INTRODUCTION. 27 



ceed in answering the questions above outlined. 

 The fact is that this problem of the mechanical 

 explanation of vital phenomena forms the cap- 

 stone of the arch, the sides of which are built of 

 the doctrines of the conservation of energy and 

 the theory of evolution. To the presentation of 

 these problems the following pages will be de- 

 voted. The fact that both the doctrine of the 

 conservation of energy and that of evolution are 

 practically everywhere accepted indicates that the 

 mechanical nature of vital forces is regarded as 

 proved. But there are still many questions 

 which are not so easily answered. It will be 

 our purpose in the following discussion to ascer- 

 tain just what are these problems in dynamical 

 biology and how far they have been answered. 

 Our object will be then in brief to discover to 

 what extent the conception of the living organism 

 as a machine is borne out by the facts which have 

 been collected in the last quarter century, and 

 to learn where, if anywhere, limits have been 

 found to our possibility of applying the forces 

 of chemistry and physics to an explanation of 

 life. In other words, we shall try to see how 

 far we have been able to understand living 

 phenomena in terms of natural force. 



OUTLINE OF THE SUBJECT. 



The subject, as thus presented, resolves itself 

 at once into two parts. That the living organism 

 is a machine is everywhere recognised, although 

 some may still doubt as to the completeness of 

 the comparison. In the attempt to explain the 



