l86 NUTRITION, DIETETICS AND ANIMAL HEAT 



or its equivalent. The potential energy of the foods keeps 

 up the body temperature and supplies force for doing work. 

 It is converted into heat and kinetic energy. Kinetic energy 

 is working energy, and is represented in the body chiefly 

 by muscular contractions. 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 con- 

 verted into heat. The kinetic energy may be taken as rep- 

 resenting so much heat, and the total production of heat 

 (including kinetic energy) as representing the total produc- 

 tion of energy. Or, to state the case differently, the potential 

 energy of the food is converted into heat, a part of which ap- 

 pears as kinetic energy. .By far the largest part of this po- 

 tential 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 con- 

 verted 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 oxida- 

 tion 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, pro- 

 duce, 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 one calorie will raise one gram 424.5 

 meters. The terms kilo-calorie, or kilogramdegree, and kilo- 



