When Snow started his investigations into the cause of cholera, he believed contagion was the main cause for many if not most infectious diseases. Farr and Nightingale, on the other hand, believed disease arose from a relationship between social conditions and generation of miasma. Remember, the miasma theory was the idea that heavy airborne molecules given off by rotting filth and infected people were the cause of zymotic disease. It was thought that these particles entered the lungs and then proceeded to the bloodstream where they multiplied and caused sickness and disease. Of course, Snow was right and Farr was wrong but it was not until he thoroughly studied cholera after Snow’s death that Farr abandoned his belief in the miasmic theory of epidemics. Question – Can you think of any other theories of health or disease that have changed during your lifetime?
