232 NERVOUS SYSTEM. 



ing with woorara. In the latter case, the circulation was 

 kept up by artificial respiration. 



Without following out the various observations which go 

 to show that the influence of the depressor-nerve upon the 

 arterial pressure is independent of the force or frequency of 

 the heart's action, and is due to some cause which operates 

 upon the vessels themselves, we will simply give the results 

 of the experiments upon the splanchnic nerves. If the abdo- 

 men be opened, and one or more of these nerves be divided, 

 the arterial pressure is immediately diminished. After this, 

 if the peripheral extremities of the divided nerves be galvan- 

 ized, the pressure rapidly returns to the normal standard. 

 These experiments " demonstrate that the splanchnic nerves 

 constitute the most important vaso-motor nerves in the en- 

 tire organism." 



This point being settled, the depressor-nerves were gal- 

 vanized after section of the splanchnic nerves, in some cases 

 exaggerating the general arterial pressure by compressing 

 the aorta, and in others, leaving the aorta free. " The irrita- 

 tion of the depressor-nerve after section of the splanchnic 

 nerve produced still a diminution in the blood-pressure, but 

 the absolute value of this diminution is much less than it was 

 during the irritation of the depressor-nerve before the sec 

 tion of the splanchnic." 



These experiments show pretty conclusively that the di- 

 minished pressure in the arterial system following stimula- 

 tion of the central ends of the depressor-nerves after division 

 is due to a reflex action on the blood-vessels of the abdomi- 

 nal organs, taking place through the splanchnic nerves. We 

 are sufficiently familiar with reflex paralyzing action upon 

 the blood-vessels through the sympathetic system ; and when 

 we call to mind the immense extent of the abdominal vascu- 

 lar system, we can readily understand how, if the resistance 

 to the flow of blood be diminished by paralysis of the mus- 

 cular coats of the small arteries, the pressure in the larger 

 arteries would be reduced. 



