“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.  Knock on the door, Dodo.”

“I’m afraid to,” said Dodo, clasping her hands behind her.  “Mammy says that room is full of birds, and that we must never go in there.  Suppose when the door opens they should get out and fly away?”

“Mammy was right in telling you not to go in without asking, because there are a great many books and papers there that father values, and you might upset them.  But the birds that are there are not alive.  They are dead birds that father has collected from all parts of America—­stuffed birds, such as you have seen in the glass cases in the Museum.”

“But, Cousin Olive,” said Nat in astonishment, “if Uncle Roy has shot enough birds to fill a big room, why won’t he let me pop at a few with my shooter?”

“You must ask him why yourself, Nat.  Knock again, Dodo.  Father, may we come in?  The children are here, with pockets full of questions;” and Olive opened the door of the study, which Dodo named “the wonder room” that very day.

It was a very long room on the southwest side of the house.  The sun streamed in through three wide windows, and at one end there was a deep fireplace with brass andirons upon which some logs smouldered, for though it was a mild May day the great room felt cool.  Around the room were deep cases with glass doors, from which peeped all kinds and sizes of birds, while between the tops of the cases and the ceiling the spaces were filled by colored bird pictures.  The Doctor’s desk stood in front of one window, heaped with papers and books; down the middle of the room were low book-cases standing back to back, and where these ended, before the hearth, was a high-backed settle, almost as long as a bed.