6 INTRODUCTION 



them. The law of the conservation of energy merely 

 expresses the same truth in different words. The 

 theory of causality has a tremendous importance, both 

 in science and in philosophy, as it eliminates from 

 human speculations the supernatural or marvellous 

 element, and compels man to seek explanations which 

 admit of none but natural factors. It obliges him to 

 create conceptions of the world which presuppose no 

 miraculous act of creation, of creation from nothing. 



It has led man to abandon, in the first place, the 

 geocentric conception of the planetary system and 

 secondly, the anthropocentric viewpoint in the study 

 of animal nature. Likewise it has compelled him to 

 reject the too facile explanations offered by teleo- 

 logical systems and to consider causal explanations as 

 the only satisfactory ones. 



Our mind is not ripe yet for drawing from the 

 idea of causality all the conclusions to which it may 

 lead; the intellectual bequests of the past are weigh- 

 ing too heavily upon us and too many obstacles are 

 retarding the development of our thought along that 

 line. We may say, however, that in many branches 

 of knowledge, and especially in the study of the in- 

 organic world, this idea prevails absolutely. 



The next step forward consisted in applying to the 

 study of the organic world the methods and general- 

 isations adopted in the study of the inorganic world. 

 The task was an arduous one, the more so as the scant 



