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 • 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