114 ORGANISM AND ENVIRONMENT 



but the lower forms of animal and vegetable life the 

 body is made up of cells and cell-territories, and that 

 each cell is a centre of life. The life of the body as 

 a whole is maintained by co-operation amongst the 

 constituent cells. In the course of the common life 

 the individual cells are constantly perishing and being 

 reproduced, but the continuity or persistence of the 

 common life is as evident throughout these changes as 

 throughout the nutritive processes in which the chemi- 

 cal molecules passing through the body are constantly 

 being replaced. 



Not only do the constituent cells reproduce them- 

 selves and perish, but so does the whole organism it- 

 self ; and its death is evidently just as much a normal 

 phenomenon as is the death of any of its constituent 

 cells. Death has sometimes been compared to the 

 wearing out of a machine, but such a comparison 

 throws no light on death, since the body is not a 

 machine. Besides death and reproduction, there are 

 many other biological phenomena which show us that 

 life is not merely the life of individual organisms, but 

 the life of a society of organisms. It is the life of a 

 family, and beyond that the life of a species ; or if we 

 endeavour to push the biological analysis still further, 

 the life of the universe itself, though such a life must 

 remain outside the limits of clear mental vision until 

 we can connect biological with physical and chemical 

 conceptions. 



The distinctively biological conception which I have 

 endeavoured to formulate more definitely in these lec- 

 tures enables us to interpret what are ordinarily re- 



