198 THE ORIGIN OF LIFE 



which we already know, as sterilisation would, 

 since it is merely a question of size, and those 

 germs which have not yet grown to a suflEcient 

 size may not be eliminated. 



He has answered his critics, who have repeated 

 these filtration experiments with negative results, 

 by pointing out that bacteriological filters do 

 produce in organic liquids which have passed 

 through them chemical changes of a similar nature 

 to those produced by heat, so much so that with 

 one filtration, it is said, positive results may be 

 obtained which are rendered impossible by two 

 or three filtrations. This seems to us to leave 

 the subject very much where it was so far as the 

 appearance of life de novo is concerned. But where 

 heterogenesis has actually been seen, if these ciliated 

 infusoria are really infusoria and not merely artificial 

 bodies which resemble them, the phenomenon must 

 be admitted to be most remarkable. Dr. Bastian, in 

 his more recent work, would no doubt be able to 

 throw more light upon the subject.^ 



To turn to the opposite school. Professor Japp, 

 in his famous British Association Address, has 

 emphasised that Pasteur was led to entertain his 

 predilection for biogenesis chiefly on account of the 

 difficulty which he experienced in explaining the 

 origin of the behaviour of the tartrates. 



^ Dr. C. W. Saleeby's book on this subject is expected 

 in the course of the next twelve months or so : it will 

 doubtless contain valuable contributions tp the discussion of 

 the subject, 



