290 FUNCTIONS OF THE NERVOUS SYSTEM. 



that these movements are produced by a mere physical change in the nervous 

 centres; the consciousness of the individual not being affected in their per- 

 formance, and sensation having therefore no necessary participation in them. 

 As the movements witnessed in the lower animals, under the same circum- 

 stances, are altogether of a similar character, there seems no good reason to 

 attribute to their Spinal Cord an attribute, of which it is certainly destitute in 

 Man. There is no essential difference, either in structure, or in the nature of 

 the actions performed by them, between the Spinal Cord and the Medulla 

 Oblongata, which can warrant us in assigning to the latter a function that the 

 former does not possess : and if the reflexions of the Spinal Cord do not 

 involve sensation, there is good reason for concluding, that this change is not 

 a necessary element in those of the Medulla Oblongata. It is perfectly true, 

 that it usually accompanies in us the greater number of actions, to which that 

 division of the centre is subservient; for example, those of respiration and 

 deglutition : and it is scarcely possible for such an accident to occur in the 

 Human being, as the separation of the Medulla Oblongata from the brain, 

 without the destruction of the independent functions of both. It is not likely 

 that we can ever have the power of ascertaining, by the testimony of a patient 

 so affected, that the Respiratory movements are performed without the neces- 

 sary intervention of sensation ; as we have been able to do in regard to other 

 reflex movements. But as the general fact is, that there is no positive ground 

 whatever for regarding any part of the Spinal Cord as a serisorium independent 

 of the brain, and that the Respiratory movements certainly correspond in all 

 their conditions with the actions denominated reflex, there would seem no 

 good reason for maintaining that sensation is an element in their production, 

 whilst it is admitted to be not essential in the case of the less regular con- 

 vulsive actions already described. The character of adaptiveness to a designed 

 end, in regard to their combination and succession, which the movements of 

 respiration and deglutition exhibit, has been shown to be no proof of their 

 dependence on sensation. 



371. The question has been often put to those who advocate this view, 

 why the sensation should be so constantly associated with these changes, if 

 not essential to produce the motion? An objection might fairly be made to 

 any reasoning from final causes, in a question of facts; but the inquiry may 

 be easily answered. In many instances the production of sensations is the 

 stimulus necessary for the excitement of other actions, which are required 

 for the continued maintenance of those in question. This may be rendered 

 more comprehensible by a simple illustration. A cistern filled with water 

 may be speedily emptied by a cock occasionally opened at the bottom ; but, 

 if it communicate with a reservoir, by means of a valve opened by a ball 

 floating on the surface of the water it contains, it may be kept constantly full. 

 The lower cock is opened, and the water flows out; and, in consequence of 

 the lowering of the surface thus produced, the floating valve above is opened, 

 and the cistern is refilled from the reservoir. Now here the action of the ball- 

 cock at the top is not essential to the flow of water at the bottom, but is 

 rather consecutive upon it. Just so is it with regard to those movements of 

 Animals, which are concerned in the ingestion of their food. The muscular 

 contractions required to propel it along the alimentary canal, from the stomach 

 downwards, are provided for, without even the intervention of the nervous 

 system. To bring it within reach of these, a muscular apparatus is provided, 

 by which anything that comes within its grasp is conveyed downwards, 

 through a reflex operation, originating in the impression made upon the sur- 

 face of the pharynx. Now this action, in the ordinary condition, may be 

 considered as attended with sensation, in order that the Animal may be called 

 upon to execute those other movements, which will bring food within the 



