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The Cornell Reading-Courses 



Second, it must have water supplied to it, in order to have a medium 

 by which the energy of the fuel may be transferred to the engine. Third, 

 it must have fuel, to yield up energy to do work; energy is the power 

 to do work. 



In the same way the body must have three things supplied to it : First, 

 it must have repair material, as has been explained. For this repair 

 material a certain amount of protein must be supplied in the food. In 

 contrast with the engine, when the body is given more repair material 



Fig. 4. — An animal may be likened to an engine. Besides maintaining herself and 

 making her own repairs, this cow has manufactured from the matter and energy in 

 her food over 500 pounds of butter in one year 



(protein) than is needed the residue may be used for building new parts 

 or to produce energy. Second, the body must have a sufficient amount 

 of water, to aid in forming bones and new tissue, in the circulation of 

 food material, and in the withdrawal of waste material. This water is 

 supplied directly and in the succulent part of food. Third, the body 

 requires energy, as we have seen, to do its inside construction work, to 

 perform labor, to make milk, and so on. . This energy is derived largely 

 from the carbohydrates and fat, and partly from the protein, in the food. 

 To carry the analogy a little further: The engine and the boiler do 

 not turn all the energy derived from fuel into power, but a good deal of 



