EXERCISE. 95 



higher temperature ; it has parted with much of its oxygen 

 and has taken up a large quantity of carbonic acid, also 

 various products from chemical changes that have occurred 

 in the food materials supplied the muscle by the blood, 

 and in the muscle itself. Obviously this is the condition 

 demanded for the integrity of a muscle, for it is now receiv- 

 ing a full supply of fresh blood and there is free and rapid 

 drainage of all its noxious waste matters. Go a little fur- 

 ther and by means of proper food in sufficient quantity 

 and an abundance of pure air render the blood rich in 

 nutritive elements and oxygen, also allow the muscle due 

 intervals of rest, and it must be not only healthy but 

 increase in size and weight. 



As exercise acts on a single muscle so it acts on the 

 muscular system as a whole — it enlarges and strengthens 

 it. But the muscles themselves are not the only parts of 

 the body that are benefited by exercise, for brought into 

 action by it they in turn increase the rapidity of the flow 

 of blood to the heart. This vital organ also works more 

 vigorously and a larger quantity of blood is sent through 

 the lungs ; while the breathing is quickened and more 

 oxygen absorbed. The fires within are now brightened 

 up, and in consequence the skin and other organs of secre- 

 tion and excretion are brought into action to get rid of the 

 excess of heat and the clinkers and ashes, as it were, the 

 products of combustion. Thus exercise acts as a spur and 

 brings every important organ in the body into more active 

 play. 



Now, deprive the body of sufficient exercise and note 

 the result. The digestive organs are among the first to 

 show signs of distress and decline in power, and their work 

 is but sluggishly and imperfectly performed ; the food con- 

 stituents taken up from them by the blood are not properly 

 oxidized ; drainage of noxious products is not only impeded 



