MUSCULAR SYSTEM 381 



being formed. The chief ones of these products are 

 carbon dioxide, water, and nitrogenous wastes. 



Frequently we become fatigued. This is probably 

 not because the muscles and nerves are being over- 

 worked, but because the waste products are not being 

 removed fast enough. A good blood circulation is nec- 

 essary to remove these wastes and to carry food and 

 oxygen for rebuilding the tissues which are being used. 



Exercise. A certain amount of vigorous exercise 

 each day is essential to keep the body in the best 

 physical condition, for, as everyone knows, if the mus- 

 cles are not used for a time they become weak and 

 flabby. Regularity in exercise is as important as regu- 

 larity in eating. The kind and amount of exercise 

 should vary with the individual. It should be vigorous 

 enough so that one feels fatigued but not exhausted. 

 The ideal exercise involves the action of the greatest 

 number of muscles. 



Exercise taken in the spirit of play is most bene- 

 ficial, because it not only results in free and varied 

 activity, but it also rests the mind. As a result of 

 exercise the whole body is improved, respiration and 

 circulation are increased, the muscles are developed, 

 and the mind is made more alert and active. 



Questions 



1. What part of the body by weight is muscle ? 



2. Of what use to the body are the muscles ? 



3. What special property is possessed by muscle? 



