In the 19th century, Cuba and other tropical areas were plagued with several diseases that typically struck in large outbreaks. One of the worst tropical diseases was yellow fever. If a canal was to be built between the two oceans, somebody had to figure out how to stop yellow fever from spreading, and that meant first understanding what caused it to spread in the first place. Scientists and health experts had many ideas: Some experts thought that certain chemicals in the atmosphere spread yellow fever, others believed the disease was transmitted on surfaces of objects, bugs, and people’s hands. But Dr. Carlos J. Finlay believed that mosquitoes were the culprits.
For years, researchers had considered Finlay’s idea far-fetched, but not after 1901. In that year, a United States government health commission looked closely at Finlay’s research. According to results of scientific experiments accumulated and published by Finlay over the previous decades, yellow fever was indeed transmitted by mosquitoes. Based on this idea, Finlay had already helped the US Army to stop yellow fever in Havana, Cuba, three years earlier, in 1898. Following a similar but more ambitious plan, the 1901 health commission decided that the disease could also be fought in Panama, where thousands of workers would have to live for years. Declare war on the mosquitoes of Panama, and the long-sought canal would finally be possible.
Photo and reference: http://www.visionlearning.com/en/library/Inside-Science/58/Carlos-J.-Finlay/217