the rapidity of their progress_ towards a fatal termination. Some of
them act instantaneously, and the effects of most of them are in general
fully developed within an hour or little more. But this character is by
no means uniform. The most violent may be made to act, so as to bring on
their peculiar symptoms slowly, or even by imperceptible degrees. Thus
arsenic, which usually causes violent symptoms from the very beginning,
may be so administered as to occasion at first nothing more than slight
nausea and general feebleness; and afterwards in slow succession its
more customary effects. In like manner corrosive sublimate may be given
in such a way as to cause at first mild salivation, and finally gangrene
of the mouth. Even many vegetable poisons might be administered in the
same way. The well-known consequences of digitalis in medicinal doses
will serve as a familiar instance. A still better illustration is
supplied by the medicinal effects of the alkaloid of nux-vomica, whose
action in other circumstances is most rapid and violent: Strychnia in a
moderate dose will cause death by violent tetanus in two or three
minutes; but when given in frequent small doses as a remedy in palsy, it
has been known to bring on first starting of the limbs, then stiffness
of the jaw, afterwards pain and rigidity of the neck; and these effects
might be increased so gradually, that the patient would seem to die
under ordinary tetanus. Nevertheless, the foregoing considerations being
kept always in mind, it still remains true, that the effects of poisons
for the most part begin suddenly, when the dose is large. This is an
important circumstance in regard to certain active poisons, such as the
mineral acids, oxalic acid, arsenic, strychnia, &c. For when it is
considered that in criminal cases they are given for the most part in
unnecessarily large doses, it follows that if the effect ascribed to
these poisons in such doses have not begun suddenly, the suspicion is
probably incorrect.
The same remarks may be applied to the sudden termination of the
symptoms. Poison is for the most part given criminally in doses so large
that it proves rapidly fatal. Yet this is not always the case; the
diseased state occasioned by poisons has often been prolonged, as will
be seen hereafter, for several weeks, sometimes for several months; nay,
a person may be carried off by a malady, the seeds of which have been
sown by the operation of poison years before.
The present would be the proper place for noticing the important
question regarding the interval of time, after which, if death
supervenes, it cannot be laid to the charge of the person who
administered the poison. It is unnecessary, however, to say much on the
subject. According to the English law, death must take place within a
year. As to the Scottish law, it may be inferred from what has been said
by the late Baron Hume on the subject of homicide generally, that a
charge of poisoning is relevant although the person should die at a
period indefinitely remote, and that it will infer the pains of law,
provided the operation of the poison can be distinctly traced,
unmodified by extraneous circumstances, from the commencement of the
symptoms to the fatal termination.[69] Of course the influence of these
modifying circumstances in lessening the criminal’s responsibility will
increase with the interval. The question for the medical jurist to
determine in such a case would therefore be, the distance of time to
which death may be delayed in the case of poisoning generally, and in
that of the particular poison. This question cannot be answered even
with an approach to precision, except in the instance of a few common
poisons. Most vegetable and animal poisons prove fatal either in a few
days or not at all; but some mineral poisons may cause death after an
interval of many days. It appears probable that arsenic may cause death
after an interval of several months, and it is well ascertained that the
symptoms of poisoning with the mineral acids have continued
uninterruptedly and without modification for eight months, and then
terminated fatally.