My own opinion on this subject is strong, and to the effect that none of these operations should be undertaken before a period of from two to three months after the injury, unless there is evidence of progressive enlargement. In every case which came under my own observation progressive contraction and consolidation took place up to a certain point under the influence of rest. When this process has become stationary, and the surrounding tissues have regained to a great extent their normal condition, the operations are far easier, and beyond this more likely to be followed by success. It appears to me that one argument only can be raised against the above opinion, viz. the possibility of healing of the recent wound in the vessels when the force of the circulation is lowered by proximal ligature. Such experience as that quoted from Sir W. Stokes and two of Mr. Ker's cases, mentioned below, support this possibility, but in all the reported results were recent. Against them I can only advance my knowledge of several mishaps following early operation. In concluding these observations on injuries to the arteries and aneurisms, a few general remarks as to the occurrence of gangrene after operation must be added. 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.