54 LOUIS PASTEUR. 



butyric ferment lives without free oxygen. Is there 

 not, said Pasteur, a hidden relation between the 

 property of being a ferment and the faculty of living 

 without free oxygen ? Are not vibrios which impera- 

 tively require for their nutrition and multiplication the 

 presence of oxygen gas those which will never have the 

 properties of ferments ? 



Pasteur then contrived a series of experiments with 

 the view of placing in parallelism these two curious 

 physiological facts : life without air and the charac- 

 teristics of ferments. 



We know how wine and beer are prepared. The 

 must of grapes and the must of beer are placed in 

 wooden vats, or in barrels of greater or less dimen- 

 sions. Whether the fermentation proceeds from germs 

 taken from the exterior surface of the grapes, or 

 from a small quantity of ferment sown in the must 

 under the form of yeast, as in the fermentation of 

 beer, the life of the ferment, its multiplication, the 

 augmentation of its weight, are so many vital actions 

 which to a certainty cannot borrow from the free 

 oxygen of the external air, or from that originally 

 dissolved in the must, an appreciable quantity of this 

 gas. All the life of the cells of the ferment which 

 multiplies itself indefinitely appears then to take place 

 apart from free oxygen gas. In certain breweries 

 in England the fermenting vats have sometimes a 

 capacity of several thousands of hectolitres ; and the 



