BACTERIA AND FERMENTATION 129 



ately when the acetic acid has reached a percentage as high 

 as 14. But if the acid be removed, and fresh alcohol added, 

 the process recommences. 



The second method, sometimes called by the Germans 

 the " quick vinegar process," is to pour the weakened 

 acohol through a tall cylinder filled with wood-shavings, 

 having first added some warm vinegar to the shavings. 

 After a number of hours the resulting fluid is charged with 

 acetic acid. What has occurred ? Liebig maintained that 

 a chemical and mechanical change had brought about the 

 change from the alcohol put into the cylinder and the vine- 

 gar drawn off at the exit tube. It was reserved for Pasteur 

 to demonstrate by experiment that the addition of the warm 

 vinegar to the shavings was in reality an addition of a living 

 micro-organism, which, forming a film upon the shavings, 

 became " the mother of vinegar," and oxidised the alcohol 

 which passed over it, inducing it to become aldehyde and 

 then acetic acid. 



Mycoderma Aceti (described by Persoon 1822, Kiitzing 

 1837, and Pasteur 1864). It must be understood that this 

 term is the name rather of a family than an individual. 

 Pasteur believed it to be a specific individual, but Hansen 

 pointed out that it was composed of two distinctly different 

 species (Bacterium aceti and B. pasteurianmri), and subse- 

 quently other investigators have added members to the 

 acetic fermentation group of which M. aceti is the type. 



This bacterium is made up of small, slightly elongated 

 cells, with a transverse diameter of 2 or 3 /a, sometimes 

 united in short chains of curved rods. They frequently 

 show a central constriction, are motile, and produce in old 

 cultures involution forms. The way in which the cells act 

 and are made to perform their function is as follows: A 

 small quantity, taken from a previous pellicle, is sown on 

 the surface of an aqueous liquid, containing 2 per cent, of 

 alcohol, i per cent, of vinegar, and traces of alkaline phos- 



9 



