Vegetable and animal poisons may be altogether destroyed by the process
of digestion. This observation will explain why sometimes no poison
could be found in cases of poisoning with crude opium or other vegetable
solids. A French physician, M. Desruelles, has related the case of a
soldier, who died six hours and a half after swallowing two drachms of
solid opium, and in whose stomach nothing was found but a yellowish
fluid, quite destitute of the smell of the drug.[98]
Some mineral poisons, such as corrosive sublimate, lunar caustic, and
hydrochlorate of tin, are also decomposed in the stomach. But they are
not removed beyond the reach of chemical analysis. The decomposition is
the result of a chemical, not of a vital process; and the basis of the
poison may be found in the solid contents of the stomach under some
other compound form. Other poisons again may be apt to elude detection
by altering their form, by combining with other substances, without
themselves undergoing decomposition. Thus it appears from a case related
by Mertzdorff of Berlin, that, in poisoning with sulphuric acid, after
the greater part of the poison is discharged by vomiting, the remainder
may escape discovery by being neutralized: For, although he could not
find any free acid in the contents of the stomach, he discovered 4½
grains in union with ammonia by precipitation with muriate of
baryta.[99]
It may be also right to mention another kind of decomposition which may
render it impossible to detect a poison that has been really
swallowed—namely, that arising from decay of the body. In several recent
cases bodies have been disinterred and examined for poison months or
even years after death. In these and similar cases it would be
unreasonable to expect always to find the poison, even though it existed
in the stomach immediately after death. Some poisons, such as oxalic
acid, might be dissolved and then exude; others, such as the vegetable
narcotics, will undergo putrefaction; and others, such as prussic acid,
are partly volatilized, partly decomposed, so as to be undistinguishable
in the course of a few days only. The mineral poisons, those at least
which are solid, are not liable to be so dissipated or destroyed. Some
authors, indeed, have said that arsenic may disappear in consequence of
its uniting with hydrogen disengaged during the progress of
putrefaction, and so escaping in the form of arseniuretted-hydrogen gas;
and they have endeavoured to account in this way for the non-discovery
of it in the bodies of the people who had been killed by arsenic, and
disinterred for examination many months afterwards.[100] But the
supposition is by no means probable: at least arsenic has been detected
in the body fourteen months, nay, even seven years, after interment. For
farther details, on this curious topic, the reader may turn to the
article Arsenic.
On the whole, the result of the most recent researches is that the
effect of the spontaneous decay of dead animal matter in involving
poisons in the general decomposition appears to be much less
considerable than might be anticipated. For this most important
medico-legal fact, the toxicologist is indebted to the experimental
inquiries of MM. Orfila and Lesueur.[101] The poisons tried by them
were—sulphuric and nitric acids, arsenic, corrosive sublimate,
tartar-emetic, sugar of lead, protomuriate of tin, blue vitriol,
verdigris, lunar caustic, muriate of gold, acetate of morphia, muriate
of brucia, acetate of strychnia, hydrocyanic acid, opium, and
cantharides. They found that after a time the acids become neutralized
by the ammonia disengaged during the decay of animal matter;—that by the
action of the animal matter the salts of mercury, antimony, copper, tin,
gold, silver, and likewise the salts of the vegetable alkaloids, undergo
chemical decomposition, in consequence of which the bases become less
soluble in water, or altogether insoluble;—that acids may be detected
after several years’ interment, not always, however, in the free
state;—that the bases of the decomposed metallic salts may also be found
after interment for several years;—that arsenic, opium, and cantharides
undergo little change after a long interval of time, and are scarcely
more difficult to discover in decayed, than in recent animal
mixtures;—but that hydrocyanic acid disappears very soon, so as to be
undistinguishable in the course of a few days.