Even in ancient occasions individuals are unaware in the existence of living organisms invisible towards the eye, causing disease. essaystone As a result, the ancient Greek scientist and doctor Hippocrates expressed this assumption in one particular of his operates. But come to grips with their study of mankind has been able only following the Dutch optician van Leeuwenhoek within the XVI century made the initial microscope and saw firsthand the bacteria inside a drop of water. Nonetheless, a lot of in the class scientist denied the existence of pathogens inside a handful of centuries after the invention of Leeuwenhoek.