CHAPTEE Y. 



THE COEEESPONDENCE BETWEEN LIFE AND ITS 

 CIECUMSTANCES. 



§ 27. We habitually distinguish between a live object 

 and a dead one, by observing whether a change which we 

 make in the surrounding conditions, or one which Nature 

 makes in them, is or is not followed by some perceptible change 

 in the object. By discovering that certain things shrink when 

 touched, or fly away when approached, or start w^hen a noise 

 is made, the child first roughly discriminates between the 

 living and the not- living ; and the man when in doubt 

 whether an animal he is looking at is dead or not, stirs it 

 with his stick ; or if it be at a distance, shouts, or throws a 

 stone at it. Yegetal and animal life are alike primarily 

 recognized by this process. The tree that puts out leaves 

 when the spring brings a change of temperature, the flower 

 which opens and closes with the rising and setting of the 

 sun, the plant that droops when the soil is dry, and re-erects 

 itself when watered, are considered alive because of these in- 

 duced changes ; in common with the zoophyte which contracts 

 on the passing of a cloud over the sun, the worm that comes to 

 the surface when the ground is continuously shaken, and the 

 hedgehog that rolls itself up when attacked. 



Not only, however, do we habitually look for some response 

 when an external stimulus is applied to a living organism, 

 but we perceive a fitness in the response. Dead as well as 

 living things display changes under certain changes of con- 



