128 BACTERIA 



called aldehyde, further oxidation of which produces the 

 acetic acid. We may express it chemically thus ; 



Alcohol. Aldehyde. Water. 



C 2 H 6 O (+ oxygen and the ferment) = C 8 H 4 O -f H 2 O. 



The aldehyde becomes further oxidised : 



C 2 H 4 O + O = C 2 H 4 O 2 (acetic acid). 



Now this method of simply oxidising alcohol to obtain 

 acetic acid may be carried out chemically without any fer- 

 ment. If slightly diluted alcohol be dropped upon platinum 

 black y the oxygen condensed in that substance acts with 

 energy upon the spirit, and union readily occurring, acetic 

 acid results. Here the whole business of the platinum 

 sponge is to persuade the oxygen of the air and the hydro- 

 gen of the alcohol to unite. In the ordinary manufacture 

 this is accomplished by the vegetable cells of Mycodenna 

 aecti. 



There are two chief methods adopted in the commercial 

 manufacture of vinegar, both of which depend upon the 

 presence of the Mycoderma. The method in vogue at 

 Orleans when Pasteur (about 1862) commenced his studies 

 of the vinegar organism was to fill vats nearly to the brim 

 with a weak mixture of vinegar and wine. Where the pro- 

 cess is proceeding the surface is covered with a fragile 

 pellicle, " the mother of vinegar," which is produced by 

 and consists of certain micro-organisms whose function is 

 to convey the oxygen of the air to the liquor in the vats, 

 thus oxidising the alcohol into vinegar. This oxidation 

 may be carried on even beyond the stage of acetic acid 

 (when no more alcohol remains to be oxidised), resulting in 

 carbonic acid gas, which escapes into the air. But as in the 

 alcoholic, so in the acetic, fermentation, there comes a time 

 when the presence of an excess of the acid inhibits the 

 further growth of the organism. This point is approxim- 



