CHAPTER XIII. 



THE FIVE SENSES. SENSE OF TOUCH. 



1 . \A sensation is the perception of an impression made on 

 some organ.' By our sensations we receive a knowledge of 

 what is passing within or without the body. They are ac- 

 cordingly{divided into internal and external^ fAn internal 

 sensation, is one which is produced by causes acting within 

 the system, as hunger and thirst / but an external sensation 

 is one that is occasioned by the impression of a body, exter- 

 nal to the part impressed, as sight, hearing} &c. 



2. No sensation, we have seen, can be perceived unless it 

 is transmitted to the brain. When ideas, which have been 

 called '<fthe images of sensible objects,* are reflected upon 

 and compared with each other, we exert thought and judg- 

 ment ; and when they are recalled, we are said to exert the 

 memory. Thus are the senses avenues to knowledge, though 

 they do not give rise, as some have stated, to our intellect 

 and moral powers.) With every sense an animal discovers 

 a new world ; thus creation is to it increased or diminished, 

 accordingly as its senses are more or less numerous. A 

 sensation lasts a certain time after the exciting cause has 

 ceased. Thus if a piece of wood, with one end ignited is 

 whirled round, we see a luminous ring ; the sensation pro- 

 duced by the wood in each point of the circle continuing 

 till the wood arrives at that point again ; a rocket forms a 

 train. 



3. {The external senses are Jive in number; touch, taste, 

 smell, hearing, and vision. ; These are all situated at the sur- 

 face of the body, so as to be capable of acting on external 

 bodies. (Most of them are under the control of the will ; at 

 least they may be exercised actively or passively^ and by 



