Case Study- Germ Theory

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The Rabbit Island Experiment
Tuberculosis Treatment
Tuberculosis
• Tuberculosis is an infectious disease that has plagued
humankind for most or all of its history.
• Evidence of the disease has been found in mummified
Egyptian and Peruvian remains from as early as 4000 years
ago.
• The pathogen, Mycobacterium tuberculosis (MTb), was
identified in 1874 by Robert Koch, a Prussian scientist who is
frequently hailed as the father of infectious disease and the
germ theory of infection.
• MTb is a relatively slow-growing bacteria. Its waxy outer coat
provides a physical protection against immune defense
• Only about one in three people exposed to the bacteria
actually develop tuberculosis, due to differences in genetic
susceptibility/resistance genes of the host, and probably
due to differences in actual dose received
• Recovery, progression, and death rate vary from individual
to individual.
• The bacteria is introduced most typically through
inhalation of microbes
• Port of entry is typically the lungs, where infection may in
some cases be resolved by the host immune system, but in
other cases there is difficulty in slowing or stopping the
doubling of the invading microbe inside host macrophages.
The Rabbit Island Experiment
• Please Read The Rabbit Island Experiment
• Highlight any important information as you go
• Circle any new or unknown vocabulary
Common Belief
• TB was caused by “bad blood” (genetics)
• Or was caused by dank conditions such as
obnoxious smells and “bad air”
Discovery!
• In 1882, Robert Koch discovered that TB was
caused by the bacterium Mycobacterium
tuberculosis
• He could grow it in the lab, and infect animals
• This lead to the “Germ Theory” of infection
which stated that infectious diseases were
caused by germs
The Rabbit Island Experiment
• Dr. Trudeau gets TB after caring for his sick
brother
• He knew that a large number of people who
get TB die
• In NY where he lived, most people came home
to inadequate housing, food, ventilation,
sanitation, and little to no relaxation time
He’s dying….Oh wait….
• He moved to the wilderness of upstate NY
• After a while he got better!
• He began to think of the cause and cure for TB
Dr. Trudeau’s Experiments
• Was intrigued by the correlation between
healthy outdoor lifestyle and decided to
develop an experiment to test his hypothesis
Experiments
• 1. Infected rabbits + cramped conditions/no
light/no fresh air/no exercise/not enough food
• 2. Healthy rabbits+ cramped conditions/no
light/no fresh air/no exercise/not enough
food/damp
• 3. Infected rabbits+ sunshine/fresh/air/plenty
of food/exercise
Results
• Group 1: 20% survival
• Group 2: 100% survival
• Group 3: 80% survival
What do these results tell us?
Homework Assignment
1. Describe the results of the experiment.
2. Use your results to write an overall conclusion to the
Rabbit Island Experiment
3. Develop an answer to each of Dr. Trudeau’s questions
4. Do his results support the germ theory of infection?
Why or why not?
5. What does the data suggest might be good
environmental conditions for TB patients?
6. What might be the effect of crowding on effective
exposure rate of individual animals to the MTb
bacteria?
7. What dependent variable in the Rabbit Island
Experiment. Also, list all of the ID variables you can think
of in the experiment.
8. Select any one of the ID variables you have listed and
design an experiment similar to Dr. Trudeau’s. State your
experimental question (What are you trying to find out)?
Formulate a hypothesis, how will you manipulate your
treatment groups? Then imagine possible outcomes.
9. What would you have changed about the Rabbit
Island Experiment?
10. If you were the mayor of NYC in the 1890s, and
knew of Dr. Trudeau’s experiments, what sort of public
policies might you try to enact in order to combat the
public health menace? What obstacles might you
encounter

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