Humours and Miasma: Science in Society 8.

Humoral theory and miasma theory: two long-lasting medical paradigms now consigned to the history of human error but which shaped our ideas about health and disease and the development of medical practice and public health for many centuries.

Humoral theory

The theory of humours was one of the main paradigms for understanding health and disease for many centuries going back to ancient Chinese and Indian Ayurvedic traditions but it didn’t survive the scientific and experimental approach to medicine which became dominant the 19^th century.

The theory takes its name from the word ‘humours’ meaning fluids. Health was thought to come from the proper balance of four ‘humours’ or fluids in the body; black bile (also known as melancholy), yellow bile, blood, and phlegm. Anything that upset the equilibrium between these humours, such as a change in the weather, could lead to disease.

The theory was formalised by Hippocrates (ca. 460–370 BCE) and built on by Arabic doctors such as Ibn-Sinna (‘Avicenna’) and  al-Razi (‘Rhazes’) in the 9th century. It was also used to explain human temperament through four main personality types connected to the humours and caused by an excess of one or another: melancholic, sanguine, choleric, and phlegmatic.

Each humour was associated with properties of hotness, coldness, dryness, and wetness as well as one of the four seasons.

Blood: Sanguine temperament (active, energetic, robust), associated with Air and Spring.

Yellow bile: Choleric temperament (decisive, ambitious, quick to anger), associated with Fire and Summer.

Black bile: Melancholic temperament (thoughtful, reserved, suspicious), associated with Earth Autumn.

Phlegm: Phlegmatic temperament (peaceful, lazy, quiet) associated with Water and Winter.

Each individual’s humoral balance was connected with other phenomena—such as climate, diet, occupation, location, planetary alignment, sex, age, and social class. The combined holistic effect of these might differ between individuals. Humoral treatments, or regimens, were designed to restore the proper humoral balance through bloodletting, enemas or purges, diet and lifestyle changes and by individualised medications. Doctors relied on personal knowledge of their patient and the inspection of blood, urine, and other fluids produced by the body; and on the patient’s description of their symptoms.

The appeal of the humoralism which dominated medicine and formed its heritage lay in its comprehensive explanatory scheme, which drew upon bold archetypal contrasts (hot/cold, wet/dry etc.) and embraced the natural and the human, the physical and the mental, the healthy and the pathological. While reassuringly intelligible to the layman, it was a supple tool in the hands of the watchful bedside physician and open to further theoretical elaboration.

From chapter 2 ‘Doctors’ from ‘Blood and Guts’ by Roy Porter (2002).

18th century depiction of the 4 temperaments

Miasma theory

Miasma theory was the principal paradigm of the spread of disease across many parts of the world for thousands of years. Miasma was the name given to poisonous and foul-smelling ‘bad air’ or ‘night air’ arising from decomposed matter and containing ‘miasmata’ coming from soil and other non-human sources. Disease was assumed to arise from this foul air rather than passing between individuals. This belief gave priority to ventilation and exposure to ‘fresh air’ as preventative measures. For example, the war nurse, Florence Nightingale (1820–1910) based her efforts to make hospitals sanitary and fresh-smelling on miasma theory.

In the early nineteenth century, belief in miasma theory led people to fear fog which was thought to indicate the presence of miasma. Some people regarded miasma as being able to completely alter the properties of the air.

By the 19^th century the medical community was split on the question of how disease was spread. Believers in miasma theory thought that disease could proliferate without physical contact while ‘contagionists’ believed that disease was transmitted through physical contact. At this time, the living conditions of Britain’s crowded cities in were very unsanitary and there were regular outbreaks of fatal diseases such as cholera. Miasma seemed to explain the spread of cholera and other diseases in places where the water was undrained and very foul-smelling, such as the banks of the river Thames with its presumed concentration of deadly miasmata.

The wide acceptance of miasma theory during the cholera outbreaks overshadowed the findings of London doctor, John Snow (1813-1858) who made the connection between cholera and typhoid epidemics and contaminated water sources, suggesting that there was some means by which the disease was spread from person to person via what he called a ‘morbid material’ in the water supply. During the cholera epidemic of 1854, Snow traced high mortality rates among the citizens of Soho to a water pump in Broad Street. Snow convinced the local authorities to remove the pump handle and this led to a marked decrease in cholera cases in the area.

Sanitary reformers wanted to reduce the spread of disease and improve public health and proposed reform on the basis of miasma theory. Their proposals contributed to major improvements in drainage and sewage systems which did lead to a reduced incidence of cholera and actually helped to support miasma theory for a while. Miasma theory was consistent with the observations that disease was associated with poor sanitation and the associated foul smells. However, it was not consistent with the findings of experimental microbiology which were to lead to the germ theory of disease.

By the late 19^th century, there was enough scientific evidence to support a germ theory of disease transmission which accounts for disease proliferation by both direct and indirect physical contact. In 1876 the German microbiologist Robert Koch (1843-1910) proved beyond doubt that anthrax was caused by a bacterium and in 1884, working in Bombay (Mumbai), he was able to isolate the bacterium which causes cholera. These discoveries brought a decisive end to miasma theory.

Even though miasma theory was comprehensively disproved by the discovery of pathogenic bacteria, and later viruses, it did help to make the connection between poor sanitation and disease and led to public health reforms and encouraged good sanitation measures.

A cholera epidemic depicted as miasma

Questions:

1. Why do you think these paradigms remained dominant for so long?

2. Humoral theory is no longer the basis for our understanding of health and disease. Are there any aspects of its application which can be related to modern medical practice?

3. ‘Miasma’ theory is no longer used as an explanation for the spread of infectious disease and was overtaken by the germ theory in the late 19^th century. Are there any cases of the two theories being compatible with each other?

4. Choose one of these statements to explain:

(a) Despite being wrong, miasma theory helped to promote public health.

(b) In science, every incorrect theory contains the seeds of a more accurate one.

See also:

How we do science – Science in Society 3: developing and testing scientific explanations.

Introduces the idea of paradigms or scientific belief systems and includes the story of Ignaz Semmelweis.

The germ theory of disease – Science in Society 6: Pasteur, Koch and the microbe hunters.