RESPONSES TO GRAVITY 243 



organ, connected by means of nerve chains to the skeletal 

 muscles, that helps us keep our balance in walking or skating, 

 and in recovering our position when we trip. In addition 

 to this, the movements of the viscera and the strain of the 

 muscles at the joints help to keep us aware of the body's 

 position and of changes in the position at all times. 



Since the introduction of airships into the army and navy, it has 

 become necessary to give certain classes of recruits a special kind of 

 physical examination, for the purpose of discovering whether the 

 equilibration reflexes are in good working order. Unless a person 

 can respond quickly to changes in bodily position, he can never learn 

 to control a machine that moves in the three dimensions of space. 



