After the Spanish-American War, in which more U. S. soldiers were killed by yellow fever than in battle, the War Department sent a medical commission to Cuba to find, if possible, the cause and cure of this deadly tropical disease. The commission was headed by Dr. Walter Reed. With him was Dr. James Carroll. In Cuba they found Dr. Jesse W. Lazear, European-trained microbiologist, and Cuban Dr. Aristides Agramonte.
Limited in its experiments by the fact that animals are immune to yellow fever, the commission was forced to consider the theory of an eccentric Scottish medic history. who had an unsubstantiated notion that yellow fever was transmitted from human to human by mosquitoes. The commissioners tested Dr. Carlos Finlay's theory on themselves. Dr. Carroll caught yellow jack from one of the Finlay mosquitoes. Dr. Lazear died of it. Even then their experiments were scientifically incomplete. Dr. Reed called for four soldiers to volunteer as human guinea pigs. Two of them got bites from Finlay mosquitoes. The other two were placed in insanitary surroundings where, if the disease could be transmitted by contagion, they were sure to catch it. When only the two soldiers who were bitten by mosquitoes contracted yellow jack, it amounted to Science's first important victory over yellow fever, the beginning of the final extermination of that plague.