MIASMA THEORY

• The miasmatic theory of disease held that diseases such as cholera or the Black Death were caused by a miasma (Greek language: "pollution"), a noxious form of "bad air".

• Miasma is considered to be a poisonous vapor or mist that is filled with particles from decomposed matter (miasmata) that could cause illnesses and is identifiable by its nasty, foul smell (which, of course, came from the decomposed material).

• A representation of the cholera epidemic of the nineteenth century. Before 1830 cholera was unknown in the western hemisphere. It became one of the most feared epidemic diseases of the nineteenth century.

• Dr. William Farr, then assistant commissioner for the 1851 census and a career employee of the government's General Register Office.  For a while, Farr was convinced that cholera was transmitted by air. He reasoned that soil at low elevations, especially near the banks of the River Thames, contained much organic matter which produces miasmata.  The concentration of such deadly miasmata would be greater at lower elevations than in communities in the surrounding hills.  His calculations in 1852 seemed to support this theory.

Explanation: Observed mortality rates for cholera are very similar to what would be expected based on a predictive formula derived by William Farr (dotted line).  Farr felt that the statistical relationship supported his miasma theory. Later it was shown that the finding was coincidental, with more access to contaminated drinking water at lower elevations

GERM THEORY• The alternative theory, supported by John Snow, held that cholera

was caused by a germ cell, not yet identified.  He reasoned that this germ was transmitted from one person to another by drinking water. Snow's germ theory was deemed "peculiar" by John Simon, head medical officer of London, but has since met the test of time.  What was this peculiar theory? 

• Here is a summary written by Dr. Simon:• "This doctrine is, that cholera propagates itself by a ‘morbid matter'

which, passing from one patient in his evacuations, is accidentally swallowed by other persons as a pollution of food or water; that an increase of the swallowed germ of the disease takes place in the interior of the stomach and bowels, giving rise to the essential actions of cholera, as at first a local derangement; and that ‘the morbid matter of cholera having the property of reproducing its own kind must necessarily have some sort of structure, most likely that of a cell." 

• While Dr. Simon clearly understood John Snow's theory, he joined others in questioning the relevance of the germ theory to cholera

• 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 Ghost Map

• Snow movie trailer

• Dr. John Snow

Paradigms or beliefs as knowledge filters

Impossibility of seeing the world with ‘clean’ eyes.

Paradigms can help us to organise our beliefs into more meaningful patterns, the danger is that they can act as knowledge filters. They can trap us into particular ways of looking at things and can close our minds to other ways of looking at things.

“To a person with a hammer everything looks like a nail”

When you buy a certain car you begin to notice them everywhere

When you are expecting a baby you

see pushchairs everywhere