60 LOUIS PASTEUE. 



atmospheric oxygen in the destruction of animal and 

 vegetable matters after death. It is easy to under- 

 stand, indeed, that fermentation and putrefaction only 

 represent the first phase of the return to the atmo- 

 sphere and to the soil of all that has lived. Fermenta- 

 tions and putrefactions give rise to substances which 

 are still very complex, although they represent the 

 products of decomposition of fermentable matters. 

 When sugar ferments, a large proportion of it becomes 

 gas ; but alongside of the carbonic acid gas which 

 is formed, and which is, indeed, a partial return of 

 the sugar to the atmosphere, new substances, such 

 as alcohol, succinic acid, glycerine, and materials of 

 yeast, are produced. When the flesh of animals 

 putrifies, certain products of decomposition, also very 

 complex, are formed with the vapour of water and 

 the other gases of putrefaction. Where, then, does 

 nature find the agents of destruction of these secondary 

 products ? 



The great fact of the destruction of animal and 

 vegetable matters is accomplished by slow combustion, 

 through the appropriation of atmospheric oxygen. 

 Here, again, one must banish from science the pre- 

 conceived views which assumed that the oxygen seized 

 directly on the organic matter after death, and that 

 this matter was consumed by purely chemical pro- 

 cesses. It is life that presides over this work of death. 



If fermentation and putrefaction are principally 



