THEORY OF FERMENTATION 291 



of the bunches derive the power of starting their vital 

 phenomena. 1 This air, however, especially when the grapes 

 have been stripped from the bunches, is in such small propor- 

 tion, and that which is in contact with the liquid mass is 

 so promptly expelled by the carbonic acid gas, which is evolved 

 as soon as a little yeast has formed, that it will readily be 

 admitted that most of the yeast is produced apart from the 

 influence of oxygen, whether free or in solution. We shall 

 revert to this fact, which is of great importance. At present 

 we are only concerned in pointing out that, from the mere 

 knowledge of the practices of certain localities, we are in- 

 duced to believe that the cells of yeast, after they have 

 developed from their spores, continue to live and multiply 

 without the intervention of oxygen, and that the alcoholic 

 ferments have a mode of life which is probably quite ex- 

 ceptional, since it is not generally met with in other species, 

 vegetable or animal. 



Another equally exceptional characteristic of yeast and 

 fermentation in general consists in the small proportion 

 which the yeast that forms bears to the sugar that de- 

 composes. In all other known beings the weight of nutri- 

 tive matter assimilated corresponds with the weight of food 

 used up, any difference that may exist being comparatively 

 small. The life of yeast is entirely different. For a certain 

 weight of yeast formed, we may have ten times, twenty 

 times, a hundred times as much sugar, or even more de- 

 composed, as we shall experimentally prove by-and-bye ; that 

 is to say, that whilst the proportion varies in a precise 

 manner, according to conditions which we shall have oc- 

 casion to specify, it is also greatly out of proportion to the 

 weight of the yeast. We repeat, the life of no other being, 

 under its normal physiological conditions, can show any- 

 thing similar. The alcoholic ferments, therefore, present 

 themselves to us as plants which possess at least two singular 

 properties : they can live without air, that is without oxygen, 

 and they can cause decomposition to an amount which, 



1 It has been remarked in practice that fermentation is facilitated by 

 leaving the grapes on the bunches. The reason of this has not yet been 

 discovered. Still we have no doubt that it may be attributed, principally, 

 to the fact that the interstices between the grapes, and the spaces which the 

 bunch leaves throughout, considerably increase the volume of air placed at 

 UN service of the germs of ferment. 



