THE 



PHYSIOLOGICAL THEORY 

 OF FERMENTATION 



I. ON THE RELATIONS EXISTING BETWEEN OXYGEN 

 AND YEAST 



IT is characteristic of science to reduce incessantly the 

 number of unexplained phenomena. It is observed, for 

 instance, that fleshy fruits are not liable to fermenta- 

 tion 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 disengaged, and the sugar disap- 

 pears and is replaced by alcohol. Now, as to the question 

 of the origin of these spontaneous phenomena, so remark- 

 able in character as well as usefulness for man's service, 

 modern knowledge has taught us that fermentation 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 fer- 

 mentations in natural saccharine juices, we may ask whether 

 we must still regard the reactions that occur in these 

 fermentations as phenomena inexplicable by the ordinary 



289 

 (10) HC xxxviii 



