there are bred certain minute creatures which cannot be seen by the eyes, but which float in the air and enter the body through the mouth and nose and cause serious diseases
https://en.wikipedia.org/wiki/Marcus_Terentius_Varro
ref https://www.reddit.com/r/todayilearned/comments/clrxda/til_a_roman_scholar_predicted_microbiology_over/
origin - https://www.pipiscrew.com/?p=15156 a-roman-scholar-predicted-microbiology-over-2000-years-ago