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These vary in extent and nature. The instrument by which they are inflicted, the violence attending the injury, and the nature and importance of the parts divided, or in the neighbourhood of the wound, must all be attended to, for, from an accurate knowledge of these circumstances, the treatment of the case comes to be conducted accordingly. Wounds are divided into incised, punctured, bruised, and lacerated; that is, into such as are inflicted by a sharp-edged, sharp-pointed, or an obtuse body. In the first kind, there is greater or less effusion of blood, according to the size and number of the vessels divided. Some extend but a little way beyond the subcutaneous cellular tissue, and are consequently attended with but slight bleeding; others penetrate to a greater depth, and occasion hemorrhage from a large vessel, or other alarming symptoms, by having reached some important organ; others, though not of so great a depth as the former, may still, on account of their mere extent, be accompanied with very considerable loss of blood from a number of small branches. It is seldom that fatal effects immediately follow external wounds; but they may and do occur when bloodvessels of the first class only are cut. They are most likely to prove suddenly fatal when the arteries are only partially divided, and when the large veins accompanying them are also involved. When the artery is cut through, its extremities retract, effusion takes place into the sheath and compresses the orifice; the formation of a coagulum within the vessel is thus promoted, and the hemorrhage arrested. But, when a portion only of the circumference is divided, the blood continues to flow through the aperture and onwards, as if into a smaller ramification of itself, no retraction or contraction of the vessel can occur, coagulation is slow, and the bleeding profuse. I have seen a wound of so small a vessel as the internal mammary prove almost instantaneously fatal. Wounds of the large internal vessels for the most part prove immediately fatal; as wounds of the heart, or the large vessels passing to and from its cavities, at the root of the lungs, or at the upper part of the liver. When the heart, or the vessels within the pericardium, have been divided, it can be readily understood how life should be immediately destroyed, since the blood effused into the cavity of the pericardium by its pressure completely arrests the action of the heart. But occasionally punctured wounds, in such situations, have not been followed by instant death. In such cases, alarming symptoms occur at the time, but subside, and the patient may for some time suffer no uneasiness, but afterwards expires suddenly during muscular exertion, or perhaps in a fit of violent passion. Blood must have been effused into the pericardium at the first, causing symptoms of, or actual, syncope; but then the aperture in the vessel had become obstructed by coagulum before blood had been poured out in such quantity as to effectually prevent the actions of the heart; at a future period the coagulum gives way, and the subsequent effusion is limited only by the pericardial cavity being completely filled. In wounds, hemorrhage is the symptom which most alarms the bystanders, and which demands immediate attention; but, to operate successfully, the surgeon must divest himself of all fear, and learn to look boldly on the open and bleeding mouths of arteries. Effusion of blood ceases spontaneously, even from considerable vessels, on faintness supervening, and thus many lives are saved; but as soon as reaction commences it generally recurs, and may prove fatal, unless proper measures be resorted to.

When an artery is divided, its extremity retracts within the sheath, it also contracts, and coagulation occurs; thus the orifice is obstructed, and a temporary barrier formed to further hemorrhage. The tube, however, is permanently closed by effusion of lymph from its orifice, and consolidation of the surrounding parts.

The circumstances which follow division of an artery are these:—The immediate effect is retraction of its ends within the investing sheath, and a simultaneous contraction of the coats, so as to diminish the calibre. From the superior orifice there is necessarily a profuse flow of blood, which is discharged through the sheath that formerly enclosed that part of the vessel which has retracted. After considerable effusion of blood, the flow becomes slower and less profuse; particles of blood adhere to those filaments which previously connected the artery to the sheath, but which were lacerated by the sudden retraction of the divided extremity; these particles coagulate, and lessen the canal through which the blood is discharged, whilst they present an irregular surface, on which the blood continues to be deposited and to coagulate; and thus the aperture in the sheath is ultimately closed. This external coagulum is found to commence at the extremity of the artery, where it is of a cylindrical form, and shuts up the mouth of the vessel; it then extends along the canal in the sheath, frequently assuming a conical form; and, if a free discharge has been allowed for the blood, it will terminate at the cut margin of the sheath, otherwise it will be found continuous with the coagulum blocking up the external wound. Also, when hemorrhage has been resisted by the shutting of the external wound, blood is infiltrated into the cellular tissue around the bleeding point, and there coagulates; but this circumstance can be productive of little or no pressure on the parietes of the vessel, so as to assist those other natural means which obstruct it. The flow of blood through the divided vessel being prevented, the circulating fluid necessarily passes through the nearest collateral branches, leaving the blood in the extremity of the larger trunk in a state of comparative rest; consequently, coagulation occurs in this situation. The internal coagulum, however, is small, and not sufficient to occupy completely the cavity of the vessel; it is of a conical form, its apex being towards the heart, and opposite to the first collateral branch, and its base resting on the external coagulum, and there adhering to the internal surface of the artery. But, whilst this latter process is advancing, the capillary vessels supplying the cut margins of the artery have begun to act; they throw out coagulating lymph, and continue to do so until their secretion has completely filled the vessel immediately opposite to its divided margins; thus a third and more effectual coagulum is formed,—one of plastic matter, situated between the external and internal coagula of blood, and in general closely adherent to them. Lymph is also effused externally to the artery and its sheath, forming a dense stratum, which separates the extremity of the vessel from the external wound; it becomes organised, forms granulations, and thus the parts are consolidated, and the wound cicatrised. When the artery is permanently obstructed by the adhesion of its cut margins, the external coagulum can be dispensed with, and is gradually absorbed. Afterwards all the newly formed parts are condensed, and diminish in size; the artery contracts, its internal surface finally embraces the coagulated blood which lay loose in its canal; its coats appear to be thickened, and it is firm and hard. Ultimately, in consequence of the continuance of absorption, it becomes much more attenuated, so as scarcely to differ from the surrounding cellular tissue. Similar changes occur in the lower extremity of the divided artery; in general it retracts farther, its orifice is more contracted, and, the flow of blood being much less profuse than in the superior, the natural means for its temporary closure are sooner accomplished. When an artery has been divided close to the origin of a collateral branch, no bloody coagulum can form internally, for the blood in that situation is necessarily in a state of constant motion.

If the hemorrhage is suppressed artificially, either by ligature, or by otherwise well-applied pressure, no external coagulum is formed; there appears only the internal bloody coagulum, the lymphatic effusion, and consolidation of the compressed part. The natural contraction and retraction cannot occur in vessels partially divided; hemorrhage, therefore, is more violent and dangerous from a partial than from a complete section. Again, transverse wounds are more dangerous than longitudinal; in the latter, the edges of the wound are spontaneously approximated on account of the structure of the vessels, whilst, from the same cause, the margins of the latter continue separate, and, in fact, the aperture is a complete circle; the lips of an oblique wound will be more or less apart, in proportion as it approaches to the transverse direction. When an artery has been punctured, the wound in the sheath perhaps does not correspond with that in the vessel; blood, therefore, accumulates between the vessel and its sheath, and there coagulates. The wound is thus compressed, its edges kept in contact, and the farther escape of blood prevented; the lips of the incision are then agglutinated by effused lymph, and cicatrisation occurs. This, however, cannot be expected to take place unless methodical pressure has been applied from the first. Even from small punctures blood is effused under the sheath and into the neighbouring cellular tissue, rapidly, and in such quantity as to prevent adhesion. The effusion continues, and a false aneurism is formed. If a considerable part of the circumference has been divided, the lymph may be, and generally is, superabundant, and often to such an extent as to close up the canal of the artery at that point; but, if the aperture is minute and in a longitudinal direction, lymph will seldom be effused in greater quantity than is sufficient for the cicatrisation; and, though it should be superabundant, it is afterwards removed by the absorbents. In all cases, the cellular tissue round the wounded point is much thickened and condensed by the deposition of lymph, but this gradually disappears after cicatrisation has been completed. Sometimes, and generally when the wound has been transverse and large, the process of adhesion is disturbed, and suppuration occurs; in this case the wound in the vessel communicates with the fistulous track in the externally effused lymph, and may be the source of troublesome hemorrhage. In other instances of extensive transverse wounds, the undivided slip ulcerates, and the artery becomes obliterated, by means of the same natural processes that occur in complete division. In cases of laceration of an artery, when its coats have been forcibly torn rather than divided, little or no bleeding takes place. The vessel retracts; the lacerated margins of its inner coat become puckered up, so as to contract greatly the orifice of the vessel; the lacerated sheath is pulled out to a point, and closed at a little distance from the divided inner coats. If a large artery is torn asunder in the dead body, this stretching out and contraction of the sheath will prevent injection passing; in short, the immediate effects of the injury are such as to favour the instant formation of coagula, by which the hemorrhage is arrested until the orifices of the vessel be permanently closed by the adhesive process. Thus, in instances where the whole of an extremity has been torn off, the patients have generally lost but a very small quantity of blood.

From wounds of veins the blood flows, not in a sub-saltatory but in a uniform stream: its colour is dark, and the flow is easily suppressed. The common opinion is, that to place a ligature on a vein is dangerous, and to be scrupulously avoided. The process of reparation, besides, in a wounded vein, is different from that in an artery. Veins are less disposed to the secreting action by which adhesion is perfected; and, when inflamed, the inflammation is extremely apt to extend along the coats of the vessel; which latter circumstance has been ascribed to the great proportion of cellular tissue in their coats. When punctured longitudinally, the lips of the wound remain in contact, and cicatrisation, by means of effused lymph, is soon effected; in fact, the wound heals by the first intention. But if opened obliquely or transversely, not to a great extent, the immediate result is discharge of blood, and, when this has ceased, a coagulum forms in the wound, the margins of which remain separate; and this coagulum generally communicates with blood effused into the sheath of the vessel. After some time, the lips of the wound, encircling the coagulum which occupies the aperture, and which has temporarily averted the hemorrhage, become somewhat turgid, and increased in vascularity; they then appear to assume a secreting action, by which a membranous substance, of extreme delicacy, is produced; and the extent of this membrane is increased until it form an expansion, investing the outer surface of the clot; it then becomes thickened, by addition of matter, similar to itself, from the recent vessels which ramify in it. At the same time it forms adhesions to the surrounding cellular tissue, and resembles the original tunics of the vein. After being consolidated, so as to prevent the flow of blood through that part, the coagulum, formed to arrest the hemorrhage until a more complete barrier should be furnished, is gradually absorbed. But the membrane long remains smooth, thin, and diaphanous, and can be thereby readily distinguished from the original coats. This reparative process is much longer in being finished than the corresponding one in arteries; and, from what has been stated, it is evident that the two actions differ in other respects than the time requisite to complete them. When a vein has been completely divided, the extremities are closed by means similar to those which have been already detailed in regard to arteries.

In many, nay in most, instances of hemorrhage from a wounded artery, the surgeon cannot wait for the natural processes by which the flow of blood is arrested, but must have recourse to immediate and certain means. In division of the smaller arteries, or in minute wounds of the larger, pressure, well applied, will often be sufficient. In both cases it immediately stops the flow: in the former, it prevents the blood from penetrating into that portion of the sheath which has been vacated by the retracted artery; and it being thereby confined, and kept in a state of rest, coagulation soon takes place. At the same time, the compression brings the divided margins of the vessel into close apposition, and thereby permanent closure, by adhesion, is quickly accomplished. In the latter, the mere circumstance of the escape of blood being prevented, naturally hastens the closure of the minute aperture by the natural process; and, if the compression be accurate and very firm, the opposite surfaces of the vessel, being brought in contact, may adhere, and the canal be obliterated at the wounded point. It is obvious that, in this latter class, pressure can only be of advantage immediately after the infliction of the wound, and not when blood is extravasated to a great extent.

Pressure may be used along with styptics, or along with escharotics, actual or potential. They may be often employed when pressure ought not; styptics promote the contraction and retraction of the divided extremities, and thereby expedite the formation of a coagulum. Escharotics form a slough, which, adhering to the extremity of the vessel, stops the flow of blood, and the cut margins of the vessel, being stimulated by the application, soon cohere. Active stimulating applications merely cause effusion quickly of coagulated lymph, and thus often arrest hemorrhage from very vascular surfaces better than the so-called styptics. Not unfrequently, after the separation of the slough, it is found that union has not taken place, and hemorrhage is renewed; from this circumstance, the remedy cannot be trusted to, except when the divided vessels or vessel are of small size. It may be stated, generally, that these means are of little avail without methodical pressure. In oozing from small vessels, pressure may be applied by means of agaric, sponge, or lint. In bleeding from small vessels, where there is general oozing from the surface, and pressure cannot readily be made, applications tending to produce effusion of lymph—stimulants, such as turpentine or creosote, are often remarkably efficacious, and very speedily so; but in wounds of the larger vessels, the most efficient mean is a graduated compress of lint placed immediately on the external wound, and supported by a firmly-applied bandage. The bandage ought to encircle not only the wounded part, but every part of the limb with a uniform tightness, not so great as to arrest the general circulation; the parts are thereby supported, and engorgement prevented. This method, when employed previously to the effusion of much blood into the cellular tissue, has proved effectual in wounds even of the brachial, femoral, and carotid arteries. When blood has been extensively injected into the limb, when the aperture in the vessel has remained pervious, and when a large diffused aneurism exists, bandaging is worse than useless. By its application in such a case the limb becomes discoloured and swells extensively; there is a risk of mortification from impeded circulation. If a small quantity only of blood has escaped, its diffusion and increase may be prevented by the bandage: but a cyst will nevertheless be formed in the cellular tissue; its parietes will communicate with the margins of the aperture in the artery, its cavity with the canal of the vessel; an aneurism of the false kind will be established, and will run the course of one arising spontaneously.

A ligature, well applied, is the only means that can be relied on. The immediate effect of a tightly-drawn ligature is to avert the flow of blood, to divide the internal and middle coats at the deligated point, the cellular coat remaining entire, and to narrow the canal for some extent above the point at which it is applied. Coagulation then occurs within the vessel above the ligature, provided there is no collateral branch in the immediate vicinity. The ruptured margins of the internal coat effuse lymph and cohere; lymph is effused also in the cellular tissue, exterior to the artery and to the ligature; by the compression of the ligature, ulceration occurs in those parts which it envelopes, and the foreign body is discharged; but before this occurs the canal of the vessel has been obliterated by an internal coagulum, and by the effused lymph. Afterwards, the same absorption and consolidation occur as in a divided artery, the orifice of which has closed permanently and spontaneously.

When from a punctured wound profuse hemorrhage ensues, there is reason to suspect that an important vessel has been hurt, and the bleeding point must be sought for. After the artery giving out the blood has been discovered, the external wound must be enlarged, so as to expose the vessel, and admit of the convenient application of a ligature. It will not be sufficient to include the vessel above the wounded point, for the lower part will, after some time, be supplied with blood by the collateral branches almost as freely as by the large trunk, and, consequently, bleeding will be renewed. Two ligatures are to be employed, one above, the other below, the wound. The wounded vessel must be exposed, as already stated, but not detached more than is sufficient for the application of the ligature; and at the same time the ligatures ought to enclose nothing but the vessel. Neither ought the ligatures to be placed at any considerable distance, but as close to the wounded point as possible; otherwise circulation in the included part may be restored. The ligature, round, narrow, and firm, ought to be tightly applied. Cases of hemorrhage have occurred in which the tying of the vessel immediately above the wound has been successful; but these are few, and by no means afford any authority for the general adoption of such a measure. If the vessel is merely punctured, it is necessary to apply the ligature by means of a blunt pointed needle, and the parts are to be disturbed as little as possible. If, however, the artery is completely divided, its cut extremities are to be drawn out of their sheath by a hook or forceps, and the ligatures applied close to the connections of the vessel; the vasa vasorum, in the immediate vicinity of the deligated point, being left to carry on those processes by which obliteration is accomplished. In punctured or partial wounds of arteries, it deserves consideration whether the hemorrhage may not be restrained by the application of slight pressure, so regulated as to prevent the flow of blood laterally through the wound, but not so forcibly applied as to stop the onward current of the blood along the vessel, from the part of the tube above to that below the puncture. Some experiments made by Dr. Davy seem favourable to this view; as bleeding from the carotid arteries, partially divided transversely, in dogs was easily arrested by the means above-mentioned, the wound of the vessel readily healing, so as to preserve its tube entire; whereas, when the pressure was increased, the hemorrhage became violent. The subject is mentioned as one worthy of a further experimental investigation. The instrument which will generally be found most useful for laying hold of the vessel is the common dissecting forceps, but a tenaculum will, in certain circumstances, be more convenient. By far the most convenient machine is that here represented.