THE BEGINNINGS OF LIFE. 473 



tatingly in favour of the latter possibility. So that 

 we have an analogical argument of great force, and, in 

 addition, most overwhelming experimental evidence, 

 tending to oppose a mere dogma (omne vivum ex vivo) 

 which many erroneously believe to be a legitimate 

 inference from every-day experience. I say that this 

 inference is erroneous, because, whilst we do know 

 something about the ability which most organisms 

 possess of reproducing similar organisms, we cannot 

 possibly say, from direct observation, that every organism 

 which exists has had a similar mode of origin. The 

 cases in which organisms may have originated de novo 

 are the very cases in which their mode of origin must 

 elude our observation; for it can actually be shown 

 that some organisms make their appearance in fluids 

 after precisely the same fashion as crystals that is to 

 say, they can be seen to arise independently of all 

 pre-existing visible germs l . 



Germs, therefore, which cannot be seen, and which 

 nobody knows, are not only presumed to exist, but 

 (contrary to all evidence) they are to be deemed 

 capable of resisting the influence of far higher tempe- 



1 Having made this announcement on a previous occasion, and 

 having had the satisfaction of finding it pooh-poohed as an idle state- 

 ment, I, still believing in its truth, am glad to ascertain that others hold 

 the same opinion. Dr. Burdon Sanderson says in a recent Memoir 

 (Thirteenth Report of the Medical Officer of the Privy Council, 

 p. 62) : ' From the most careful and repeated examinations of water 

 known to be zymotic, we have learnt that such waters often contain no 

 elements or particles whatever which can be detected by the microscope.' 



