Treatise on Poisons by Sir Robert Christison
5. _Difference of tissue_ is an interesting modifying power in a
1191 words | Chapter 10
physiological point of view, but does not bear so directly on
medico-legal practice as the rest, and may therefore be passed over
cursorily.
On the corrosives and irritants a difference of tissue acts but
indirectly: their effects vary not so much with the tissue as with the
organ of which it forms part. But as to poisons which act through the
blood, their energy must evidently depend on the activity of absorption
in each texture.
The cutaneous absorption is slow, on account of the obstacle presented
by the cuticle, and by the intricate capillaries of the true skin.
Accordingly many active poisons are quite inert when applied to the
unbroken skin, or even to the skin deprived of the cuticle. Hydrocyanic
acid, perhaps the most subtle of all poisons, was found by Coullon to
have no effect when dropped on the skin of a dog.[55] Some authors have
even gone so far as to deny that poisons can be absorbed at all through
the skin, unless they are pressed by friction through the cuticle. But
this is an error; most gaseous poisons, such as carbonic acid and
sulphuretted hydrogen, and some solid poisons when volatilized, such as
the vapours of cinnabar, will act though simply placed in contact with
the skin; and there is distinct evidence that corrosive sublimate will
bring on mercurial action in the form of a warm bath, or when used as a
liniment.
On the mucous membrane of the stomach and intestines, poisons act much
more energetically than on the skin; which clearly depends in a great
measure on the superior rapidity of absorption there,—or, according to
some, on the facility with which poisons come in contact with the
sentient extremities of nerves.
The serous membranes possess an activity of absorption which hardly any
other unbroken texture can equal. Accordingly many poisons act much more
rapidly through the peritonæum than through the stomach. When oxalic
acid is introduced under the same collateral circumstances into the
stomach of one dog and the peritonæum of another, the dose may be so
apportioned, that the same quantity, which does not prove fatal to the
former, kills the latter in fourteen minutes.[56]
While the preceding modes in which poisons enter the blood are indirect,
they may be introduced directly by a wound in the vein. There is no way
in which poisons, that act through the blood, prove more rapidly fatal.
Some which act very slowly through the stomach cause instant death when
injected into a vein. A peculiar variety of this mode of introducing
poisons deserves to be distinguished, namely, the application of them to
a wound. If the surface bleeds freely, they may not act at all, because
they are washed away. But if they adhere, they soon enter the divided
veins. Hence, if they act in small doses, this mode of applying them is
hardly less direct than if they were at once injected into a vein.
So far the effect of difference in tissue has been determined. Poisons
that act through the blood act least energetically on the skin, more
actively on the alimentary mucous membrane, still more so on serous
membranes, and most powerfully of all when introduced directly into a
vessel. There are other textures, however, which merit notice, although
their place in the scale of activity has not been exactly settled.
On the mucous membrane of the pulmonary air-cells and tubes, poisons act
with a rapidity which is scarcely surpassed by their direct introduction
into a vein. This is plainly owing to the exceeding delicacy and wide
surface of the membrane. Hence three or four inspirations of carbonic
oxide gas will cause instant coma. A single inspiration of the noxious
gas of privies has caused instant extinction of sense and motion. Nay,
liquid poisons have been known to act through the same channel with
almost equal swiftness. For M. Ségalas found that a solution of extract
of nux-vomica caused death in a few seconds when injected in sufficient
quantity into the windpipe; and that half a grain will thus kill a dog
in two minutes, while two grains will rarely prove fatal when injected
into the stomach, peritonæum, or chest.[57]
As to the nervous tissue, it is a fact worthy of mention, that the
poisons which appear to act on the sentient extremities of the nerves,
do not act at all on the cut surface of the brain and nerves, or upon
any part of the course of the latter. This has been proved with respect
to most active narcotics.
The power of the cellular tissue as a medium of absorption, has not
been, and cannot easily be, ascertained. On the one hand it is difficult
to apply poisons to it, without also applying them to the mouths of
divided vessels; and, on the other hand, it is difficult to make a set
of experiments for comparison with others on the stomach, pleura, or
peritonæum, as the cellular tissue does not form an expanded cavity, and
consequently, the extent of surface to which a poison is applied cannot
be made the same in each experiment of a series. It is a ready medium,
however, for admitting poisons into the blood, especially if an
artificial cavity be made where the tissue is loose, as, for example, by
separating the skin from the muscles of the back with the finger
introduced through a small incision in the integuments.
The variations caused by difference of tissue in the activity of poisons
have been viewed in the previous remarks as depending chiefly on the
relative quickness with which absorption goes on. But in this way it is
impossible to explain the whole amount of the differences sometimes
observed. Some poisons cause death when applied to a wound in the
minutest quantity, but are quite harmless when swallowed in large doses:
Others are diminished a little in activity, but still remain powerful
and fatal poisons. There is not much difference in the power of arsenic
when it is applied to different textures, the skin excepted. But oxalic
acid injected into the peritonæum will act eight or ten times more
rapidly than when swallowed and the poison of the viper may prove fatal
to a man through a wound in almost invisible doses, while the whole
poison of six vipers may be swallowed by so small a creature as a
blackbird, with complete impunity.[58] Differences in the absorbing
power of the tissues cannot explain these facts.
The only rational way of accounting for them is by supposing that a part
of the poison is decomposed,—the change being greatest where absorption
is slowest and the power of assimilation strongest, namely, in the
stomach,—and least where absorption is quickest and assimilation almost
wanting, namely, in a wound. This explanation derives support from the
different effects of change of tissue on poisons of the different
kingdoms. Mineral poisons are least, and animal poisons are most,
affected in their action by differences of tissue, while vegetable
poisons hold the middle place:—an arrangement which coincides with the
respective difficulty of decomposition among mineral, vegetable, and
animal substances generally, whether under physical or under vital
processes.[59]
Reading Tips
Use arrow keys to navigate
Press 'N' for next chapter
Press 'P' for previous chapter