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Full text of "Medical Jurisprudence And Toxicology"

CAUSES   MODIFYING   THE   ACTION   OF   POISONS

tered in a" large 'dose, produces a local corrosive action, and may result in
instantaneous death from shock, but in a smaller dose it may prove fatal "by
acting on the heart, while in still smaller doses it acts on the spinal nervous
system and the brain.

2.    Form.—Under this head will have to be considered—(a) Physical
State;   (b)   Chemical Combination;   (c)  Mechanical Combination.

(a)  Physical   State.—Poisons   administered   in   the   form   of   gases   or
vapours act at once and most energetically.   Poisons in the form of solutions
act much more rapidly than powders.   Poisons in the form of solids act 'very
slowly, because they are difficult to be absorbed and, in some cases, may
prove quite harmless.

(b)  Chemical Combination.—The action of a poison depends upon the
solubility   or  insolubility  resulting  from  a  chemical   combination.   Thus,
silver nitrate and hydrochloric acid are both strong poisons when taken
separately but, when combined, form an insoluble salt of silver chloride
which   is   almost   innocuous.    Similarly,   baryta    X^ariuni   dioxide)    and
sulphuric acid act as poisons, if administered separately but, in combination,
form an insoluble salt, barium sulphate, which has "no poisonous Affects on
the system.   In the same way strong acids and alkalies, when administered
together, are rendered inert by their neutralizing effect.

'It should be borne in mind that certain poisons which are almost
" insoluble in water may become dissolved in the acid secretion of the stomach,
and are then readily absorbed into the blood. For instance, lead carbonate,
white precipitate and copper arsenite, which are insoluble in water, are thus
rendered sufficiently soluble for absorption through the mucous membrane
of the stomach. -                           - , r,                                      - -          '

(c)  Mechanical Combination.—The' action of a poison may T>e altered
very much if combined mechanically with inert substances.    For instance, a
small dose of a concentrated mineral acid produces a corrosive action, but
the same dose, largely diluted with water, may be taken internally with
impunity.   A heavy poisonous powder, when mixed with water, will settle
down at the bottom of a vessel, and the victim fails to take it; while it would
have been swallowed had it been taken with a fluid of nearly the same
specjfiq gravity as that of the powder.   For this reason arsenic - is usually
mixed with milk, tea, coffee or cocoa -\frhen administered < for homicidal pur-
poses.   Alkaloids, when taken with animal -charcoal, are rendered more or
less inert.                                             < *'           ,             -

3.    Mode of Administration.—The rapi<ilty of -the action of a poisdii
depends upon the mode in which it is'intrdduced into the system.   ThuSj a
poison acts most rapidly when inhajed in;?a gaseous or vaporous form or
introduced into the blood current by injection'into a-vein, V>y
injection,-or by application to an o^en wound. < -Next in rapidity is the

of a poison which is*applied to, a serous surface, niext when introduced i
cellular tissue, and .a&ext when applied - to a mucous membrane.   The
rapid is the action of a poison applied to the- unbroken skin.   In this case a
drug dissolved in oil acts more rapidly than a watery solution.

A poison ingested into the stomach acts more rapidly than when injected,
into the  rectum,  since the  absorptive  power of  the  stomach and '-
intestine is greater than that of'the large intestine and rectum.
is eliminated a,s rapidly(as* it 4s absorbed, no poisonous
to-occur*,  On li^e/G^3^;teEtd, if, tfee irate of absorp^w
of eliiiii&ation, rthe potsexk tei$fe % accumulate in 'the
cumulative action.   For, £xafmpfe, mercury, lead,.