484 THE POSTERIOR PITUITARY AND THE NERVOUS SYSTEM. 



Galen had already noticed that death ensued when a cer- 

 tain spot in the floor of the fourth ventricle close to that 

 which is now known as the center of the vagus was injured. 

 But Legallois and Flourens have added much to our knowl- 

 edge of its physiological relations, and the spot in question, 

 as we have seen, is still considered as the respiratory center. 

 "The results of various investigations show, however," says 

 Eeichert, 1 "that Flourens's area, as well as certain other parts 

 of the medulla oblongata that have been looked upon by others 

 as being respiratory centers, are not such, but are largely or 

 wholly collections of nerve-fibers which arise chiefly in the 

 roots of the vagal, spinal accessory, glosso-pharyngeal, and 

 trigeminal nerves, and which, therefore, are probably nerve- 

 paths to and from the respiratory center. Moreover, excita- 

 tion of the "nceud vital" does not excite respiratory movements, 

 but simply increases the tonicity of the diaphragm; nor is the 

 destruction of the area always followed by a cessation of res- 

 piration. While the precise location of the center is still in 

 doubt, there is abundant evidence to justify the belief in its 

 existence in the lower portion of the spinal bulb." That we 

 are again dealing with the aggregate of centers to which we 

 have referred as the "vagal system" is clear. Indeed, Flourens 

 located his "vital knot" in an area five millimeters wide be- 

 tween the nuclei of the vagus and spinal accessory nerves 

 again in the lower end of the calamus scriptorius : i.e., a region 

 comprised in the area to which the Weber brothers applied 

 one electrode, the other being in the nose, when cardiac arrest 

 or inhibition was first observed by them. 



An interesting relationship seems to us to exist between 

 these two sets of experimental results. Indeed, the area to 

 which we refer as that of the "vagal system" thus becomes the 

 source of antagonistic effects involving the same structures: i.e., 

 the Weber brothers caused arrest of the heart by overstimula- 

 tion (not "inhibition" considered as a physiological function) 

 in the manner defined in the preceding chapter, while the le- 

 sion produced by Flourens in the same area, when sufficiently 

 severe, arrested the flow of impulses to and from the heart. 



1 Reichert: Loc. cit., p. 456. 



