52 EXERCISE. 



8. Exercise. After good air and food the most im- 

 portant condition for keeping the muscles healthy is 

 that they be used regularly, or exercised. A muscle left in 

 idleness dwindles in size and becomes worse in quality: 

 instead of being hard, firm, and ready to contract, it be- 

 comes soft, flabby, and feeble. This fact is well shown 

 in the muscles of an arm or leg which has been kept mo- 

 tionless for a few weeks while a broken bone is healing. 

 When the bandages and splints are taken off, the mus- 

 cles are nearly powerless, and much smaller than those 

 of the opposite limb, which have been kept in use. 

 Only by careful continued exercise, do they regain their 

 former size and strength. The opposite fact, that mus- 

 cles when used grow bigger and become more powerful, 

 is illustrated by the huge " brawny" arm of a blacksmith. 



9. Too Much Exercise is as Harmful as too Little. When 

 a muscle is at work, it is used up faster than new muscle- 

 substance is made; also, waste substances are produced 

 faster than the blood can carry them off. After a time, 

 this causes a feeling of being tired, which is Nature's 

 signal that it is time to rest. To exercise until we are a 

 little tired, does no harm; indeed, rather benefits than 

 hurts the muscles, if followed by proper repose. During 

 a time of rest following moderate work, more blood than 

 usual flows to the muscle, conveying more nourishment 

 than is needed for its repair; and so it grows larger and 



8. After good food and air what is next in importance for our mus- 

 cles? How does continued idleness affect them ? Illustrate. Give an 

 example of the improvement of muscles by exercise. 



9. Why do we feel tired after hard muscular work ? What happens 

 when we rest our muscles after moderate fatigue ? How does repeated 

 overwork affect the muscles ? The body in general ? What is neces- 

 sary for healthy muscles? How is this illustrated by the heart ? The 

 breathing muscles ? 



