96 THE HUMAN BODY. 



from the energy liberated when parts of the body are burned, 

 or, as the chemists say, oxidized, just as that used by a 

 locomotive comes from the burning or oxidation of coal or 

 wood in its furnace. In consequence of this constant oxi- 

 dation, which destroys the tissues of the body as coal is 

 destroyed in a furnace, new materials must constantly be 

 supplied to make up for those used for oxidation. These 

 new materials are provided in our food. One chief reason 

 of our needing to eat, is that we may replace the parts of 

 the body which have been burned in order to set free the 

 energy which we spend in our muscular movements. 



Why the body is warm. As a working steam-engine is 

 1 warm so are our bodies, because all the energy which is set 

 free when substances are burned in them, is not turned 

 into mechanical work, but some of it appears as heat. 

 This keeping warm is a very important matter, for experi- 

 ment shows that no tissue of the human body works well 

 when cooled down even a few degrees below 98.5 F., 

 which is its natural healthy temperature. Careful experi- 

 ments prove that when a muscle does work it becomes 

 hotter, and we all know that exercise makes us warm. 

 This shows that the oxidation or burning which takes 

 place in a working muscle does not all become turned into 

 mechanical work, but a good share of it appears as heat. 

 What is true of muscle is true of all other organs of the 

 body: when they work, no matter what their kind of work, 

 their substance is oxidized, and some of the energy set free 



What is the chemical term for burning? What does food supply? 



Point out a chief reason for our need of eating? 



Why are our bodies warm ? Why is it important that they should 

 be warm ? How is the temperature of a muscle affected when it 

 works ? Do other organs resemble muscles in this respect? 



