ENERGY SUPPLY OF THE CELL 67 



different tissues and of different organisms are not specific, but that 

 in all organs of all plants, animals and microorganisms, the same 

 three proteolytic mechanisms are found which are characterized by 

 their optimal pH of 3.5, 5.5 and 7.5 respectively. 



(i) SUMMARY OF FACTS 



The large majority of bacteria can exist only if they 

 have at their disposal organic or inorganic food which 

 they can decompose. The amounts of energy produced 

 by such decomposition can be measured or calculated. 

 Such decompositions, we call fermentations, using the 

 broadest meaning of this term. 



In several cases, it has been possible to separate from 

 the living cell the agent that causes fermentation. In 

 other cases, it could be shown that fermentation may 

 continue after the cells have lost the power of reproduc- 

 tion by drying, acetone or alcohol treatment, or ultra- 

 violet irradiation. 



Ultra-filtration and dialysis have shown that fermen- 

 tation is brought about by the inter-reaction of several 

 agents. 



In the fermentation by yeast, colon bacteria, butyric 

 acid bacteria, acetone bacteria or others, intermediary 

 products of fermentation have been isolated which 

 demonstrate that the fermentation is not one process, 

 but a succession of several chemical reactions. 



The type of fermentation may be changed altogether 

 by changing the reaction of the medium, or by adding 

 sulfites, or by changing the oxygen supply, and even by 

 changing the concentration of the substrate. 



SUMMARY OF THEORIES 



Bacteria require, for maintenance as well as for 

 growth, a source of energy which, for most species, can 



