CHAPTER XII 

 BACTERIAL RESPIRATION 



THE term respiration has undergone a continuous 

 expansion in its meaning. Originally "respiration" 

 in animals signified the exchange of oxygen and 

 carbon dioxide through the lungs, then it was used to 

 describe the transfer of oxygen to and the removal of 

 carbon dioxide away from tissues. Later still the term 

 connoted the general oxidation processes of cells, and, 

 finally, now that it is recognised that these processes are 

 almost always concerned with the energy requirements of 

 the cells, the expression has come to mean any energy 

 producing biological reaction, even when the reaction 

 takes place under anaerobic conditions. It is in this sense 

 of a chemical reaction producing energy in the cell, 

 whether aerobically or anaerobically, that we shall 

 employ it. 



Chemists tend to regard bacteria, yeasts and moulds, 

 merely as useful reagents which can bring about many 

 reactions, such as the synthesis of acetone, butyric acid, 

 butyl alcohol and so on, some of which he cannot yet 

 carry out in the laboratory. The tendency of the biologist, 

 on the other hand, is to regard these reactions or products 

 as accidents more or less incidental to the life of the cell, 

 useful accidents it may be, in that they sometimes pro- 

 vide a means of identifying or helping to identify the 

 organism (as is the case with sugar fermentation re- 

 actions), or in that they provide some product like alcohol 

 which he values. 



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