FAILURE OF MECHANISTIC THEORY 59 



to be impossible, this need not affect the 

 practical value of the mechanistic theory in 

 biology. In ultimate analysis the ordinary 

 working conceptions of physics and chemistry 

 present great difficulties ; but no one doubts, 

 for example, the practical value of the 

 hypotheses of mass, energy, atoms, and 

 molecules. Similarly, there may be ultimate 

 difficulties about a mechanistic theory of life, 

 and yet the practical value of this theory 

 may remain. 



There is certainly some truth in this 

 argument. We often treat a living organism, 

 or some portion of it, as if it were nothing but 

 a collection of ordinary matter, or a machine 

 actuated by the ordinary forces of nature. As 

 will be pointed out more fully below, this 

 mode of treatment is sometimes the best 

 that is practicable, and its value cannot be 

 doubted. In so treating the facts we are, 

 however, leaving out of account almost all 

 those phenomena which are apparently specific 

 to living organisms, and with which biology 

 mainly deals. In actual fact the failure of 

 the mechanistic theory of reproduction cuts 

 deep into our conceptions of almost every 



