Complex sentence: They noted that a glycerin-bile-potato mixture grew bacilli that seemed less virulent, and changed the course of their research to see if repeated subculturing would produce a strain that was attenuated to be considered for use as a vaccine.
Split into simpler sentences: They noted that a glycerin-bile-potato mixture grew bacilli that seemed less virulent. They changed the course of their research to see if repeated subculturing would produce a strain that was attenuated to be considered for use as a vaccine.