The Mosquito Theory Nobody Believed for Twenty Years

This dangerous research was done using human volunteers, including some of the medical personnel, who allowed themselves to be bitten by mosquitos infected with yellow fever.

Finlay was the first to theorize, in 1881, that a mosquito was a carrier, now known as a disease vector, of the organism causing yellow fever: a mosquito that bites a victim of the disease could subsequently bite and thereby infect a healthy person.