118 LOUIS PASTEUR 



times its weight of alcohol into acetic acid in five 

 days. 



It is now known that several species of micro- 

 organism may ferment alcohol into vinegar, but for 

 the most part they closely resemble each other and 

 may readily be distinguished from other organisms 

 that are frequently associated with them. The 

 vinegar-producing organisms multiply at an almost 

 incredible rate. So long as alcohol is present they 

 transform it to acetic acid, but when their preferred 

 food is exhausted they may attack the acetic acid 

 itself and transform it into carbon dioxide and 

 water. Vinegar exposed to the air often, therefore, 

 becomes weaker and its acid may in time entirely 

 disappear. Not only wine should be shielded from 

 air to keep it from turning sour, but vinegar should 

 be similarly protected to keep it from growing 

 weak. Pasteur found that if vinegar is heated, thus 

 killing its organic life, it may be kept clear and 

 pure for a long time. 



Pasteur's studies introduced several improve- 

 ments in the methods of producing vinegar which 

 were the means of saving millions of francs to the 

 manufacturers. In a lecture before the Chamber 

 of Commerce at Orleans, which was largely attended 

 by vinegar makers, doctors, and students, he gave 



