Measurement of Energy 161 



beings. When we ask from whence comes the energy 

 given up by the plant compounds, we arrive at our 

 last stage of inquiry. Here we enter the domain of 

 plant life, and it is a notable triumph of the human 

 intellect that we are able to declare with certainty that 

 the ceaseless and multiple activities of life on this 

 planet are sustained by an energy which comes to the 

 plant in the sun's rays through almost limitless space. 

 It is obvious that if the internal and external work 

 performed by the animal is sustained by the food, it 

 is desirable to measure the energy available in differ- 

 ent feeding stuffs, provided, of course, that they differ 

 in this respect, as we know they do. In order to 

 measure anything, we must have a standard or unit of 

 measurement. In this case it cannot be a unit of 

 space or of mass, that is, we cannot declare that corn 

 meal contains so many cubic feet or pounds of avail- 

 able energy. Energy has neither dimensions nor weight. 

 If we measure it at all, it must be by units of tem- 

 perature or of work performed. Units of this kind 

 are applied to the measurement of food energy. The 

 one most commonly in use is the Calorie, this being 

 the energy which in terms of heat is sufficient to raise 

 the temperature of one pound of water 4 Fahren- 

 heit. Expressed in terms of work, the Calorie is very 

 nearly 1.53 foot tons, or in other words, it is equiv- 

 alent to the work involved in lifting one ton 1.53 

 feet. Heat units are expressed in both the large 

 Calorie and the small calorie. When the former is in- 

 dicated, the word begins with a capital letter. The 

 Calorie represents 1,000 calories. 



