CARDIOVASCULAR CHANGES DURING CEREBRAL ANEMIA 27 



average ouflow from the cord to the sympathetic chain is apparently 

 in the region of the 6th to 8th thoracic. Yet the outflow is not restricted 

 to the lower thoracic region, for fibers in the higher thoracic region even 

 as high as the 1st or 2nd, have in these experiments been found of some 

 importance both for the maintenance of the level and the changes 

 of blood pressure. Such a curve as that obtained from cat 30 (fig. 3) 

 shows convincingly that in some animals a good proportion of fibers 

 leave the spinal cord to enter the sympathetic chain above the level of 

 the 5th thoracic vertebra. 



While therefore the anatomical findings of Langley and Ranson for 

 the average level of outflow have in the main been verified, the involve- 

 ment of higher levels already indicated by the various physiological 

 researches quoted by Langley has received a rather striking con- 

 firmation. 



In such an instance, the physiological evidence may well have pre- 

 cedence over the anatomical, for whereas a small bundle of fibers is 

 most difficult to stain and trace microscopically, a weak physiological 

 effect, when definitely isolated, is quite unmistakable. The involvement 

 of these fibers from the higher levels within the splanchnic system, be- 

 comes of particular importance when the entire burden of the splanch- 

 nic function is restricted to these levels. Since the very high out- 

 flow presumably goes by way of the stellate ganglion, it is necessary to 

 differentiate between the effect of the splanchnic fibers proper and the 

 accelerators. However, in these cats in which an abdominal or high 

 spinal section completely abolished the rise, the cardiac nerves seemed 

 completely impotent against the lowered peripheral resistance. 



Accordingly, the vasomotor impulses that travel through the splanch- 

 nic nerves to the coeliac ganglion may leave the cord as high as the 

 first or second thoracic. They may, however, stay in the cord through- 

 out the thoracic region and leave it even below the diaphragm. Ran- 

 son 's results on the very low level at which the splanchnic nerve leaves 

 the chain in cats, is in close agreement with these findings. 



There thus appears to be a double pathway for the splanchnic out- 

 flow in the thorax, one within the cord, the other outside of it. The 

 outflow of the splanchnic fibers from the cord to the sympathetic chain 

 seems distributed over the entire thoracic region, the relative distribu- 

 tion varying from one individual to another. 



In this light the impossibility of abolishing the anemic rise by a sec- 

 tion which implicates only part of the splanchnic system is explicable. 

 The wide distribution of the splanchnic fibers would make it difficult 



