CHAPTER II 

 MECHANISM OF METABOLISM* 



GENERAL THEORY OF METABOLISM 



ANABOLISM, KATABOLISM, METABOLISM. It has been stated that 

 microorganisms need food for at least two different purposes : building 

 material and building energy. They may need it for other purposes 

 also, e.g., for motion. The sum of all changes which the food undergoes 

 in the body, including the deterioration of the cells, is called metabol- 

 ism. Metabolism consists of several separate functions: One of 

 them is the construction of new cells, or parts of cells, called anabol- 

 ism, another the deterioration of cells, called katabolism, and the most 

 important quantitatively is the fermentation or respiration. The 

 fermentation or respiration processes are fairly well understood; many 

 of them can be produced in the chemical laboratory without micro- 

 organisms. Katabolism is the sum of many processes some of which 

 are well understood while others are still unknown. The synthetic, 

 anabolic processes of the cell, however, are almost entirely unknown, 

 and we can only speculate regarding the various means by which the 

 cell grows. The explanations of the different cell activities began, 

 as in most other fields of theoretical microbiology, with a close analogy 

 with animal and plant metabolism, but owing to the comparative 

 simplicity of the microorganisms, they led to the establishment of new 

 facts and theories which proved afterward useful for the understand- 

 ing of the metabolism of the more complex organisms where the multi- 

 plicity of facts prevented a clearer insight into the separate processes. 



INTRA- AND EXTRA-CELLULAR FERMENTATION 



DECOMPOSITION OF INSOLUBLE FOOD. Many microorganisms feed 

 upon cellulose, starch, fat, gelatin, keratin and other insoluble com- 

 pounds. Microorganisms, with the exception of some protozoa, 



* Prepared by Otto Rahn. 



203 



