CHAPTER XX. 

 THE SENSE OF SIGHT. 



The Sense of Sight. In the fable of the blind man 

 carrying the lame man whose eyes were good, we have an 

 illustration of the dependence of the various organs on 

 each other. We have considered how all our knowledge, 

 both of the condition of our bodies and of the external 

 world, comes through the nervous system. Now, so far 

 as the senses we have studied are concerned, we learn 

 almost nothing of the external world except from actual 

 contact. But sight reveals objects at a distance. With- 

 out the eye the body is comparatively helpless. The lame 

 man that the body carries is a slight burden in comparison 

 with the assistance which he renders. We can well afford 

 to carry with us all the time two of these lame men to 

 keep posted as to the objects beyond our reach. Of course 

 touch is a great aid to our interpretations of what we see. 

 But sight is evidently the main avenue of knowledge, the 

 royal road along which come the messages which bring us 

 the most news, which give us the keenest delight ; which 

 makes us aware of most that we know of this world, and 

 the only means of knowing that there are other worlds 

 than the one we inhabit. 



Protection of the Eye. The eye is set well back in 

 its socket and guarded by three projecting bony promi- 

 nences, the brow, cheek bone, and the bridge of the nose. 

 It is further protected by the eyelids and eyelashes. 



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