Science in Society 1
The germ theory of disease
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The story of Ignaz Semmelweis
Women are vulnerable of infections after giving birth. Hospitals were set up for the delivery of infants.
They were mainly used by the poorer women who could not afford medical care in their own homes.
1 5 of the women who gave birth to a baby in the hospitals of European cities died from puerperal
fever/childbed fever.
Symptoms:
 Severe pain
 Tenderness abdomen
 Rapid pulse
 High fever
 Inflammation womb
 Vomiting
 Convulsions
Which eventually could lead to death.
The risk of fever rose but it depended on who delivered the baby. Ignaz Philipp Semmelweis was a
Hungarian physician, who is known for gathering scientific evidence to show how the disease spread.
Semmelweis’s evidence and idea
Semmelweis found out that the disease was spread by an infectious agent. He insisted that his student
wash their hands in chlorinated lime between each patient. He spread his ideas but met with strong
opposition.
Opposition to Semmelweis
It was hard for doctors to admit that they themselves had spread the disease and killed their patients
instead of curing them. The disease was caused by a transferable agent. Getting water was not easy and
chlorinated lime would eventually damage the skin of the hands. Semmelweis had a major breakdown. He
died from an infection at the age of 47.
Cholera in London.
A new disease
Cholera:
 Severe stomach pain
 Produce vast amounts of watery diarrhoea
 Sometimes vomit
The disease spread quickly.
Most people who suffered from cholera:
 Were poor
 Lived in large towns
 Lived in overcrowded homes
 Had poor sanitation.
Doctors thought the disease was spread by touch or bad air (miasma).
John Snow came to the conclusion that cholera was caused by a poison, which reproduced in the human
body and was found in vomit and diarrhoea of cholera patients. His hypothesis was that ‘disease is
communicated by something that acts directly on the alimentary canal. The excretions of the sick at once
suggest themselves as containing some material which being accidentally swallowed might … multiply
itself.’ He published a pamphlet with an explanation for the killer disease but it was largely ignored.
The Broad Street pump
Another cholera outbreak hit London in 1854. In a small neighbourhood John Snow saw that they all got
their drinking water from the same source – the Broad Street pump. When he persuaded the panicstricken local officials to have the handle removed, the epidemic was contained and began to subside.
Snow also studied a region of South London where houses in the same streets were supplied by
two separate water companies. The people who were supplied by the Vauxhall Water Company were far
more likely to develop cholera. The water supplied came from the lower Thames, after it has passed
through London and received most of the city’s sewage.
Epidemiology is the branch of medical research which unravels the causes of disease by
gathering data from large samples.
Pasteur and microbes
The work of Semmelweis and Snow led to the acceptance of the idea that infectious diseases are brought
about by an infectious agent which is transferred from one individual to another and causes disease. Two
people are now remembered for their part in establishing the theory, Louis Pasteur (French scientist) and
Robert Koch (German doctor).
Pasteur was born in 1822 and lived until the age of 72. He was interested in fermentation and the new
theory was that fermentation was caused by microscopic yeast cells and was not simply a chemical
reaction. Pasteur produced the evidence to persuade the people that the theory was correct, as a result he
became very interested in microbes and where they come from.
At the time there was a widespread belief that living things could arise from dead things, this was
the theory of spontaneous generation. In 1859 Pasteur decided to join the debate. His experiment
showed that the microorganisms which grew in broth, turning it cloudy and mouldy, did not appear by
spontaneous generation but were already present in the air.
In 1866 Pasteur was asked to investigate killer diseases that were destroying large numbers of
silkworms. By keeping the healthy eggs away from all the contact with living silkworms he made sure that
the eggs would produce moths free of disease. The infected silkworms were identified by Pasteur’s careful
observations.
He found out that healthy worms became infected when allowed to nest on leaves used by
infected worms and some worms died shortly after infection, others weeks later and some not at all.
Koch and bacterial diseases
Koch devised the techniques for growing cultures of bacteria on agar jelly. He also worked out how to
study bacteria by using dyes to stain them on glass slides, so they could be seen and recognised under a
microscope. With these methods he found out the cause of 11 diseases, including:
 Anthrax (1863)
 Tuberculosis (1882)
 Cholera (1883)
Koch investigated the conditions which would stop the germs from reproducing. In 1905 he was awarded
the Nobel prize for Medicine. By the end of the nineteenth century the idea that infectious diseases were
caused by germs was almost universally accepted.
Resistance to infection
Success in curing the diseases depended on social action by politicians and others to relieve poverty and
improve housing.
Sanitary engineers  installed piped water supplies and constructed enclosed sewers.
Nutritionists  research which helped to develop guidelines for the diet of children.
This greatly cut down the deaths from infectious diseases.
Ways in which the human body defends itself against infection:
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Tears contain an enzyme which destroys microbes.
Mucus traps microbes and tiny hair sweep the mucus op to the throat.
Acid in the stomach kills microbes on food.
Unbroken skin prevents microbes entering the body.
Blood clots seal a break in the skin while the wound heals.
Immunisation
It is known that once someone has had smallpox the cannot catch the disease again. This led to
experiments. The first people tested were criminals from Negate prison. This method of immunisation
was made illegal in England by 1840.
Jenner and cowpox
Edward Jenner, who was a doctor practising medicine, was told by the local farmers that the girls who
milked the cows often suffered from the mild disease cowpox but rarely caught the more severe and often
fatal smallpox. Jenner tested the theory that deliberately infecting people with cowpox would protect
them from smallpox. He took pus from cowpox spots and scratched it into the arm of James Phipps, a
healthy boy. The boy recovered from cowpox and two months later Jenner scratched pus from the spots of
someone suffering from smallpox into the boy’s arm. The boy did not develop smallpox.
Jenner had shown that infecting someone with a mild disease could give protection against a fatal
illness. The pus from the cow was the first example of vaccination (Latin name cow  vacca).
Pasteur and chicken cholera
In 1879 Pasteur was studying a disease called chicken cholera. He and his assistant were injecting healthy
chickens with the bacteria and showing that microbes grown outside the body did infect healthy chickens
so that they rapidly became ill and died.
By mistake an assistant injected a batch of chickens with a culture of microbes which they had
grown but had then left standing for several weeks. The chickens were ill for a time but then recovered,
when the chickens were given a second injection – this time using freshly grown microbes, the birds
stayed healthy.
The microbes which had stood over the holiday had become weakened. Pasteur had discovered
the basis of vaccination using a weakened (attenuated) form of the infective agent.
Pasteur and anthrax
Following his work on chicken cholera, Pasteur set out to develop a vaccine for anthrax, a disease of
animals which is highly infectious. Pasteur showed that an infectious agent was being brought up from the
buried corpses by worms.
Louis Pasteur had suffered a very severe stroke. Although he recovered and his mind was
unaffected, his speech, gait and ability to use his hands were never the same again. Pasteur had to rely
heavily on his team of trusted fellow scientist to carry out the experiments he dreamed up.
Robert Koch had developed a way of culturing anthrax spores. Pasteur immediately used this new
technique to grow anthrax bacteria but none of the methods he attempted seemed to give reliable results.
Toussaint, a young vet, claimed to have produced a successful vaccine using a different method.
Pasteur claimed that it was unreliable and announced his own vaccine was on the way. Pasteur kept the
anthrax bacteria warm and after eight days the microbes were much weakened and were no longer fatal.
Rossignol, a vet, threw down a very public challenge to Pasteur. Pasteur accepted the challenge,
although he was not sure if his vaccine would work.
The trial took place at Pouilly-le-Fort. A crowd gathered and found all the vaccinated sheep alive
and all the unvaccinated sheep dead or dying.
The vaccination had a major effect on farming for generations to come – but the confirmation of
the germ theory of disease was to have even greater implications for the health and wellbeing of people all
over the world.
Pasteur and rabies
Pasteur and his assistants had developed a technique of vaccination to protect dogs from rabies. They
discovered that they could prepare an effective vaccine by drying out parts of the spinal nerves from
rabbits which had been infected with rabies.
When a rapid dog bites people they develop a fatal disease, hydrophobia. In 1885 a young boy
was bitten by a rapid dog. His mother brought him to Pasteur. Pasteur knew that if they did nothing the
boy would die. They vaccinated the boy and he survived. This success brought many others in search of a
cure. Not all those who were treated survived, mostly because they were vaccinated too long after they
had been bitten.
This was the first example of a laboratory-based medical breakthrough which became a major
news story. His work on rabies led to the creation of the Pasteur Institute as a centre of research.