148 CONCERNING} PRESENT 



his predecessors had hitherto believed to be dead. The proof of 

 this being so would for them (as believers in the chimera assump- 

 tion) lie in the simple fact that living things had appeared within 

 the experimental vessels. Such see-saw work might go on indefi- 

 nitely. Conviction would probably never be brought about, because 

 this ever-recurring objection could not possibly be met, unless the 

 experimenter confined himself to sterilising degrees of heat which 

 would allow little chance of success. The last experiments I 

 published on this subject, together with this kind of interpretation 

 of their results given by others, were of such a nature as to convince 

 me of the futility of further attempts in this direction. They tended 

 to show the practical insolubility of the question by flask experi- 

 ments with superheated fluids, because of the immediate renunciation 

 by opponents of previous beliefs, whenever results would otherwise 

 show that ' spontaneous generation ' had been demonstrated. For 

 that reason I ceased to make and publish further experiments of 

 this kind. 



Anterior to the publication in 1876 of my experiments on the 

 fertilisation of boiled acid urine by an accurately neutralising 

 dosage with boiled liquor potassse,' it had been generally inferred 

 by '.all workers on this subject that the continued barrenness of 

 urine and other acid fluids previously superheated was a proof that 

 heat to the extent employed was adequate to kill any organisms or 

 their germs pre-existing in such fluids. 



This view was based upon the fact that living Bacteria or their 

 germs seemed invariably to increase and multiply in suitable fluids 

 placed under conditions favourable for fermentation. 



It must be admitted, however, that this assumed proof was 

 fallacious. Life may persist even when there is not sufficient 

 vigour in the living things to enable them to grow or multiply in 

 the previously heated medium in which they find themselves. 



And as long as such inert or partially devitalised organisms 

 remain in certain fluids, they may never regain sufficient vigour to 

 enable them either to grow or to multiply. They may continue as 

 if dead, though not actually dead. 



But in other fluids of a different chemical constitution, or 

 nutritive value, it is certainly possible that such partially devitalised 

 organisms may become reinvigorated (especially if their revival be 

 further aided by more stimulating conditions) so as to enable them 



' " Proceed, of Royal Soc," 1876, vol. xxv., p. 149, and " Journ. of Linn. Soc." 

 (Zool.), vol, xiv., 1877— these being my last contributions to this side of the question. 



