posed to any source
of prolonged irritation. Atheroma may affect arteries in any part of the
body; in some instances almost every vessel is diseased, in others only
a few, or even parts of one vessel. It is a very common result of
endocarditis extending into the aorta, which we find perhaps the most
frequent seat of atheroma. As a result of this condition the affected
vessel becomes impaired in its contractile power, loses its natural
strength, and, in consequence of its inability to sustain its accustomed
internal pressure, undergoes in many cases dilatation at the seat of
disease, constituting aneurism. In an atheromatous vessel, calcareous
deposits soon occur, which render it rigid, brittle, and subject to
ulceration or rupture. In such vessels the contractility is destroyed,
the middle coat atrophied and beyond repair. Atheroma in the vessels of
the brain is a frequent cause of cerebral apoplexy. No symptoms are
manifested by which we can recognize this condition during life.

CONSTRICTION OF AN ARTERY.

This is usually the result of arteritis, and may partly or wholly be
impervious to the flow of blood. When this occurs in a large vessel it
may be followed by gangrene of the parts; usually, however, collateral
circulation will be established to nourish the parts previously supplied
by the obliterated vessel. In a few instances constriction of the aorta
has produced death.

ANEURISM.

Aneurism is usually described as true or false. True aneurism is a
dilatation of the coats of an artery over a larger or smaller part of
its course. Such dilatations are usually due to chronic endarteritis and
atheroma. False aneurism is formed after a puncture of an artery by a
dilatation of the adhesive lymph by which the puncture was united.

_Symptoms._--If the aneurism is seated along the neck or a limb it
appears as a tumor in the course of an artery and pulsating with it. The
tumor is round, soft, and compressible, and yields a peculiar
fluctuation upon pressure. By applying the ear over it a peculiar
purring or hissing sound may sometimes be heard. Pulsation, synchronous
with the action of the heart, is the diagnostic symptom. It is of a
slow, expansive, and heavy character, as if the whole tumor were
enlarging under the hand. Aneurisms seated internally may occupy the
cavity of the cranium, chest, or abdomen. As regards the first, little
is known during life, for all the symptoms which they produce may arise
from oth