contract in such situations by the ingestion
of bitter plants.[145] Upon these occasions nature is very kind, for the
particular situation that engenders endemic diseases is generally
congenial to the growth of the plants that operate as antidotes to them.
I have offered these views upon the subject of _Bitter Extractive_, from
a conviction that they will essentially contribute to the establishing
of just and philosophical notions, respecting the necessity and _modus
operandi_ of many vegetable tonics.
As the action of tonics is gradual, so their operation is not followed
by that exhaustion consequent upon the use of diffusible stimulants.
The substances which compose the class of tonics are derived from the
vegetable and mineral kingdoms; those of the former are generally
bitter, and produce their effects by a primary action on the stomach,
and are not absorbed into the circulation, as experiments upon _Bitter
Extractive_ have most fully demonstrated; those derived from the mineral
kingdom, comprehending several of the metals, appear in some instances
to pass into the circulation, although several of them, like the
vegetable tonics, act primarily on the _primæ viæ_; I apprehend this
observation applies to the _nitrate of silver_, which certainly
possesses considerable powers as a tonic in certain cases of dyspepsia,
for which it may perhaps be indebted to the bitterness which
distinguishes it.