HOW DO WE CONTROL THE HUMAN MACHINE? 385 



Wright Pierce 



In a sprint the race usually depends upon the start. How did these boys get 

 off " on the gun " ? 



of the legs and arms. Toes dig into the ground ; muscles 

 are tensed, and the boys are off. The nervous system 

 has been the director and is responsible for their success 

 or failure in the race. 



The Central Nervous System. We know in a general 

 way what the nervous system is. There are really two 

 parts to the nervous system : a central portion consisting 

 of the brain and spinal cord, which are protected by the 

 bones of the skull and spinal column, and a number of 

 paired nerves which leave the central nervous system 

 and seem to run to all parts of the body. The nervous 

 system is made up of cells like the rest of the body, 

 but these cells are of various shapes and sizes and many 

 of them have very long threadlike tails. These are the 

 structures that make up the nerves. The nerves are 

 made up of two kinds of cells. In one kind the cells 

 pick up the sensation on the outside of the body by 

 H. & w. sci. i26 



