PROTEIN SENSITIZATION OR ANAPHYLAXIS 249 



viscera are compressed, the pressure invariably rises. It 

 follows that the low blood pressure in anaphylactic shock 

 is due to decreased peripheral resistance from marked 

 peripheral vasodilatation. 



The next question is to determine whether the dilata- 

 tion is due to paralysis of the vasomotor centre or that of 

 the periphery. At first it seemed that the trouble might 

 be central, because stimulation of the vasomotor centre 

 failed to increase the blood pressure. But this is negatived 

 by the fact that stimulation of the peripheral vasomotor 

 apparatus otherwise than through the centre also failed 

 to increase the pressure. Not only did irritation of the 

 terminal end of the splanchnic fail to raise the pressure, 

 but the intravenous injection of from 0.1 to 0.2 mg. of 

 adrenalin, which in normal animals is followed by marked 

 increase in pressure, in anaphylactic shock is either wholly 

 without effect or has but slight influence. 



It is generally held that the capability of increasing blood 

 pressure possessed by adrenalin is due to its action on the 

 nervous apparatus in the vessel walls, and possibly in part 

 on the vessel muscle. It follows that the vasodilatation 

 of anaphylactic shock is due to paralysis of the peripheral 

 vasomotor apparatus. Stimulation of the vasomotor centre 

 naturally fails to raise the pressure because the end appa- 

 ratus does not work. It should be stated that this failure 

 of adrenalin to raise the pressure occurs only in the stage of 

 deep depression when the pressure is low. If the pressure 

 begins to rise, as recovery begins, then the administration 

 of adrenalin carries it up rapidly. That the fall in blood 

 pressure in anaphylactic shock is due to a transitory paralysis 

 of the peripheral vasomotor apparatus seems to be quite 

 conclusively demonstrated. 



As has been shown by Boehm, barium chloride causes a 

 marked and fairly persistent increase in blood pressure, 

 which is due to its stimulating effect upon the smooth 

 muscles of the vessel walls. In anaphylactic shock even 

 when the pressure has fallen to the lowest point, the adminis- 

 tration of barium chloride causes a marked rise. Moreover, 



