• The Italian scientist Fracastorius (1485-1553), understood the concept of disease and postulated that the disease is transmitted by individual particles or seeds from one person to another.
• Anton van Leeuwenhoek (1685), with his microscope, that was little over 2 inches, described the existence of microbes. In his letter to the Royal Society of London, September 17, 1683, described may little life forms those can't be seen with out a microscope.  

Although people understood about the existence of microbes, but could not be related to the diseases, till 1857.