PASTEUR ON FERMENTATION. 



715 



and you will also understand that this example embraces the destruc- 

 tion of all the species by which life is manifested upon the face of the 

 earth. 



If I should describe the destruction of a single grape, abandoned 

 to itself, I should show you only one of the laws of the phenomena ; 

 but there are two principal ones, and in order to pass them both in 

 review I shall suppose that all the fruits of a vineyard have been 

 gathered and placed in a gigantic heap, in an immense reservoir, as 

 large as a mountain, if you choose. Under the influence of the weight 

 the grapes are separated from the stems, broken more or less, and 

 allow their contents to escape in the form of a sugary liquid. By a 

 fortunate coincidence (which M. Colin might at his ease and by the 

 aid of sentiment look upon as an express desire of Providence to fur- 

 nish man what is called wine), it happens that at the period of the ma- 

 turity of the grape its surface and that of the stems are covered here 

 and there in the form of a fine dust by an extraordinary number of 

 the germs of a small cellular plant which has the faculty, its germina- 

 tion once commenced, under the influence of a very small quantity of 

 air, to multiply indefinitely in the entire absence of free oxygen gas 

 this was proved at our last meeting and to provoke, correlatively 

 with its life, the decomposition of sugar into carbonic-acid gas which 

 is set free, and an alcohol which remains in solution in the liquid. 



In the must of the grape the principal substance, after the water, 

 is the sugar; it constitutes 20.25 parts in 100, sometimes even more; 

 now, the decomposition accomplished by the ferment of which we have 

 just spoken eliminates in the form of carbonic-acid gas more than half 

 of this sugar, and thus a considerable portion of the organic matter of 

 the grape returns to the atmosphere. 



This singular phenomenon, which has struck the imagination of men 

 ever since the beginning of the world, is accompanied by an intense heat 

 and a bubbling of the whole mass, but as the sugar disappears the 

 movement slowly ceases. As soon as quiet is restored, our im- 

 mense cask is found to be filled with an alcoholic liquid which is 

 the habitual drink of men living in southern countries. Scarcely has 

 the carbonic-acid gas ceased to escape, when an attentive eye sees a 

 pellicle form upon the surface, a pellicle which is extremely thin and 

 insignificant in appearance, but in which reside a new life and new 

 phenomena well worth our attention : this pellicle is formed of a myco- 

 dermic plant (of two, in fact, but for the sake of brevity I shall con- 

 sider only one) which, strictly speaking, we might class with that one 

 which has just flourished in our cask and decomposed the sugar, but 

 which has now fallen inert to the bottom. Still, if our two little plants 

 resemble one another in their anatomical structure, they are very dif- 

 ferent physiologically. The cells of the ferment which destroyed the 

 sugar lived and multiplied without air; the new cells, on the other 

 hand, spread over the surface of the liquid in an unbroken pellicle, 



