THEORY OF FERMENTATION SIS 



with a great surface of liquid, fermentation Is rapid. For 

 the same quantity of sugar decomposed much more yeast is 

 formed. The air with which the liquid is in contact is ab- 

 sorbed by the yeast. The yeast develops very actively, but 

 its fermentative character tends to disappear under these con- 

 ditions ; we find, in fact, that for one part of yeast formed, 

 not more than from four to ten parts of sugar are trans- 

 formed. The fermentative character of this yeast never- 

 theless, continues, and produces even increased effects, if 

 it is made to act on sugar apart from the influence of free 

 oxygen. 



"It seems, therefore, natural to admit that when yeast 

 functions as a ferment by living apart from the influence 

 of air, it derives oxygen from the sugar, and that this is 

 the origin of its fermentative character. 



" M. Pasteur explains the fact of the immense activity at 

 the commencement of fermentations by the influence of the 

 oxygen of the air held in solution in the liquids, at the time 

 when the action commences. The author has found, more- 

 over, that the yeast of beer sown in an albuminous liquid, 

 such as yeast-water, still multiplies, even when there is 

 not a trace of sugar in the liquid, provided always that 

 atmospheric oxygen is present in large quantities. When 

 deprived of air, under these conditions, yeast does not 

 germinate at all. The same experiments may be repeated 

 with albuminous liquid, mixed with a solution of non-fer- 

 mentable sugar, such as ordinary crystallized milk-sugar. 

 The results are precisely the same. 



" Yeast formed thus in the absence of sugar does not 

 change its nature; it is still capable of causing sugar to 

 ferment, if brought to bear upon that substance apart from 

 air. It must be remarked, however, that the development 

 of yeast is effected with great difficulty when it has not a 

 fermentable substance for its food. In short, the yeast of 

 beer acts in exactly the same manner as an ordinary plant, 

 and the analogy would be complete if ordinary plants had 

 such an affinity for oxygen as permitted them to breathe 

 by appropriating this element from unstable compounds, in 

 which case, according to M. Pasteur, they would appear as 

 ferments for those substances. 



