1. How has our understanding of the causes of disease changed over time?


The way that people have explained how contagious diseases are caught and transmitted has changed considerably over time.

Contagious diseases are passed from person to person.

In the 4th century BC Hippocrates, a Greek physician who is often called the “Father of Medicine”, wrote about diseases being imbalances of blood, phlegm, black bile and yellow bile in the body. Too much or too little would cause disease. Patients would be given certain foods to make them vomit or have blood taken from them to restore the levels of these liquids in the body. Medicine was based on these ideas until the 1800’s.

More on: Medicine in the Middle Ages

The Middle Ages was a grim time to be poorly. In the 1350s, the average life expectancy was perhaps 30-35. Infant mortality was extremely high where 1 in 5 children died before their first birthday and many women died in childbirth. Treatments continued to be a mixture of herbal remedies, bleeding and purging, and supernatural ideas.


Most doctors believed the Greek theory from Galen, a doctor during the Roman Empire, that you became ill when the 'Four Humours' - phlegm, black bile, yellow bile, blood - became unbalanced.

They believed in many different explanations for ill health, some of which were associated with the supernatural. For example, the will of God, the stars, demons, sin, bad smells, charms and luck, witchcraft or astrology.

During epidemics, people would blame witches, nobility or groups who were culturally different such as Jewish people, and attack them. When a disease like the Black Death hit England in 1348, the doctors were powerless to stop it killing half the population. There were both supernatural and natural explanations for it, for example, some people said that God had sent it as a punishment, others that the planets were in the wrong conjunction, or that it was caused by 'foul air'.

Recently, historians have suggested that many medieval treatments were successful, especially the herbal remedies. Nevertheless, there were other types of cures used in the Middle Ages that many people would not consider today. For example:

bleeding, applying leeches, smelling strong posies or causing purging or vomiting

cutting open buboes, draining the pus and making the patient hot or cold, eg by taking hot baths

trepanning - cutting a hole in the skull

praying, or whipping themselves to try to earn God's forgiveness

lighting fires in rooms and spreading the smoke, tidying rubbish from the streets and banning new visitors to towns and villages

In the early 1800’s it was then thought that contagious diseases were caused by “bad air”, which were bad smells that came from rotting things. It was not believed that these diseases were passed from person to person. Keeping the air smelling fresh would prevent you from becoming sick.

Florence Nightingale, a British nurse who revolutionised nursing in the 1800’s believed in this theory and worked hard to keep hospitals fresh-smelling. The artists picture to the left is showing cholera (an illness that can cause diarrhoea so severe the person dies) as a robed skeleton emitting a deadly black cloud.

More on: The 19th Century American Country Doctor

During this time, there were significant scientific discoveries such as William Harvey's discovery of the circulation of the blood in 1628, and Anton van Leeuwenhoek's observation of bacteria in 1683. However, despite these discoveries:

doctors still did not know that germs caused disease – until the middle of the 19th century, they blamed a 'miasma' (a bad smell)

doctors were too expensive for most people

In the face of an infectious disease like the Great Plague of 1665, doctors were powerless.


Many people resorted to using quack doctors (someone without real medical knowledge or qualifications) and crazy cures:

A lot of treatment was about making the room and the patient smell nice (doctors wore full body suits – with a 'beak' that was crammed with herbs – so that they wouldn't smell a bad smell).

Explorers found some new drugs in America (eg quinine), but doctors didn't know how or why they worked. Tobacco was said to cure everything from wind to snake bites.

They continued superstitions such as 'touching for the king's evil' (they thought the touch of a king would cure the skin disease scrofula).

After 1880 doctors changed their thinking and came up with the now accepted theory that micro-organisms (viruses and some bacteria and fungi) cause some diseases and illnesses. These disease causing micro-organisms are called pathogens.

We now know that cholera is caused by a bacteria, Vibrio cholera.


Pathogen: A microorganism that causes disease.

Microorganism: A small living thing.

Contagious: A disease or illness that is able to be passed from person to person.

Transmitted: When a disease or illness is spread from one person to another.