DETECTION OF POISONS.
The detection of a poison is, in many instances, no easy matter; it
should not therefore be rashly undertaken, except by one well skilled in
the minutiae of the processes to be adopted; but on the other hand, there
are so many points of practical importance which may be noted by the
practitioner in charge, that his attention should be specially directed
to these. The exact determination of the cause of death will depend
partly on the symptoms noted during life and on the appearances
found after death. These come within the province of the ordinary
practitioner; on the other hand, the special physical, chemical and
physiological portion of the inquiry should be referred to the expert.
In a book of this scope it is impossible to give full details with
regard to these last, but a brief sketch nay be useful.
The physical examination, say of the contents of the stomach and
intestines, should commence with noting the smell, color, and general
appearance of the matters submitted for examination. The odor, for
instance, may be useful in indicating the presence of prussic acid, of
alcohol, of opium, or of phosphorus. The color may indicate the presence
of salts of copper, of fragments of cantharides, &c. The general
appearance may give some clue to the mode of introducing the poison, the
kind of food or drink used to conceal it, &c. Seeds of poisonous plants
may be found: this is especially the case in India, where the seeds of
datura are frequently used for criminal purposes; or the poisonous
substance may have been administered in such quantity that a portion of
it may at once be secured for analysis. This not unfrequently happens in
poisoning by arsenic. It is not enough to employ the naked eye in
examining these suspected matters; a hand lens of some power should be
used; in this way characteristic crystalline forms, botanical
peculiarities, and such like, may be made out.
Still these are merely introductory to the most important part of the
research, which ought to be undertaken systematically, especially if
the quantity of material to be operated on is small. Most frequently the
matters to be examined are mixed, some soluble, some insoluble; but
there may also be submitted for analysis portions of the pure substance.
The object of the analyst is to obtain the substances which he has to
examine chemically in as pure a condition as possible, so that there may
be no doubt about the results of his testing; also, of course, to
separate active substances from those that are inert, all being mixed
together in the stomach and alimentary canal. Again, in dealing with
such fluids as the blood, or the tissues of the body, their natural
constituents must be got rid of before the foreign and poisonous body
can be reached. There is this difficulty further to contend with: that
some of the most poisonous of substances are of unstable composition and
readily altered by chemical reagents; to this group belong many
vegetable and most animal poisons. These, therefore, must be treated
differently from the more stable inorganic compounds. With an inorganic
poison we may destroy all organic materials mixed with it, trusting to
find it still recognizable after the process; not so with an organic
substance: that must be separated by other than destructive means.
When the mixture submitted for examination consists of bodies perfectly
soluble and perfectly insoluble, simple filtration may suffice to secure
their separation; but this is rarely the case, some colloidal material
being ordinarily mixed with the crystalloid, and the plan of separating
them by _dialysis_, as proposed by Graham, not being altogether
successful. When the substances looked for are volatile, distillation
may be employed to secure them in a state of purity; in this way
prussic acid is separated; but in the case of the poisonous alkaloids
other means must be adopted.
I. In the separation of such an alkaloid as strychnia, for example, the
suspected material is first of all acidulated by one of the weaker
mineral or stronger vegetable acids (hydrochloric acid is best), and the
whole carefully heated over a water bath. After a time this mixture is
to be filtered, and the filtrate well washed with boiling distilled
water, and the filtered fluid subjected to evaporation. When dry the
substance is to be rubbed up with distilled water, and again filtered;
this process to be repeated until a tolerably pure product be obtained.
This is next to be neutralized by hydrogen sodium carbonate, or
bicarbonate of soda, and the freed alkaloid taken up by rubbing or
shaking it with chloroform or ether, and the whole set aside in a
well-corked tall test tube. Finally, the ether or chloroform containing
the alkaloid is to be removed by a pipette and allowed to evaporate
spontaneously, when the alkaloid will probably be left behind in a state
fit for testing. This process is a modification of that invented by
Stas, in following out the case of the Count Bocarme.
II. For the destruction of organic matter in the search for an inorganic
poison, such as arsenic, a process introduced by Fresenius and Von Babo
is commonly employed. Its essentials are as follows: The organic matter
is to be reduced to as fine shreds as possible, and mixed with about
one-eighth of its bulk of pure hydrochloric acid. This is to be heated,
and, as it boils, from time to time crystals of potassic chlorate are
added, until the solids are reduced to a straw-yellow fluid. This is
next treated with hydrogen sodium sulphite, or bisulphate of soda,
until a distinct smell of sulphurous acid is given off, after which
sulphuretted hydrogen is to be passed through the fluid, concentrated if
necessary, for some hours, thus throwing down most metallic poisons in
the form of sulphide. This precipitate is to be collected and further
tested.
When exceedingly small quantities are dealt with the microscope is of
use, and the plan of subliming alkaloids and examining their crystals
under the microscope, introduced by Guy and Helwig, will be found very
useful. The shape of crystalline poisons is a valuable means of
determining their identity; arsenic and antimony may thus be readily
distinguished, as may other well known substances.
The spectrum has not yet been applied to toxicological research,
although it has been employed to determine the existence of a blood
stain.