more minutely they are divided, and hence most energetically when in
solution. Some which are very energetic in the fluid state, hardly act
at all when undissolved. Morphia, the alkaloid of opium, may be given in
powder to a dog without injury in a dose, which, if dissolved in oil or
alcohol, would soon kill several. Previously dissolving poisons favours
their action in two ways,—by diffusing them quickly over a large
surface, and by fitting them for entering the bibulous vessels. Poisons,
before being absorbed, must be dissolved; and hence, those which act
though solid and insoluble in water, must, as a preliminary step, be
dissolved by the animal fluids at the mouths of the vessels. In this way
the poisonous effects of carbonate of baryta and arsenite of copper are
explained; for though insoluble in water, they are soluble in the juices
of the stomach.
Differences in aggregation, like differences in quantity, may affect the
kind as well as the degree of action. Camphor in fragments commonly
causes inflammation of the stomach; dissolved in spirit or olive oil, it
causes delirium or tetanus and coma.
The reduction of certain poisons to the state of vapour serves the same
end as dissolving them. When poisons are to be introduced by the skin,
no previous operation is more effectual than that of converting them
into vapour.