听力原文： The classic case in medical history of a typhoid carrier is that of Mary Mallon. During a New York typhoid epidemic she was found working as a cook and thus very readily spread the disease to others. She persisted in finding employment as a cook both in private service and in various institutions. She even changed her name to avoid detection. For eight years she continued to carry and spread typhoid wherever she went. Finally she was made to live in a hospital. There her work could be regulated so that she did not pass on typhoid. She lived in hospital for twenty-three years, until her death in 1938. For thirty-one years she had been a known carrier of the disease without herself suffering any ill effects. (30)