How it began
Carlos Finlay, a Cuban physician born in 1833, worked with a United States yellow fever commission that came to Cuba in 1879. The commission concluded that the agent that spread the disease must be in the air. That finding, together with microscope slides of tissue from victims, led Finlay to focus on the blood vessels and on the biting insect that reaches them. On August 14, 1881, he presented a paper to the Academy of Sciences in Havana titled "The Mosquito Hypothetically Considered as the Transmitting Agent of Yellow Fever."
How it spread
Members of the United States Army Yellow Fever Board arrived in Cuba in 1900 and visited Finlay at his home in Old Havana. He shared his ideas, his publications and a sample of mosquito eggs. The board used mosquitoes hatched from his eggs to test the hypothesis and, after a series of experiments, showed that Finlay had been right. Walter Reed, who led the board, wrote that it was Finlay's theory and that he deserved much for having suggested it.
Who pushed back
Finlay expected doubt. He told the Academy that nothing less than an absolutely incontrovertible demonstration would persuade his colleagues to accept a theory so much at variance with prevailing ideas about yellow fever. He was called a crank and a crazy old man. He spent the next 20 years trying to prove the hypothesis and carried out 102 experimental inoculations on human volunteers, but the theory did not gain acceptance until the start of the new century.
What lasted
William Crawford Gorgas later led the public health campaign that protected the Panama Canal project from yellow fever. Gorgas said that Finlay's reasoning in choosing the Stegomyia mosquito as the carrier was the best piece of logical reasoning that could be found anywhere in medicine. Between 1881 and 1901 Finlay wrote more than 40 published works on yellow fever, about a third of them on mosquito transmission.
