260 FEAGMENTS OF SCIENCE. 



with a single small aperture open to the air, through 

 which it is observed 'not to imbibe oxygen, but to pour 

 forth carbonic acid. Whence comes the volumes of 

 oxygen necessary to the production of this latter gas? 

 The small quantity of atmospheric air dissolved in the 

 wort and overlying it would be totally incompetent to 

 supply the necessary oxygen. In no other way can the 

 yeast-plant obtain the gas necessary for its respiration 

 than by wrenching it from surrounding substances in 

 which the oxygen exists, not free, but in a state of 

 combination. It decomposes the sugar of the solution 

 in which it grows, produces heat, breathes forth car- 

 bonic acid gas, and one of the liquid products of the 

 decomposition is our familiar alcohol. The act of fer- 

 mentation, then, is the result of the effort of the little 

 plant to maintain its respiration by means of combined 

 oxygen, when its supply of free oxygen is cut off. As 

 defined by Pasteur, fermentation is life without 

 air. 



But here the knowledge of that thorough investi- 

 gator comes to our aid to warn us against errors which 

 have been committed over and over again. It is not 

 all yeast-cells that can thus live without air and pro- 

 voke fermentation. They must be young cells which 

 have caught their vegetative vigour from contact with 

 free oxygen. But once possessed of this vigour the 

 yeast may be transplanted into a saccharine infusion 

 absolutely purged of air, where it will continue to live 

 at the expense of the oxygen, carbon, and other con- 

 stituents of the infusion. Under these new conditions 

 its life, as a plant, will be by no means so vigorous as 

 when it had a supply of free oxygen, but its action as a 

 ferment will be indefinitely greater. 



Does the yeast-plant stand alone in its power of 

 provoking alcoholic fermentation? It would be singu- 



