32 WHAT IS LIFE 



casts out the useless refuse from its body. In some 

 manner or another all living bodies and all living 

 cells must be fed, must change their food into the 

 materials suitable for their own use and must get 

 rid of waste and superfluous portions. In this 

 brief statement is included the whole vast science 

 of physiological chemistry, even to glance at which 

 Metabolism would be impossible in this book. Speaking in the 

 most general manner it may be said that these 

 metabolic changes, as they are called, are of two 

 kinds. On the one hand less complex and more 

 stable substances are built up into other substances 

 of diametrically opposite character, they being more 

 complicated in their nature and less stable. During 

 this " anabolic " process energy is absorbed. 



And on the other hand there is the reverse 

 process called " catabolic," in which these unstable, 

 complex substances are broken up into simpler and 

 more stable matters, a process accompanied by the 

 giving out of energy. Further one must remember 

 that the chemical processes which take place in a 

 cell may be looked at, from quite another point of 

 view, as dual. There are the processes which are 

 carried on for the renewal of the cell itself and for 

 the maintenance of the various energies of which it 

 is the seat, and this is true whether the cell is 

 isolated a unicellular organism or whether it is 

 one of many as a portion of a multicellular organ- 



