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But where did the mold come from? Most likely, the mold came from La Touche's room downstairs. La Touche had been collecting a large sampling of molds for John Freeman, who was researching asthma, and it is likely that some floated up to Fleming's lab.
Fleming continued to run numerous experiments to determine the effect of the mold on other harmful bacteria. Surprisingly, the mold killed a large number of them. Fleming then ran further tests and found the mold to be non-toxic.
What does "floated up" mean? Did the mold float up from the room downstairs to his room through the floor?