Germ theory of disease

The germ theory of disease, also called the pathogenic theory of medicine, is a theory that proposes that microorganisms are the cause of many diseases. Although highly controversial when first proposed, it is now a cornerstone of modern medicine and clinical microbiology, leading to such important innovations as antibiotics and hygienic practices.

The ancient historical view was that disease was spontaneously generated instead of being created by microorganisms which grow by reproduction. One of the earliest references to this theory appears in On Agriculture by Marcus Terentius Varro wherein there is a warning about locating a homestead in the proximity of swamps which reads "...and because there are bred certain minute creatures which cannot be seen by the eyes, which float in the air and enter the body through the mouth and nose and there cause serious diseases."