Act 4, Scene 1: Why has the Duke sent to Padua for an opinion, and what answer does he receive?

The Duke wants a doctor's council about the case. A doctor, in this case would have been a learned man skilled in the art of law. He sends to Doctor Bellario in Padua but finds the doctor is sick. The doctor, however, says that he is sending a young man instead, which happens to be Portia.