I'm not exactly sure why, but IBD has a story on Walter Reed today. Maybe it's an anniversary or something. It does solve the mystery of exactly what got the premier federal hospital named after him.
According to their article, Walter Reed proved that mosquitos were spreading Yellow Fever. Getting short shrift in the same is Carlos Finlay, the Cuban doctor who originally figured out that mosquitos were the culprit. Don't take my word for it. Years ago, National Geographic did a pretty exhaustive story on the Yellow Fever research in which Finlay figured a bit more prominently.
Please note that some that the researchers and subjects were exposed to the deadly disease on purpose. Can you imagine that happening today?