138 ELEMENTS OF PHYSIOLOGY 



thinnest muscles will grow large and strong, and the 

 flabbiest muscles will acquire a healthy tone, through 

 regular use. The condition of an arm carried in a sling is 

 an illustration of the effects of disuse. 



4. The Skeleton. The bones are better nourished, but 

 the chief benefit of exercise to them comes through the 

 improved strength and tone of the muscles by which 

 the bones are held in proper position. Thus deformed 

 cartilages and stretched ligaments, with the accompanying 

 round shoulders, flat chest, and spinal curvature are pre- 

 vented. A person with good muscles sits, stands, and 

 carries himself erect. One with weak muscles is apt to 

 slouch down. 



5. The Brain. The aid given to the heart by the con- 

 traction of the muscles makes the blood bound forward in 

 the vessels, and the pure fresh blood enables the brain to 

 work with greater ease and pleasure. This fresh blood is 

 still purer because of the increased expansion of the lungs. 



6. The Lungs. Gentle and slow exercise has little ef- 

 fect upon the lungs, but rapid and vigorous exercise expands 

 them till every nook and cell is filled, and the chest is de- 

 veloped and enlarged. A good-sized chest is very neces- 

 sary to good health. 



7. The Heart. The heart is aided in its work, as already 

 pointed out Long-continued exercise puts more demands 

 upon the heart, which becomes strong with the rest of the 

 muscles. With people who take no exercise, the heart 

 cannot be said to become flabby, but it may become weak, 

 just as any other muscle. 



8. The Digestive Organs. Exercise gives a good 

 appetite and prevents trouble in the stomach and clogging 

 of the intestines from which lazy people are apt to suffer. 



9. General Effects. It promotes good humor, prevents 

 vice and dissipation, gives one the agreeable look of health 

 and vigor. It is not the pitcher in the baseball team, or 



