Old lady Finkelstein sidled up to a guest at one of her daughter's social evenings. She heard him addressed as doctor and now she said, diffidently, "Doctor, may I ask a question?"
"Certainly," said he.
"Lately, I've had this funny pain right in through here..."
The guest interrupted her uncomfortably. "I'm terribly sorry," he explained, "but I'm a doctor of philosophy."
"Oh," said Mrs. Finkelstein, "I'm sorry." She turned away, but then overcome with curiosity, turned back and asked,
"Just one more question, doctor. Tell me, what kind of disease is philosophy?"