When Mr. Gilmer examined Heck Tate, Heck told the jury that Bob Ewell had "fetched" him, and he went as quickly as he could to find Mayella lying on the floor. She was beaten pretty badly. He asked her who beat her, and she said Tom Robinson did.
When it's Atticus' turn, he asks the same question 3 times to make a very valid point. "Did you call a doctor, Sheriff?" He does this point out that there was no evidence of Mayella being raped. Tom was on trial for raping her, not beating her. She did not go to the doctor; therefore, there was no evidence of rape. The second piece of information that was so important was how Mayella was beaten. It was her right side that was beaten so badly. Atticus made sure that Heck was certain of that side. Heck repeated this several times as well. They were making it as simple as they could for the jury. This is significant because Tom has no use of his left hand. That means he could not have been the one to beat her, either.