574 THE ANIMAL BODY AS A MACHINE 



enumerated the subjects were at rest, and although their respiratory 

 and cardiac muscles were contracting and the skeletal muscles main- 

 tained in tone or even contracting, yet, the whole of the organism being 

 enclosed within a heat-insulated system, the effect of all these move- 

 ments ultimately appeared and was estimated in the form of heat. 

 The case is different when, as in many of Atwater's experiments, the 

 subject was made to perform external work, by operating a stationary 

 bicycle which was so arranged that the rotation of the wheels raised 

 a weight. The energy output was not in this case expressed entirely 

 in the form of heat, but in part in the form of Mechanical Work. We 

 can express this work in terms of heat-units, however, just as we can 

 express heat in terms of electrical units or electrical units in terms of 

 mechanical work again. Since no energy is ever lost and all forms of 

 energy are equivalent to one another, the heat-value consumed in 

 performing mechanical work can be directly calculated from the known 

 mechanical equivalent of heat. The following are the results which 

 Atwater obtained in the investigation of this problem: 



Calories. 



Income per Output per 



twenty-four twenty-four Difference. 



Days. hours. hours. per cent. 

 Rest experiments: 



7 experiments with E.G. . 25 2268 2259 -0.4 



1 experiment with A.W.S. 3 2304 2279 -1.1 



3 experiments with J.F.S. 9 2118 2136 +0.8 



1 experiment with J.C.W. 4 2357 2397 +1.7 



Average ." . , 41 2246 2246 0.0 



Work experiments : 



2 experiments with E.G. . 8 3865 3829 -0.9 



4 experiments with J.F.S. 12 3539 3540 0.0 



14 experiments with J.C.W. 46 5120 5120 0.0 



Average ... 66 4682 4676 -0.1 



To within one part in a thousand the output of heat plus work was 

 equal to the calorific value of the foodstuffs consumed . We can hardly 

 doubt that this minute discrepancy was of purely technical origin and 

 that these experiments represent the culmination of the proof which 

 Lavoisier had sought a hundred years previously, that the energies of 

 life are derived simply and solely from the chemical energy of the 

 foodstuffs. 



The fundamental importance of these investigations cannot be over- 

 rated, for they reveal to us in the clearest possible manner the fact that 

 life is the outcome of a complex of forces which it does not create. We 

 are enabled by them to confidently state that if there is such an entity 

 as "Vital Force" created and generated out of nothing by living organ- 

 isms, then the inconspicuousness of its effects is commensurate with the 

 inconspicuousness of its origin. They must be confined to somewhat 

 Jess than a one thousandth part of the total activity of the organism. 



