1 66 GENERAL PHYSIOLOGY 



on in the living protoplasm. The living cell is in a state of un- 

 stable equilibrium. Protoplasm is being constantly built up and 

 just as constantly broken down. These two processes, the 

 building up and the tearing down, always go hand in hand. 

 The building up, constructive, or synthetic process is given 

 a special name, anabolism. The tearing down, destructive, 

 or analytic process is spoken of as catabolism. 



Anabolism. Anabolism includes, according to Vines, 

 all of the chemical processes going on in the cell which lead to 

 the formation of complex substances from simple ones. The 

 cell is constantly absorbing raw material as food, assimilating 

 it, and building it up into protoplasm. The exact way in which 

 assimilation is accomplished is unknown. The requirements 

 of bacteria, so far as their food is concerned, is first that it be 

 soluble, although it is true, as will be pointed out later more 

 specifically, that the bacteria are able to produce substances 

 which dissolve insoluble material and make it possible for 

 them to take up substances that are not soluble. The second 

 requirement is that they have the right kind of food, and the 

 bacteria as a whole can make use of a great many different 

 kinds of food, and may be classified on this basis. Bacteria, 

 with the exception of one group, are unable to make use of the 

 carbon dioxide of the air as a source of carbon. Some bac- 

 teria are able to live on dead organic matter ; another group 

 require that their food be living organic matter. A classifica- 

 tion of bacteria according to their nutritive requirement has 

 been proposed by Fischer, and is as follows : 



