508 ELEMENTARY BIOLOGY 



individual's isolated efforts. It is always the product of human 

 intercourse. Not only does its production involve the inter- 

 change of thought and experience of many people ; it involves 

 also the preservation of thoughts and experiences for genera- 

 tions. Each one adds a little to what has gone before ; if he 

 did not know what had been learned before him, he would 

 have to start at the beginning, and so each one could get no 

 farther than a child's experience. 



Unless we think about the matter for some time, we are not likely 

 to realize how far-reaching is our dependence upon others for the 

 thousands of ideas useful or entertaining that we absorb from 

 our surrounding civilization, through books, through customs, through 

 instruction, through social intercourse and various institutions, such 

 as the church, clubs, games, election campaigns, and so on. We get 

 our ideas not only from our immediate neighbors but from all 

 corners of the earth, not only from our contemporaries but from 

 the remotest antiquity. 



Again, our applications are largely social. We have seen 

 this to be the case in hygienic matters. It is impossible for 

 me to save myself from tuberculosis infection by minding my 

 own business or by refraining from spitting etc. My safety 

 depends in large part upon what other people do. The same 

 principle holds in the matter of fighting any plant or animal 

 pest, whether it is merely a nuisance or a menace to our eco- 

 nomic welfare. The same thing holds in utilizing most of the 

 great discoveries or inventions, such as the telephone or the 

 wireless, the steam engine or the electric light. 



The development of inventions depends not only upon the accumu- 

 lated knowledge of the past but also on the possibility for joint use. 

 It is only after years of experience with electric-lighting plants, for 

 example, that we may at last contrive to establish a small plant for 

 serving an isolated farmhouse ; at first the development is possible 

 only where people live together in communities and exchange their 

 services readily. 



