xiv MUSCLES AND EXERCISE 205 



called the belly. At one or both ends of some muscles we 

 find a strong, thin band of connective tissue called a tendon. 



4. A muscle is made of bundles of fibers held together by a 

 thin sheath of connective tissue. A fiber consists of still smaller 

 threads called fibrils or muscle cells. 



5. The muscle cells are arranged side by side to form the 

 thickness of a muscle, and end to end to form its length. 



6. All muscles are well supplied with blood vessels, nerves, 

 and lymphatics. They are well-nourished organs. 



7. When a muscle contracts it changes its shape without 

 altering its bulk. It becomes shorter and thicker because each 

 muscle cell has the peculiar power to change its form in that 

 way. 



8. A muscle cannot remain contracted very long without 

 becoming fatigued. It uses up food material and produces 

 waste matter. 



9. Most of the voluntary muscles are arranged in pairs, so 

 that one bends a limb and the other straightens it. 



10. In order to keep the muscles in a healthy condition, 

 they must have an abundant supply of wholesome foods, pure 

 air, and proper exercise and rest at regular intervals. 



11. Proper exercise in which a person takes a lively interest 

 improves the nutrition of all the organs of the body, and there- 

 fore conduces to health and vigor. 



12. Over-exercise enlarges the walls of the heart and arter- 

 ies, impairs the cardiac valves, injures the respiratory organs 

 and the brain, and is followed by excessive fatigue. 



13. Physical training tends to a harmonious development 

 and a perfect control of all the muscles of the body. It gives 

 grace in carriage and ease in movement, and may be employed 

 to develop the weak or neglected muscles. 



14. Exercise should not t>e taken just before or immediately 

 after a full meal. Moderate daily exercise should be taken by 

 all. 



