THE BEGINNINGS OF LIFE. 297 



various difficulties appearing fatal to this explanation 

 of the mode of origin of the multitudes of plastide- 

 particles and Bacteria, we are left with only two other 

 possible modes of origin: either (b) they have been 

 developed from a multitude of pretty evenly dissemi- 

 nated invisible germs, or (c) they have been produced 

 de novo in the fluid by a process of Archebiosis. 



Thus the solution of this great problem passes beyond 

 the reach of actual demonstration. Microscopical 

 evidence enables us to bring it to this stage now, and 

 it may perhaps never enable us to do more. It reduces 

 us to a consideration of two rival hypotheses, and to a 

 careful consideration of whatever evidence may be 

 forthcoming to influence us in our choice between these 

 two possible explanations. Nothing that can be said 

 about the abundance of recognisable atmospheric germs 

 can directly affect the solution of this problem. It 

 is one which, if it has to do with germs at all, has to 

 do with invisible germs. But invisible germs can have 

 only a hypothetical existence, and even to this they can 

 lay no claim, unless observed phenomena cannot be 

 explained without such postulation. We must not 

 forget the old and well-approved logical rule, 



' Entia non sunt multiplicanda praeter necessitatem.' 



The c law of parsimony' may well be quoted for the 

 benefit of those who would ruthlessly people the atmo- 

 sphere with such countless myriads of 'entities 1 .' 



1 Some of those who are so eager to demonstrate the prevalence of 

 'germs,' are frequently carried away, by their enthusiasm, beyond the 



