The contents of the sac consist of fluid blood and a varying amount of clot which is deposited in concentric layers on the inner aspect of the sac, where it forms a pale, striated, firm mass, which constitutes a laminated clot.  Near the blood-current the clot is soft, red, and friable (Fig. 72).  The laminated clot not only strengthens the sac, enabling it to resist the blood-pressure and so prevent rupture, but, if it increases sufficiently to fill the cavity, may bring about cure.  The principle upon which all methods of treatment are based is to imitate nature in producing such a clot.

Sacculated aneurysm, as compared with the fusiform variety, tends to rupture and also to cure by the formation of laminated clot; natural cure is sometimes all but complete when extension and rupture occur and cause death.

An aneurysm is said to be diffused when the sac ruptures and the blood escapes into the cellular tissue.

#Clinical Features of Aneurysm.#—­Surgically, the sacculated is by far the most important variety.  The outstanding feature is the existence in the line of an artery of a globular swelling, which pulsates.  The pulsation is of an expansile character, which is detected by observing that when both hands are placed over the swelling they are separated with each beat of the heart.  If the main artery be compressed on the cardiac side of the swelling, the pulsation is arrested and the tumour becomes smaller and less tense, and it may be still further reduced in size by gentle pressure being made over it so as to empty it of fluid blood.  On allowing the blood again to flow through the artery, the pulsation returns at once, but several beats are required before the sac regains its former size.  In most cases a distinct thrill is felt on placing the hand over the swelling, and a blowing, systolic murmur may be heard with the stethoscope.  It is to be borne in mind that occasionally, when the interchange of blood between an aneurysm and the artery from which it arises is small, pulsation and bruit may be slight or even absent.  This is also the case when the sac contains a considerable quantity of clot.  When it becomes filled with clot—­consolidated aneurysm—­these signs disappear, and the clinical features are those of a solid tumour lying in contact with an artery, and transmitting its pulsation.

A comparison of the pulse in the artery beyond the seat of the aneurysm with that in the corresponding artery on the healthy side, shows that on the affected side the wave is smaller in volume, and delayed in time.  A pulse tracing shows that the normal impulse and dicrotic waves are lost, and that the force and rapidity of the tidal wave are diminished.

[Illustration:  FIG. 71.—­Radiogram of Aneurysm of Aorta, showing laminated clot and erosion of bodies of vertebrae.  The intervertebral discs are intact.]