26 ENVIRONMENT OF PLANTS AND ANIMALS 



fixed in one spot practically all their lives. Certain tiny plants 

 and most animals move from place to place, either in air, water, 

 on the earth or in the earth, but they maintain relatively the 

 same conditions in environment. Birds are perhaps the most 

 striking exception, for some may fly thousands of miles from 

 their summer homes to winter in the south. Other animals, too, 

 migrate from place to place, but not usually where there are 

 great changes in the surroundings. A high mountain chain with 

 intense cold at the upper altitudes would be a barrier over which, for 

 example, a bear, a deer, or a snail could not travel. Fish like trout 

 will migrate up a stream until they come to a fall too high for them 

 to jump. There they must stop because their environment limits 

 them. 



Man in his Environment. - - Man, while he is like other animals 

 in requiring heat, light, water, and food, differs from them in that 



he has come to live in a 

 more or less artificial en- 

 vironment. Men who 

 lived on the earth thou- 

 sands of year ago did not 

 wear clothes or have elab- 

 orate homes of wood or 

 brick or stone. They did 

 not use fire, nor did they 

 eat cooked foods. In 

 short, by slow degrees, 

 civilized man has come to 

 live in a changed environ- 

 ment from that of other 

 animals. The living to- 

 gether of men in com- 

 munities has caused cer- 

 tain needs to develop. 

 Many things can be sup- 



A new apartment house, with out-of-door " 



sleeping porch. plied in common, as water, 



milk, foods. Wastes of all 

 kinds have to be disposed of in a town or city. Houses have come 



