330 PHYSIOLOGY AND HEALTH. 



CHAPTER II. 



Sensation is in Brain. Produced by Impressions on outer Ends of 

 Nerves, and carried on Nerve to Brain. No Sejisibility nor Power 

 of Motion in Part which does not communicate with Brain. 

 Cutting Nerve, or Pressure on Nerve, paralyzes Parts to which it is 

 distributed. Foot asleep. , Injury^ of Spinal Cord paralyzes Parts 

 below. 



755. SENSORY nerves carry impressions from their outer 

 extremities in the organs of sense, and in the flesh, to their 

 ends in the brain, where the sensation is excited. The trunk 

 of the healthy nerve has no feeling, and receives no impres- 

 sions ; it is merely a messenger to carry the impressions from 

 the points where they are made, to the brain, where they are 

 recognized. Sensation is not in the outer end of the nerve, 

 nor in its trunk, but in the brain, at the inner end of the 

 nerve. There are, then, three things in this work of sensa- 

 tion : 1st, the extremity of the nerve, which first receives the 

 impression ; 2d, the brain, which perceives the impression ; 

 and, 3d, the connecting line of nerve between them ; and 

 if either of these be wanting, or injured, there can b no 

 healthy sensation. The power of motion requires the same 

 three things the brain, through which the rnind determines 

 or wills the motion ; the nerve, to carry this volition or di- 

 rectipn to the muscle ; and the nervous termination, which 

 imparts the stimulus to the moving texture. 



756. The power of motion, and the sensibility of any part, 

 require this constant and uninterrupted nervous communica- 

 tion with the brain. ; and if, from any cause, this connection be 

 suspended, if any nerve be cut, or divided, or pressed, the 

 power both of motion and of feeling is destroyed, or im- 

 paired, in the part where the nerve terminates. The familiar 

 circumstance of the foot being asleep is caused by the pres- 

 sure upon the nerves that lead down the leg to this extremity. 

 The communication between the terminations of the nerves 

 below and the brain above is thus interrupted, and then the 



