Читать книгу Surgical Experiences in South Africa, 1899-1900 - George Henry Makins - Страница 20

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Before proceeding to the actual description of the wounds inflicted by modern military rifles, it is necessary to prefix a few remarks on the mechanism and mode of production of these injuries.

Recent tendency in the construction of military rifles has been in the direction of reduction of bore, and a corresponding one in the calibre of the bullet, the resulting loss of weight in the latter as an element in striking power being compensated for by the attainment of an augmentation of velocity in the flight of the projectile, and a comparatively flat trajectory.

Changes in this direction have endowed the weapons with increase both in range and accuracy of fire; while the greater rapidity with which magazine rifles can be discharged and, in consequence of reduction in weight, the greater number of cartridges which can be carried by each man, also form important factors in the possible deadliness of warfare at the present day. None the less the experience of the present campaign has scarcely justified the early prognostications expressed as to a great increase in the number and severity of wounds amongst the combatants.[5] This comparative immunity is to be explained mainly on two grounds. The increased distance which for the most part separated the two bodies of men, a feature no doubt accentuated by the mode of warfare adopted by the Boer, and his strong sense of the folly of close combat on equal terms, tended to efface one of the chief characters, velocity of flight, on the part of the projectile. The want of effectiveness of the small-calibre bullet as an instrument of serious mischief also kept down the mortality.

Since the year 1889 the calibre of the bullet in our own army has been reduced from that of the Martini-Henry (.450 in.) to one of .309 in. in the Lee-Metford, and a consequent reduction in weight from 480 to 215 grains. To allow of the satisfactory assumption of the more complicated rifling by the more rapidly projected bullet, the lead core has been ensheathed in a mantle of denser metal. The bullet itself is of an original calibre (.309 in.) somewhat exceeding the bore of the rifle barrel (.303 in.), in which way a species of 'choke' is obtained and deep rifling of the surface ensured. Beyond this the comparative transverse and longitudinal measurements and shape have been altered in order to maintain weight, preserve a proper balance during flight, and increase the power of penetration. These alterations with slight differences in detail embody the general principles that underlie the construction of each of the weapons adopted by European nations. It will be well here to consider the influence of each alteration from the point of view of the surgeon.

Calibre.—The effect of the diminution of calibre is (a) to reduce the area of impact of the bullet on the part impinged upon, and hence to lower the degree of resistance offered by the tissues; this to a certain extent tends to neutralise the augmented striking force resulting from the increased velocity of flight. (b) To limit considerably the destructive powers of the bullet, as a smaller area of tissue is exposed to its action. (c) To allow of the production of very 'neat' injuries and the frequent escape of important structures, also the production of remarkably prolonged subcutaneous tracks in positions where such would be regarded as scarcely possible, and in point of fact were impossible with the older and larger projectiles.

Length.—The comparative increase in length of the bullet is, from the surgical point of view, only of material importance in increasing the weight and therefore the striking power, and in so far as it is a mechanical necessity for the flight of the projectile on an axis parallel to its long diameter, and so tends to ensure impact on the body by the tip of the bullet. This latter is, however, surgically favourable as ensuring a smaller wound.

Weight.—The decrease in weight must be regarded on the whole as altogether to the advantage of the wounded individual, since it cannot be considered to be entirely compensated for by the resulting increased velocity of flight, unless the range of fire is moderately close.

Shape.—The ogival tip and general wedge-like outline, while decreasing the aerial resistance to and increasing the power of penetration possessed by the bullet, at the same time allow the escape of some structures by displacement, while others are saved from complete destruction by undergoing perforation. Beyond this the sharper the tip, the smaller is the area of the body primarily impinged upon, the less the resistance offered to perforation, and to some degree the less the destruction of surrounding tissues.

Increased velocity of flight.—This multiplies the striking force, and compensates in part for decrease in volume and weight of the bullet. It is customary to speak of the velocity as 'initial' and 'remaining.' Initial velocity is the term employed to express the velocity at the time of the escape of the bullet from the barrel; this is also designated as 'muzzle velocity.' 'Remaining velocity' expresses that obtaining during any subsequent portion of the flight of the projectile.

The greatest initial velocity is obtained with the use of bullets of the smallest calibre, but this is not of the practical importance which might be assumed, since the remaining velocity of flight of such projectiles falls more rapidly than that of those of slightly greater mass. Thus, although there may be a difference of a hundred metres per second in initial velocity between two rifles of calibres varying from 6.5 to 8 millimetres (.303-.314 in.), at the end of 1,000 metres the discrepancy is greatly reduced, while at 2,000 metres it hardly exists. Under such circumstances the projectile of greater weight and volume, as possessing the greater striking force, is considerably the more formidable of the two. This is the more important if it be allowed, as I believe to be the case, that velocity per se is of no practical import in the case of wounds of the soft parts of the body, which after all form the preponderating number of all gunshot injuries. The effect of the higher degrees of velocity differs, however, with the amount of resistance met with on the part of the body; hence its serious import is well exemplified when parts of the osseous skeleton are implicated, although even here considerable variations exist, dependent upon the structure of that part of the bone actually involved. The most obvious ill effect of injuries from bullets travelling at high rates is seen in the case of the various parts of the nervous system, and here it is undeniable. High velocity and striking force are also responsible for the prolonged course sometimes taken by bullets through the body.

The actual degree of velocity, as judged by the range of fire at which an injury is received and the resulting injury, is very hard to estimate on account of the many and varying factors which enter into its determination. The mere recital of some of these will suffice to make this evident.

1. Quality of the individual cartridge employed, as to loading, the materials employed, and their condition.

2. The condition of the rifle as to cleanliness, heating, and the state of the grooves of the barrel.

3. The angle of impact of the bullet with the part injured.

4. Resistance dependent on the weight of the whole body of the man struck, or of an isolated limb.

5. Special peculiarities of build in the individual struck, such as thickness and density of the integument and fasciæ, strength and thickness of the bones, &c.

6. State of tension of the muscles, fasciæ, and ligaments at the moment of impact, and fixity or otherwise of the part of the body struck.

7. The degree of wind, temperature, and hygroscopic conditions of the atmosphere.

These form some of the more important points which have to be taken into consideration, in addition to a mere calculation of the actual distance from which a wound has been received from a particular rifle, and taken with the unsatisfactory nature of the evidence as to the latter, which is usually alone obtainable, it is clear that definite assumptions are scarcely possible. In a great number of cases I came to the conclusion that the only indisputable evidence of low velocity was the lodgment of an undeformed bullet. There is little doubt, moreover, that the general tendency of wounded men was to minimise the range of fire at which they were struck, and again that in the majority of cases in this campaign it was quite impossible to determine whence any particular bullet had come, since the enemy was seldom arranged in one line, but rather in several. Again, smokeless powder was generally employed. Beyond this, in some cases where there was no doubt of the short distance from which the bullet was fired, the wounds were due to 'ricochet' of portions of broken-up bullets. The following instance well illustrates this. A sentry fired five times at two men within a distance of six paces, knocking both down. One man received a severe direct fracture of the ilium, the bullet entering between the anterior superior and inferior iliac spines and emerging at the upper part of the buttock. The entry and exit apertures were large but hardly 'explosive,' as a subcutaneous track four to five inches long separated them. Besides this both men had other lesser injuries; thus in the second two perforating wounds of the arm existed. The latter were not unlike type Lee-Metford wounds, and were regarded as such until a few days afterwards when a hard body was felt in the distal portion of one track and removed. This proved to be a part of the leaden core only, and the similar wound had no doubt been produced by a like fragment, the bullet having broken up on striking the stony ground.

Trajectory.—The comparative flatness of this depends on the construction of the rifle and the propulsive force employed, and varies as does velocity with the nature, excellence, and amount of the explosive, the correctness of the principles upon which the bullet is devised, and the mechanical perfection of its manufacture. Its importance naturally consists in the manner in which it affects the possibility of covering objects on a wide area of ground and thus creating a broad 'dangerous zone.' A bullet fired on level ground from any one of three of the rifles referred to later (Lee-Metford, Mauser, Krag-Jörgensen), sighted to 500 yards and fired from the shoulder in the standing position, will cover some part of an erect man of average height during the whole extent of its flight. A body of men within that distance is therefore in a position of extreme peril in the face of a good shooting enemy.

The importance of a flat trajectory is progressively lost, however, with any rifle, as the weapon is gradually sighted to greater distances. Thus when sighted to 2,000 yards the bullet from the Lee-Metford rifle rises 174 feet, and a whole army might comfortably be situated over a considerable area within that distance. The importance of flatness of trajectory is also influenced by the nature of the ground occupied by the combatants. Thus when the area to be covered consists in ground first rising then falling from the rifleman, the trajectory will become more or less parallel to the surface crossed, and the 'dangerous zone' will be correspondingly increased in extent. On the other hand, when the ground slopes away from the rifleman the rise of the projectile is exaggerated, and reaches its most limited capacity of covering an intervening space when the flight crosses a hollow.

Revolution of the bullet.—It only remains in this place to say a few words concerning the revolution imparted to the bullet by the rifling of the barrel. This ensures the flight of the projectile on a line parallel to its long axis, and notably increases its power of penetration.

Both these properties of the flight are to the advantage of the wounded, since, as already mentioned, the more exactly the impact corresponds to a right angle with the skin, the more limited will be the area of contusion, even if it be of the most severe character, while to the twist of the bullet must be ascribed a not inconsiderable part in the explanation of the ready and neat perforations of narrow structures which are frequently produced.

It has been pointed out that the Lee-Metford bullet turns on its own axis once in a distance of ten inches, while the Mauser revolves once in a distance of eight and eleven-sixteenths inches; hence not more than at most two revolutions are made in tracks crossing the trunk, and not more than half a full revolution in the perforation of a limb. None the less, no one can deny the influence of the one half turn of supination in entering a perforating tool of any description, both as preventing splintering, and in preserving the surrounding parts from damage.

Beyond this, the spiral turn of the bullet, by diverting a part of the transmitted vibrations into a second direction, must, in the case of wounds of the body, help to throw off contiguous structures, and while those that are in actual contact are more severely contused, the surrounding ones suffer somewhat less direct injury. It must be borne in mind, also, that rapidity of revolution does not fall pari passu with that of velocity of flight, but that the former undergoes a comparatively slighter diminution until the bullet is actually spent. Hence, the influence of revolution is felt, however low the velocity may be, provided sufficient striking force is retained to enter the body. A word must be added here as to the surface of a discharged bullet; this, in taking the rifling of the barrel, becomes permanently grooved. The depth of the groove differs with the variety of rifle. In the Lee-Metford the grooves are deep (.009), in the Mauser slightly less so (.007), but the surface of both bullets is comparatively roughened when revolving in the body, and this circumstance, since the projectile exactly fits its track, may influence the degree of the surface destruction of tissue, and somewhat aid in the clean perforation of bone, since a little bone dust is always found at the entrance aperture of a canal in cancellous bone.

During the campaign many varieties of rifle projecting bullets of widely differing calibre were employed by the Boers, many of whom as sportsmen preferred the rifle to which they were accustomed to a regulation weapon, and an illustration of a large variety of bullets from cartridges which I collected from arsenals and camps is given below (p. 96). The great majority of the men, however, were armed with small-calibre weapons of some sort, and as the wounds produced by these are of chief interest at the present day, I shall say little of any others, beyond an occasional reference to Martini-Henry rifle wounds which may be considered to represent approximately those made by large leaden sporting bullets.