the possibilities. It is not necessary to assume that an actual
substance so diffuses itself, but the influence exerted may be thought
of as a force, possibly some form of molecular motion, which is set in
action at the area of injury and extends from this. No actual
substance passes along a nerve when it conveys an impulse.

We have left the injured area with an increased amount of fluid and
cells within it, with the blood vessels dilated and with both cells
and fluid streaming through their walls, and the cells belonging to
the area actively repairing damages and multiplying. The process will
continue as long as the cause which produces the injury continues to
act, and will gradually cease with the discontinuance of this action,
and this may be brought about in various ways. A foreign body may be
mechanically removed, as when a thorn is plucked out; or bacteria may
be destroyed by the leucocytes; or a poison, such as the sting of an
insect, may be diluted by the exudate until it be no longer injurious,
or it may be neutralized. Even without the removal of the cause the
power of adaptation will enable the life of the affected part to go
on, less perfectly perhaps, in the new environment. The excess of
fluid is removed by the outflow exceeding the inflow, or it may pass
to some one of the surfaces of the body, or in other cases an incision
favors its escape. The excess of cells is in part removed with the
fluid, in part they disappear by undergoing solution and in part they
are devoured by other cells. With the diminishing cell activity the
blood vessels resume their usual calibre, and when the newly formed
vessels become redundant they disappear by undergoing atrophy in the
same way as other tissues which have become useless.

When these changes take place rapidly the inflammation is said to be
acute, and chronic when they take place slowly. Chronic inflammation