The children gazed at Rap in surprise. It was a new idea that a poor little fellow like him should know more than they, who had both parents and nice clothes, and had been to school in a big city. That he should be able to tell stories about birds seemed wonderful. But they were not selfish, and instead of being jealous felt a great respect for Rap. "Now," said the Doctor, "we will see what a good neighbor to House People a bird is, and how in working for himself he helps them also." "How can birds possibly work to help people?" asked Dodo and Nat together; but Rap smiled to himself as if he knew something about the matter, and said, "They eat the bugs and worms and things that kill the gardens and fields." "You are right again," said the Doctor heartily. "What is one thing that man and every other animal must have to keep him alive?" "_Food_!" shouted Nat, and then grew very red, as the others laughed, because since he had been at Orchard Farm his appetite had grown so that though he ate twice as much as Olive and Dodo he seemed always hungry. "Yes, food. Bread, meat, vegetables, and fruits, but bread first of all. What is bread made of?" "Wheat, I think," said Nat. "Rye, too--mother's rye-bread is drea'fly good," said Rap. "Don't forget Mammy Bun's corn-bread," added Olive. "All your answers are right, for many different kinds of bread are used in various parts of the country; but whether it is made from wheat-flour, or rye-flour, or corn-meal, it all grows from the ground, does it not? "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?"