In creating two isolated environments, Reed and his team were able to introduce volunteers into controlled experiments. There was absolute certainty in the results. They also used a multitude of volunteers, in case any of them had an immunity to yellow fever, which develops if one has already had the disease.

The only instances of contracting yellow fever occurred with people who were isolated in a sterile environment and exposed to mosquitoes known to have been infected with yellow fever with a proper incubation time. This last detail was the missing piece from Carlos Finlay's experiments.

Acknowledging the breakthroughs that the Cuban researcher had achieved, Reed welcomed Finlay to Camp Lazear to observe the tests.

Carlos Finlay