CHAPTER VII. 

 BACTERIAL METABOLISM-ENZYMES. 



IT was pointed out in the last chapter that bacteria require food 

 for at least two purposes building material and the liberation 

 of energy. In fulfilling these functions the foods are profoundly 

 changed; at times they are broken up into comparatively simple 

 products, after which they are built into the complex molecules 

 composing the bacterial cell; at other times they are split and the 

 energy utilized; at still other times they are completely oxidized, 

 the organisms thus obtaining all the stored potential energy. The 

 sum of all these changes which the food undergoes, including the 

 deterioration of the cell, is called metabolism. These changes con- 

 sist of two separate processes; the one construction of new cells 

 or parts of cells is a process of synthesis and is called anabolism. 

 The other is analytical or the breaking-down of the cell and is 

 called katabolism. Although these two processes are usually going 

 on simultaneously in the cell, yet it is true that during the first few 

 hours after inoculation of a culture the anabolic aspect predominates; 

 later the katabolic phase predominates. That this should be the 

 case can be readily seen, for the bacterial cell must be morphologi- 

 cally complete before it can bring about its characteristic energy 

 transformations, which continues until the death of the cell. 



Moreover, recent investigations have demonstrated that it is 

 just as true of bacteria as of animals that "it is as essential to 

 break down complex nitrogenous food substances into their simple 

 components before they can be utilized, as it is to reduce the walls 

 of an old church brick by brick before they can be made over into 

 a modern schoolhouse." The development and present status of 

 our knowledge of this represents one of the most interesting and 

 valuable chapters of bacteriology. 



Early Theories of Fermentation. Even as early as 1595 the great 

 medical chemist, Labavius, considered fermentation a process akin 

 to digestion, and von Helmont (1648) stated that out of the ferment 

 something passes into the fermenting liquid which grows in it as 

 a seed. But it was the great chemist, Liebig, who first developed 

 the purely chemical explanation of fermentation. It was he who 

 developed the idea of catalysis, a word already invented by 

 Berzelius. Liebig compared fermentation changes to the action 

 of finely divided platinum which possesses the power of bringing 

 about the union of gases at low temperatures. The ferment he 



