MAN'S BRAIN 503 



(fabrics) out of other material. He has strengthened his arm 

 by means of sticks and stones, and has lengthened his legs 

 that is, increased his speed by means of iron and brass. He 

 has extended the reach of his eyesight millions of miles beyond 

 the surface of the earth, and has seen into the world of the 

 little, a thing no other backboned animal has ever done. He 

 can hear the footsteps of a fly (although he does not need it 

 either for protection or for food), and he has caught vibrations 

 through miles of space. In every direction man has made up 

 for his organic insufficiency by using his thinking organ to 

 guide his hand. 



