1658

Using a 32-power microscope, in his Scrutinium Pestis, the Jesuit priest Athanasius Kircher described microscopic “worms” in plague victims, which he suspected caused the disease. Most likely, he was viewing pus cells, or perhaps red blood cells. Twelve years earlier, in 1646, he had written that “a number of things might be discovered in the blood of fever patients”  (Hajdu).