ded. This was not uncommon, and in the main was no
doubt attributable--(1) to the lowering of the vitality of the
surrounding tissues by creeping blood extravasation, and sometimes to
actual pressure by the extravasation on the vessels necessary for the
establishment of the collateral circulation. (2) To the frequency with
which both artery and vein required to be ligatured.

Beyond these common causes, however, others must be advanced, dependent
on the general and local condition of the nervous system in these cases.
In general mental state many of the patients were much shaken, and in
others the condition spoken of as local shock in a former chapter had
been marked. In a third series obvious individual nerve lesions were
co-existent with those to the vessels. Beyond this a fourth nervous
element of unknown quantity, the effect of the form of injury on the
vaso-motor nerves accompanying the great vessels, must be taken into
consideration.

I believe all these factors were of importance, since it appeared to me
that gangrene occurred more often than I should have expected. In one
case which I have heard of, gangrene followed a very slight injury to
the foot in a patient who had apparently made an excellent recovery
after ligature of the femoral artery.

The nervous factor seems another element in favour of reasonable delay
in active interference with traumatic aneurisms of the above varieties
in the absence of threatening symptoms.

It is worthy of remark that no case of gangrene due to aneurism came
under my notice, except subsequently to operation.

Since the above chapter was written, my friend, Mr. J. E. Ker, has sent
me his experience in the treatment of four aneurisms, which is of such
interest that I insert it as an addendum.

_Arterial haematomata._--(1) Popliteal, treated by local incision. Both
artery and vein completely divided. Ligature of the four ends. Cure.
(2) Traumatic aneurism of upper third of forearm. Treated by rest and
pressure by bandage. On the eighth day pulsation and bruit ceased
spontaneously, and the remains of the sac steadily consolidated until
the man's discharge on the twenty-sixth day.

_Arterio-venous aneurisms._--(1) At junction of brachial and axillary
arteries. Proximal ligature. Cure. (2) Arterio-venous aneurism at the
bend of the elbow. Ligature of the brachial at the junction of the
middle and lower thirds of the arm. Cure.

FOOTNOTES:

[14] The murmur is still present