TSB OXYGEN FOOD OF THE BODY. 103 



The oxygen food of the body. Hitherto we have only 

 considered the energy-supply of the bcdy from one side ; 

 we have regarded it as dependent on the constant supply 

 of things which can be oxidized. But this is only half the 

 question : if substances are to be oxidized there must be a 

 provision of oxygen to oxidize them. 



In order that a steam-engine may work and keep warm 

 it is not merely necessary that it have plenty of coal, but 

 it must also have a draught of air through its furnace. 

 Chemistry teaches us that the burning in this case consists 

 in the combination of a gas called oxygen, taken from the 

 air, with other things in the coals: when this combination 

 takes place a great deal of heat is given off. The same 

 thing is true of our bodies ; in order that food matters 

 may be burnt in them and enable us to work and keep 

 warm, they must be supplied with oxygen; this they get 

 from the air by breathing. We all know that if his sup- 

 ply of air be cut off a man will die in a few minutes. II is 

 food is no use to him unless he gets oxygen from the air to 

 combine with it ; while he usually has stored up in his 

 body an excess of food matters which will keep him alive 

 for some time if he gets a supply of oxygen, he has not 

 stored up in him any reserve, or, if any, but a very small 

 one, of oxygen, and so he dies very rapidly if his breathing 

 be prevented. In ordinary language we do not call oxygen 

 a food, but restrict that name to the solids mid liquids which 

 we swallow : but inasmuch as it is a material which we 

 must take from the external universe into our bodies in or- 



Why do we need oxygen ? What does a working steam-engine 

 need in addition to coal? What happens in the furnace of an engine? 

 Why do we need to breathe ? What happens if a man's air supply 

 be stopped ? Why does a man die sooner of want of air than of want 

 of food ? Why is* oxygen entitled to be called a food ? 



