46 DEPENDENCE OF NERVES AND MUSCLES. 



The cells of the brain are sending messages to the muscles. 

 There must be a distinct series of nerve impulses for the con- 

 trol of each muscle. The impulses must be in the proper 

 sequence and of the right degree of strength to make each 

 muscle shorten just at the right time, with the right force, 

 for the right length of time, or we shall have muscular con- 

 fusion instead of orderly and accurate movements. 



In playing a game of tennis the brain is an organist with 

 five hundred keys before him. And before he has finished 

 the tune, he has had occasion to use nearly every one of 

 them, especially if the player is not only dextrous but am- 

 bidextrous. 



The precision and rapidity of these movements are most 

 wonderful. Imagine an organist with so many keys, or a tel- 

 egraph operator sending out so many messages over so many 

 wires in so brief a space of time, and getting them all right. 

 Yet we have learned all this. The new-born babe has little 

 more than the power and the tendency to move. Most of his 

 acts are not orderly. He gradually learns to hold up his 

 head, to sit, to grasp objects, to walk, to throw, and execute 

 all the co-ordinated movements that we now discover to be 

 primarily under the management of the two Master Tissues (as 

 Foster calls them), Nervous Tissue and Muscular Tissue. 



Dependence of Nerves and Muscles. It may have 

 happened to you that after sitting long in one position you 

 attempted to stand, but found that you could not do so. One 

 leg failed to act at the bidding of your will. Pressing on the 

 foot caused little, if any, sensation. 



Or, perhaps, you may have awakened in the night and 

 found one arm numb and unable to move. 



When the foot is " asleep " we get little sensation from it ; 

 we hardly know whether it is touching the floor or not. Press- 

 ing on it with the other foot causes no pain. 



