We are told that the observation made by Amussat," that in gun-shot wounds where all the parts were lacerated, the extremities of even the larger. essels did not bleed, suggested to him the application of the phenomenon to practical surgery, and led to the practice of the torsion of arteries. This operation con sists in laying bare a portion of the divided artery, and carefully detaching it from the sur rounding cellular membrane until its own cel lular tunic is distinctly to be seen ; it is then seized with a forceps, not unlike the common artery-forceps of Bell, and twisted on its axis until the extremity engaged between the blades is completely detached by the torsion. This forms something like a knot or knuckle at the end of the vessel, which mechanically blocks it up ; a coagulum is formed within, and the remainder of the process is said nearly to re semble that which succeeds the application of a ligature. Not having practised torsion on a vessel of any considerable size in the human subject, nor had an opportunity of examining after death a case thus treated, I am unable to comprehend, with sufficient precision, the exact process that is established. In experimenting on the femoral arteries of dogs, I have always found that the immediate obstacle to the flow of blood was a coagulum situated at the orifice, and apparently entangled in the lacerated cel lular coat; but for the reasons already men tioned, little confidence can be placed in such investigations.
Hitherto we have been considering those wounds of arteries, which, however important in other respects, are not attended by hemor rhage, and although ignorant of the operations of nature in effecting this result, it is of the less con sequence, inasmuch as it is not likely we shall attempt to imitate them, or entrust a large sized vessel to torsion alone. The wounds of arteries, accompanied by loss of blood, present themselves under very different circumstances ; there is always anxiety, agitation, and dismay on the part of the sufferer, and it may be that promptness and decision in the practitioner shall be required to preserve life. In any of these awful situations, coolness and self-pos session can alone ensure a freedom from em barrassment, and these qualities cannot be ex pected in any individual who has neglected to make himself acquainted with the nature of the mischief that has occurred, and the means by which it may be remedied.
The phenomena attendant on arterial hae morrhage occasioned by incised and punctured wounds exhibit remarkable varieties, according to the size, and of course to the structure of the vessel ; to the circumstance of its having been fairly divided, or only notched, or punc tured ; to the wound being so large and patu ions as freely to permit the escape of all the blood externally, or so small or oblique that the fluid, though withdrawn from the circula tion, is still retained within the limb. There is still another condition of wounded artery in which the blood that escapes from it is poured into an adjacent vein, and continues to circulate, though not in its proper vessel. However,
these latter cases are usually considered and described as forms of aneurism, and will, therefore, not be noticed until there is an op portunity of comparing the different species of that disease one with another.
`When a large artery is divided in an open wound, it may happen that the patient dies almost instantaneously, not from the absolute quantity of blood lost, but from its being with drawn too suddenly from the circulation, just as syncope is often produced by the rapid abstraction of blood in the common operation of phlebotomy. However, this is not uniformly the case, and experience has proved that vessels of such size and importance as the carotid and femoral arteries may be divided, and yet suffi cient time allowed for the successful interposi tion of art. Mr. Guthrie states, that when the femoral artery is cut across in the upper part of the thigh, the patient does not always bleed to death, although frequently lost; while if the division takes place in the middle or lower half of the thigh, the bleeding will probably cease of itself. When,fi however, an artery of still smaller size is divided, the powers of nature are almost always competent to restrain the haemorrhage, and consequently it is from an examination of vessels of this class under such circumstances that a knowledge can be ob tained of the nature and extent of these powers.
When a vessel of moderate size is divided, the blood is poured forth in jerks from its open mouth in a large and full stream ; soon, however, this stream is seen to become dimi nished in size, and most probably it ceases to flow per saltum. If the patient faints, the bleeding perhaps ceases altogether, nor will it be renewed unless accident or indiscretion gives to the blood an impetus sufficient to overcome the obstacle that opposes its exit, whatever that may be. When the artery is divided, its middle coat retracts immediately that its natural state of tension is removed, withdrawing with it the lining membrane, but leaving the cellular, to which it is but loosely attached, hanging out beyond it. It contracts, too, in diameter, as is evidenced by the diminished stream of blood. The power by which this contraction and re traction are performed is a vital property inhe rent in the artery itself; it has been called muscularity, and endless arguments have thus been raised about a name, as if no tissue in the body but muscle could be capable of contrac tion. But it operates in a manner very different from the rapid and decided contraction ofmuscle ; it is slow, gradual, and continued, and, there fore, is longer in bringing the large vessel into a state favourable for the suppression of heemor rhage than the small one. The next step is the entanglement of blood in the cellular coat of the vessel and its consequent coagulation when it comes to press in the most advantageous direction on its open mouth, and the hcemor rhage is stopped.