THE NERVOUS CONTROL OF THE BLOOD VESSELS 1047 



brought about by the stimulation of the suprarenals and the discharge of 

 adrenaline into the general circulation. Simultaneously with this second 

 rise of blood pressure, we notice in the curve given in Fig. 479 a diminished 

 volume of the heart due to more effective contraction of this organ. 



This diminished volume of the heart is often associated with a marked 

 quickening of the heart rate, both effects being due to the action of adrenaline 

 on the heart. During asphyxia the rise of arterial pressure is largely brought 

 about through the intermediation of the splanchnic nerves and is therefore 

 also associated^with the discharge of adrenaline. It is on this account that 



Le 



eg 

 volu 



ume 



B.P. 



Spl. exc. 



Time 

 10 sec. 



FIG. 480. Effect of excitation of splanchnic nerves on the blood pressure and 

 on the volume of the denervated hind limb of the cat. (BAYLISS.) 



in the whole animal, provided that sufficient oxygen is supplied, very large 

 percentages of carbon dioxide may be inhaled without causing fatal dilata- 

 tion of the heart, the effect of the adrenaline discharged into the blood stream 

 serving to counteract the injurious influence of carbon dioxide on the heart 

 muscle. These two chemical influences, the local production of carbon- 

 dioxide and the discharge of adrenaline into the general circulation, must 

 always be kept in mind in trying to account for the behaviour of the blood 

 vessels under the most various conditions. Thus in Fig. 480 is shown the 

 effect of temporary stimulation of the splanchnic nerve on the blood pressure 

 and on the volume of the hind limb of the cat. It will be noticed that the 

 volume of the hind limb increases passively with the rise of pressure and then 

 diminishes much below its previous amount. This diminution is due to the 

 discharge of adrenaline into the blood stream as the result of stimulation of 

 the splanchnic nerve, and is absent if the suprarenals have been previously 

 destroyed.' The curve shown in Fig. 481, which with the foregoing one was 

 taken by Bayliss to indicate a local adaptation of the blood vessels to their 

 internal pressure, is probably brought about by the local production of carbon 

 dioxide (von Anrep). Temporary occlusion of the abdominal aorta is here 



