REFLEX FUNCTIONS OF THE MEDULLA. 281 



warm-blooded animals, all the parts of the brain have been gradually 

 cut away from above, down to the medulla oblongata, and the spinal 

 cord has then also been detached below it, and yet respiration has 

 continued for a short time (Longet) ; and in the frog, both the brain 

 and spinal cord have been removed, and respiration has been long 

 sustained, provided that the medulla oblongata remained uninjured. 

 Again, the medulla oblongata itself has been alone destroyed, when 

 respiration was instantly arrested, the animal dying asphyxiated. It 

 is sufficient for a very small portion of the back part of the medulla, 

 in the floor of the fourth ventricle, to be destroyed, in order to pro- 

 duce this effect, and indeed the destruction of a very minute point, 

 hence named the vital knot (nceud vital], has been deemed sufficient for 

 this purpose. But there seems reason to think, that, the part con- 

 cerned as a centre in governing respiration, is of greater extent ; it is 

 believed to correspond with the portion from which the deep roots of 

 the pneumogastric nerves take their origin, which occupies the back 

 part -of the medulla; for the restiform bodies and the pyramids may 

 be removed without interfering with the respiratory acts. A trans- 

 verse section through the gray matter of the medulla oblongata, at the 

 point of the calamus, suddenly stops the respiratory movements; but 

 after a longitudinal median section of the medulla, these continue. 

 Hence both sides of the body possess their proper respiratory nervous 

 centre. Irritation of the medulla oblongata diminishes the number of 

 the respirations ; a result also produced by general pressure on the 

 brain, the effects of which are transmitted to the medulla. The paths 

 of conduction of the motor impulses concerned in respiration, named, 

 by Sir C. Bell, the respiratory tracts, are located in the white fibres 

 of the lateral columns of the cord. (Bell, Schiff.) The office of the 

 medulla oblongata, as the controlling centre of respiration, affords an 

 explanation of its importance in regard to the vital activity generally. 

 Through it, the heart is indirectly, and also directly, affected, for the 

 vagi nerves, which regulate the heart's movements, arise from this 

 part. Galvanic irritation of the medulla, like that of the vagi nerves, 

 causes temporary arrest of the heart's actions ; its destruction dimin- 

 ishes the frequency and strength of those movements. 



There is reason to conclude, from analogy, that the reflex move- 

 ments of deglutition must likewise have their special governing centre, 

 which is supposed to be placed at the back of the medulla, near the 

 vital knot. 



As a reflex centre of a more general kind, the medulla oblongata 

 is further regarded as the seat of excitation of symmetrical epileptic 

 seizures, such as occur after ligature of the great vessels of the neck. 



The medulla oblongata is probably also a centre for certain parts 

 of the sympathetic system ; and a cross section through the restiform 

 bodies, like division of the posterior columns of the cord, is followed, 

 probably from similar reasons, by an exalted sensibility of the trunk 

 and limbs. 



Like the reflex acts of the spinal cord, those which take place 

 through the intervention of the medulla oblongata are likewise inde- 

 pendent of the will, and are not necessarily associated with conscious- 



