7 2 



Life and Health 



As a result of fatigue the normal irritability of muscular 

 tissue becomes weakened, and its force of contraction is 

 lessened. There is, also, often noticed in fatigue a peculiar 

 tremor of the muscles, rendering their movements uncertain. 

 The stiffness of the muscles which occurs during severe 

 exercise, or the day after, is a familiar result of fatigue. 



103. Fatigue serves 

 as Nature's Warning. 

 The sense of fatigue is 

 Nature's warning to put 

 us on our guard. It is 

 a kind of regulator which 

 serves .in the ordinary 

 actions of life to warn us 

 not to exceed the limits 

 of useful exercise. 

 Fatigue summons us to 

 rest long before all the 

 force of the motor organs 

 has been expended, just 

 as the sensation of hun- 

 ger warns us that we 

 need food, long before 

 the body has become weak from the lack of nourishment. 

 104. A Period of Rest Necessary. Rest is necessary for 

 the tissues, that they may repair the losses sustained in 

 doing work. A period of rest must alternate with a period 

 of activity. Even the heart has its periods of absolute 

 rest to alternate with those of work. Were it not for this 

 power to repair and renew its tissues, the body would soon 

 be worn out. 



The periods of rest should vary with the kind of exercise. 

 Thus, exercise which produces breathlessness requires 



FIG. 40. Showing how the Muscles of 

 the Back may be developed by a 

 Moderate Amount of Dumb-Bell Exer- 

 cise at Home. 

 (From a photograph of the living model.) 



