CHAPTER V 

 FOOD AND DRINK 



115, The Necessity for Food. In a general way the 

 body may be compared to a steam engine in good working 

 order. An engine consumes fuel to obtain from it the 

 energy necessary to do its work ; so, we consume within 

 our bodies certain nutritious substances to obtain from them 

 the energy necessary for our activities. Just as the energy 

 for the working of the engine is obtained by the combus- 

 tion of fuel, so the energy expended by our bodies in the 

 form of muscular work or heat results from the combustion 

 or oxidation within us of the food we eat. Unless this 

 energy is provided for the body it will have but little power 

 of doing work, and, like an engine without steam, must 

 soon become motionless. 



116. Waste made good by Food. A steam engine, from 

 the first stroke of its piston rod, begins to wear out, and 

 before long needs repair. All work involves waste. The 

 engine, unless kept in thorough repair, would soon stop. 

 So it is with our bodies. In their living cells chemical 

 changes are constantly going on ; complex substances are 

 being broken up into simpler combinations. It is impossible 

 to move a single muscle, or even to think for one moment, 

 without causing some substance in the muscular or brain 

 tissue to become of no further use in the body. 



In short, so long as the body maintains its activities, 

 there must result a waste of substance which corresponds 



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