“Now the next sort of food—­meat, the flesh of animals—­oxen, sheep, pigs, and poultry—­what do they feed on?”

“Oxen eat grass and hay and meal,” said Dodo, in great haste lest some one else should speak first.

“Sheep eat grass and hay too.  I’ve seen them over in the pasture on the hill,” said Nat.

“Pigs will eat any old sort of thing,” said Rap.  “Sour milk and snakes and swill and rats.”

“Ugh!” shivered Dodo.  “Are all those nasty things in sausages?” “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 plants begin or renew their growth.  Spring is also the season when the eggs of many insects hatch out and when others come from the cocoons in which they have slept all winter.