ENERGY SUPPLY OF THE CELL 81 



The only exception is the urea fermentation, and, 

 possibly, some similar decompositions of acid amids in 

 protein cleavage. 



Oxygen exchange between two different types of 

 molecules depends upon the special cell mechanism 

 as well as upon the energy liberated. Oxidation does 

 not always take place when oxygen is available. 



Some strictly aerobic bacteria can be made to exist 

 anaerobically by supplying them with highly oxidized 

 compounds acceptable to the species. 



Anaerobic growth of facultative organisms is possible 

 only with special substrates. Many substances not 

 permitting anaerobic growth will allow abundant growth 

 of the same species in air. 



Some strictly anaerobic bacteria may be made to 

 grow in unprotected testtube cultures if certain chemical 

 substances are added. 



SUMMARY OF THEORIES 



Fermentation depends upon activation of certain 

 hydrogen atoms of the substrate as well as upon an 

 appropriate acceptor for the activated hydrogen. The 

 acceptor may be the same substrate, or part of it, or a 

 different substance, or elementary oxygen. 



An exception to this type of fermentation is the urea 

 fermentation. Energy in this process is not liberated 

 by the hydrolysis proper, but by the heat of neutraliza- 

 tion between ammonia and carbonic acid. 



Streptococci and Clostridia cannot activate oxygen 

 to function as hydrogen acceptor. This lack has no 

 direct relation to anaerobiosis, for streptococci grow 

 fairly well in air. 



The distinction between aerobic, facultative and 

 anaerobic species is indefinite. Besides the properties of 



