ITS MODE OF ACTION. 255 



when they induce bodies with which they are in 

 contact to enter into the same state of decompo- 

 sition. The disturbance in the attraction of .the 

 constituents of the peroxide of hydrogen effects a 

 disturbance in the attractions of the elements of 

 the oxide of silver, the one being decomposed, on 

 account of the decomposition of the other. 



Now if we consider the process of the fermenta- 

 tion of pure sugar, in a practical point of view, we 

 meet with two facts of constant occurrence. When 

 the quantity of ferment is too small in proportion 

 to that of the sugar, its putrefaction will be com- 

 pleted before the transformation of all the sugar is 

 effected. Some sugar here remains undecomposed, 

 because the cause of its transformation is absent, 

 viz. contact with a body in a state of decompo- 

 sition. 



But when the quantity of ferment predominates, 

 a certain quantity of it remains after all the sugar 

 has fermented, its decomposition proceeding very 

 slowly, on account of its insolubility in water. 

 This residue of ferment is still able to induce fer- 

 mentation, when introduced into a fresh solution of 

 sugar, and retains the same power until it has 

 passed through all the stages of its own transfor- 

 mation. 



Hence a certain quantity of yeast is necessary 

 in order to effect the transformation of a certain 

 portion of sugar, not because it acts by its quantity 

 increasing any affinity, but because its influence 



