A HISTORY OF SCIENCE 



dents of the subject had vastly over-estimated the im- 

 portance of micro-organisms. 



And so it came as a new revelation to the generality 

 of scientists of the time, when, in 1857 and the succeed- 

 ing half -decade, Pasteur published the results of his 

 researches, in which the question had been put to a 

 series of altogether new tests, and brought to unequiv- 

 ocal demonstration. 



He proved that the micro-organisms do all that his 

 most imaginative predecessors had suspected, and 

 more. Without them, he proved, there would be no 

 fermentation, no putrefaction no decay of any tissues, 

 except by the slow process of oxidation. It is the mi- 

 croscopic yeast -plant which, by seizing on certain 

 atoms of the molecule, liberates the remaining atoms 

 in the form of carbonic-acid and alcohol, thus effect- 

 ing fermentation ; it is another microscopic plant 

 a bacterium, as Devaine had christened it which in 

 a similar way effects the destruction of organic mole- 

 cules, producing the condition which we call putre- 

 faction. Pasteur showed, to the amazement of biolo- 

 gists, that there are certain forms of these bacteria 

 which secure the oxygen which all organic life requires, 

 not from the air, but by breaking up unstable mole- 

 cules in which oxygen is combined ; that putrefaction, 

 in short, has its foundation in the activities of these so- 

 called anaerobic bacteria. 



In a word, Pasteur showed that all the many familiar 

 processes of the decay of organic tissues are, in effect, 

 forms of fermentation, and would not take place at all 

 except for the presence of the living micro-organisms. 

 A piece of meat, for example, suspended in an atmos- 



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