CHAPTER III. 

 MECHANISM OF METABOLISM. 



GENERAL THEORY OF METABOLISM. 



ANABOLISM AND KATABOLISM. The study of the physiological 

 mechanism of the cell is the most interesting and most difficult problem 

 of biological research, for it tries to discover the secret of life processes. 

 The physiological mechanism of the cell consists of three parts generally 

 distinguished one from the other, being interdependent upon each other 

 Fermentation, intra- and extra-cellular, katabolism, the dissociation of 

 cell substances, and anabolism, the assimilation of food in the synthetic 

 processes of the cell. The katabolic processes have been studied suc- 

 cessfully for a long time, and our knowledge of the digestion of organic 

 and inorganic substances has a definite chemical basis. Digestive pro- 

 cesses can be accomplished in vitro, but the cell is required to furnish 

 the digestive agent which, after being removed from the cell, may be 

 treated as a definite chemical compound. The katabolism, consisting 

 of many destructive chemical processes, some of which are well-defined 

 and some wholly unknown, represents the degeneration of the cell. The 

 study of the anabolic or synthetic processes is to a large extent speculation. 

 Very meager is the positive knowledge of the chemical changes involved, 

 and only the very simplest of these reactions can be duplicated in vitro. 



The problems of digestion have attracted the attention of scientists 

 long before microorganisms were known, and the knowledge of the digest- 

 ive processes of man and animals have helped the microbiologist in 

 many ways. Again, many results of microbiological research which 

 could be obtained only with single-celled organisms are employed now 

 to great advantage in general physiology. 



INTRA- AND EXTRA-CELLULAR FERMENTATION. 



DECOMPOSITION OF INSOLUBLE FOOD. It has been stated' before that 

 many microorganisms feed upon cellulose, starch, fat, gelatin, keratin 

 and other insoluble compounds. It has also been previously stated that 

 microorganisms, with the exception of some protozoa, depend upon 



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