PRODUCTS OF METABOLISM. 



only in acetic fermentations, not from sugar, but from alcohol, by a very 

 simple process of oxidation. 



CH 3 CH 2 OH+ 2 0=CH 3 COOH+H 2 O 



Alcohol Acetic acid 



If there is not plenty of air present, the oxidation may not become 

 complete and small amounts of acetaldehyde may form. 



CH 3 CH 2 OH+O=CH 3 COH+H 2 O 



Alcohol Aldehyde 



Some acetic bacteria can destroy acetic acid by oxidizing it completely 

 CH 3 COOH+ 4 O = 2CO 2 + 2H 2 O 



Molds frequently form acetic acid from sugar or starch; the peculiar 

 acid taste of moldy fruit preserves is due partly to this acid. 



Another product of fermentation of sugars which has been mentioned 

 already in various places, is butyric acid (CH 3 CH 2 CH 2 COOH). It 

 has the very pungent odor of rancid butter. Butyric acid is formed not 

 only from carbohydrates, but also from butter fat and from proteins. 

 The production from cellulose has been discussed at the beginning of 

 this chapter. The difficulty of giving an equation for butyric fermentation 

 of dextrose has been pointed out in the chapter on chemical equations. 

 Butyric acid is, like acetic acid, not the only product of fermentation. 

 It is always accompanied by other acids and alcohols. The butyric 

 bacteria are distinguished and named according to the predominating 

 products of fermentation. They were known as B. (Clostridium) buty- 

 ricus, B. butylicus, B. lactobutyricus and B. lactopropylbutyricus. Recent 

 investigations of Bredemann have made it probable, however, that most 

 of these bacteria are only varieties of the same species. The amounts of 

 the different acids and alcohols formed by one strain vary with varying con- 

 ditions so much that a dominance of the one or the other product cannot be 

 used for diagnostic purposes. Butyric acid is also produced from lactic 

 acid and from glycerin. These fermentations have a theoretical interest, 

 because they represent a synthesis by bacteria; glycerin or lactic acid, 

 with three carbon atoms, are changed to butyric acid with four carbon 

 atoms. 



In the decomposition of sugars by bacteria, mainly monobasic acids 

 are formed; lactic, acetic and butyric acids are predominant, though 

 occasionally succinic acid is also found. Yeasts change the sugar to 

 alcohol and carbon dioxide almost exclusively. The mycoderma 



