FOOD OF MICROORGANISMS 225 



pounds have, as a rule, the ability to decompose several compounds, 

 and some bacteria are common scavengers, able to feed on organic acids, 

 sugars, fats and proteins. 



Oxygen Relations. It is characteristic of many microorganisms to 

 provide for their energy without using free oxygen. One such example 

 has already been given in urea fermentation. 



(NH 2 ) 2 CO + 2 H 2 = (NH 4 ) 2 C0 3 



Urea Ammonium carbonate 



Very common is the decomposition of sugars without oxygen. 

 The two most typical fermentations of this type are the alcoholic and 

 the lactic fermentations. 



C 6 H 12 O 6 = 2 C 2 H 5 OH + 2 CO 2 + 22 Cal. 



Sugar Alcohol 



C 6 H 12 O 6 = 2C 3 H 6 O 3 + 15 Cal. 



Sugar Lactic acid 



In fermentations of this type, the changes take place without an 

 oxygen gas partaking in the reactions. These fermentations seem to 

 be essentially reactions of the oxygen atoms within the sugar molecule. 

 One side of the molecule is reduced while the other side is oxidized. 

 In the sugar molecule, each carbon atom has one oxygen atom. In 

 the products of fermentation, carbon dioxide has two oxygen atoms to 

 one carbon atom, and in alcohol there is only one oxygen atom for two 

 carbon atoms. In the lactic fermentation, the oxygen, which is dis- 

 tributed evenly in the sugar, is shifted to one side of the molecule in 

 lactic acid. 



H H H H H O 



O O O O O || 

 Dextrose, H C C C C C C 



H H H H H H 



H H O 



o I! 



Alcohol, HC CH C Carbon dioxide, 



H H || 

 O 



H H 

 H O O 



Lactic acid, HC C C 



H H || 

 O 



15 



