376 THE PHILOSOPHY OF BIOLOGY 



gates. But when this energy becomes equally dis- 

 tributed among the molecules of all the aggregates, 

 the matter in which it inheres becomes inert. If we 

 could, by a sorting process like that of Maxwell's 

 hypothetical demons, a process which does not expend 

 the energy with which it deals, separate the molecules 

 which were moving slowly from those which were 

 moving more quickly, we could make this energy 

 again available. But it must clearly be understood 

 that our physics is the physics not of individual mole- 

 cules, but of aggregates of molecules. 



