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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 
