FERMENTATION 27 



or putrid broth, can be filtered out from the air, 

 leaving it sterile : and, in air thus sterilised, no 

 liquid will ferment or putrefy. 



By 1859 the year of publication of The 

 Origin of Species Pasteur was in the thick of 

 the fight over the Origin of Life. Was it possible 

 for bacteria to come of themselves, or was it not ? 

 If, in a flask of broth, supposed to be sterilised, 

 they made their appearance, and the broth went 

 bad, was it absolutely certain that they had got in 

 from outside ? Was it not possible that they had 

 been spontaneously generated in the broth? Must 

 all life, even lives so minute as these, be the work of 

 life ? Surely, life must begin somewhere : why not 

 here, struck out of air and broth like sparks out of 

 steel and flint ? Long ago, men had ceased to believe 

 in the spontaneous generation of grubs, maggots, 

 tape-worms, and so forth : but these ultimate 

 invisible particles, these mere beginnings, might 

 they not be too small to be included under the law, 

 Omne vivum ex vivo ? Besides, it is a pleasant 

 creed that life is always coming of itself, emerging 

 out of not-life, as Aphrodite came of herself out of 

 the foam of the sea. 



He set himself to the hard business of proving a 

 negative. Among his opponents, the most notable 

 were Pouchet and Joly. In England, the con- 

 troversy was between Tyndall and Bastian. It 



