236 Professor Victor Horsley [April 6, 



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 filled with fluid, eg. 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 displace- 

 ment (explosive effect) of the contents, into a very severe rise of 

 pressure, most marked on the side of entry. The lines of force which 

 this pressure takes are 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 examination. 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 com- 

 municated in the same way to the fluid in the ventricular cavities 

 (Duret's " choc cephalo-rachidien "), which tunnel the brain down to 

 the medulla oblongata. The medulla oblongata is thus subjected to 

 pressure from two sources: (1) the hydrodynamic displacement of 

 the brain en masse ; (2) the direct crushing effect clue 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. Pathological Considerations. — The experiments, the results of 

 which I now wish to lay before you, constitute 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 



