22 THE STORY OF THE LIVING MACHINE. 



with an inevitable loss of a portion of the energy 

 as radiant heat. With this understanding, we may 

 now ask if the living body can be properly com- 

 pared with a machine. 



A General Comparison of a Body and a Machine. 

 That the living body exhibits the ordinary types 

 of energy is of course clear enough when we 

 remember that it is always in motion and is 

 always radiating heat two of the most common 

 types of physical energy. That this energy is 

 supplied to the body as it is to other machines, in 

 the form of the energy of chemical composition, 

 will also need no further proof when it is remem- 

 bered that it is necessary to supply the body with 

 appropriate food in order that it may do work. 

 The food we eat, like coal, represents so much 

 solar energy which is stored up by the agency of 

 plant life, and the close comparison between feed- 

 ing the body to enable it to work and feeding the 

 engine to enable it to develop energy is so evident 

 that it demands no further demonstration. The 

 details of the problem may, however, present some 

 difficulties. 



The first question which presents itself is 

 whether the only power the body possesses is, as 

 in the case with other machines, to transform 

 energy without being able to create or destroy it ? 

 Can every bit of energy shown by the living or- 

 ganism be accounted for by energy furnished in 

 the food, and conversely can all the energy fur- 

 nished in the food be found manifested in the 

 living organism ? 



The theoretical answer to this question in 

 terms of the law of the conservation of energy is 

 clear enough, but it is by no means so easy to 

 answer it by experimental data. To obtain ex- 



