l injuries. The
haemorrhage from a large vein so damaged is usually profuse, but it is
more readily controlled by external pressure than that from an artery.
When a vein is merely punctured, the bleeding may be arrested by
pressure with a pad of gauze, or by a lateral ligature--that is, picking
up the margins of the rent in the wall and securing them with a
ligature without occluding the lumen. In the large veins, such as the
internal jugular, the femoral, or the axillary, it is usually possible
to suture the opening in the wall. This does not necessarily result in
thrombosis in the vessel, or in obliteration of its lumen.

When an _artery and vein are simultaneously wounded_, the features
peculiar to each are present in greater or less degree. In the limbs
gangrene may ensue, especially if the wound is infected. Punctured and
gun-shot wounds implicating both artery and vein are liable to be
followed by the development of arterio-venous aneurysm.

#Entrance of Air into Veins--Air Embolism.#--This serious, though
fortunately rare, accident is apt to occur in the course of operations
in the region of the thorax, neck, or axilla, if a large vein is opened
and fails to collapse on account of the rigidity of its walls, its
incorporation in a dense fascia, or from traction being made upon it. If
the wound in a vein is thus held open, the negative pressure during
inspiration sucks air into the right side of the heart. This is
accompanied by a hissing or gurgling sound, and with the next expiration
some frothy blood escapes from the wound. The patient instantly becomes
pale, the pupils dilate, respiration becomes laboured, and although the
heart may continue to beat forcibly, the peripheral pulse is weak, and
may even be imperceptible. On auscultating the heart, a churning sound
may be heard. Death may result in a few minutes; or the heart may slowly
regain its power and recovery take place.

_Prevention._--In operations in the "dangerous area"--as the region of
the root of the neck is called in this connection--care must be taken
not to cut or divide any vein before it has been secured by forceps, and
to apply ligatures securely and at once. Deep wounds in this region
should be kept filled with normal salt solution. Immediately a cut is
recognised in a vein, a finger should be placed over the vessel on the
cardiac side of the wound, and kept there until the opening is secured.

_Treatment._--Little can be done after the air