30 THE FITNESS OF THE ENVIRONMENT 



of life is firmly established in the world of our 

 senses. On the whole the composition of 

 living matter, its physical structure, the 

 changes of matter and energy which consti- 

 tute the metabolic process, together with the 

 totality of such changes, which make up the 

 fundamental economic process of that largest 

 community which consists of all living beings, 

 are all clearly defined. 



C 



THE CHARACTERISTICS OF LIFE 



Under the circumstances it is certainlv no 



t/ 



rash enterprise to seek a definition of some 

 of the essential characteristics of life. Al- 



a knowledge of its kind, after recognizing the truth that it is 

 only a surface knowledge. 



"For the conclusions we lately reached and the definition 

 emerging from them, concern the order existing among the 

 actions which living things exhibit ; and this order remains the 

 same whether we know or do not know the nature of that 

 from which the actions originate. We found a distinguish- 

 ing trait of Life to be that its changes display a correspond- 

 ence with coexistences and sequences in the environment; 

 and this remains a distinguishing trait, though the thing 

 which changes remains inscrutable. The statement that 

 the continuous adjustment of internal relations to external 

 relations constitute Life as cognizable by us, is not invali- 

 dated by the admission that the reality in which these rela- 

 tions inhere is incognizable." — Herbert Spencer, "The 

 Principles of Biology." New York and London, 1909, Vol. 

 I. Revised and enlarged edition, pp. 122-123. 



