THE BIOLOGICAL ACTIVITIES OF BACTERIA 51 



from weak solutions of ethyl alcohol. This process, which is the basis of 

 vinegar production, is universally carried out by bacterial ferments. 

 While possessed to some extent by a considerable number of microorgan- 

 isms, acetic acid formation is a function pre-eminently of the bacterial 

 groups described by Hansen, including " Bacterium aceti" and "Bac- 

 terium pasteurianum." To these two original groups a number of others 

 have since been added. 



The organisms are short, plump bacilli, with a tendency to chain- 

 formation, and occasionally showing characteristically swollen centers 

 and many irregular involution forms. In the production of vinegar, as 

 generally practiced by the farmer with cider or wine, these bacteria 

 accumulate on the surface of the fluid as a pellicle or scum which is 

 popularly known as the "mother of vinegar." Destruction of these 

 bacteria by disinfectants or by sterilization with heat promptly arrests 

 the process of vinegar formation. Chemically, the conversion of the 

 alcohol consists in a double oxidation through ethyl aldehyde into acetic 

 acid as shown in the following formulae: 



1. C 2 H 5 (OH) + O = CH 3 (COH) 

 Alcohol Ethyl aldehyde 



2. CH 3 (COH) + O = CH 3 (COOH) 

 Acetic acid 



Alcoholic Fermentation (Zymase). The formation of alcohol as an 

 end product of fermentation is of great importance in a number of the 

 industries, primarily in the production of wine and beer. While accom- 

 plished by a number of bacteria, this form of fermentation is carried 

 out chiefly by the yeasts. 



Expressed in formulae the simplest varieties of alcoholic fermenta- 

 tion, from mono- and disaccharids, may be represented as follows: 



C 6 H 12 6 = 2C 2 H 5 (OH) +2C0 2 

 Dextrose Ethyl alcohol 



or 



C 12 H 22 lt + H 2 O = 4C 2 H 5 (OH) + 4CO 2 

 Saccharose Ethyl alcohol 



In all cases the process may not be so simple as indicated by the equa- 

 tions, since by-products, such as higher alcohols, glycerin, succinic 

 and acetic acids, may often be found in small traces among the end- 

 products of such fermentations. The conditions which favor alcoholic 



