has actually entered the
vein beyond endeavouring to maintain the heart's action by hypodermic
injections of ether or strychnin and the application of mustard or hot
cloths over the chest. The head at the same time should be lowered to
prevent syncope. Attempts to withdraw the air by suction, and the
employment of artificial respiration, have proved futile, and are, by
some, considered dangerous. In a desperate case massage of the heart
might be tried.

THE NATURAL ARREST OF HAEMORRHAGE AND THE REPAIR OF BLOOD
VESSELS

#Primary Haemorrhage.#--The term primary haemorrhage is applied to the
bleeding which follows immediately on the wounding of a blood vessel.
The natural process by which such haemorrhage is arrested varies with the
character of the wound in the vessel and may be modified by accidental
circumstances.

(a) _Repair of completely divided Artery._--When an artery is
_completely_ divided, the circular fibres of the muscular coat contract,
so that the lumen of the cut ends is diminished, and at the same time
each segment retracts within its sheath in virtue of the recoil of the
elastic elements in its walls, the tunica intima curls up in the
interior of the vessel, and the tunica externa collapses over the cut
ends. The blood that escapes from the injured vessel fills the
interstices of the tissues, and, coagulating, forms a clot which
temporarily arrests the bleeding. That part of the clot which lies
between the divided ends of the vessel and in the cellular tissue
outside, is known as the _external clot_, while the portion which
projects into the lumen of the vessel is known as the _internal clot_,
and it usually extends as far as the nearest collateral branch. These
processes constitute what is known as the _temporary arrest of
haemorrhage_, which, it will be observed, is effected by the contraction
and retraction of the divided artery and by clotting.

The _permanent arrest_ takes place by the transformation of the clot
into scar tissue. The internal clot plays the most important part in the
process; it becomes invaded by leucocytes and proliferating endothelial
and connective-tissue cells, and new blood vessels permeate the mass,
which is thus converted into granulation tissue. This is ultimately
replaced by fibrous tissue, which permanently occludes the end of the
vessel. Concurrently and by the same process the external clot is
converted into scar tissue.

If a divided artery is _ligated at its