293 PHYSIOLOGY AND HEALTH. 



tions of digestion, respiration, nutrition, and of the brain. 

 The amount of this exercise may vary according to the con- 

 stitution, and habit, and powers of the individual. It is best 

 when so varied as to bring into play all the muscles of the 

 body. It should be taken out of doors, and in the free air. 

 This is necessary for all men and all women, of whatever 

 occupation, and especially for those of no occupation. 



CHAPTER XIV. 



Amount of Exercise may be greater than Health requires. Body 

 grows strong with judicious Labor. Limit to Man's Increase of 

 Strength. Fulness of Strength maybe maintained to Old Age, 

 with proper Care. Man has a limited Power of Endurance. 

 No more Strength must be expended in the Day than is restored 

 in the Night. Men worn out by excessive Toil. Length of 

 Life differs with Amount of Labor. 



689. THAT amount 'of exercise which is necessary for 

 health is not the limit of muscular power. If it were, we 

 should be able to accomplish but a small part of the work 

 which we now do, and the labors of the farm and workshop 

 would not be effected. We have a power of muscular con- 

 traction and of motion, which may be applied to the ordinary 

 purposes of life. With this we cultivate the soil and carry 

 on the operations of the mechanic arts, we navigate ships, 

 and perform all our labor for pleasure or for profit. 



690. It becomes a question to every man who works for 

 profit, or who exercises more than is needed for the bare 

 maintenance of health, how much can he work ? Have 

 the moving animal frame, the muscles and the bones, an in- 

 definite power. of endurance and action? It needs no physi- 

 ological explanation to show that there is a limit to this 

 power of labor. Then there comes another question Where 

 is that limit? How long can a man labor ? How much may 

 he labor each day, and not. wear upon his permanent health, 

 nor interfere with his continuance of life? To a certain 



