Scrutinium physico-medicum contagiosae luis, quae pestis dicitur.

Kircher, a Jesuit scholar and polymath, not specifically trained in medicine, was probably the first to employ the microscope in investigating the cause of disease. He mentioned that the blood of plague patients was filled with a “countless brood of worms not perceptible to the naked eye, but to be seen in all putrefying matter through the microscope” (Garrison). He could not have seen the plague bacillus with his low-power microscope, but he probably saw the larger micro-organisms. He was the first to state explicitly the theory of contagion by animalculae as the cause of infectious diseases.