In response to his groundbreaking theory on the cause of yellow fever, Carlos Finlay was called a "crank" and a "crazy old man." The derision hurt the doctor whose homeland was devastated by the disease, but he would live to see his work vindicated.

Becoming a Doctor
Finlay was born in Cuba on December 3, 1833. His father, Edward, a Scottish-born physician, and his mother, Eliza, a native of France, educated him at home and later enrolled him in school in France. Bouts of childhood illness interrupted his schooling, but he was able to enroll in the Jefferson Medical College in Philadelphia, where he earned his medical degree on March 10, 1855. Eschewing the chance for a lucrative practice in the States, he returned home to Cuba to begin his career.

Scientific Inquiry

Establishing a general medical and ophthalmology practice in Havana, Finlay spent much of his free time on scientific investigation, including the study of yellow fever. He was appointed to work with the U.S. National Health Board Yellow Fever Commission when it traveled to Cuba in 1879. The commission found that "the agent capable of transmitting the disease must be in the air." That conclusion and microscopic slides of tissue from yellow fever victims led Finlay to focus on the blood vessels and the biting insect that accesses them. 
 

A Hypothesis Scorned

On August 14, 1881, Finlay presented a paper to Havana's Academy of Sciences called "The Mosquito Hypothetically Considered as the Transmitting Agent of Yellow Fever," concluding: "I understand but too well that nothing less than an absolutely incontrovertible demonstration will be required before the generality of my colleagues accept a theory so entirely at variance with the ideas which have until now prevailed about yellow fever." He was correct about that, as evidenced by the stony silence that followed his presentation and the "universal ridicule" he received thereafter, as his son would recall. Finlay spent the next 20 years trying to prove his hypothesis, conducting 102 experimental inoculations on human volunteers. But his mosquito theory would not gain acceptance until the dawn of the new century.

Conclusive Results
Arriving in Cuba in 1900, members of the U.S. Army Yellow Fever Board visited Finlay at his home in Old Havana. They used mosquitoes hatched from his eggs to test the hypothesis that the insects transmitted the disease and after a series of experiments, showed that Finlay had been correct. The head of the board, Walter Reed, noted that "it was Finlay's theory, and he deserves much for having suggested it." William Crawford Gorgas, who later spearheaded a public health campaign that protected the Panama Canal project from the disease, said of Finlay: "His reasoning for selecting the Stegomyia [mosquito] as the bearer of yellow fever is the best piece of logical reasoning that can be found in medicine anywhere."

Celebrated in Cuba
Finlay was subsequently appointed chief sanitary officer of Cuba, a position he held into his 70s until his retirement in 1909. During that period, his work contributed to a reduction in the country's mortality rate of infantile tetanus. After his death on August 20, 1915, his achievements lived on in Cuba, which produced a flattering biography in 1985, requested by Cuban president Fidel Castro, and with the Finlay Medical Society, an organization of medical professionals.