126 The Study of Animal Life TARTU 



Still, this gives no distinction between the blowing of 

 wind and the life of man ; but the other characteristics of 

 life will be realised as we proceed in our analysis ; it is 

 certain that without movement there is no life. Further 

 thought may lead us to define life as that " complex of 

 forces which produces form." Thus the star-like crystals 

 of a snowflake, the diamond drops of dew, the over- 

 shadowing mountains, would all be imaged in our 

 minds as living, though of more lowly life than the 

 lichens of the bare hill-tops, the grass of the plains, or man 

 himself. We have no space here to trace the connections 

 between such an idea and the beliefs of all simple peoples, 

 and the inspirations of all poets, but the similarity is 

 evident, and the usefulness in philosophy of such general- 

 ised conceptions is great. 



But the physiology which we shall sketch here will be a 

 narrower one ; it will be confined to the life of plants and 

 animals, and we shall attempt to show precisely how that 

 life is separated from the life of the dust and of the air. 



2. The Seat of Life. Now in what parts within the 

 living body are the life forces most actively at work ? 



When we look at any living creature we are all too 

 willing, even if the wonder of life stirs within us, to remain 

 satisfied with a vague apprehension of a mystery. It is 

 strange that so many generations of men passed away 

 before any steps were taken towards a conception of the 

 intimate material processes of life and growth and death. 

 The moving train has been watched, but the engine and 

 the stoker have been almost unnoticed. 



Let us consider the growth of a tree. The outward manner 

 of its growth we can observe, a few superficial details of its 

 inner life we already know, and of this knowledge we may 

 look for great expansion, but the ultimate processes of its 

 life are still a complete mystery to us. 



The tree is alive, but is it all alive ? Cut a stake from 

 its heart and plant it in the ground ; it will not grow, and 

 shows no signs of life, but we are not puzzled ; the tree, we 

 think, can only live as a whole, and we know how easily 

 most living things are killed by local injuries. But if we 



