Leonard Hill also pointed out that the first effect of anæmia of the bulbar region was in the nature of stimulation, the vaso-motor centre being influenced in such a manner as to produce a general rise of blood-pressure. A further degree of compression may again produce the same result, the arterial pressure rising considerably above the normal. Later on, the medullary centres--and more especially the vaso-motor--become exhausted, with consequent grave fall in blood-pressure. The pulse, previously slow and full, becomes rapid, small, readily compressible, and irregular in rhythm, whilst the respiration, previously deep and regular, becomes gasping, irregular, and Cheyne-Stokes in character. The sequence of events may be depicted in another manner. In cerebral compression, the battle--as pointed out by Schüster--largely resolves itself into a life and death struggle between the attacking compression force on the one hand and the defending vaso-motor centre on the other. Up to a certain point the vaso-motor centre holds the whip-hand. The capillary anæmia as produced by the compression force--cerebro-spinal tension, &c.--brings about a condition which not only acts as a stimulus to the vaso-motor centre but also exercises a marked effect on the vagus and respiratory centres. The blood-pressure rises, the pulse is slowed in rate, and its tension markedly increased, whilst the respiration is slightly irregular both in depth and rhythm. The vaso-motor centre thus attacked sends out further impulses so as to raise the blood-pressure to slightly above requirements. The bulbar centres are again flushed with blood, the vaso-motor centre ‘slacks off’, and the blood-pressure falls again. The compressing force is, however, still active and full of fight. A further capillary anæmia results. The vaso-motor centre again responds and the blood-pressure rises higher than ever, the pulse-rate is further slowed, and the respiration is deeper, less regular, and even stertorous. This combat continues, and, in the presence of an active compression force, there is that rhythmic activity of the vaso-motor centre which is represented by the well-known Traube-Herring curves; again, the height to which the vaso-motor centre drives the blood-pressure may be taken as representing the activity of the compression force. When the compressing force rises above a certain limit the _débâcle_ occurs--the vaso-motor centre retires from the fight, there is a rapid fall in blood-pressure, the medulla is emptied of blood, and both cardiac and respiratory centres share in the defeat (rapid pulse of poor volume and Cheyne-Stokes respiration).