OF THE NERVOUS SYSTEM IN GENERAL. 477 



Difg6s,* by ingeniously bringing together physiological and 

 pathological facts, places the seat of sensibility in the cerebel- 

 lum, and that of voluntary motion in the hemispheres of the 

 brain, admitting that the sensation is transmitted to the side 

 of the cerebellum corresponding with the impression; on the 

 contrary, as has been known for a long time, volition is trans- 

 mitted from one side of the brain to the opposite side of the 

 body. 



These different opinions, contradictory in some points, rest 

 all of them upon facts more or less well observed; new facts 

 are necessary to dissipate the uncertainties which still remain 

 upon this subject. 



The transmission of sensation takes place by the posterior 

 part of the spinal marrow, and that of motion by its anterior 

 part. There are, as will be seen hereafter, special nerves for 

 each of these functions. 



The spinal marrow, which in these functions has only the 

 office of a conductor, is the seat or the origin of the principle 

 of irritability. If the spinal marrow of a living animal be di- 

 vided in its middle, the posterior part of the body becomes 

 insensible and immoveable. If the skin of this part of the 

 body be irritated, the irritation, though not perceived, deter- 

 mines involuntary motions in the muscles of this part. If the 

 spinal marrow be removed, and in consequence the central 

 connections of the nerves destroyed, movements of irritation 

 in the skin can be no longer excited. 



The circulation is under the influence of the entire spinal 

 marrow, and of all the motory nerves which are derived from 

 it; the particular action of the heart also, but mediately, being 

 immediately under the influence of the sympathetic nerve. 

 Respiration is under the direction of the superior and lateral 

 part of the spinal marrow; digestion under the combined in- 

 fluence of the par vagum and sympathetic. 



Secretion, absorption, vital heat and nutrition, are under the 

 influence of all parts of the nervous system. 



761. Nothing is known respecting the manner in which 



* Memoire inedit. 



