Complex sentence: Bartholow worked with practitioners of allopathic, homeopathic, and eclectic medicine, and he used ideas from each in his research and in his own practice, which grew to be the largest in the city.
Split into simpler sentences: Bartholow worked with practitioners of allopathic, homeopathic, and eclectic medicine, and he used ideas from each in his research. He also created his own practice, which grew to be the largest in the city.