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

• 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 stuffAedes Theory – mosquito genus

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

• 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