76 THE BEGINNINGS OF LIFE. 



importance of the influence of external conditions as 

 compared with that attributable to the inherent 

 aptitudes of living protoplasm has been dwelt upon 

 perhaps more strongly than by any previous writer, 

 and has led Mr. Lewes to announce a most important 

 modification of the Darwinian hypothesis. Before I 

 had read Mr. Lewes's essay, though several months after 

 it had been published, the results of my own experi- 

 ments had driven me to adopt a similar notion. 

 When once it had been proved that living matter 

 could come into being de novo^ a belief in the truth 

 of such doctrines was a logical necessity, as further 

 explanations will suffice to show. 



Crystals can be traced back only as far as their first 

 emergence in a speck-like form from the fluid in which 

 they arise ; and similarly, some organisms can be traced 

 back to the minutest visible specks which appear in 

 a filtered infusion of organic matter. Concerning the 

 existence of invisihle germs of organisms we have no 

 knowledge — we know no more of them, and have little 

 more right to assume their universal diffusion than 

 we have to calculate upon the universal diflPusion of 

 invisible crystalline germs. We have seen, moreover, 

 how the experimental evidence completely upsets the 

 mere hypothesis that all living things which now appear 

 have been derived from pre-existing living things ; 

 and on the other hand, we know that an over- 

 whelming amount of evidence can be brought forward 

 to show that the first particles of organisms may be 



