INNERVATION OF THE BLOOD-VESSELS OF DIFFERENT ORGANS 425 



this instrument. Quite naturally, the excitation of the chorda tym- 

 pani then gives rise to an augmentation of the venous pressure and 

 flow, because the resulting vasodilatation allows a greater quantity 

 of arterial blood to pass through this gland. The stimulation of the 

 sympathetic, on the other hand, then leads to a diminution in the 

 venous pressure and flow, because the vasoconstriction immediately 

 following, serves to place a greater resistance in the path of the 

 arterial blood. 



The superior cervical ganglion is also connected by postganglionic 

 fibers with the blood-vessels of the brain. This fact has been demon- 

 strated by Jenson 1 who has measured the venous return from this 

 organ with the aid of a stromuhr inserted in the external jugular vein. 

 Under this condition, the stimulation of the distal end of the cervical 

 sympathetic nerve invariably led to a diminution in the blood flow 

 through this vein. The fact, that the cerebral blood-vessels are equip- 

 ped with vasoconstrictor powers, has also been established by Wiggers, 2 

 who measured the quantity of fluid perfused through the blood- 

 vessels of an excised brain before and during the administration 

 of adrenalin. Very similar reductions in the cerebral blood-supply 

 have also been incited by the direct stimulation of the internal carotid 

 artery at the point where it enters the skull. It is entirely probable 

 that the constrictor fibers follow this artery in their course to intra- 

 cranial parts. Less convincing are the results obtained with the help 

 of the plethysmograph, but several observers (Weber) claim to have 

 noted certain variations in the volume of the brain which could not 

 be explained in any other way than by assuming that this organ is 

 innervated by constrictor and dilator fibers. 



The Greater Splanchnic Nerve. This nerve embraces those fibers 

 of the thoracic outpouring of sympathetic fibers which are destined 

 to regulate the caliber of the blood-vessels of the abdominal organs, 

 inclusive of the kidneys, adrenal bodies, stomach, intestine, liver, 

 pancreas and spleen. These organs, which are commonly called 

 the splanchnic organs, are not reached by them directly but only by 

 way of several relay stations forming the so-called solar plexus. The 

 latter embraces the right and left suprarenal, and the mesenteric and 

 celiac ganglia. The connection between these and the organs just 

 enumerated, is effected by several postganglionic paths, such as the 

 renal, mesenteric, splenic, celiac and hepatic plexuses. 



The point to be especially emphasized at this time is that these 

 nerves control the blood supply of extremely large and vascular struc- 

 tures and possess, therefore, an almost dominating influence upon the 

 distribution of the total quantity of the circulating blood. This 

 statement can be substantiated by the following simple experiment. 

 If the general blood pressure is recorded by means of a mercurial mano- 

 meter connected with the carotid artery, it will be seen that the di- 



1 Pfluger's Archiv., ciii, 1904, 195. 



2 Am. Jour, of Physiol., xiv, 1905, and xxi, 1908. 



