CHAPTER XXV 

 DIGESTION 



What we call living embraces a multitude of different 

 activities. In your bodies while you are reading this 

 paragraph, muscles are contracting, nerves are conducting 

 stimuli, air is being drawn into and expelled from the lungs, 

 the blood is surging through the blood vessels, absorption 

 is taking place through epithelial membranes, waste 

 matter is being eliminated from the blood, every cell is 

 being built up and torn down, chemical changes are tak'ng 

 place in every bit of living matter. It is these chemical 

 changes that keep your body warm and supply the energy 

 for its various activities. Were the chemical changes to 

 stop, everything else would stop, and the body would 

 become inert and cold. We might compare our bodies to a 

 steam engine whose supply of energy comes from the 

 burning of coal in the furnace, or in other words the 

 chemical union of carbon and perhaps a certain amount of 

 hydrogen with the oxygen of the air. The movement of 

 levers and wheels depends on the expansion of steam which 

 is caused by the heat generated by chemical changes. 

 Without the burning coal the engine would be inert and 

 cold. To keep the engine running, more coal is continually 

 added to the furnace, the ashes or unburned waste are 

 removed, and there are arrangements for removing the 

 smoke and carbon dioxide resulting from the burning of the 

 fuel. 



What fuel is to the engine food is to our bodies. Our 

 food supplies not only the material from which our bodies 



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