CHAPTER II.
THE DOCTOR'S WONDER ROOM Nathaniel and Theodora, who were called Nat and Dodo for short, were standing in the hallway outside Dr.Hunter's door, engaged in a very lively argument.
"I say birds are animals," blustered Nat, pounding his fists together after a fashion of his own.
"And I'm as sure as anything that they _can't_ be," persisted Dodo, "because they have feathers, and nothing else has." "That doesn't prove anything.

Everything that lives and grows is either an animal or a vegetable.

Do you think that birds grow like potatoes and are dug out of the ground, or come off trees like apples ?" And Nat gave himself an air of great wisdom, such as brothers are apt to wear when they are in the fifth reader, and their sisters are only in the third.
"But isn't there anything besides animals and vegetables that they might be?
Perhaps they are minerals," said Dodo, brightening up as she thought of the word.
"Oh! oh! what a stupid you are, Dodo! Minerals! Why those are rocks and such things, that can't move and don't live." Nat laughed rather rudely, and, putting his hands in his pockets, began to whistle.
"I think you might tell me _what_ kind of an animal a bird is, and why it has feathers and can fly, instead of laughing," said Dodo in a shaky voice; for her feelings were very tender and she remembered too late what minerals are.
"Yes, tell her, Nat," said Olive, who came through the hall just then.
"Are you holding your knowledge tight in your pockets, or whistling to keep from telling it ?" Nat scowled a minute and then said frankly, for every one was frank with Olive, "I really don't know what sort of an animal a bird is, though I'm sure it _is_ an animal.

Don't you think Uncle Roy will tell us ?" "I'm sure he will be glad to, if he is not very busy, and he is seldom too busy to talk of birds.

He is writing a book now of all the things he knows about them.