202 HUMAN PHYSIOLOGY CHAP. 



The simple exercises of any system can be given in 

 the regular class room if necessary, without apparatus 

 or music. During the gymnastic period the room should 

 be well ventilated, so that an abundance of pure air may 

 be carried to all the organs of the body. The exercise 

 should be pleasant and short, but sharp and vigorous, 

 otherwise it will be of little value. 



141. Time of Exercise. Exercise should be taken 

 regularly every day, so that the body becomes used 

 to it and does not feel fatigue too easily. A small 

 amount of moderate exercise taken every day is more 

 beneficial than a greater amount once a week. If the 

 exercise is regular, a little more may be taken each suc- 

 ceeding day until the muscles become hard and strong, 

 so that it is almost impossible to fatigue them. 



Moderate exercise can be safely taken any time of 

 day except immediately after a full meal. At such a 

 time a large amount of blood is needed in the stomach 

 and intestines, and if drained off to the muscles the 

 foods will not be properly digested and absorbed. The 

 best time for severe physical exertion is about two hours 

 after a meal. The exercise indulged in after supper 

 should be rather light. 



142. Fatigue and Rest. : The fatigue of a muscle is 

 due to two causes. The food supply in the muscle and 

 in the blood is used up, and the cells become fatigued 

 from a lack of nourishment. The second cause of 

 fatigue is the formation of certain waste products by 

 the action of the muscles, and their accumulation in 

 the cells and lymph. The muscular stiffness and sore- 



