INTRODUCTION 29 



as all positive knowledge entitles us to believe 

 would make the experimental vessels as void of 

 living things as was the earth when its surface 

 first began to cool below the boiling-point of water 

 if, I say, in such cases simple organisms can 

 be shown to appear almost at will in the experi- 

 mental vessels, we should obtain the best possible 

 warrant for the conclusion that " spontaneous gen- 

 eration ' is no myth, and that simple living units 

 of well-known kinds can now be evolved, even 

 within experimental vessels, as other living things 

 must originally have been evolved on the cooling 

 surface of the earth. 



If a genesis of living matter occurred in some 

 one place in far-remote ages, and if such a pro- 

 cess can be shown still to occur, it would be only 

 natural to conclude that the same chemico-physical 

 processes have, in all probability, been operative 

 in innumerable regions over the surface of the 

 earth, not only in primeval but in all succeeding 

 ages up to the present day. 



I have long held such a belief upon the basis 

 of my own experiments, of the type made by 

 Pasteur, Tyndall, and others, with organic in- 

 fusions, but in which positive results were obtained 

 not otherwise explicable in accordance with exist- 



