INTRODUCTION 7 



through which we can characterize life is unnecessary to 

 science because, being outside the physical forces, it cannot 

 influence them in any way. We must therefore separate 

 the metaphysical world from the phenomenal world which 

 acts as its base, but which cannot borrow anything from it. 

 Leibnitz expressed this delimitation in the following way: 

 "The body develops mechanically, and the mechanical laws 

 are never violated in natural movements. Everything takes 

 place in the soul as though there were no body, and every- 

 thing takes place in the body as though there were no soul." ' 



In brief, if Hfe can be defined with the help of a special 

 metaphysical concept, concludes Claude Bernard, it is never- 

 theless true that mechanical, physical, and chemical forces 

 are the only efficient agents of the living organism, and that 

 the physiologist must take their actions alone into account. 

 As Descartes says, 'We think metaphysically, but we Uve 

 physically.' 





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