INTRODUCTION 
O NE may sit with a book in his hand that is ad¬ 
mittedly full of charm, fascination, romance, and 
yet be unable to get any pleasure at all out of it because, 
forsooth, it is written in French and he reads only English. 
In the same way the Book of Nature may be open be¬ 
fore him through all the days of his life, but not having 
the key to it, he will be unable to dip into its mysteries 
or to appreciate its miracles. 
The world of living things is so large and so compli¬ 
cated that it is hard for the undirected observer to as¬ 
semble any degree of order from its chaos. It is as though 
all the books in the Congressional Library were thrown 
together in an unorganized pile. The casual student 
would be discouraged in attempting to find what he 
wanted in the mass. 
But an understanding of nature can be organized just 
as these books can be classified and assigned to their 
proper shelves. When information is properly grouped, 
understanding begins to dawn and puzzling situations 
clear up like fog before the sun. 
In nature, for example, there are animate and inani¬ 
mate objects — those that are alive and those that are 
not. There is, for example, a bird on a twig or a stone in 
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