224 SENS ATI OX DEPENDS ON THE BRAIN. 



2. All Kinds of Sensation Depend on the Brain. You 



have already learned that when the nerve-fibres of the 

 foot are cut anywhere on their way to the brain, the foot 

 loses feeling (p. 199). This is true of every other part 

 of the body which has feeling, whether it be merely a 

 part possessing some common sensation, or an organ of 

 one of the special senses. Also, if the brain be acted upon 

 by chloroform or ether, or certain parts of it be seriously 

 diseased or injured, feeling is lost, although the nerves 

 and the sense-organs may be quite unaffected. We thus 

 learn that all feeling is due to some change in the brain. 

 Usually, when we have a sensation, whether of sight, 

 hearing, pain, or any other kirfU, it is due to the fact that 

 some sensory nerve (p. 196) has been set at work, and 

 has carried a message to the brain. This message has 

 then set at work, or excited, a part of the brain, which 

 makes us see or smell; and so on. The mind has learned 

 from what parts of the body these messages to the brain 

 usually start, and we have come to think of each kind of 

 feeling as being in the organ or place from which the 

 message starts, and not in the brain itself. When the 

 eye is closed we do not see, so we think the sense of 

 sight is in the eye. Yet it really is in the brain: all that 

 the eye does is, when light acts on it, to send messages 

 along its nerve to the brain, and set to work that part of 

 the brain which has feelings of sight; and so it is with 

 our other senses. 



2. What results when all the nerve-fibres coming from any part of 

 the body which has feeling, are cut ? How may loss of feeling be 

 caused without affecting the sense-organs or the nerves ? What is 

 thus proved ? To what is a sensation usually due ? What happens 

 when the message sent by the sensory nerve reaches the brain ? 

 How has the mind come to connect certain feelings with certain parts 

 of the body ? Illustrate. What sometimes happens as regards sen- 

 sations in disease ? Results ? 



