64 VETERINARY BACTERIOLOGY 



Acetic Acid. Acetic acid is the most important and the 

 characteristic constituent of vinegar. It is produced by several 

 species of bacteria by the oxidation of ethyl alcohol according 

 to the following reaction : 



C 2 H 5 OH + 2 = CH 3 COOH + H 2 O. 



Alcohol. Acetic acid. 



Any solution containing alcohol, if left in contact with free oxygen, 

 will commonly undergo this fermentation spontaneously, as 

 Bacillus acetiy the organism usually responsible, is ubiquitous. 

 To insure rapid and efficient fermentation the cider or other 

 alcoholic solution is sometimes inoculated with mother of vinegar, 

 a mass of the organism which commonly forms a mat upon the 

 surface of the fermenting liquid. 



Fig. 30. Butyric acid bacteria, Bacillus bulyricus. (Adapted from Fischer.) 



Butyric Acid. Under anaerobic conditions saccharine solutions 

 are apt to undergo butyric acid fermentation as a result of the 

 development of the Bacillus butyricus or a related form. The 

 reaction may be represented as follows: 



C 6 H 12 6 = C 3 H 7 COOH + 2C0 2 + 2H 2 . 



Dextrose. Butyric acid. 



Butyric acid has an exceedingly disagreeable odor and taste, 

 hence the growth of this organism in any saccharine or starchy 

 food substance renders it unfit for use. Inasmuch as these 

 organisms are all spore producers, they resist heat well, and as 

 they are anaerobic they will grow when sealed in a can and all 

 air excluded. Rancidity in butter is sometimes due, in part 

 at least, to the development of butyric acid. 



Decay and Putrefaction. A distinction is sometimes made 

 between the terms decay and putrefaction. The former is said to 



