104 BACTERIA AND FERMENTATION 



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), 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. Pasteur ianum), and subsequently 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 /m, 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, 1 per cent, of vinegar, and traces of alkaline phos- 

 phates. Very rapidly indeed the little isolated colonies spread, and 

 becoming confluent, form a membrane or pellicle over the whole area 

 of the fluid. When the surface is covered the alcohol is converted to 

 acid. After this it is necessary to add, each day, small quantities of 

 alcohol. When the oxidation is completed the vinegar is drawn off, 

 and the membrane is collected and washed, and is then again ready 

 for use. It ought not to remain long out of fermenting liquid, nor 

 ought it to be allowed to over-perform its function, for thus having 

 oxidised all the alcohol it will commence oxidation of the vinegar. 



In wort-gelatine Bacterium Pasteurianum develops as round 

 colonies with a smooth or wavy border, whilst B. aceti has a tendency 

 towards stellate arrangement. Spores have not been observed, and 

 from a morphological point of view the two species behave alike. 

 Neither produces any turbidity in the liquid containing them. In 

 order to flourish, B. aceti requires a temperature of about 33 C. and 

 a plentiful supply of oxygen. In a cool store or cellar there is, 

 therefore, nothing to fear from B. aceti. Frankland has isolated a 

 Bacillus ethaceticus, which is a fermentative organism producing 

 ethyl-alcohol and acetic acid. By oxidation the ethyl-alcohol may be 

 converted into acetic acid. 



3. Lactic Acid Fermentation 



Cause, Bacillus acidi lactlci; medium, milk-sugar, cane-sugar, glucose, dextrose, 

 etc. ; result, lactic acid. 



The process set up by the lactic ferment is simply a decomposition, 

 an exact division of one molecule of sugar into two molecules of 

 lactic acid, there being neither oxidation nor hydration. The con- 



