The miasma theory held that diseases like cholera and the Black Death were caused by polluted air called miasma. Miasma was thought to be a poisonous vapor or mist filled with particles from decomposed matter that caused illness and had a foul smell. John Snow supported the germ theory that cholera was caused by an unidentified germ cell transmitted through drinking water, not miasma. His theory was initially seen as peculiar but is now accepted.

4. 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).

5. • 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.

6. • 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.

7. 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

9. 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

10. • 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.

11. • The Ghost Map
• Snow movie trailer
• Dr. John Snow

12. 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