1906.] Recently-Discovered African Arrow Poison. 19 



Section of the Vagi. 



(a) Section before the Injection of the Poison. — The effect of section of both 

 vagi before the injection of the poison is to do away with the slowing of the 

 pulse and the slight fall in the blood pressure, which occurs after the first 

 rise in the pressure ; there are in addition no depressions in the curve at this 

 time. 



The pressure gradually rises in a long curve to its maximum height and 

 then gradually falls till death. In addition to this there is little or no 

 increase in the pulse rate towards the end. The respiration has the usual 

 vagus type and is unaffected by the poison, only becoming irregular as the 

 heart stops and continuing for some time after the blood pressure has fallen. 



Section of one vagus only does not produce .any such alteration in the 

 character of the curve as is produced when both vagi are divided. 



Since the blood pressure rises in spite of section of both vagi, to as great 

 an extent as it does when they are intact, the conclusion follows that the first 

 rise of blood pressure is not due to paralysis of the vagi, and since there is no 

 notable alteration in the pulse rate during this rise confirmatory evidence is 

 obtained that the rise of blood pressure is chiefly due to vaso-motor con- 

 striction. The absence of slowing of the pulse during the initial rise and 

 likewise the absence of the usual slight fall in pressure at this time when the 

 vagi are cut, indicate that these phenomena are due to a stimulation of the 

 vagus centre in the medulla, the effect having been abolished by section of 

 the vagi. 



I shall show later that there is no evidence whatever that the poison acts 

 upon the central nervous system and therefore it is rendered most probable 

 that this irritation of the vagus centre is not due to a direct action of the 

 poison, but is merely the usual stimulation that occurs as a result of a rise of 

 blood pressure. 



(b) Section after Injection of the Poison. — Section of one vagus brings about 

 a rise in the blood pressure and acceleration of the pulse at an early period 

 whilst the blood pressure is rising, and section of the vagus on the other side 

 does not increase this rise at a slightly later period. It is only at an early 

 period of the injection whilst the blood pressure is rising that section of the 

 vagus causes a further rise, section at a late period, and especially when the 

 blood pressure is falling, bringing about no change whatever in the blood 

 pressure curve or the rate of the heart. In one case section of the right 

 vagus 54 minutes after injection followed by section of the left vagus 

 19 minutes later produced no rise at all. The section, therefore, to produce 

 any rise in blood pressure must be done at an early period after the injection. 



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