A poor boy was selling goods from one door to another to pay for his studies. One day he found that he had almost no money, and he was hungry. So he decided to ask for a meal. But when a woman opened the door, he only dared to ask for a glass of water. To his surprise, she gave him a large glass of milk. He drank it and then asked how much he should pay her. She said, "You don't have to pay me anything. Mother has taught us never to accept pay for a kindness" He was deeply moved and was determined to help those in need. The boy's name was Howard Kelly. Many years had passed. One day that woman became seriously ill. The local doctors could not help her. So they sent her to a big city where her rare   disease would be studied by specialists  . Dr. Howard Kelly was called in for advice. When he entered her room in the hospital, he immediately spotted the woman. Howard Kelly was determined to do his best to help her. The struggle was long, but together they succeeded in the end. After some time the woman received a bill for her treatment. She was worried that the amount would be so large that it would take the rest of her life to pay for it. However, when she looked at the bill, she found words on the side of the bill. They were, "Paid in full with a glass of milk." The woman came to a big city because  _  .
she was ill and no local doctors could help her she was invited by a group of specialists to a study she wanted to visit the poor boy whom she had helped her rare disease could only be dealt with by Dr. Howard Kelly