238 Prof. V. Horsley on Destructive Effects of Projectiles. [April 6, 



I would also draw your attention to the fact that therein is also the 

 centre of origin of the vagus nerve, which nerve has the power of 

 slowing the heart. Thus there are two important centres in the 

 medulla which are liable to be affected by changes of tension around 

 them induced, as above stated, when the bullet traverses the cerebral 

 hemispheres in a transverse direction. It may be that the centres 

 are principally affected by the mechanical pressure of the explosive 

 effect, but this latter of necessity produces a certain amount of 

 anaemia of the nerve centres ; some of the effect may also be produced 

 by that condition too. Supposing that the artificial respiration has 

 been properly carried out, and the respiratory centre is revived into 

 activity, there is yet another condition to be overcome, without which 

 the animal or person dies, and for a long recognised reason, namely, 

 that the bullet having in its passage cut through various blood- 

 vessels, blood is poured out within the skull, and consequently raises 

 very severely the intra-cranial tension. This constitutes, as a matter 

 of fact, a second cause of death, for under these circumstances the 

 accumulated blood causes such severe compression that it not only 

 again paralyses the respiratory centre but also irritates the vagus 

 centre, causing a marked slowing of the heart. The proof of the 

 truth of this statement is given at once the moment we cut the vagi 

 nerves, for if these are divided the heart immediately resumes its 

 former rhythm. The next curves are to exhibit the increase in the 

 intra-cranial tension, which occurs the moment the bullet enters the 

 skull. The line drawn by the Marey's tambour shows a violent 

 increase of pressure at the moment of shot (first or explosivo effect) 

 and a certain recoil therefrom, this recoil being directly changed for 

 a steady increase in tension brought about by the secondary cause of 

 death, namely, the haemorrhage, of which I have already spoken. To 

 treat such haemorrhage only ordinary surgical measures are requisite, 

 but these will be impossible if the activity of the respiratory centre 

 has not previously been restored in the manner already indicated. 



To sum up, the basis of scientific discussion of the nature and 

 causation of the phenomena evoked by bullet wounds of the cerebral 

 hemispheres must rest on two principal factors — the velocity of the 

 projectile and the development of hydrodynamic movement in the wet 

 living tissues. 



I am glad to have had the opportunity of laying before you the 

 facts on a subject which combines the pleasure of pure physical 

 research with the interest inseparable from the resolution of patho- 

 logical problems. 



[V. H.] 



