1 86 NUTRITION, DIETETICS AND ANIMAL HEAT 



The foods thus possess a certain potential energy, an energy 

 which may be converted directly or indirectly into heat, or its 

 equivalent. The potential energy of the foods keeps up the 

 body temperature and supplies force for doing work. It is con- 

 verted into heat and kinetic energy. Kinetic energy is working 

 energy, and is represented in the body chiefly by muscular con- 

 tractions. But, since this kinetic energy has its source in the 

 transformation of food stuffs, and since kinetic energy and heat 

 are mutually convertible, it may be assumed that all the potential 

 energy of the foods is converted into heat. The kinetic energy 

 may be taken as representing so much heat, and the total pro- 

 duction of heat (including kinetic energy) as representing the 

 total production of energy. Or, to state the case differently the 

 potential energy of the food is converted into heat, a part of 

 which appears as kinetic energy. By far the largest part of this 

 potential energy, however, is converted directly into heat. Not 

 more than one-fifth of the heat produced in the body can be 

 utilized to do work, and a part of that work is actually converted 

 indirectly into heat, and contributes to the total heat of the 

 body, by overcoming friction incident to respiration, circulation, 

 movements of the joints, muscles, etc. 



Potential Value of Foods. It is estimated that the oxidation 

 in the body of one gram of fat produces 9,300 calories of heat, 

 one gram of carbohydrate 4,100 calories, and one gram of proteid 

 4,100 calories. These figures represent the potential energy of 

 the several foods. Fats, it is seen, produce, weight for weight, 

 more than twice as much energy as other foods, but reasons have 

 been given why they cannot be used exclusively. 



A calorie is the amount of heat necessary to raise i Kg of 

 water from o to i C. A grammeter is the amount of energy 

 necessary to raise i gram i meter. Now since heat and work 

 are only different forms of energy, these two units calorie and 

 grammeter have each equivalents in terms of the other. One 

 calorie equals 424.5 grammeters; that is, the force represented by 



