He was much too well aware of the nature of the promise which he had made to the departing mother to do that.

He had constantly visited his little niece, and long before the first twelve years of her life were over had lost all consciousness of his promise, and of his duty to the mother, in the stronger ties of downright personal love for the only creature that belonged to him.
When Mary came home the doctor was like a child in his glee.

He prepared surprises for her with as much forethought and trouble as though he were contriving mines to blow up an enemy.

He took her first into the shop, and then into the kitchen, thence to the dining-rooms, after that to his and her bedrooms, and so on till he came to the full glory of the new drawing-room, enhancing the pleasure by little jokes, and telling her that he should never dare to come into the last paradise without her permission, and not then till he had taken off his boots.

Child as she was, she understood the joke, and carried it on like a little queen; and so they soon became the firmest of friends.
But though Mary was a queen, it was still necessary that she should be educated.