An accomplished wizard once lived on the top floor of a tenement
house and passed his time in thoughtful study and studious thought.
What he didn't know about wizardry was hardly worth knowing, for he
possessed all the books and recipes of all the wizards who had lived
before him; and, moreover, he had invented several wizardments
himself.

This admirable person would have been completely happy but for the
numerous interruptions to his studies caused by folk who came to
consult him about their troubles (in which he was not interested),
and by the loud knocks of the iceman, the milkman, the baker's boy,
the laundryman and the peanut woman. He never dealt with any of
these people; but they rapped at his door every day to see him about
this or that or to try to sell him their wares. Just when he was
most deeply interested in his books or engaged in watching the
bubbling of a cauldron there would come a knock at his door. And
after sending the intruder away he always found he had lost his
train of thought or ruined his compound.

At length these interruptions aroused his anger, and he decided he
must have a dog to keep people away from his door. He didn't know
where to find a dog, but in the next room lived a poor glass-blower
with whom he had a slight acquaintance; so he went into the man's
apartment and asked:

"Where can I find a dog?"

"What sort of a dog?" inquired the glass-blower.

"A good dog. One that will bark at people and drive them away. One