The poisons of which we are about to offer the physiological and
chemical history, although more numerous than those which belong to the
mineral kingdom, are, notwithstanding, of far less importance in a
forensic point of view. With the exception of opium, and some few
others, they must be considered as objects of accidental, rather than of
criminal poisoning; and even with respect to the former narcotic, it may
be said to afford more frequently the means of destruction to the
suicide, than to the assassin.
The sensible qualities of smell, taste, and sometimes colour, which so
eminently characterise deleterious plants, must necessarily render them
ill calculated to favour that secresy, which constitutes the
indispensable companion of crime; while their bulk, and the
pharmaceutical preparation which they require, are alike inconsistent
with the hope of concealment.
Thus we receive, as it were, from Nature, that protection which art can
no longer supply; and the commission of crime is either prevented or
discovered, in cases where the powers of chemistry would fail in its
detection.
The objects which constitute the vegetable kingdom differ from every
species of mineral matter, not only in their peculiar organized
structure, but in the chemical arrangement of their elements; those of
inorganic matter are generally combined in very simple proportions, as
one and one, or one and two, &c. whereas in organized bodies, their
proportions are much more complicated; and _Dr. Ure_ observes,[394] that
such substances derive the peculiar delicacy of their chemical
equilibrium, and the consequent facility with which it may be subverted
and new modelled, to the multitude of atoms grouped together in a
compound; hence too, as _Mr. Children_[395] has observed, is one reason
of our utter inability to reproduce even the simplest body of this
class, when once its elements have been separated; it is not in the
diversity of these elements, but in the manner in which they are
grouped, that this peculiarity consists, for, continues the accomplished
chemist last mentioned, “vegetable substances seldom contain, as
essential, more than three principles—_oxygen_, _hydrogen_, and
_carbon_, and sometimes _azote_. With four simple elements then, a brief
alphabet for so comprehensive a history! has a bountiful Omnipotence
composed the beautiful volume of the living world, where, turn to what
page we may, fresh loveliness meets the eye, fresh cause of admiration
and delight.”
The analysis of vegetable bodies resolves itself into two parts, each of
which constitutes an equal object of interest to the forensic physician;
who, it will be shewn, may occasionally derive important information
from both. The first relates to the discovery of the _proximate_
principles of a vegetable substance. The second, to that of its
_ultimate_ elements. By the _proximate_, or, as they are sometimes
termed, the _immediate_ principles, we mean those compound substances
which exist in the living plant in a state identical with that, under
which chemical processes exhibit them, and are chiefly separable by the
action of different solvents. The number of these principles is
considerable, as _gum_, _starch_, _sugar_, _gluten_, _extractiue_,
_tannin_, _oils_, _acid_, _&c. &c._ By the _ultimate_ elements, we
understand those, of which the _proximate_ are composed, as _oxygen_,
_hydrogen_, _carbon_, and _azote_. In submitting a plant to destructive
analysis, for the purpose of obtaining its ultimate elements, we shall
derive compounds, which formed no part of the vegetable structure, and
which result from a new arrangement of the elements composing it;
_acetic_ and _carbonic acids_, for example, are obtained by the
destructive distillation of several vegetable substances, in which
neither of these acids existed ready formed, but only their
elements.[396] It may easily be imagined to what numerous fallacies such
a law of composition must have given origin, in the earlier periods of
chemical inquiry; and it is equally evident, that the utmost refinement
of chemical science, and the most rigorous methods of analysis, will be
required to enable us to deduce any satisfactory conclusion with respect
to the quality of a plant, from these data. Such perfection, indeed, has
not hitherto been attained, but the period is probably not far distant,
when our most sanguine anticipations upon this point may be realised. We
have only to trace the history of this branch of chemistry for the last
century, to become satisfied of its gradual and important progress
towards such an epoch, and of the improvements of which this department
of vegetable analysis is farther susceptible; let us, for the sake of
illustration, only compare the rude results obtained by the academicians
of Paris, at about the commencement of the seventeenth century, with
those of _MM. Gay-Lussac_ and _Thenard_[397], or with those, very lately
instituted in this country by _Dr. Ure_,[398] and we shall perceive that
while the former of these experimentalists, by the aid of heat, were
unable to form the slightest distinction between the most inert, and the
most poisonous species of plants, the latter, by means of the same
agent, aided by the modern doctrine of equivalent ratios, has succeeded
in establishing the proportions in which the elements of each vegetable
body combines; and with such accuracy, as to discriminate between
substances, which bear the greatest analogy to each other; as between
the varieties of sugar, and those of oil; and even between common flax,
and the same substance prepared according to the improved process of
_Mr. Lee_. This statement is sufficient to show the capability of
ultimate analysis, on certain occasions, to identify vegetable bodies;
but we are, at present, scarcely advanced far enough in such an
investigation, to make it subservient to the detection of vegetable
poisons. Nor has our knowledge with regard to proximate analysis, been
less successfully advanced. The late researches of the French and German
chemists have demonstrated the existence of several new alkaline bodies
in the class of vegetable poisons, to which some of these plants appear
to be exclusively indebted for their activity, as the _poppy_,
_hellebore_, _colchicum_, _&c._; and whose characters are so distinct
and striking, as to enable the chemist to recognise their presence by
appropriate re-agents. In other cases, the virulence of a plant would
appear to depend upon the combination of several[399] proximate
principles; while in some few instances there exist in the same
individual vegetable, two distinct elements of activity, as illustrated
by the interesting history of tobacco.
In cases of vegetable poisoning it will occasionally occur, that some
remains of the plant may be collected; and seeds, portions of the fungi,
and leaves, may be found in the contents of the stomach; whence a
knowledge of botany becomes indispensable. This branch of science is,
moreover, important to the toxicologist, as enabling him to pursue the
study of plants with greater precision; for experience has shewn that
there is a wonderful analogy between the structure of those plants which
resemble each other in medicinal operation. Thus those which, from their
dismal and dusky appearance, have been arranged under the title of
_Luridæ_, are in general highly poisonous; they also possess a very
peculiar and disagreeable smell, so that Nature has, upon this occasion,
kindly given us notice of approaching danger, by means of our senses.
Of equal importance with the knowledge of the generic and specific
characters, is that of their sensible qualities, and the changes which
these latter undergo by pharmaceutical preparation.
Cl. III. ACRID, or RUBEFACIENT POISONS.
Most of the subjects of this class constitute articles of Materia
Medica; so that ignorance on the one hand, and accident on the other,
may render them the unexpected source of mischief. With respect to the
physiological action of these bodies, the reader has only to refer to
our classification at page 207, to perceive that it will not admit of
generalization; for each division, it will be observed, contains
individuals which belong to the class of acrid poisons.
As the history of most of these articles is to be found in works on
Materia Medica, we shall not enter so fully into their properties, as we
might otherwise have considered necessary.
CAMBOGE or GAMBOGE.
This beautiful gum-resin is obtained by making incisions in the leaves
and young sprouts of the _Stalagmitis Cambogioides_[400] (Polygamia
Monæcia—_Nat. ord._ Tricoccæ. _Wild_:) It is first collected, in the
kingdoms of Siam and Ceylon, in cocoa-nut shells, and is thence
transferred into large earthen jars, where it remains until it is nearly
dried to a cake, when it is formed into rolls, and wrapped up in leaves.
It is imported into Europe[401] in cases and boxes. Its deep yellow
colour, which is so materially brightened by being wetted, and its
shining fracture, are characters sufficiently striking to enable the
practitioner to identify it; and when we add to these the history of its
habitudes with different menstrua, the chemist will have no difficulty
in detecting its presence, viz. when triturated with water, two-thirds
of its substance are speedily dissolved, and a turbid solution results;
alcohol dissolves nine-tenths, and forms a yellow transparent tincture,
which is rendered turbid by the addition of water; sulphuric ether
dissolves six-tenths of the substance; it is also soluble in alkaline
solutions, and the resulting compound is not rendered turbid by water,
but is instantly decomposed by acids, and the precipitate so produced is
of an extremely brilliant yellow colour, and soluble in an excess of
acid.
Its action upon the animal œconomy is that of a powerfully drastic
purge. We are, however, not acquainted with any case in which death
followed its administration. From the experiments made upon animals, it
would appear to produce its effects by a local action on the textures,
with which it comes in contact, and it will accordingly be found in the
third class of our physiological classification, (page 207.)