xx THE INFLUENCE OF ENVIRONMENT 387 



A living animal is almost always cither acting upon 

 its surroundings or being acted upon by them, and life 

 is the relation between two variables a changeful 

 organism and a changeful environment. And since 

 animals do not and cannot live in vacuo, they should be 

 thought of in relation to their surroundings. You may 

 kill the body and cut it to pieces, and the result may be 

 interesting, but you have lost the animal just as you 

 lose a picture if you separate figure from figure, and all 

 from the associated landscape or interior. The three 

 Fates are sisters, they are thoroughly intelligible only as a 

 Trinity. 



The most certain of all the relations between an 

 organism and its surroundings is the most difficult to 

 express. We see a small whirlpool on a river, remaining 

 for days or weeks apparently constant, with the water 

 circling round unceasingly, bearing the same flotsam 

 of leaves and twigs. But though the eddy seems the 

 same for many days, it is always changing, currents are 

 flowing in and out ; it is the constancv of the stream and 



/ 



its bed which produces the apparent constancy of the 

 whirlpool. So, in some measure, is it with an animal 

 in relation to its surroundings. Streams of matter and 

 energy are continually passing in and out. Though we 

 cannot see it with our eyes, the organism is indeed a 

 whirlpool. It is ever being unmade and remade, and 

 owes much of its apparent constancy to the fact that the 

 conditions in which it lives -the currents of its stream- 

 are within certain limits uniform. 



And as we cannot understand the material aspects of 

 an animal's life without considering the streams of matter 

 and energy which pass in and out, neither can we under- 

 stand its higher life apart from its surroundings. To 

 attempt a natural history of isolated animals, whether 

 alive or dead, is like trying to study man apart from 

 society. 



At present, however, we have to do with the relation 

 between external and internal changes. In a smithy 

 we see a bar of hot iron being hammered into useful 

 form. Around a great anvil are four smiths with their 



