62 LOUIS PASTEUR. 



of mould suspended in the air, or associated with the 

 substances contained in the vessels, neither did he 

 avoid other infinitely small germs of the class 

 aerobics. 



After some time the air of all the vessels of the 

 two series was submitted to analysis, when, behold, a 

 very interesting fact ! In the vessels where life had 

 been withdrawn from the organic matters that is 

 to say, where there were no germs the air still con- 

 tained a large proportion of oxygen. In the vessels, 

 on the contrary, where the microscopic organisms 

 had been allowed to develop, the oxygen was totally 

 absent, having been replaced by carbonic acid gas. 

 And, further, for this absorption and total consumption 

 of the oxygen gas a few days had sufficed ; while in the 

 vessels without microscopic life there remained, after 

 several years, a considerable quantity of oxygen in a 

 free state, so weak is the proportion of oxygen that 

 the organic matters consume directly and chemically 

 when the infinitely small organisms are absent. 



But can these microscopic organisms, after having 

 decomposed or burnt up all these secondary products, 

 be in their turn decomposed ? 



How, cried M. Bouillaud, repeating his question, 

 can they be destroyed or decomposed? How can 

 their materials, which are of the same order as those 

 of all the living creatures of the earth, be gasified and 

 caused to return to the atmosphere ? After having 



