138 PASTEUR: THE HISTORY OF A MIND 



bles the preceding in its need of oxygen the mycoderma 

 of wine. 



The latter, although it is more frequent than the 

 mycoderma of vinegar, nevertheless has less grievous 

 effects, because, not stopping half way, it pushes quite 

 to term the oxidation of the alcohol, and makes out of 

 it immediately water and carbonic acid. This carbonic 

 acid replaces the oxygen absorbed from the air, and by 

 reestablishing the pressure, prevents a new influx of air 

 and of oxygen. Thus the development of the myco- 

 derma of the wine, which takes place on the surface of 

 all the casks which are not full, ordinarily passes unper- 

 ceived, although sometimes the layer which covers the 

 liquid may be thick. When it has exhausted all the 

 oxygen which exists above it in the closed cask, it renews 

 its supply only slowly; and when this happens it con- 

 sumes it entirely and leaves no trace of it, in a free state, 

 in the liquid below. It is an impenetrable filter for the 

 oxygen, as impenetrable as a wall of glass. 



That granted, did the practices employed in wine- 

 making favor the wine or its parasites? In examining 

 the question from this entirely new point of view, Pasteur 

 was not slow in recognizing that, far from being formid- 

 able to the wine, it is the oxygen which makes it, which 

 takes away the acid and rough taste of new wine, and 

 which makes it more and more fit to drink. It is also 

 the oxygen which divests it little by little of its coloring 

 matter, yellows what is left, and gives to it gradually 

 that onion-skin tint, with which our ancestors were 

 familiar, and of which we are ignorant, because they 

 knew the worth of life, and we know only its cost. 

 Finally, as its action increases, the oxygen, after having 

 given to the wine the taste of old wine, ends by consum- 

 ing it and spoiling it. When he had studied a subject 

 Pasteur loved to sum up the ideas which he had ac- 



