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- 
