There is really no way to overstate the importance of Girolamo Fracastoro's bold
about the roots of infection. His idea that infections were caused by "seeds," living things unseen to the naked eye, was followed by deductions that included the spread of contagion, incubation periods, the organs affected by particular infectious agents, the vulnerable age for a particular disease, the idea that a survivor of an infection is protected against future infections, the ability of a disease to pass from mother to child through nursing, and many other valuable observations. His genius, while respected and supported, was not definitively proven until over 100 years later, with the advent of the microscope.