Some volunteers slept for weeks in the blood-soaked, vomit-stained faecal-contaminated nightgowns of recently deceased disease victims.
Others allowed themselves to be bitten mercilessly by (uninfected) mosquitoes.
I asked two volunteers, Private John R. Kissinger and clerk John J. Moran, why they were agreeing to such life-threatening experiments. They said "We volunteer solely for the cause of humanity and in the interest of science".
None of these subjects came down with yellow fever.