Читать книгу Surgical Experiences in South Africa, 1899-1900 - George Henry Makins - Страница 28
Type Wounds
Оглавление1. Nature of the external apertures.—The apertures of entry and exit in uncomplicated cases are very insignificant, but the size naturally varies slightly with that of the special form of bullet concerned. As will be shown moreover, the difference in size is the only real distinguishing characteristic in many cases between wounds produced by the modern bullet of small calibre and those resulting from the use of the older and larger projectiles of conical form. I have been very much struck on looking over my diagrams of entry, and especially exit, wounds to find that they reproduce in miniature most of those figured in the History of the War of the Rebellion; some of these diagrams are reproduced in this chapter.
Aperture of entry.—The typical wound of entry with a normal undeformed bullet varies in appearance according to whether the projectile has impinged at a right angle or at increasing degrees of obliquity, or again, to whether the skin is supported by soft tissues alone, or on those of a more resistent nature such as bone or cartilage.
Fig. 16.—Mauser Entry and Exit Wounds.
A, entry in buttock; circular opening filled with clot and crossed by a tag of tissue. B, exit in epigastrium near mid-line; irregular slit form, with well-marked prominence. Specimens hardened in formalin immediately after death; the resulting contraction has slightly exaggerated the irregularity of outline of the entry wound
Fig. 17.
Gutter Wound of outer aspect of shoulder, caused by a normal Mauser, which subsequently perforated a man's leg. At the central part the gutter was ¾ in. deep a few days after the injury
When the bullet impinges at a right angle the wound is circular, with more or less depressed margins, and of a diameter, corresponding to the size of the bullet occasioning it, from a quarter to a third of an inch. The description 'punched out' has been sometimes applied to it, but it would be more correct to reverse the term to 'punched in,' since the appearance is really most nearly simulated by a hole resulting from the driving of a solid punch into a soft structure enveloped in a denser covering. The loss of substance, moreover, in the primary stage is not actually so great as appears to be the case, fragments of contused tissue from the margin being turned into the opening of the wound track. The true margin therefore is not sharp cut, and the nature of the line differs somewhat according to the structure of the skin in the locality impinged upon. Thus the granular scalp and the comparatively homogeneous skin of the anterior abdominal wall will furnish good examples of the nature of the slight difference in appearance. From the first the margin is also often somewhat discoloured by a metallic stain, similar to that seen when a bullet is fired through a paper book. This ring is, however, narrow, and not likely to be noticeable when the bullet has passed through the clothing. In any case it is subsequently obscured by the development of a narrow ring of discoloration due to the contusion. This latter varies in width, and still later a halo of ecchymosis half an inch or more in diameter surrounds the original wound.
Fig. 18.—Oblique Exit Gutter.
Diagram enlarged to actual size from case shown in fig. 24, p. 64.
With increasing degrees of obliquity of impact more and more pronounced oval openings of entry result, culminating in an actual gutter such as is seen in fig. 17.
In all oval openings the loss of substance is more pronounced at the proximal margin, while the wound is liable to undergo secondary enlargement at the distal margin, since in the former the epidermis is mainly affected, while in the latter the epidermis is spared as an ill-nourished bridge, the deeper layers of the skin suffering the more severely. When the wound occurs in regions, such as the chest-wall or over the sacrum, where the skin is firmly supported, the oval openings are often very considerable in size, reaching a diameter at least double that of the circular ones. In the case of the oval openings the depression of the margins is not such a well-marked feature as in wounds resulting from rectangular impact of the bullet, since the distal margin is really lifted.
Fig. 19.
Oval Entry Wound over third sacral vertebra. Exit wound, anterior abdominal wall. Slightly starred variety. Diagram made on second day
Aperture of exit.—The wound of exit in normal cases offers far more variation in appearance than that of entry, this variation depending on several circumstances: first, the want of support to the skin from without, and such other factors as the degree of velocity retained by the travelling bullet, the locality of the opening, and the density, tension, and resistance offered by the particular area of skin implicated.
When the range has been short and the velocity high, it is often difficult to discriminate between the two apertures. Both may be circular and of approximately the same size, and the only distinguishing characteristic, the slight depression of the margin of the wound of entrance, may be absent if any time has elapsed between the infliction of the injury and examination by the surgeon. One very strong characteristic if present is the general tendency of the margins, and even the area surrounding the exit wound itself, to be somewhat prominent. Fig. 16 shows this point, although the wound from which it was drawn had been produced thirty-six hours before death. The specimen was then hardened in formalin and still preserves its original aspect. This character is, however, more frequently displayed in wounds received at mean, or longer, ranges. In wounds produced by bullets travelling at the highest degrees of velocity it is often absent.
Fig. 20.
Circular Entry back of arm; exit (bird-like) in anterior elbow crease
Fig. 21.
Circular Entry over patella. Starred exit of elongated form in popliteal crease
When the range of fire has been greater and the velocity retained by the bullet lower, slit wounds are common, or some of the slighter degrees of starring. Actual starring I never saw, but reference to figs. 20 and 21 will show a tendency in this direction, also a close resemblance to the starred wounds resulting from perforations by large leaden bullets. Such wounds, I believe, are usually the result of a somewhat low degree of velocity.
Slit exit wounds may be vertical or transverse (fig. 20) in direction, and the production of these is dependent on the locality in which they are situated, the thickness, density, and tension of the skin, and the nature of the connection of the latter with the subcutaneous fascia in the locality. Thus in wounds of different parts of the hairy scalp, so little variation exists in the relative density and structure of the skin, that, in spite of the want of external support at the aperture of exit, it is often difficult to discriminate offhand the two apertures, if neither bone nor brain débris occupies that of exit.
If, however, a wound crosses from side to side a region such as the thigh where well-marked differences exist in the subjacent support, thickness, and elasticity of the skin implicated in the apertures, the wound of entry, if in the thick skin of the outer aspect, was usually circular, while the exit in the thin elastic skin of the inner aspect was either slit-like or starred. The difficulty in laying down any general rule as to the occurrence of circular or slit apertures of exit in any definite region is, however, great, as may be seen by reference to the accompanying diagrams taken from two patients wounded at Paardeberg (figs. 22 and 23).
In fig. 22 the bullet entered the outer and posterior aspect of the left buttock, crossed the limb behind the femur, and emerged at the inner aspect by a vertical slit: the bullet then entered the scrotum by a vertical slit, and emerged by a typical circular aperture; re-entered the right thigh by a transverse slit aperture, and, striking the femur in its further course, underwent deformation, and finally escaped by an irregular aperture ¾ of an inch in diameter. The occurrence of exit slits in the adductor region is common, and to be explained by the tendency of the comparatively thin elastic skin to be carried before the bullet; the slit entry in this position must, I suppose, be explained by the comparatively slight support afforded by the underlying structures, which are often in a condition of hollow tension. The scrotal wounds are perhaps more difficult to account for, but in this case the fact of the distal aperture being directly supported by the right thigh is a ready explanation of the circular exit, while the skin corresponding to the slit entry was no doubt carried before the bullet, and finally gave way in the line of a normal crease.
Fig. 22.
Entry and Exit Wounds in both thighs and scrotum.
From right to left: 1. Circular entry in left buttock behind trochanter. 2. Vertical slit exit in adductor region. 3. Slit entry in scrotum (probably inverted before bullet broke the surface, and then a slit occurred in a normal crease). 4. Circular exit in scrotum (here supported by surface of right thigh). 5. Transverse slit entry in right adductor region. 6. Irregular 'explosive' exit, the bullet having set up on contact with the front surface of the femur, but without having caused solution of continuity of the bone
In fig. 23 all the wounds are circular except the final exit, which was irregular as a result of the bullet in this case also having struck the femur in the second thigh. Considerable variation also exists in the size of the circular apertures; this illustrates the secondary enlargement often occurring in such wounds, and most marked at the apertures of entry, as the more contused. Both diagrams were made from patients eight days after the reception of the wounds.
Fig. 23.
Wound of both Thighs. First and second entry typical circular wounds. First exit a small circular wound; the bullet 'set up' on contact with the femur without causing solution of continuity of the bone, and second exit is irregular and large.
This diagram is of considerable interest when compared with fig. 22. I believe the comparative regularity in the wounds to have been due to a higher degree of velocity of flight on the part of the bullet
Lastly, vertical or transverse slits may be looked for with considerable confidence in situations in which transverse oblique or vertical folds or creases normally exist in the skin, and depend on the lines of tension maintained by the connection of the skin in these situations to the underlying fascia. Thus I saw well-marked transverse and vertical slits in the forehead corresponding with the creases normally found there, and in this situation I noted some slit entries. Transverse slits were common in the folds of the neck, the flexures of the joints (fig. 20), and the anterior abdominal wall either in the mid line or in creases like those stretching across from the anterior superior iliac spines. Again they were seen in the palms and soles, but here more readily tended to assume the stellate forms. Vertical slits are less common; they occurred with the greatest frequency in the posterior axillary folds.
Oval apertures of exit are far less common than those of entry, since the most common factor for the production of an oval opening, bony support, is never present. In long subcutaneous tracks, or very superficial wounds, they are however sometimes met with and may terminate in a pointed gutter (see figs. 18 and 24).
The greatest modifications in the appearance and nature of the apertures of entry are dependent on previous deformation of the bullet, when all special characteristics are lost, and it becomes impossible to form any opinion as to the type of bullet concerned. These modifications are naturally far more common in the aperture of exit, since the bullet so often acquires deformity in the body as the result of impact with the bones. Further remarks on this subject will be found with the description and comparison of the various bullets on p. 81.
Fig. 24.—Superficial Thoracico-abdominal Track.
Small entry: discoloration of surface over costal margin from deep injury to skin; well-marked 'flame' gutter exit (see fig. 18)
2. Direct course taken by the wound track.—This character primarily depends on the velocity with which bullets of small calibre are made to travel, and on the small area of the tissues upon which they operate. In this relation the degree of velocity retained by the bullet is often of minor importance, provided it be sufficient to penetrate the body. Fired within a distance of 2,500 yards there is little doubt that a bullet of the Lee-Metford, Mauser, or Krag-Jörgensen types, passes straight between the apertures of entry and exit when these are of the type outline, even when the bones are implicated. By reason of the small size of the projectiles, their shape, and the spin and velocity transmitted to them, there is no reason why at a sufficiently short range they should not traverse the body from the crown of the head to the sole of the foot. The necessary conditions of position and distance for such an injury are obviously not often obtained, but it may be pointed out that the Belgian Mauser rifle at a distance of five yards is capable of driving a bullet 55 inches or nearly five feet into a log of pine-wood. Many examples of long tracks will be referred to later, but the following instances may be of interest in this relation. A bullet entering at the occipital protuberance traversed the muscles of the neck, passed through the thoracic cavity, fractured the bodies of the third and fourth and grooved the seventh and eighth dorsal vertebræ, grooved the seventh and eighth and fractured the ninth and tenth ribs, traversed the muscles of the back and finally lodged against the ilium; the whole length of this track measured some 25 inches. Again, at the battle of Belmont a Mauser bullet entered the pelvis of a horse just below the anus, and traversed the entire trunk before emerging from the front of the chest: it may be of interest to mention that this animal was alive and moving about the next day, but I am sorry I can give no further information regarding his fate.
Fig. 25.—Superficial Track on external surface of Thigh. Local discoloration of skin five weeks after reception of injury
The possibility of contour tracks travelling around the walls of the chest or abdomen has therefore rarely to be considered, except in occasional instances where the bullet fired from a long range has impinged against a bone and is retained in the body. The small volume of the bullets, however, allows the production of very prolonged direct subcutaneous tracks in the body wall, in positions where they would be manifestly impossible with projectiles of larger calibre.
Figs. 24 and 25 illustrate wounds of this nature. In the case figured in fig. 24 the bullet entered over the third rib in a vertical line above the right nipple; it then coursed obliquely down, crossing the seventh costal cartilage, and finally emerged 3 inches above the umbilicus. Where the track crossed the prominence of the thoracic margin the skin was so thinned as to undergo subsequent discoloration, while a distinct groove was evident there on palpation. In some similar cases I have seen the central part of the track secondarily laid open as a result of the thinning of the skin and consequent sloughing due to the interference with its vitality.
Short of sloughing, the skin may show signs of alteration of vitality for a long period after the injury; thus fig. 25 depicts the condition seen in a superficial wound of the thigh five weeks after the injury. The line of passage of the bullet between the two openings was still clearly visible as a dark red coloured streak. Grooves in such cases are generally readily palpable in the early stages, while later the want of resistance is replaced by the readily felt firm cord representing the cicatrix. These points are of much importance in discriminating between perforating and non-perforating wounds of the abdomen, and are again referred to in that connection.
The direction of the tracks obviously depends on the attitude assumed by the patient at the moment of impact of the bullet and the direction whence the firing has proceeded. The frequent assumption of the prone position during the campaign led to the occurrence of a large proportion of longitudinal tracks in the trunk, or trunk and head, which will be referred to later. Certain battles were in fact strongly characterised by the nature of the wounds sustained by the men. Thus at Belmont and Graspan, where some rapid advances were made in the erect attitude, fractured thighs were proportionately numerous, while at Modder River, where many of the men lay for a great part of the day in the prone position, glancing wounds of the uplifted head, of the occipital region, or longitudinal tracks in the trunk and limbs were particularly frequent. I very much regret that the material at my disposal does not allow me to add some remarks as to variation in the nature of the wounds according to whether they were received from an enemy firing from a height or from below, but it is possible that some information on this subject may be forthcoming when the returns of the Service are made up, since it is naturally of great importance as to the effect of trajectory in the proportionate occurrence of hits.
3. Multiple character of the wounds.—The same conditions responsible for the length and directness of the tracks, account for the frequently multiple character of the wounds implicating either the limbs or viscera—thus, lung, stomach, liver; neck, thorax, abdomen; abdomen, pelvis, thigh. Also for the frequent infliction of two or more separate tracks by the same bullet—thus, arm and forearm with the elbow in the flexed position; both lower extremities; both lower extremities, penis or scrotum; leg, thigh, and abdomen, with a flexed knee; upper extremity and trunk, and more rarely one upper and one lower extremity. Again, it was remarkable how often the same bullet would inflict injuries on two or more separate men, not unfrequently dealing lightly with the first and inflicting a fatal injury on the second, or vice versâ. The small calibre of the bullet, moreover, allows of the neatest and most exact multiple injuries. Thus in a patient who was crawling up a kopje on all fours, the flexed middle digit of the hand was struck. The bullet entered at the base of the nail, first emerged at the distal interphalangeal flexor fold, re-entered the metacarpo-phalangeal fold, and finally emerged from the back of the hand between the third and fourth metacarpal bones.
4. Small 'bore' of the tracks, and tendency of the injury to be localised to individual structures of importance.—Here we meet with the most striking characteristic of the injuries, and evidence that reduction of calibre affects more strongly the nature of the lesion than does any other element in the structure of the modern rifle. The diameter of the track slightly exceeds that of the external apertures, probably as a result of the more ready separability of the elements of the structures perforated than exists in the skin. The calibre, moreover, tends to be fairly even throughout when soft structures only are implicated, though local enlargements result wherever increased resistance is met with. Thus a strong fascia may offer such resistance as to increase locally the bore of the track, and in this particular the state of tension of the fascia when struck will affect the degree of the enlargement. The most striking instances of local enlargement of the track are of course seen when a bone lies in the course of the bullet, but we must here bear in mind the introduction of a new element—the propulsion of comminuted fragments together with the bullet itself. In cases of fracture the distal portion of the track is in consequence many times larger than the proximal. The most striking examples of small even tracks are seen, on the other hand, in punctures of the elastic and practically homogeneous lung tissue, where the wounds are extremely small.
On transverse section of the track the gross amount of actual tissue destruction occupies a lesser area than that corresponding to the diameter of the bullet. The destructive action of the projectile is in fact exerted mainly on the tissues directly lying in its course, the track being opened up during the rush of the passage of the bullet, partly as a result of its wedge-like shape and partly as a result of the throwing off of the tissues forming the walls of the track by a diversion of a portion of the force in the form of spiral vibrations dependent on the revolution of the bullet. Again, the opening out of the tissues may be aided by the direction taken by the first and strongest as well as the simplest series of vibrations transmitted, which would assume the shape of a cone of which the point of impact forms the apex.
The escape from actual destruction by structures lying in the immediate neighbourhood of the track is indeed often surprising, but not perhaps so astonishing as the perforation of long narrow structures such as the peripheral nerves and vessels, without irreparable damage to the parts remaining, and this although the structures themselves may be of a diameter not exceeding that of the bullet itself. The capacity of these projectiles to split such structures as tendons was already well known before our experience in this campaign, but the injuries to the nerves and vessels of the same character came as a surprise to most of us. The lateral displacement of tissues seems to bear a strong resemblance to what is seen on the passage of an express train, when solid bodies of considerable weight are displaced by the draught created without ever coming into contact with the train itself. The tendency to lateral displacement is still more strongly exhibited when dense hard structures such as bone are implicated. Here the fragments at the actual points of impact on the proximal and distal surfaces of a shaft are driven forwards, while the lateral walls of the track in the bone are simply comminuted and pushed on one side without loss of continuity with their covering periosteum.
The extension of this form of displacement to a degree amounting to a so-called explosive character in the case of the soft tissues, even when the bullet passed at the highest degrees of velocity, was, however, never witnessed by me, and I very much doubt the existence of a so-called 'explosive zone' so far as wounds of the soft parts are concerned. On the contrary, I am inclined to believe that the highest degrees of velocity are favourable to clean-cut neat injuries of the soft tissues. I saw a large number of type wounds of entry and exit inflicted at a range of under fifty yards.
5. Clinical course of the wounds.—The tendency of simple wounds such as are above described to run an aseptic course was very marked, and, given satisfactory conditions, deep suppuration and cellulitis were distinctly rare. It may also be confidently affirmed that when suppuration did occur, with apertures of entry and exit of the normal small type, this was always the result of infection from the skin, or infection subsequent to the actual infliction of the wound. The infrequency of suppuration depended on the aseptic nature of the injury, the smallness of the openings, the small tendency of the track to weep and furnish serous discharge in any abundance, the comparative rarity of the inclusion of fragments of clothing or other foreign bodies, and possibly in some degree on the purity and dryness of the atmosphere, which favoured a firm dry clotting of the blood in the apertures of entry and exit, and consequent safe 'sealing of the wound.'
As to the aseptic nature of the injury, it will be well to first consider the question of the sterility of the bullet. Putting laboratory experiments on one side, the large experience of this campaign seems to prove to absolute demonstration that, bearing in mind the very large proportion of instances of primary union in simple tracks, the surgeon has nothing to fear on the part of the bullet itself. This is the more striking when we remember that these bullets shortly before their employment were carried in a dirty bandolier, and freely handled by men whose opportunities of rendering either their hands or implements aseptic were as bad as it is possible to conceive.
Several explanations are to hand, but none of them conclusive. Two must, however, be shortly considered. First, the surface of the bullet, except its tip and base, is practically renewed by passage through the barrel. Secondly, there is the question of the heat to which it is subjected. As far as cauterisation of the tissues is concerned, this question has been practically settled in the negative, since actual determinations of the heat immediately after the moment of impact have been made, and again it has been shown that butter is not melted, and that neither gunpowder nor dynamite is exploded, by firing bullets through small quantities of those materials. Again, the absence of any sign of scorching of the clothes of the wounded is strong evidence against the possibility of any considerable heat being applied to the tissues of the body; while another observation, although of less importance as affecting spent bullets only, that bullets, which have perforated the body but lie between the skin and the clothing, leave no sign of cauterising action on either, may be mentioned. None the less, the sources of heating while the bullet is passing from the barrel are many and obvious. Thus there is the heat consequent on explosion of the powder, the warm state of the barrel itself when the rifle has been fired a few times consecutively, and the heat resulting from the force and friction essential to the propulsion of the bullet through the barrel. Again, bullets covered with wax before their introduction into the barrel retain no trace of this when they have been fired, although at any rate the portion covering the tip is not exposed to friction on the part of the rifle, and lastly the base of the bullet has no other explicable reason for its innocuousness than subjection to a certain degree of heat. While not claiming any cauterising action on the tissues by the bullet, I should therefore still be inclined to allow the probability of the heat to which the surface of the bullet is exposed exerting a cleansing action on the projectile. In regard to this point it is interesting to bear in mind that shots from an ordinary gun seldom or never give rise to infection.
Foreign bodies were rarely carried into the wounds with the bullet. I saw several instances in which portions of the metal of cigarette cases and of cartridge cases when the bullet had perforated cartridges in the wounded man's bandolier, and in one instance small pieces of glass from a pocket mirror, must have been carried in without any obvious ill effect. Fragments of clothing, on the other hand, in every case caused suppuration: clothing was not often carried in, the khaki linen was perforated with a clean aperture, most commonly a slit; but the thick woollen kilts of the Highlanders, and thick flannel shirts, occasionally furnished fragments. The introduction of large pieces of clothing is a sure proof of irregularity of impact on the part of the bullet. The frequency with which portions of cloth were introduced from the kilt was one of the strongest surgical objections to its retention as a part of the uniform on active service.
Retained bullets themselves remained as foreign bodies in a certain number of cases. I cannot say that suppuration never followed the retention of a bullet, since in two of the instances where I saw such removed they lay in a small cavity containing at any rate a 'purulent fluid.' In one of these the bullet was a Martini-Henry, and in both the bullet had been imbedded for some weeks, and had certainly not occasioned a primary suppuration of the wound.
The favourable influence of the pure and dry nature of the atmosphere in this campaign must certainly not be underrated, and in support of this influence I think I may say, from the experience of cases that I saw coming from Natal where the climate and surroundings were not so favourable as on the western side, that suppuration was more common and more severe in the moister atmosphere.
Putting aside all the above remarks, however, I am inclined to think that a general tendency to primary union and the absence of suppuration will always be a feature of wounds from bullets of small calibre, and that this favourable tendency is attributable to certain inherent characters of the injuries. Of these the nature and small size of the openings, the dry character of the lining of the track due to superficial destruction and condensation of the tissue forming its wall, the small disposition to prolonged primary hæmorrhage, and the absence of any great amount of serous exudation during the early stages of healing are the most important.
A mechanical factor of great importance also exists in the spontaneous collapse and automatic apposition of the walls of the track. This closure is rendered additionally effective in many cases by the interruption of the continuous line in the wounded tissues consequent on alteration in the position of the parts traversed when an attitude of rest is assumed by the injured part. The indisposition to suppuration and the apparent unsuitability of the tissue lining the track for the development and spread of infecting organisms are well illustrated by several observations. Thus, even if the bullet be thoroughly aseptic, the fragments of destroyed skin driven into the track by the bullet can scarcely be free from organisms; yet these seldom give rise to trouble. Again, if for any reason a deep portion of a track becomes infected and suppurates, there is no tendency for the spread of infection along the line of wounded tissue, but rather for the development of a local abscess, pointing in the ordinary direction of least resistance, irrespective of the course originally taken by the bullet.
PLATE I.
Mauser Wound of Entrance, a little more than 48 hours after infliction. About 12/1.
G. L. Cheatle.
Section of the entry segment of an aseptic Mauser wound removed a little over forty-eight hours after its infliction. Magnified twelve diameters.
The margins of the opening are still sloping and depressed, indicating the originally 'punched-in' nature of the aperture. A thin stratified layer of epidermis completely closes it. No scab remains.
The wound track is occluded by an effusion of lymph, commencing organisation of which is shown under a higher magnifying power by the presence of leucocytes near the margin of the bounding tissue, and some giant cells. The effusion of lymph occupies a slightly wider area immediately beneath the papillary layer of the skin, then narrows, and broadens again as the subcutaneous fascia is reached, indicating the effect of resistance in widening the area of damage.
The subcutaneous connective tissue bounding the track shows little sign of alteration beyond a general slight tendency of the lines of structure to deviate in the direction of the passage of the bullet.
No hæmorrhage is apparent beyond a small collection of blood situated immediately beneath the new layer of epidermis at the left-hand corner of the opening.
Range probably within 800 yards. Seat of wound, abdominal wall a highest point of iliac crest.
Fig. 25 (a), a (plate I.) represents a section carried across an aseptic aperture of entry. The specimen was removed by Mr. Cheatle from a patient who died forty-eight hours after reception of the injury. It shows well the small amount of gross destruction suffered by the subcutaneous tissue, and the rapid repair which follows, since macroscopically the track is scarcely discernible. Reference to plate I. shows the remarkable fact that even at this early date considerable progress towards definite healing has occurred, and a thin layer of stratified epidermis covers the original opening. The question may be raised whether the origin of this epidermal layer is not in part a floating up of the margins of the main aperture.
During the course of healing some variation takes place in the appearance of the apertures, especially that of entry. This, at first contracted, later becomes somewhat relaxed, while in many cases a small halo of ecchymosis develops around it. The blood-clot occupying its centre now contracts, the margins rapidly become approximated centripetally, and a small circular dark spot only remains, which is later replaced by a small red cicatrix. The dark central spot under these circumstances consists of the contused margin of the wound in the skin, and a small proportion of blood-clot which finally comes away as a small dry scab. When slight local infection occurs in place of simple contraction and dry scabbing, the process is prolonged, the contused margin separates by granulation, the clot in the opening breaks down, and a small ulcer of somewhat larger proportions than the original wound remains and takes some days to heal.
