Part I: THE NATURE OF
ALL LIVING THINGS
When you thinkof"livingthings,"youprobablythink first of the animals
and people you are most familiar with. You might think of yourpets-adog,
a cat, ahamster,a canary, a tankof tropicalfish-orof the animals in the
zoo, or ofhumananimals, your parentsand friends. Thinkaboutit some
more, and you will realizethatplants are living, too. You might think of your
favorite tree for climbing,ofthe leaves yougatherduringfall, orperhapsof
the crocuses and snow drops which everyone is so glad to see pushingthrough
the snow in early spring.
Remember, too,thatmany of the inert, lifeless things you use every day
originally had life. The wood in your desk came from a tree, as did thepaper
on which thisbookisprinted. Threadsfor a pure silk tie or dress were spun
by thecaterpillarsof silk moths. The wool in your wintercoatonce kept a
sheep warm. The coal weburnto provideheathad its origin in giant fern
trees which existed millions of years ago, and thendisappearedfrom theearth
as its climate changed.
These are the living things which come most readily to mind. But there
are thousandsofotherliving organisms on theearth-inthe air and in the
water. Lookinto ajarof water which you have taken from apond. You will
see tiny water animals dartingabout,but there are others there, too,thatare
much too small to be visible to your"naked,"or unaided eye. To see them
you will need a microscope. With its help, you will be able to watch minute,