Complex sentence: The eight doctors in the town, who belonged to the Donora Medical Association, made house calls much like the firefighters during the period of intense smog, often visiting the houses of patients who were treated by the other doctors in town.
Split into simpler sentences: The eight doctors in the town, whom belonged to the Donora Medical Association, made house calls, much like the firefighters, during the period of intense smog. Often visiting the houses of patients whom were treated by the other doctors in town.