SURGICAL SHOCK 25 



condition of extreme shock. The outflow was 

 naturally less than normal, but on cutting the sciatic 

 nerve there was a prompt and considerable increase 

 in the flow. Therefore the vasomotor centre must 

 still have been sending out tonic impulses. Again, 

 they found that in normal animals stimulation of the 

 central end of the cut vagus causes a rise in blood- 

 pressure. The rise is just as marked, in proportion, 

 if the experiment is repeated in an animal in a state 

 of extreme shock. Therefore, again, the centre 

 cannot be exhausted. Porter found that the fall 

 of blood-pressure due to stimulation of the depressor 

 nerve also takes place, and is proportionally as 

 marked, in shocked animals. Tyrrell Gray and 

 Parsons found that when an animal is in a state of 

 shock consequent on an operation on the hind limbs, 

 so that stimulation of the sciatic nerve causes a fall 

 instead of a rise of blood-pressure, yet stimulation 

 of the brachial nerves will still produce a rise. The 

 fatigue, therefore, was in the afferent pressor paths, 

 not in the vasomotor centre. 



We are left, then, with the conclusion that although 

 shock commonly induces a fall of blood-pressure, 

 the vasomotor centre is not primarily exhausted, 

 and the vessels may be contracted. How can this 

 paradox be explained ? Boise believes that the 

 cause of shock is spasm of the heart, but his view 

 has met with little favour, and his experimental 

 evidence is unsatisfactory. All observers agree that 

 the heart has not seriously failed in shock. It 

 responds excellently for a time to the extra work 

 put upon it by a large saline transfusion. It is true 



