A fellow prostitute goes to the hospital to visit her girlfriend who is about to have heart transplant (donated by a man) . She's worried about the friend so she asks the doctor...

Prostitute: "I'm worried about my friend doc, what if her body rejects the man's organ?"

Surgeon:"Well, she's 36 years old and quite healthy. How long has she been in business?

Prostitute: "She's been working since she was 19 years old, but what the hell does that have to do with anything?"

Surgeon: "Well, she's been working 17 years and hasn't rejected an organ yet! Has she!!"