Treatise on Poisons by Sir Robert Christison
1. The evidence derived from _the effects of suspected food, drink, or
1270 words | Chapter 29
medicine_ is better than that drawn from the effects of the vomited
matter or contents of the stomach. But an important objection has been
made to both, namely, that what is poison to man is not always poison to
the lower animals, and that, on the other hand, some of the lower
animals are poisoned by substances not hurtful to man.
A good deal of obscurity still hangs over the relative effects of
poisons on man and the lower animals. There are two species, however,
whose mode of life in respect to food closely resembles our own, and
which, according to innumerable experiments by Orfila, are affected by
almost all poisons exactly in the same way as ourselves, namely, the cat
and dog, but particularly the latter.
In general poisons act less violently on these animals; thus two drachms
of opium are required to kill a middle-sized dog,[105] while twenty
grains have killed a man, and undoubtedly less would be sufficient. It
appears that one poison, alcohol, acts more powerfully on them than on
man. There are also some poisons, such as opium, which, although
deleterious to them as well as to man, nevertheless produce in general
different symptoms. Yet the differences alluded to are probably not
greater than exist between man and man in regard to the same substances;
and therefore it may be assumed, that, on the whole, the effects of
poisons on man differ little from those produced on the dog and cat.
The present objection is generally and perhaps justly considered a
stronger one, when it is applied to other species of animals. But it
must be confessed after all, that our knowledge of the diversities in
the action of poisons on different animals is exceedingly vague, and
founded on inaccurate research; and there is much reason to suspect,
that, if the subject is studied more deeply, the greater number of the
alleged diversities will prove rather apparent than real. Both reasoning
and experiment, indeed, render it probable, that some orders, even of
the perfect animals, such as the _Ruminantia_, are much less sensible
than man to many poisons, and especially to poisons of the vegetable
kingdom. But so far as maybe inferred from the only accurate inquires on
the subject, their effects differ in degree more than in kind. Some
exceptions will without doubt be found to this statement. For example,
oxalic acid, besides inflaming the stomach, causes violent convulsions
in animals, but in man it for the most part excites merely excessive
prostration; and opium most generally excites in man pure sopor, in
animals convulsions also. Other exceptions, too, exist by reason of
functional peculiarities in certain animals. Thus irritant poisons do
not cause vomiting in rabbits or horses, because these animals cannot
vomit; neither do they appear to cause much pain to rabbits, because
rabbits have not the power of expressing pain with energy. But
exceptions like these, and particularly such as are unconnected with
functional peculiarities, will probably prove fewer in number, and less
striking than is currently imagined. For it is, on the other hand, well
ascertained, that many, indeed most of the active poisons whose effects
have been examined by a connected train of experiments, produce nearly
the same effects on all animals whatever from the highest to the lowest
in the scale of perfection. It has been fully proved, that arsenic,
copper, mercury, the mineral acids, opium, strychnia, conia, white
hellebore, hydrocyanic acid, cyanogen gas, sulphuretted hydrogen, and
many others, produce nearly the same effects on man, quadrupeds, birds,
amphibious animals, and even on fishes and insects.[106]
Accordingly there are cases, in which the evidence from experiments on
animals with suspected articles of food is unequivocal. For example;—a
sexton and his wife, who had got a bad name in their village in
consequence of informing against the bailiff for smuggling, and who were
on that account shunned by all the neighbours, accused the bailiff and
his wife of having tried to poison them by mixing poison with their
bread. Immediately after eating they were attacked, they said, with
sickness, griping, swelling, and dizziness; and they added, that a cat
was seized with convulsions after eating a part of it, had sprung away,
and never returned. A large portion of the loaf was therefore sent to
the Medical Inspector of the district; who reported, that it seemed
exactly similar to another unsuspected loaf;—that, although he was not
able to detect any poison, it might after all contain one,—vegetable
poison particularly;—but that he could hardly believe it did, for he fed
a dog, a cat, and a fowl several days with it, and they not only did not
suffer any harm, but even appeared very fond of it.[107] In this case it
was clear that poisoning was out of the question. On the other hand, the
effects of some poisons on man may be developed so characteristically in
animals as to supply pointed evidence. Thus, in the case of Mary
Bateman, an infamous fortune-teller and charm-worker, who after cheating
a poor family for a series of years, at last tried to avoid detection by
poisoning them, it was justly accounted good evidence, that a portion of
the pudding and the honey, supposed to have been poisoned, caused
violent vomiting in a cat, killed three fowls, and proved fatal to a dog
in four days, under symptoms of irritation of the stomach such as were
observed in the people who died.[108]
It has been farther objected to experiments on animals with suspected
articles of food, drink, or medicine, that it is difficult to administer
poison to them in a state of concentration, and to prevent it from being
discharged by vomiting. This objection, however, may be obviated by
performing the experiment in the way recommended by Professor Orfila. A
small opening is made into the gullet, previously detached from its
surrounding connexions, the liquid part is introduced by a funnel thrust
into the opening, and the solid portion previously made into little
pellets is then squeezed down. Lastly, the gullet is tied under the
aperture. The immediate effect of the operation is merely an appearance
of languor; and no very serious symptom is observable till four or five
days at soonest after the tying of the gullet. Hence if signs of
poisoning commence within twenty-four hours, they are independent of the
injury done by the operation.[109] This process requires some adroitness
to execute it well. It cannot be tried successfully but by a practised
operator, who, for reasons already given, would hardly ever try
experiments of the kind with suspected articles. Mention is here made of
it, therefore, chiefly because it is the best mode of experimenting in
those cases in which it is necessary, as will presently be seen, to
determine disputed points in the physiology of poisons.
I may here shortly notice a method which has been lately proposed for
detecting poisons that enter the blood, and which is founded on their
effects on animals. M. Vernière suggests that advantage may be taken of
the extreme sensibility of the medicinal leech to procure at least
presumptive evidence, when no evidence can be procured in any other
manner. He has related some experiments to prove that the leech, when
placed in the blood of dogs killed by nux-vomica, is affected even when
the quantity of the poison is exceedingly small.[110] It is extremely
doubtful whether any importance can be attached to this criterion, as
every one knows that the leech is apt to suffer from a variety of
obscure causes, and among the rest from some diseased states of the
body.
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