We take for granted the knowledge that infection is caused by microscopic organisms. But the road to this scientific truth has been long and winding, and medical professionals have taken some pretty odd detours along the way. Hindsight being 20/20, we can examine this path and see the seeds - or germs - of germ theory as we know it today.
There's Something in the Air
The first recorded theory in Western medicine about the cause of disease was written by Hippocrates of Cos (of the Hippocratic Oath) around 400 BCE. He rejected supernatural explanations for disease and instead proposed that illness was caused by the patient's environment: climate, soil, water, lifestyle, nutrition, and other natural causes.
His proposal that "poisonous vapors" or "bad air" was the root cause of disease was actually a theory that sprung up all around the world, found in the writings of all of the major ancient civilizations. Called the miasma theory of disease, this idea, expressed with little variation around the world, involved the spreading of disease from the air expelled from rotting materials. The miasma theory centers around the "bad air," miasma, that carries tiny contagious particles, miasmata, which transfer infection between individuals. Illness was putrefaction passed to living things. This makes sense when one considers the symptoms of many infections and diseases: Pus, vomiting, diarrhea - all noxious stuff. This theory would persist for hundreds and hundreds of years.
Looking back at this early theory, it is not difficult to imagine these early scientists, separated by thousands of miles and sometimes thousands of years, arriving at the same conclusion after observing sickness tending to occur around dirty water, refuse, rotting food, or decomposing animals. They were definitely on the right track. All they needed was some data and a closer look.
In part 2 we will explore how these unknown, invisible miasmata brought humanity to its knees as plagues swept the globe.
Editor's Note: This post was originally published in September 2015 and has been updated for freshness, accuracy and comprehensiveness.