Michael, a 3-year-old, experiences a chronic middle-ear infection, which is common among youngsters, in part due to an increase in antibiotic-resistant bacteria. This year, despite antibiotic treatment, an infection became so advanced that he had trouble hearing. Then his left eardrum ruptured and a jellylike substance dribbled out. The pediatrician told Michael’s parents not to worry, that if the eardrum had not ruptured on its own she would have had to drain it. Suggest a reason why the physician concluded that this procedure would have been necessary to cure Michael’s problem.