26 THE LIVING WORLD. 



realize that something' is lacking ; and that though 

 scientists have explained much by hypothesis, they 

 have yet left the real question untouched. It is not 

 easy to determine definitely this life factor, a factor 

 so prominent in the minds of those who disbelieve in 

 the mechanical theory of life, and so readily ignored 

 by those who hold this theory. That there is some- 

 thing more than has been reached by this explana- 

 tion may perhaps be made evident by a further 

 consideration of the parallel between an organism 

 and a machine. The comparison between the dead 

 body and the machine is exact, for each has the 

 mechanism which will enable it to transform one 

 sort of energy into another under the right con- 

 ditions. But in the body the requisite condition is 

 the presence of life, whatever that may be, which 

 guides the chemical changes taking place. In the 

 machine the necessary condition is the presence of 

 an engineer, who guides the forces and chemical 

 changes. The comparison of the living body should 

 not be simply with the machine in motion, but with 

 the machine plus the engineer. This difference is 

 great indeed. A machine may be ever so perfect, 

 and yet will not perform its work unless its engineer 

 supply its proper conditions. Food out of the body 

 will never go through the complicated changes above 

 mentioned unless subjected to very peculiar con- 

 ditions by the chemist. Food in the body will not 

 go through these changes unless subjected to the 

 action of life. Sunlight may fall upon CO 2 , H 2 O, 

 and NH 3 eternally without producing the slightest 

 tendency toward a synthesis of these elements. But 



