viii PREFACE. 



The probabilities in favour of this interpretation of the 

 experimental evidence become, moreover, stronger and 

 stronger in proportion as the problem is viewed by 

 the light derived from various kinds of general evi- 

 dence, which I have adduced in different parts of this 

 work. 



We know that the molecules of elementary or mineral 

 substances combine to form acids and bases by virtue 

 of their own c inherent' tendencies; that these acids 

 and bases unite so as to produce salts, which, in their 

 turn, will often again combine and give rise to c double 

 salts/ And at each stage in this series of ascending 

 molecular complexities, we find the products endowed 

 with properties wholly different from those of their con- 

 stituents. Similarly, amongst the carbon compounds 

 there is abundance of evidence to prove the existence 

 of internal tendencies or molecular properties, which 

 may and do lead to the evolution of more and more 

 complex chemical compounds. And it is such synthetic 

 processes, occurring amongst the molecules of colloidal 

 and allied substances, which seem so often to engender 

 or give c origin' to a kind of matter possessing that 

 subtle combination of properties to which we are 

 accustomed to apply the epithet 'living.' 



The experimental evidence which I have brought 

 forward not only goes to prove that living matter may 

 originate in this natural manner, but that, like other 

 kinds of matter, it comes into being by virtue of the 

 operation of the same laws and molecular properties 

 as suffice to regulate its c growth.' Would it not be 

 deemed absurd if we were to assume, as a necessity, 

 the existence of one set of agencies in order to bring 



