Complex sentence: Toxemia often refers to bacterial infections, which were more often fatal in the 1920s than now, before anti-biotics, which didn't emerge as a life-saving medical treatment until the late 1930s, starting with penicillin.
Split into simpler sentences: Toxemia often refers to bacterial infections, which were more often fatal in the 1920s, before antibiotics, than now. Antibiotics didn't emerge as a life-saving medical treatment until the late 1930s, starting with penicillin.