METABOLISM 273 



actively growing and multiplying, which are found as we 

 have seen in the special growing points or layers, is equally 

 true of all cells so long as they are living. In all cases, 

 though growth and division may not be evident, we have to 

 do with processes of repair of the inevitable wasting of the 

 living substance during the operations of its life. The 

 same kind of change is evident in all cells, though the 

 immediate results of such changes differ according to the 

 part any particular cell takes in promoting the well-being 

 of the whole organism. 



If we turn from these anabolic processes we find we 

 have proceeding, side by side with them, a decomposition 

 of the protoplasm, involving a separation from its complex 

 molecule of various substances which are of less com- 

 plexity than the living material itself. These often, 

 in the first instance, include such carbohydrate and nitro- 

 genous substances as it made use of in building itself up. 

 These can again be used in reconstruction of the proto- 

 plasm, or can be further broken down into simpler substances 

 stilL So long as the protoplasm is living, it is continually 

 in a state of change or chemical activity, undergoing con- 

 stant reconstruction and decomposition. 



Besides initiating those chemical changes in which it 

 takes this prominent part, it is also the seat of a large 

 number of others into which its own molecule does not 

 immediately enter. Processes of both oxidation and reduc- 

 tion are continually going on in its substance in which are 

 involved the various materials which are found there, either 

 in solution in the water which saturates it, or in amorphous 

 form ; substances which have been transported from other 

 cells, or have been formed in the processes of the self- 

 decomposition of the protoplasm. 



These katabolic processes vary a great deal in the 

 extent to which they are carried out. They may sometimes 

 go on so far as to produce such simple bodies as carbon 

 dioxide and water, which are given off from the organism. 

 This is a very marked feature of the metabolism that may be 



