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CHAPTER YI. 



THE PHYSIOLOGICAL THEORY OF FERMENTATION. 



§ I. — On the Relations existing between Oxygen and 



Yeast. 



The object of all science is a continuous reduction of the 

 number of unexplained pbenomena. It is observed, for in- 

 stance, that fleshy fruits are not liable to fermentation so long 

 as their epidermis remains uninjured. On the other hand, 

 they ferment very readily when they are piled up in heaps, 

 more or less open, and immersed in their saccharine juice. The 

 mass becomes heated and swells ; carbonic acid gas is disen- 

 gaged, and the sugar disappears and is replaced by alcohol. 

 Now, as to the question of the origin of these spontaneous 

 phenomena, so remarkable in character as well as usefulness 

 for man's service, modern knowledge has taught us that fermen- 

 tation is the consequence of a development of vegetable cells, 

 the germs of which do not exist in the saccharine juices within 

 fruits ; that many varieties of these cellular plants exist, each 

 giving rise to its own particular fermentation. The principal 

 products of these various fermentations, although resembling 

 each other in their nature, differ in their relative proportions 

 and in the accessory substances that accompany them, a fact 

 which alone is sufficient to account for wide differences in the 

 quality and commercial value of alcoholic beverages. 



Now that the discovery of ferments and their living nature, 

 and our knowledge of their origin, may have solved the 

 mystery of the spontaneous appearance of fermentations in 



