METABOLISM OF BACTERIA 167 



I. Prototrophic Bacteria. 



Nitrifying bacteria, bacteria of root nodules, sulphur and 

 iron bacteria ; occur only in the open in nature, never parasitic, 

 always monotrophic. 



II. Metatrophic Bacteria. 



Zymogenic, saprogenic, and saprophytic bacteria ; occur in 

 the open and upon the external and internal surfaces of the 

 body, sometimes parasitic (facultative parasites), monotrophic, 

 or polytrophic. 



III. Paratrophic Bacteria. 



Occur only in the tissues and vessels of living organisms, 

 true (obligatory) parasites. 



Catabolism. By catabolism is meant all the chemical 

 processes going on in the cell which lead to the formation of 

 simple substances from complex ones (Vines). The cell 

 protoplasm is constantly being broken down and by-products 

 formed. Anabolism and catabolism are constantly going on 

 in the same cell. If organic matter of the cell is of a higher 

 state than the food from which it was formed, the anabolic 

 process has been greater than the catabolic process, and the 

 organism that builds up organic matter can be properly spoken 

 of as an anabolic organism. If as a result of similar processes 

 in an organism, the end products are lower than those of the 

 food, the organism is said to be catabolic ; so that while the 

 anabolic and catabolic processes are concurrent in the same 



