68 CHEMICAL ENVIRONMENT 



material which are usually spoken of as "physiological 

 activities."^ Some of these changes certainly occur within 

 the cell as anabolic and katabolic processes. Very little is 

 known about such changes. However, many physiological 

 activities occur without the cell and can be more accurately 

 determined. Some of these changes are to be ascribed to 

 the utilization of certain of the elements and compounds 

 in these materials as tissue builders, some as energy-yield- 

 ing reactions and still others as giving rise to substances 

 that are of direct benefit to the organism concerned in its 

 competition with other organisms. 



Though all of the twelve elements already mentioned are 

 essential for the growth of every bacterium, two of them 

 are of especial importance for the reason that most of the 

 "physiological activities" to be described in the next chap- 

 ters are centered around their acquisition and utilization. 

 These elements are carbon and nitrogen. Some few of the 

 special activities of certain groups have to do with one or 

 the other of the remaining nine, as will be shown later. 

 But generally speaking when a bacterium under natural con- 

 ditions secures an adequate supply of carbon and nitrogen, the 

 other elements are readily available in sufficient amount. The 

 reason is that these elements are most frequently secured 

 from organic compounds derived from the bodies, living or 

 dead, of other organisms, plant or animal. These bodies 

 also contain the other elements. 



Carbon Metabolism.— Carbon is necessary not only because 

 it is an essential constituent of protoplasm but because its 

 oxidation is the chief source of the energy necessary for the 

 internal life of the cell, though nitrogen and sulphur replace it 

 in this function with a few forms. This latter use of carbon 

 (for oxidation to furnish energy) constitutes what may be 

 called its respiratory function. Bacteria like other organisms 

 in their respiration utilize oxygen and give off carbon dioxide. 

 The amount of the latter given off from the cell in this 

 way is very small as compared with that which is frequently 

 produced as an accompaniment of other reactions (see 



1 The student must not forget that "physiological activities" include 

 also motion, growth, reproduction and internal metabolism. 



