FERMENTATION. 391 



of the carbon of the substance with oxygen, while the 

 hydrogen divides itself between the nitrogen, phospho- 

 rus, and sulphur, forming ammonia, phosphuretted and 

 sulphuretted hydrogen. It is to these gases that the 

 offensive smell which is given off in putrefaction is 

 principally to be ascribed. 



980. FERMENTATION. Any one of the 



What substan- . , 



ce* are capable nitrogenous substances above mentioned, 

 of producing hi j undergoing the change which is 



jermentation ? D 



called putrefaction, is capable, by its mere 

 presence, of acting as a ferment. A little putrefying 

 gluten, for example, added to a solution of sugar, will 

 convert it into alcohol and carbonic acid. Here again 

 the key-stone of the molecule is removed, or rather in 

 this case moved. The motion of the atoms of the 

 putrefying substance would seem to be the cause. 

 The effect is analogous to that of heat, through whose 

 agency, also, complex organic bodies are resolved into 

 others of simpler constitution. 



981. YEAST. The first stage in the 



What is the 



first stage in formation of yeast is the production of a 

 the process? microscopic vegetation, which consumes 

 all the protein, converting it in.to the substance of a 

 microscopic plant. Ordinary brewers' yeast is such a mi- 

 croscopic vegetation. Being produced, it passes imme- 

 diately into the putrefaction above described, effecting, 

 at the same time, the conversion of any sugar which 

 may be present into alcohol and carbonic acid. By 

 some, the growth of the microscopic plant itself, instead 

 of its subsequent change, is supposed to be the cause 

 of fermentation. 



