"No,
Dodo," laughed the Doctor; "when pigs are shut up they eat a great many
dirty things, but naturally they prefer clean food like other cattle--
corn, acorns, apples, and so forth. Besides, those 'nasty things,' as
you call them, turn into pork before they are put in sausages, for pigs
know how to make pork. So you see that all the food of the animals whose
flesh we eat comes out of the ground; and that is what the Bible means
where it says, 'All flesh is grass.' But what other things are there
that grow up out of the earth, tall and strong, each one holding a
beautiful green screen to keep the sun from drawing all the moisture
from the ground and making it too dry; shading the rivers that their
waters may not waste away; some making cool bowers for House People to
sit under, others bearing delicious fruits for them to eat, and all in
good time yielding their bodies to make fires and give out heat to warm
us?"

"Trees! Yes, trees of course," cried the children eagerly; "all kinds of
trees, for trees grow apples and pears and plums and cherries and
chestnuts and firewood too."

"Now what is there that preys upon all this vegetable life--upon every
plant, from the grass to the tree, destroying them all equally?"

"Bugs and worms and all kinds of crawlers and flyers and hoppers," said
Rap.

"Yes, every plant has an insect enemy which feeds upon its life juices.
So a set of animals has been developed by Heart of Nature to hold the
plant destroyers in check, and these animals are the birds.

"Man may do all he can to protect his gardens, his orchards, his fields
and forests, but if the birds did not help him the insects that work by
night and day--tapping at the root, boring inside the bark, piercing the
very heart of the plant, chewing off the under side of leaves, nipping
off the buds--would make the earth bare and brown instead of green and
blooming. Yet House People, both young and old, forget this. They shoot
and frighten away the birds, either because some few of their feathered
friends take grapes or other fruits and berries by way of pay, or merely
from thoughtlessness, to see how many they can hit."

"Do _all_ birds eat bugs and such things?" asked Nat. "Olive said she
used to put out grain and crumbs in winter for some kinds."

"Some birds eat animal food and some seed food, while others eat both;
but almost all birds feed their babies upon insects. The nesting season
is chiefly in spring, when all plan