318 YEAST OF FERMENT. 



has recommenced, in consequence of its being kept in 

 a warm situation for some time. 



Yeast and putrefying animal and vegetable mat- 

 ters act as peroxide of hydrogen does on oxide of 

 silver, 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 con- 

 stituents of the peroxide of hydrogen effects a dis- 

 turbance in the attraction of the elements of the 

 oxide of silver, the one being decomposed, on ac- 

 count of the decomposition of the other. 



Now if we consider the process of the fermentation 

 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 completed 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 decomposition. 



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 fermentation, when 

 introduced into a fresh solution of sugar, and retains 

 the same power until it has passed through all the 

 stages of its own transformation. 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 in increasing any 

 affinity, but because its influence depends solely on 

 its presence, and its presence is necessary, until the 

 last atom of sugar is decomposed. 



These facts and observations point out the ex- 

 istence of a new cause, which effects combinations 

 and decompositions. This cause is the action which 

 bodies in a state of combination or decomposition 

 exercise upon substances, the component parts of 

 which are united together by a feeble affinity. This 



