68 LOUIS PASTEUR 



posable nitrogenous compound, held that it was the 

 death and decay of the yeast which causes the 

 breakdown of the molecules of sugar, fermentation 

 being a consequence of death and decomposition 

 rather than of life. "In what respect," argues 

 Liebig, "does the explanation of fermentation ap- 

 pear more clear to you when you have introduced 

 a living organism? What if they are everywhere 

 present? But you see yourself that there are none 

 in the putrefactions. Let us admit, if you will, 

 although this appears very extraordinary, that the 

 meat and the sugar are destroyed by different 

 agencies. But the sugar may undergo various fer- 

 mentations very similar to alcoholic fermentation 

 and even accompanying it; lactic fermentation, 

 butyric fermentation, etc. Do you find in these 

 fermentations anything that resembles yeast? Do 

 not these behave absolutely like the putrefaction 

 of meat? Your explanation limps and encounters 

 obstacles at every step. For me, on the contrary, 

 these transformations present a common character, 

 that is, of taking place in the presence of organic 

 matter in course of decomposition. One may start 

 a lactic or a butyric fermentation by means of old 

 cheese or rotten meat. For alcoholic fermentation, 

 Colin showed in 1828 that one may bring it about 



