CHAPTER XIII. 



THE GENEKAL PHYSIOLOGY OF THE NEKV- 

 OUS SYSTEM. 



The Properties of the Nervous System. General Con- 

 siderations. If the finger of any one unexpectedly touches 

 a very hot object, pain is felt and the hand is suddenly 

 snatched away; that is to say, sensation is aroused and cer- 

 tain muscles are caused to contract. If, however, the- 

 nerves passing from the arm to the spinal cord ha^e been 

 divided, or if they have been rendered incapable of activity 

 by disease, no such results follow. Pain is not then felt on 

 touching the hot body nor does any movement of the limb 

 occur; even more, under such circumstances the strongest 

 effort of the will of the individual will be unable to cause 

 any movement of his hand. If, again, the nerves of the 

 limb have uninjured connection with the spinal cord, but 

 parts of the latter, higher up, between the brain and the 

 point of junction of the nerves of the brachial plexus with 

 the cord, are injured, then a sudden contact with the hot 

 body will cause the arm to be snatched away, but no pain 

 or other sensation due to the contact will be felt, nor can 

 the will act upon the muscles of the arm. From the com- 

 parison of what happens in such cases (which have been 

 observed over and over again upon wounded or diseased 

 persons) with what occurs in the natural condition of 

 things, several important conclusions may be arrived at: 



1. The feeling of pain does not reside in the burnt part 

 itself; although that may be perfectly normal, no sensa- 

 tion will be aroused by any external force acting upon it, 

 if the nervous cords uniting it with the centres be pre- 

 viously divided. 



2. The hot body has originated some change which, pro- 



