32S FERMENTATION ASCRIBED TO THE 



CHAPTER X. 



Fermentation ascribed to the Growth of Fungi and of Infusoria. 



The microscopical examination of vegetable and animal mat. 

 ter, in the act of fermentation or putrefaction, has lately given 

 rise to the opinion, that these actions themselves, and the changes 

 suffered by the bodies subjected to them, are produced in conse- 

 quence of the development of fungi, or of microscopical animals, 

 the germs or eggs of which are supposed to be diffused every- 

 where, in a manner inappreciable to our senses ; they are sup- 

 posed to be developed when they meet with a medium fitted to 

 afford them nourishment. 



Several philosophers have ascribed to this circumstance the 

 fermentation of wort, and of the juice of the grape. They assert, 

 that the decomposition of sugar into alcohol and carbonic acid is 

 effected by the contact of particles of the sugar with the growing 

 plants, which they view as the yeast, or ferment, without study- 

 ing more closely the final causes of the decomposition of the 

 sugar. It has been supposed that this view is opposed to the 

 theory detailed in the preceding pages, which described contact 

 as the cause of a peculiar activity or power. 



In all chemical processes, and in all changes effected by 

 chemical affinity, we observe that contact is essential for the ex- 

 ercise of the acting power. Hence, chemists describe affinity as 

 a force distinct from other powers, because it acts only in imme- 

 diate contact, or at inappreciable distances. Thus contact plays 

 an important part in every case of combination or decomposition, 

 for without contact these changes would not take place. In this 

 sense, all substances effecting combination or decomposition are 

 bodies acting by contact. 



In the theory of fermentation alluded to, it was not asserted 

 that the yeast or ferment could effect the decomposition of sugar 



