PRODUCED BY ALCOHOLIC FERMENTS. 167 



correct in principle, some source of error had always occurred ; 

 for instance, that impure air had not been absolutely excluded, 

 or the heating had not been sufficient. Details which appear 

 trifling may here acquire great importance. Thus the views 

 which were defended by Spallanzani and his supporters finally 

 prevailed, owing to the ability and perseverance with which 

 Pasteur conducted his researches. 



It was mentioned above that in 1837 Kiitzing published 

 some observations relating to an acetic acid bacterium which 

 he had discovered. This subject was again taken up by 

 Pasteur, and subjected to a thorough experimental examina- 

 tion.* He gave a good description and figure of the 

 bacterial growths found in French vinegar factories, and 

 which he named " Mycoderma aceti" His experiments de- 

 finitely proved that it was this growth which gave rise to the 

 formation of acetic acid. He also dealt with the chemical 

 side of the question. This is, indeed, one of his most 

 important researches. In France, wine is employed for the 

 manufacture of vinegar. The fermentation takes place in 

 casks which are only partially filled, and which have a 

 capacity of two to four hectoliters, and are of the usual form. 

 At suitable intervals a certain amount of the vinegar is drawn 

 off, and a corresponding quantity of wine is added to take its 

 place. The same casks are thus kept in use for several years, 

 without being completely emptied, and therefore, also without 

 being cleaned. Under these conditions, the so-called vinegar 

 eels develop in enormous numbers. Pasteur proved that 

 these small worms are able to check the development of 

 the acetic acid bacteria, and so prevent the fermentation from 

 proceeding properly in the casks thus infected ; the vinegar is 

 then said to be " sick " (malade ou tourni). He now devised 

 a new method, founded upon his theoretical investigations 



* Pasteur, " Memoire sur la fermentation acetique," J Annales scientifiques de 

 l'cole Normale superieure,' t. I, 1864. Also, ' Etudes sur la vinaigre,' Paris, 

 1868. 



