CHEMICAL ACTIVITY OF BACTERIAL METABOLISM. 65 



difficult of utilkation, which it would reduce in the absence of 

 fermentable objects. 



Every fermentation has the object of furnishing a store 

 of energy to the fermenting organism. This is attained 

 in the splitting fermentation in this way: 



In the interior of the bacterial cell the complicated 

 fermentable molecule is decomposed into smaller fragments, 

 and thus energy is set free. I will illustrate this as it 

 occurs in the common fermentations of sugar, where the 

 case is very simple: 



Or 

 Or 



Organisms growing with oxygen excluded especially 

 utilize one of these sources of energy, as the source of 

 energy at the command of aerobic varieties, residing in 

 the oxidation of resorbed substances through absorbed 

 oxygen, is cut off. Therefore all anaerobic varieties are 

 endowed with the ability to cause active fermentation of 

 sugar, while many facultative anaerobes only cause fer- 

 mentation of nutrient media containing sugar when oxy- 

 gen is excluded. 



As already mentioned on page 29, Buchner has dis- 

 covered that by expression under great weight a ferment 

 (zymase) can be obtained from the bodies of yeast-cells 

 which ferments sugar most intensely. These discoveries 

 have advanced considerably our understanding of the 

 utilization of sugar within the cells of the yeast fungus. 

 We now know that the breaking up of sugar and the re- 

 sulting gain of power originates simply "through the 

 vital process, ' ' but we recognize, in the zymase, the special 

 means which the organism makes use of for this activity. 

 Heretofore it has not been possible to obtain zymase or 

 other intracellular acting ferments from bacteria, yet, for 

 the present, we may suppose that yeasts and bacteria are 

 similar in this respect. 

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