412 THE BEGINNINGS OF LIFE. 



separated from the fermentations; whilst the change 

 which occurs when sugar is added to a mixture of 

 yeast and dextrine, is probably no less truly chemical 

 in nature, even though a living organism does take 

 part in the process. A solution of dextrine does not 

 undergo fermentation when it is mixed with beer-yeast 

 alone; though, when a certain quantity of sugar is 

 added to the mixture, a great part of the dextrine shares 

 the same fate as the sugar itself, and is converted into 

 alcohol and carbonic acid. c In this case,' Liebig says, 

 c the influence of the motion communicated to the sugar 

 atoms by the action of the yeast appears very evidently 

 to have been extended to the dextrine upon which yeast 

 itself has no action.' Facts like, these and many 

 others which might be mentioned, showing how the 

 different kinds of fermentation are influenced and 

 modified by the presence of different chemical sub- 

 stances lead most strongly to the conclusion that 

 fermentations are themselves, in essence, nothing more 

 than definite processes of chemical change which 

 certain complex bodies are apt to undergo, either by 

 virtue of their own inherent instability, or by reason of 

 the action upon them of other bodies (ferments) which 

 are at the time in a state of molecular flux, or motor-decay. 

 Such processes are, moreover, separated by no well- 

 defined line from other chemical changes. It can no 

 longer be maintained that they are chemical processes 

 which are only capable of being initiated by the 

 contact-influence of the changes taking place in living 



