A prostitute went to visit a colleague in the hospital just before she was about to have a heart transplant. The woman, concerned about her friend's welfare, went up to the surgeon who was going to perform the operation and said "Doctor, I'm worried about my friend. What if her body rejects the organ?" The doctor replied "Well, she's 34 years old and is in extremely good health apart from her heart. How long has she been in the business?" The patient's friend replied "She's been working since she was 18 years old, but what's that got to do with anything?" "Well," said the doctor, "if she's been working for 16 years and hasn't rejected an organ, I don't think she's about to start now!"