96 NUTRITION AND METABOLISM. 



dioxide, hydrogen, and methane are produced sometimes by the same 

 organism at the same time and from the same food compound. This 

 appears unusual because these gases represent the ultimate products of 

 oxidation and of reduction. The intramolecular changes caused by 

 anaerobic processes result mainly in a change of the oxygen atoms of 

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

 oxidized, as in the alcoholic fermentation, which can take place without 

 oxygen. 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 distrib- 

 uted evenly in the sugar, is shifted to one side of the molecule in lactic acid 



H H H H H 

 00000 



Dextrose, H C C C C C-C = O 

 H H H H H H 



H 

 H O 



Alcohol, HC CH Carbon dioxide, O = C = O 



H H 



H H 

 H O O 



Lactic acid, HC C C = O 

 H H 



These changes result in a liberation of energy which enables the organ- 

 isms to continue their life process. 



Some bacteria provide for oxygen by taking it from mineral compounds. 

 Through the agency of certain microorganisms, nitrates are reduced to 

 nitrogen and sulphates are reduced to hydrogen sulphide by a complete 

 removal of the oxygen from the molecule. 



Ca(NO 3 ) 2 - 50= CaO + 2N 

 H 2 SO 4 - 4 O = H 2 S 



It seems that the opportunities for the development of obligate anaero- 

 bic organisms in nature are not very numerous. They may develop in the 

 animal body, in the deeper layers of soil, and at the bottom of waters. 

 They can also develop, however, on the surface of the soil and in other 

 places where the air has free access, provided that some aerobic organisms 



