Even in ancient occasions individuals are unaware in the existence of https://www.essaystone.com/ living organisms invisible to the eye, causing illness. Thus, the ancient Greek scientist and physician Hippocrates expressed this assumption in one of his works. But come to grips with their study of mankind has been in a position only following the Dutch optician van Leeuwenhoek in the XVI century created the first microscope and saw firsthand the bacteria inside a drop of water. Having said that, many inside the class scientist denied the existence of pathogens inside several centuries following the invention of Leeuwenhoek.