CHAPTER XIX 

 THE ENERGY OF THE METABOLISM 



THE initial statement in this book that living things 

 are transformers of matter and energy is a text to which 

 we have closely adhered. In recent chapters the emphasis 

 has been placed upon transformations of matter. We 

 shall now pass on to speak of the energy evolved by animals 

 and particularly by the human body. The fundamental 

 facts are presumably clear. The energy of the income is 

 potential in the complex molecules of the food. It is 

 released in the oxidative decomposition processes of life 

 and made kinetic. It appears chiefly often solely 

 in the form of heat. Measurements of the heat production 

 of living organisms are generally to be accepted as indic- 

 ative of the total energy production. Certain exceptions 

 to the rule will soon be noted. 



Fuel Values. Since energy can be transmuted from one 

 form to another it is possible to make the units which stand 

 primarily for one kind do duty for all. It is our constant 

 practice to use the units of heat to measure all the energy 

 of metabolism. The unit which we shall employ is the 

 large Calorie, approximately defined as the amount of 

 energy required to raise the temperature of 1 kilogram of 

 water one centigrade degree. The large Calorie is invari- 

 ably distinguished from the small by the capital C. The 

 small calorie is ygVfr f the large; no further reference to 

 it will be made. When a combustible organic substance 

 of a standard composition is completely oxidized a definite 

 quantity of heat is evolved. The heat produced by 

 oxidizing 1 gram of any compound is its fuel value. 



The highest fuel value recorded is that of hydrogen, 

 about 34 Cal. This is the amount of heat produced when 



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