22 THEORIES OF SPONTANEOUS GENERATION 



that if anything existed even in that little portion of air which 

 filled up the neck it might be destroyed and lose its productive 

 faculty. 



But, in spite of all this, after some days the vessel swarmed 

 with micro-organisms. He made similar investigations on a 

 variety of organic liquors and infusions, always with the same 

 result. This naturally led him to the conclusion that it was 

 completely possible, and indeed inevitable, for micro-organ- 

 isms to arise spontaneously from putrefying organic sub- 

 stances.^" 



However, these experiments of Needham were subjected 

 to severe criticism by an Italian scientist, the priest 

 Spallanzani (1765). Spallanzani, like Needham, carried out 

 experiments with the object of establishing or refuting the 

 possibility of spontaneous generation, but, on the basis of 

 these experiments, he arrived at exactly the opposite con- 

 clusion. He asserted that the experiments of Needham had 

 succeeded because of insufficient heating of the vessels 

 containing the liquid, resulting in their inadequate sterilisa- 

 tion. Spallanzani himself carried out hundreds of experi- 

 ments in which plant decoctions and other organic liquids 

 were subjected to more or less prolonged boiling, after which 

 the vessel containing them was sealed and thus the access of 

 air to the liquids was prevented. Air, according to Spallan- 

 zani, carried the germs of micro-organisms. Whenever the 

 operation was conducted with proper attention the liquids 

 contained in the vessel did not putrefy and living creatures 

 did not appear in them.*^ 



Needham objected to this that on prolonged heating of 

 the liquids the air contained in the vessels was spoilt and 

 that this was the chief reason for the failure of micro- 

 organisms to develop. Secondly, he asserted that on prolonged 

 heating the ' vital force ' of the organic infusions was 

 destroyed. This ' vital force ' usually seems to be capricious 

 and inconstant and cannot withstand prolonged and severe 

 treatments. Thus Needham considered, not that he had 

 heated the liquids too weakly but, on the contrary, that in 

 the experiments of Spallanzani these liquors had been heated 



