174 



THE VASCULAR SYSTEM 



a subsequent section or total destruction of the spinal cord 

 (Sherrington). It is caused by the sudden interruption of the 

 nervous tonic influence which proceeds from the brain to the 

 muscular system. The incessant inflow of visual and labyrinthine 

 impulses no doubt maintain this tone ; just as the wires of a piano- 



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FIG. 21. Carotid and superior vena cava pressures' of dog. FD, animal 

 turned into the vertical feet-down posture with the cannula: in the axis of 

 rotation. The arterial pressure fell in fifty minutes from 110 to 42 mm. Hg. 

 From C to EX the animal was immersed in a bath which was deepened to the 

 chin at D. Note the increased effect of respiration on the venous pressure 

 after FD, and again after the bath. Note the fall of pressures at FD and 

 the compensatory rise in arterial pressure, which gradually weakens. 



forte are ceaselessly kept humming by the noise of the world, so 

 is the neuro-muscular system. Shock may be caused in man by 

 any severe injury, and is generally attributed to paralysis of the 

 vaso-motor centre. The centre is said to be exhausted by the 

 violence of the sensory stimulation (Crile). Porter objects to this 

 view, and says it is disproved by the fact that the centre responds 

 to excitation of a sensory nerve in the usual way, and in an anim'al 



