292 YEAST OR FERMENT. 



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 insolu- 

 bility 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 existence 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 action 

 resembles a peculiar power, attached to a body in the state of 

 combination or decomposition, but exerting its influence beyond 

 the sphere of its own attractions. We are now able to account 

 satisfactorily for many known phenomena. 



A large quantity of hippuric acid may be obtained from the 

 fresh urine of a horse, by the addition of muriatic acid; but 

 when the urine has undergone putrefaction, no trace of it can 

 be discovered. The urine of man contains a considerable 

 quantity of urea ; but when the urine putrefies, the urea entirely 

 disappears. When urea is added to a solution of sugar in the 

 state of fermentation, it is decomposed into carbonic ■. acid and 

 ammonia. No asparagin can be detected in a putrefied infusion 

 of asparagus, licorice-root, or the root of marshmallow (Althaa 

 officinalis). 



