m associated with much haemorrhage, as torn or crushed vessels
quickly become occluded by contraction and retraction of their coats and
by the formation of a clot. A whole limb even may be avulsed from the
body with comparatively little loss of blood. The risk in such cases is
secondary haemorrhage resulting from pyogenic infection.

The _treatment_ is that applicable to all wounds, with, in addition, the
ligation of the lacerated vessels.

#Punctured wounds# of blood vessels may result from stabs, or they may
be accidentally inflicted in the course of an operation.

The division of the coats of the vessel being incomplete, the natural
haemostasis that results from curling up of the intima and contraction of
the media, fails to take place, and bleeding goes on into the
surrounding tissues, and externally. If the sheath of the vessel is not
widely damaged, the gradually increasing tension of the extravasated
blood retained within it may ultimately arrest the haemorrhage. A clot
then forms between the lips of the wound in the vessel wall and projects
for a short distance into the lumen, without, however, materially
interfering with the flow through the vessel. The organisation of this
clot results in the healing of the wound in the vessel wall.

In other cases the blood escapes beyond the sheath and collects in the
surrounding tissues, and a traumatic aneurysm results. Secondary
haemorrhage may occur if the wound becomes infected.

The _treatment_ consists in enlarging the external wound to permit of
the damaged vessel being ligated above and below the puncture. In some
cases it may be possible to suture the opening in the vessel wall. When
circumstances prevent these measures being taken, the bleeding may be
arrested by making firm pressure over the wound with a pad; but this
procedure is liable to be followed by the formation of an aneurysm.

_Minute puncture of arteries_ such as frequently occur in the hypodermic
administration of drugs and in the use of exploring needles, are not
attended with any escape of blood, chiefly because of the elastic recoil
of the arterial wall; a tiny thrombus of platelets and thrombus forms at
the point where the intima is punctured.

#Incised Wounds.#--We here refer only to such incised wounds as partly
divide the vessel wall.

Longitudinal wounds show little tendency to gape, and are therefore not
attended with much bleeding. They usually heal rapidly, but, like
punctured wounds