CHAPTER X 



VITALITY 



1. Persistence of a complex specific metabolism and of a correspond- 

 ing specific organisation 2. The capacity for growth, repro- 

 duction, and development 3. Effective behaviour, registra- 

 tion of experience, and variability 4. Organism and mechanism 

 5. The uniqueness of life. 



IN the preceding chapters we have studied the activities 

 of animals, and we would round off this part of the book 

 by inquiring into the criteria of livingness, or vitality. 

 It is plain that life may be described as a series of activities 

 with the two chief ends of caring for self and caring for 

 others self-maintenance and the continuance of the 

 race ; but the more difficult question is as to the essential 

 characteristics of the organisms that are thus active. 

 Life mav also be described as a twofold relation of action 



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and reaction between organisms and their environment, 

 but what we wish to make clear though it must be tenta- 

 tively are the qualities which essentially distinguish 

 living creatures from things in general. 



1. Persistence of a Complex Specific Metabolism and 

 of a Corresponding Specific Organisation. The image of 

 the organism is the burning bush of old always afire 

 and yet not consumed. The living creature is in cease- 

 less flux, always being unmade and remade. The 

 chemical changes are pre-eminently concerned with 

 reactions in which proteid substances play an important 

 part. There are the two main aspects up-building and 

 down-breaking, synthesis and analysis, construction and 

 disruption, assimilation and disassimilation, anabolism 

 and katabolism ; and there is more besides which cannot 

 be readily classified in this way, for, as Sir Michael Foster 



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