May 31, i»94] 



NA TURE 



107 



The method of proof is so convincing I need not detain 

 you further in this discussion. 



Since the question is, we now see, all-important, it be- 

 comes a matter of no small moment to study the effect 

 exerted by bullets entering fluid (for example, water). In 

 the first place, as may be seen by these experiments, the 

 etil'ect of the perforation of a skull, filled with water, by a 

 bullet, as was first done by Kocher, is to cause the burst- 

 of the sutures. I would draw your attention to the fact 

 that the separation of the bones is most marked on the 

 side of the entry of the bullet. It was the observation of 

 this latter point which led me to think that it might be 

 possible to automatically record the disturbance of the 

 fluid, and this was effected in the following way. 



A long trough having been prepared, with one end 

 closed with rubber one-eighth of an inch thick, and a tall, 

 white, flat surface lowered vertically into the trough, the 

 latter is filled with a solution of methylene blue. A small 

 bullet of low velocity (600 feet per sec.) is fired in the long 

 axis of the trough, i cm. below the surface of the water. 

 As a result, a wave is thrown up against the white 

 screen, which is consequently marked with a blue splash, 

 the same describing a curve, indicating, firstly, ihat the 

 disturbance is greatest where the velocity and resistance, 

 increased by compression, are both at their highest, i.e. 

 soon after the bullet enters the fluid ; and, secondly, that 

 the displacement diminishes gradually as the momentum 

 lessens. 



Complete confirmation of the parallelism between soft 

 solids and fluids in their behaviour to the rapidly-moving 

 bullet is seen in comparing the cast of the track made by 

 a bullet moving through clay, with the curves obtained 

 by the water record. 



In both, the maximal displacement occurs shortly after 

 the bullet has entered the substance, and in both the 

 diminution of disturbance is much more gradual than its 

 development, and is evidently proportional in the main to 

 the loss of momentum. A final proof is aft'orded by sus- 

 pending columns of methylene blue in clear water, or salt 

 solution, and then firing through the whole. With the 

 ■380 bullet and three grains of smokeless powder the last 

 column in the 4-foot trough was not disturbed. 



This doubtless is a result which would be generally 

 foreseen, but it was worth >vhile to test it experimentally, 

 and it certainly very strikingly demonstrates how localised 

 the bursting disturbance is, which completely explains 

 the limitation of the explosive effect on the skull on the 

 side of entry. Sundry interesting subordinate points 

 arose in the course of these experiments, and have served 

 to afford the necessary control of the method, c.t;. the 

 pecuhar splash of the bullet striking the rubber end of the 

 trough alone, i.e. not penetrating ; and, again, the tracing 

 made by a bullet which, being fired a little too super- 

 ficially, records the elevation of successive waves as it 

 ricochets along the surface ; and, finally, the record of a 

 bullet deflected by the resistance of the water (as well as 

 by want of horizontality), showing a long, oblique splash 

 where it has carried up the fluid into the air. 



From all these experiments on the pure physics of this 

 subject we are justified in believing that when a bullet is 

 fired against the head (whether that of a man or any 

 other warm-blooded animal), so as to penetrate the cere- 

 bral hemispheres in a transverse direction, the following 

 series of phenomena occurs. The impact of the bullet 

 on the bone causes depression of that bone over an area 

 larger than the diameter of the uninjured bullet, this 

 causing a slight rise of tension in the skull, since that 

 cavity is completely tilled with fluid, e.g. the cerebro- 

 spinal fluid and blood in the blood-vessels, together with 

 the living brain, which, as has already been stated, is a 

 semi-viscous substance. In the next instant the bullet 

 enters the cavity, and the slight rise of tension is instantly 

 converted by the universal displacement (explosive effect) 

 of the contents, into a very severe rise of pressure, most 



NO. 1283. VOL. 50] 



marked on the side of entry. The lines of force which 



this pressure takes is shown in this diagram, and it will 

 be obvious to you that these forces will on meeting the 

 rigid skull tend, as I have already shown, to burst it, and 

 if they fail in that, then they will certainly be reflected 

 on to the brain, a matter, as we shall presently see, of 

 special pathological significance. .As you see from the 

 diagram, the brain substance must be driven against the 

 internal surface of the globular cranium. This driving 

 } of the brain against the hard bone is exemplified in every 

 post-mortem e.xamination. A good instance is seen in 

 the accompanying specimen, in which, although the 

 bullet traversed the extreme tips of the frontal lobe and 

 the olfactory bulbs, numerous bruises are seen on the 

 hinder portions, where they have been crushed against 

 the bone. Similarly evidences of the direct transmission 

 of the pressures are to be found at the base of the brain 

 in the longitudinal fissure, &c., wherever, in short, the 

 brain can be pressed against an unyielding substance. 

 The final proof of the correctness of this interpretation 

 is to be referred to directly, in which the vault of the 

 cranium is removed before the shot, so that the energy 

 of the pressure is expended in ejecting portions of the 

 brain into the air, and not so much on the basal regions, 

 as just described. So, too, the energy of the bullet is 

 communicated in the same way to the fluid in the ven- 

 tricular cavities (Duret's "choc cephalo-rachidien "), 

 which tunnel the brain down to the medulla oblongata. 

 The medulla oblongata is thus subjected to pres- 

 sure from two sources : (i) the hydrodynamic dis- 

 placement of the brain en masse : (2) the direct 

 crushing effect due to the movement of the cerebro- 

 spinal fluid in the ventricles. 



We are now brought to the aim and object of these 

 preliminary considerations, namely, the reason why these 

 disturbances within the skull cause death, and how the 

 fatal issue is produced ; in short, we must pass from the 

 questions of pure physics to the more complex problems 

 of pathology, 



(2) Pailiological Considerations. — The experiments, 

 the results of which I now wish to lay before you, con- 

 stitute a long series which was carried out last year by 

 Dr, Kramer and myself. We arranged the experiments 

 as follows : A dog was placed under ether, and one 

 femoral artery connected with a mercurial manometer 

 to give record of the heart beats and pressure of 

 the blood in the trunk arteries of the circulatory 

 system. Another similar manometer was connected 

 with the peripheral end of an artery so as to 

 record the changes of pressure in the small capillary 

 vessels, changes which I may remark incidentally are 

 usually due to those disturbances in the central nervous 

 svsteni which we call vaso-motor. Thirdly, the move- 

 rnents of respiration are traced on the recording surface 

 by means of rubber tambours known as Bert's and 

 Marey's, respectively. If the pressure within the skull 

 was also to be recorded, then a steel tube was fixed into a 

 trephine opening filled with the salt solution, and con- 

 nected by a rubber air-tube also with a Marey's tambour. 

 Occasionally we put on the same paper a record of the 

 contraction of the rectus femoris muscle, this latter being 

 directly connected with a Kick's spring myograph. At 

 the bottom of the tracing is given, firstly, the record of 

 the movements of an electro-magnet signal (Smith's) 

 interrupted by a metronome beating seconds. The last 

 line traced is that from a Smith's signal in the circuit of 

 a single cell, and one of the wires from which is made of 

 very slender brass, and fixed across the muzzle of the 

 pistol or rifle, so that when the shot leaves the muzzle it 

 cuts it and breaks the contact (Woolwich method). 



When a bullet of low velocity {600 fp,s.) strikes 

 the skull in a glancing fashion, there is only a 

 trifling disturbance of respiration, but when the 

 bullet enters the cranial cavity and sets up the 



