100 THE WONDERFUL HOUSE THAT JACK HAS 



unites with the carbon of various substances to 

 cause the burning or combustion with which all are 

 familiar. 



Of course, we know that this burning or combustion 

 is necessary to produce the heat that warms our houses 

 and the steam and energy that run engines and ma- 

 chinery. No boy or girl needs to be told that if the 

 draughts of a stove or furnace are all closed, the fire will 

 in time stop burning. Few are unfamiliar with the 

 fact that if the small holes below the chimney in a 

 lamp burner are covered, the light will go out. That 

 both of these things happen because the air is shut 

 off, is also well known. But that the freedom with 

 which fire burns depends upon the amount of oxygen 

 contained by the air that passes into it, may not be 

 as generally understood. Oxygen in the air is also 

 continually uniting with wood, iron, and other ex- 

 posed substances, and, though heat is generated, it 

 is riot sufficient to produce flame. The rust of the 

 iron and the decay of the wood are the results of the 

 combustion that we see. 



Why should we speak of these common, everyday 

 things? Is it possible that our bodies are anything 

 like furnaces or engines? Oddly enough they are 

 very similar ; and the tissues of our bodies are the coal 

 and wood with which the oxygen, taken in through 

 the lungs and skin, unites to produce the heat that 

 keeps you and me warm, and the energy that gives us 

 the power of motion. But the union of oxygen with 



