with a strip of peritoneum or omentum.

The most serious form of arterial _thrombosis_ is that met with _in the
abdominal aorta_, which is attended with violent pains in the lower
limbs, rapidly followed by paralysis and arrest of the circulation.

THROMBO-PHLEBITIS AND THROMBOSIS IN VEINS

#Thrombosis# is more common in veins than in arteries, because slowing
of the blood-stream and irritation of the endothelium of the vessel wall
are, owing to the conditions of the venous circulation, more readily
induced in veins.

Venous thrombosis may occur from purely mechanical causes--as, for
example, when the wall of a vein is incised, or the vessel included in a
ligature, or when it is bruised or crushed by a fragment of a broken
bone or by a bandage too tightly applied. Under these conditions
thrombosis is essentially a reparative process, and has already been
considered in relation to the repair of blood vessels.

In other cases thrombosis is associated with certain constitutional
diseases--gout, for example; the endothelium of the veins undergoing
changes--possibly the result of irritation by abnormal constituents in
the blood--which favour the formation of thrombi.

Under these various conditions the formation of a thrombus is not
necessarily associated with the action of bacteria, although in any
of them this additional factor may be present.

The most common cause of venous thrombosis, however, is inflammation of
the wall of the vein--phlebitis.

#Phlebitis.#--Various forms of phlebitis are met with, but for practical
purposes they may be divided into two groups--one in which there is a
tendency to the formation of a thrombus; the other in which the
infective element predominates.

In surgical patients, the _thrombotic form_ is almost invariably met
with in the lower extremity, and usually occurs in those who are
debilitated and anaemic, and who are confined to bed for prolonged
periods--for example, during the treatment of fractures of the leg or
pelvis, or after such operations as herniotomy, prostatectomy, or
appendectomy.

_Clinical Features._--The most typical example of this form of phlebitis
is that so frequently met with in the great saphena vein, especially
when it is varicose. The onset of the attack is indicated by a sudden
pain in the lower limb--sometimes below, sometimes above the knee. This
initial pain may be associated with shivering or even with a rigor, and
the temperature usually rises