Thus the immediate agent of nature, in the suppression of lmmorrhage, is pressure effected by the clot of blood, whilst the vessel is placed by its own properties in the condition most fa vorable to the operation ; and it is curious to ob serve how universally the principle has been acted on, though probably first suggested by accident,--or empiricism. The burning iron of the older surgeons produced the pressure of an eschar ; agaric and sponge entangled the blood and retained a coagulum on the spot; even the more modern invention of the ligature is in the first instance only pressure, but with the mani fest advantages of being applied directly and immediately, of being firm and not likely to slip, and independent of rest, position, and bandage, which are indispensable when other modes of compression are had recourse to.
But the permanent suppression of arterial lremorrliage can only be effected by the actual obliteration of the vessel at the spot where it had been opened or divided, a process that is the result of inflammation of the lining mem-. brave, and of the coagulating lymph thereby poured out, or of the artery ceasing to transmit blood through it, and thus becoming as it were useless in the economy. Both these influences are exemplified in the permanent cure of a wounded artery, for in an incredibly short space of time after the external coagulum has been formed, lymph is effused from the wound in the vessel : and internally, betWeen this lymph and the nearest collateral branch, another coa gulum of blood is formed, to which a consi derable degree of importance has been attached, though probably without sufficient reason. It cannot be very instrumental in controlling hw morrhage, because it does not occupy the entire capacity of the artery : its shape is conical, the base lying on the lymph poured out from the wound, from which it gradually tapers to the next branch, and it seems to be formed of a small quantity of the blood, which, being pushed into that branch, remains there, is placed out of the current of the circulation, and must coagulate. The transmission of blood to the limb below is now to be effected through the medium of the anastomosing vessels, which for this purpose become proportionably enlarged. This quality possessed by arteries of increasing their own diameters, or in other words of accommodating themselves to their contents, is curious and interesting, and although not admitting of ex planation, cannot for a moment be doubted. No fact has been more satisfactorily proved by dissection, and like the contractility of the artery already noticed, the effects of this power exhibit themselves gradually and slowly. The circu
lation of the limb seems scarcely to be inter rupted, for in a few minutes the arteries below appear, as has been observed by Dupuytren, like soft cords under the finger, evidently filled with blood,,but totally devoid of pulsation. It is a long time before this latter proof of a re stored activity in the circulation comes to be perceptible, and perhaps is never again equal to what it had been before the occurrence of the accident. The external wound, of course, heals like any other of a similar nature, and it is rare that the limb experiences any incon venience subsequently. The internal coagulum is soon absorbed, and in process of time the vessel, from the point of division to the next branch above and below, degenerates into an impervious ligamentous cord.
Such is the progress of events when the efforts of Nature are sufficient to arrest the bleeding ; but after all it is a fortunate case that ends thus, and experience teaches that there is little wisdom in leaving a moderately sized artery to her resources alone. What more frequently happens is this : the artery retracts and contracts it is true, and a coagulum forms, which, as the patient becomes faint or weak, is allowed to become consolidated, and for that time is sufficient to save him. But he recovers, or perhaps he uses some stimulus or some ex citement, and the renewed circulation gradually loosens the clot, and a fresh gush of blood takes place. This recurs frequently, and an hemor rhagic disposition is formed ; the patient be comes pale and exsanguineous, anxious, and in continual agitation, and without the interven tion of art has but a slender chance of sur viving. In these cases, art adopts the principle of the natural cure, only regulating its force, and ensuring its continued operation for the requisite period. The first object to be at tained is the application of a. sufficient degree of pressure to control the bleeding : the second to maintain that pressure for a length of time to ensure the obliteration of the vessel. This is not the place to discuss the various methods that have been adopted for the accomplishment of these ends ; suffice it that the superiority of the ligature has been so far. proved by expe rience, that few surgeons of the present day would feel satisfied in entrusting a large or im portant vessel to a less powerful or enduring compression. But the ligature is in itself not unfrequently a cause of great and frightful mis chief, and, therefore, it will be necessary to examine into all the circumstances connected with this part of the subject.