THE ORIGIN OF LIFE 135 



infusions had been boiled for a sufficient time and then sealed, 

 no organisms could be found in them, no matter how long they 

 were kept. We now know that protozoa and protophytes do 

 not originate de novo in infusions. Their sudden appearance 

 in cultures is due to the deposition of spores or cysts from 

 the air, etc. 



The possibility that the non-germination of life in sterilized 

 infusions kept in sealed containers might be due to the absence 

 of oxygen, removed by boiling and excluded by sealing, left 

 open a single loophole, of which the 19th century defenders 

 of abiogenesis proceeded to avail themselves. Pasteur, how- 

 ever, by employing sterilized cultures, which he aerated with 

 filtered air exclusively, succeeded in depriving his opponents 

 of this final refuge, and thereby completely demolished the 

 last piece of evidence in favor of spontaneous generation. Prof. 

 Wm. Sydney Thayer, in an address delivered at the Sor- 

 bonne. May 22, 1923, gives the following account of Pasteur's 

 experiments in this field: "Then, naturally (1860-1876) came 

 the famous studies on spontaneous generation undertaken 

 against the advice of his doubting masters, Biot and Dumas. 

 On the basis of careful and well-conceived experiments he 

 demonstrated the universal presence of bacteria in air, water, 

 dust; he showed the variation in different regions of the 

 bacterial content of the air; he demonstrated the permanent 

 sterility of media protected from contamination, and he in- 

 sisted on the inevitable derivation of every living organism 

 from one of its kind. 'No,' he said, 'there is no circumstance 

 known today which justifies us in affirming that microscopic 

 organisms have come into the world, without parents like 

 themselves. Those who made this assertion have been the 

 playthings of illusions or ill-made experiments invalidated by 

 errors which they have not been able to appreciate or to 

 avoid.' In the course of these experiments he demonstrated 

 the necessity of reliable methods of sterilization for instru- 

 ments or culture media, of exposure for half an hour to moist 

 heat at 120° or to dry air at 180°. And behold! our modem 



