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Pouchet. "I am afraid," wrote a scientific journalist in La 

 Presse (1860), "that the experiments you quote, M. Pasteur, 

 will turn against you. . . . The world into which you wish to 

 take us is really too fantastic. ..." 



And yet some adversaries should have been struck by the 

 efforts of a mind which, while marching forward to establish 

 new facts, was ever seeking arguments against itself, and 

 turned back to strengthen points which seemed yet weak. In 

 November, Pasteur returned to his studies on fermentations in 

 general and lactic fermentation in particular. Endeavouring 

 to bring into evidence the animated nature of the lactic ferment, 

 and to indicate the most suitable surroundings for the self- 

 development of that ferment, he had come across some compli- 

 cations which hampered the purity and the progress of that 

 culture. Then he had perceived another fermentation, following 

 upon lactic fermentation and known as butyric fermentation. 

 As he did not immediately perceive the origin of this butyric 

 acid which causes the bad smell in rancid butter he ended 

 by being struck by the inevitable coincidence between the (then 

 called) infusory animalcule and the production of this acid. 



" The most constantly repeated tests," he wrote in February, 

 18G1, " have convinced me that the transformation of sugar, 

 mannite and lactic acid into butyric acid is due exclusively to 

 those Infusories, and they must be considered as the real 

 butyric ferment." Those vibriones that Pasteur described as 

 under the shape of small cylindric rods with rounded ends, 

 sliding about, sometimes in a chain of three or four articles, 

 he sowed in an appropriate medium, as he sowed beer yeast. 

 But, by a strange phenomenon, "those infusory animalculae," 

 he said, " live and multiply indefinitely, without requiring the 

 least quantity of air. And not only do they live without air, 

 but air actually kills them. It is sufficient to send a current of 

 atmospheric air during an hour or two through the liquor 

 where those vibriones were multiplying to cause them all to 

 perish and thus to arrest butyric fermentation, whilst a current 

 of pure carbonic acid gas passing through that same liquor 

 hindered them in no way. Thence this double proposition," 

 concluded Pasteur ; ' ' the butyric ferment is an infusory ; that 

 infusory lives without free oxygen." He afterwards called 

 anaerobes those beings which do not require air, in opposition 

 to the name of aerobes given to other microscopic beings who 

 require air to live. 



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