FEEMENTATION. 53 



fall without movement to the bottom of the vessel, and 

 the butyric fermentation which was dependent on their 

 existence is immediately arrested. 



Pasteur designated this new class of organisms by 

 the 'name of anaerobies ; that is to say, beings which 

 can live without air. He reserves the designation 

 aerobics for all the other microscopic beings which, like 

 the larger animals, cannot live without free oxygen. 

 * It matters little,' added Pasteur, ' whether the pro- 

 gress of science makes of this vibrio a plant or an 

 animal ; it is a living organism, endowed with motion, 

 which is a ferment and which lives without air.' 



In meditating upon these facts, and upon the 

 general character of fermentation, Pasteur* soon found 

 himself in a position to approach more nearly to the 

 essential nature of these mysterious phenomena. In 

 what way do microscopic organisms provoke the phe- 

 nomena of fermentation ? 



The organism eats, if one may say so, one part of 

 the fermentable matter. But how does this phenome- 

 non of nutrition differ so much from that of higher 

 beings ? In general, for a given weight of nutritive 

 matter which the animal takes in, it assimilates a 

 quantity of the same order. In fermentation, on the 

 contrary, the ferment, while nourishing itself with 

 fermentable matter, decomposes a quantity great in 

 comparison to its own individual weight. Again, the 



