The Scientific Method and Yellow Fever
Genuine science requires much more than observation. Scientists must develop
explanations for their observations, then use the scientific method to test those explanations.
Why has science become so important in our lives? In part, because the scientific
method has proved to be effective in solving one problem after another.
The Fight Against Yellow Fever
During the Spanish-American War of the late 1800’s United States soldiers fighting
in Cube faced an especially deadly problem-an enemy far more terrifying than the Spanish
soldiers they were defeating on the battlefields. This enemy was yellow fever, a disease well
known in tropical Central and South America. Before the smoke of battle had cleared,
United States troops were suffering from fever and nausea, vomiting black liquid, and their
skin had turned a ghastly shade of yellow, which gave the disease it name.
Walter Reed
When United States military leaders realized that yellow fever was causing more
deaths than enemy bullets, they appealed to their government in Washington, DC. Help
came in the form of a commission headed by an army research doctor named Walter Reed.
Reed’s first step was to analyze the old ways of fighting yellow fever. Because the
disease moved from one section of a town to another, most people believed that yellow fever
must be spread from person to person. To fight the disease, they isolated the sick, boiled
their bed sheets and clothes, and sterilized their plates, cups, and forks.
These precautions would make good sense if yellow fever was transmitted by personal
contact. Reed quickly discovered, however, that none of these measures stopped the
spread of the disease.
Findlay’s Hypothesis
Reed’s commission listened to many physicians, including a Cuban doctor named
Carlos Findlay. Findlay hypothesized that the disease was spread by mosquitoes, of which
Cuba had more than its share.
Most people believed that better sanitation was the key to controlling yellow fever,
and they did not believe Findlay’s hypothesis. But Reed believed that there was not enough
evidence to draw any logical conclusions. To test Findlay’s hypotheses, Reed decided he
needed to conduct a controlled experiment.
It was thought at the time that yellow fever affected people but did not affect animals.
So Reed performed his experiment on brave but frightened groups of human volunteers.
Reed’s Experiment
Reed’s commission assembled two groups of volunteers for a terrifying experiment.
One group spent 20 nerve-wracking days wearing the filthy clothing of yellow fever patients,
sleeping on their bed sheets, and eating from plates they had used. During this time,
however, they lived behind screens that protected them from being bitten by mosquitoes.
The other group of volunteers used only fresh clothing, slept in clean beds, and
remained totally isolated from yellow fever patients. These volunteers, however, were not
protected by mosquito netting and so were bitten by mosquitoes. Unwilling to let soldiers
take a risk that they would not take themselves, three doctors on the commission joined
this group. (Reed also wanted to take part, but his associates refused his request to do so.)
The Results
What happened? Not a single volunteer in the first group developed yellow fever. But
many of the volunteers in the second group-including the three doctors-became sick with
yellow fever. One of the doctors, Jesse Lazear, died from the disease.
The results of the experiment were very clear. Yellow fever was not spread by poor
sanitation, person-to-person contact, or food. Instead, yellow fever was spread by
mosquitoes. As a result, the United States government declared war on the mosquito. And
within 90 days, the city of Havana, Cuba, was free of yellow fever.
Today, Jesse Lazear is remembered as a hero, and Findlay and Reed are recognized
as the people who led the way to conquering a terrible disease. In addition, the work of
these scientists had effects well beyond the fields of science and medicine.
For example, yellow fever had been a common disease in the Central American
country of Panama. Once the disease was under control, people in the United States began
seriously to consider building the Panama Canal.
Beyond Yellow Fever
As you know, the application of the scientific method in fighting disease did not stop
with conquest of yellow fever. In the decades since Reed’s work, biology has changed from
a science that only studies the world around us to one that makes changes in that world.
As a result, we live at one of the most remarkable times in human history. Biology
will influence life in the twenty-first century – the century in which you will spend most of
your life – to an extent never approached before. These are exciting times to be alive, and
they are especially exciting times to study the science of biology.