THE VITAL IMPETUS 161 



the usual course of development has been attempted : 

 in this case the physico-chemical reactions which 

 proceed in the normal train of events proceed in some 

 other way, and the new direction is imposed on the 

 developing embryo by the organisation which we have 

 to regard as inherent in it. This same direction and 

 autonomy must be recognised in the behaviour of the 

 adult organism as a whole. What is it ? We attempt 

 to think of it as an impetus which is conferred upon the 

 physico-chemical reactions which are the manifesta- 

 tions of the life of the organism. It is the dan vital 

 of Bergson, or the entelechy of Driesch. What is 

 included in these concepts we consider in the last 

 chapter of this book ; and before so doing it will be 

 necessary to consider the organism from another point 

 of view, that of its mutability when it is regarded as 

 one member of a series of generations. 



