Scientific Method
Yes, people really do use it!
Spanish-American War, late 1800’s
• US soldiers were stationed in Cuba
• More soldiers died of Yellow Fever (YF)
than bullets
• Symptoms of yellow fever:
– Fever
– Nausea
– Muscle pain
– Vomiting blackened blood – “the black vomit”
– Ghastly yellow skin - jaundice
Death Wagon
The Reed Commission
US Army Yellow Fever
Commission
Post Spanish-American War
research in Cuba
Walter Reed
• Knew: old way to fight
disease
– Isolate sick
– Boils clothes, sheets
– Sterilize plates, cups..
• Realized: The
disease was still
spreading
Army Research Doctor
Findlay’s hypothesis
• Carlos Juan Findlay,
Cuban doctor
• Thought disease was
spread by mosquitoes
– Had been saying it for
20 years
– Called “The Mosquito
Man”
• Most people did not
believe this
Reed’s Experiment
• Group 1
• 20 days
• used filthy clothes,
sheets, utensils of
infected YF soldiers
• Protected from
mosquitoes with
screens
Aedes Theory – mosquito genus
• Group 2
• 20 days
• Used fresh clothes,
clean sheets, utensils
• Isolated from infected
YF soldiers
• Not protected from
mosquitoes
• 3 doctors joined this
group
Formites Theory – touching infected stuff
Results
• Group 1 – no one developed yellow fever
• Group 2 – many including all 3 doctors (1
died) became sick
• US pulled out of Cuba (republic of Cuba)
left a naval base - Guantánamo Bay
(1901)
• Once the disease was under control in
Panama, the US began considering
building the Panama Canal.
Yellow Fever Quarantine
Bottom Line
• Science requires much more than
observation. Scientists must develop
explanations for their observations and
then use the scientific method to TEST
those observations.
• What steps to the Scientific Method can
you identify in the Yellow Fever
problem?
Scientific Method? Time to
create our notes.
• Problem identified
• Developed a hypothesis
• Identify independent (manipulated) & dependent
(responding) variables
• Establish a control group
• Experiment & test your hypothesis
• Record & organize your data/what you see-pictures, graphs, measurements
• Statement about what happened---conclusion
• Inform/communicate your findings
Independent (manipulated) & Dependent
(responding) Variables
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•
•
•
•
•
Manipulated variable is what you change
Responding variable is what you measure
Listen to the tomato plant example
Identify each variable and constant
Make a space on your paper for each
You and your lab partners must determine
which parts are variables and constants
The tomato plants
• 12 tomato plants were grown in 48” pots
• Each plant received the same light & water for 8
weeks during the summer
• 3 plants received nitrogen fertilizer
• 3 plants received compost tea
• 3 plants received P-N-K fertilizer
• 3 plants were not fertilized
• Weekly heights were measured
• Number of fruits were collected