CHAPTER XVI 

 THE MECHANICS OF THE LIVING MACHINE , 



IN the general comparison of the living body with a machine, 

 a number of significant conclusions are reached when we carry 

 this comparison out in detail. 



Are the Income and Outgo Equivalent? Can all of the en- 

 ergy shown by the living organism be accounted for by the energy 

 furnished by the food, and, conversely, can all of the energy fur- 

 nished in the food be accounted for in the form of energy exhib- 

 ited in the living organism? 



If the law of the conservation of energy is correct, the 

 answers to these questions must be in the affirmative. To get 

 an experimental answer is not easy, but it has been done, as 

 follows: A large box has been constructed in which is placed 

 an animal, or sometimes a human being, and then the box is 

 sealed. By means of ingenious apparatus the person inside of 

 the box is furnished with the necessary air to carry on his 

 respiration, and is given plenty of food and water; he remains 

 in this box for a varying length of time. The apparatus is 

 designed, not only to determine the exact amount of water 

 and food that the individual consumes, but also the amount of 

 oxygen he takes from the air, the carbon dioxid he breathes 

 into the air, together with all the moisture that is eliminated 

 from the body, and all other excretions. Moreover, the amount 

 of energy furnished him in his food is measured, and the amount 

 of heat liberated from his body is determined with accuracy, 

 as well as the amount of work that he does. 



If the doctrine of conservation of energy holds concerning 

 the animal body, as it does concerning other machines, it ought 

 to be found by such an experiment that the amount of energy 

 exhibited by the individual is identical with that furnished 

 in his food, and that the amount of excretions is exactly equiv- 



303 



