Lazzaro Spallazani noted a flaw in Needham’s experiment. The containers holding Needham’s beef broths had not been sealed upon boiling. So Spallazani modified Needham’s experiment, boiling infusions, but immediately upon boiling he melted the necks of his glass containers so that they were not open to the atmosphere. The microbes were killed and did not reappear unless he broke the seal and again exposed the infusion to air.