1865—1870 149 



matter which accompanies the development of the plant keeps 

 it on the surface, air being necessary to the plant; it would 

 otherwise perish and the acetification would be arrested. Thus 

 floating, the mycoderma absorbs oxygen from the air and fixes 

 it on the alcohol, which becomes transformed into acetic acid. 



Pasteur explained all the details in his clear powerful 

 voice. Why, in an open bottle, does wine left to itself become 

 vinegar? Because, thanks to the air, and to the mycoderma 

 aceti (which need never be sown, being ever mixed with the 

 invisible dusts in the air), the chemical transformation of wine 

 into vinegar can take place. Why does not a full, closed bottle 

 become acetified? Because the mycoderma cannot multiply in 

 the absence of air. Wine and air heated in the same vessel 

 will not become sour, the high temperature having killed the 

 germs of mycoderma aceti both in the wine itself and in the 

 dusts suspended in the air. But, if a vessel containing wine 

 previously heated is exposed to the free contact of ordinary air, 

 the wine may become sour, for, though the germs in the wine 

 have been killed, other germs may fall into it from the air and 

 develop. 



Finally, if pure alcoholized water does not become acetified, 

 though germs can drop into it from the air, it is because it 

 does not offer to those germs the food necessary to the plant 

 — food which is present in wine but not in alcoholized water. 

 But if a suitable aliment for the little plant is added to the 

 water, acetification takes place. 



When the acetification is complete, the mycoderma, if not 

 submerged, continues to act, and, when not arrested in time, 

 its oxidating power becomes dangerous ; having no more 

 alcohol to act upon, it ends by transforming acetic acid itself 

 into water and carbonic acid gas, and the work of death and 

 destruction is thus achieved. 



Speaking of that last phase of the mycoderma aceti, he went 

 on to general laws — laws of the universe by which all that has 

 lived must disappear. "It is an absolute necessity that the 

 matter of which living beings are formed should return after 

 their death to the ground and to the atmosphere in the shape 

 of mineral or gaseous substances, such as steam, carbonic acid 

 gas, ammoniac gas or nitrogen — simple principles easily dis- 

 placed by movements of the atmosphere and in which life is 

 again enabled to seek the elements of its indefinite perpetuity. 

 It is chiefly through acts of fermentation and slow combustion 



