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CHAPTER VII. 



Forming with Chapter VI, by Mr. George 

 S. Hudson, the Joint Prize Essay men- 

 tioned in the Preface. 



BY DR. LUCIUS NICHOLLS. 



FERMENTATION is the reduction of sub- 

 stances of high molecular composition to those 

 of a less complex nature by the agency of 

 micro-organisms, and this has a wide range 

 in commercial preparations, where both the 

 physical and chemical changes are of value, 

 thus : the making of bread, the preparation 

 of all alcoholic beverages, cheeses, tobaccos, 

 vinegars, and even the tanning of leather are 

 dependent upon it. In all these trades certain 

 definite organisms must be employed to bring 

 about the required result, and these are usually 

 present naturally ; but this is not always the 

 case. Science in this, as in most other sub- 

 jects, has in recent years thrown light upon 

 much that was perplexing, and its explanations 

 of the changes which take place in fermenting 

 matter have been of much assistance to some 

 of the interested trades. It was the genius 

 of Pasteur which first explained the so-called 



