36 THE STORY OF LIFE'S MECHANISM. 



has gained in weight, which simply means that 

 the extra energy has been stored in the body 

 for future use. No more energy can be obtained 

 from the body than is furnished, and for all 

 furnished in the food an equivalent amount is 

 regained. There is no trace of any creation or 

 destruction of energy. While, on account of the 

 complexity of the experimenting, an absolutely 

 strict balance sheet cannot be made, all the 

 results are of the same nature. So far as con- 

 cerns measurable energy, all the facts collected 

 bear out the theoretical conception that the 

 living body is to be regarded as a machine 

 which converts the potential energy of chemical 

 composition, stored passively in its food, into active 

 energy of motion and heat. 



It is found, however, that the body is a machine 

 of a somewhat superior grade, since it is able to 

 convert this potential energy into motion with 

 less loss than the ordinary machine. As noticed 

 above, in all machines a portion of the energy 

 is converted into heat and rendered unavailable 

 by radiating into space. In an ordinary engine 

 only about one-fifteenth of the energy furnished 

 in the coal can be regained in the form of motive 

 power, the rest being radiated from the machine 

 as heat. Some of our better engines to-day 

 utilize a somewhat larger part, but most of them 

 utilize less than one-tenth. The experiments 

 with the living body in the respiration appara- 

 tus above described, give a means of determining 

 the proportion of the energy furnished in the 

 form of food which can be utilized in the form 

 of motive force. This figure appears to be 



