In 1920 John Watson, along with graduate student Rosalie Rayner, conducted an emotional-conditioning experiment on a nine-month-old baby -- whom they nicknamed "Albert B" -- at Johns Hopkins University in an effort to prove their theory that we're all born as blank slates that can be shaped. The child's mother, a wet nurse who worked at the hospital, was paid one dollar for allowing her son to take part.
The "Little Albert" experiment went like this: Researchers first introduced the baby to a small, furry white rat, of which he initially had no fear. (According to reports, he didn't really show much interest at all). Then they re-introduced him to the rat while a loud sound rang out. Over and over, "Albert" was exposed to the rat and startling noises until he became frightened any time he saw any small, furry animal (rats, for sure, but also dogs and monkeys) regardless of noise.
Who exactly "Albert" was remained unknown until 2010, when his identity was revealed to be Douglas Merritte. Merritte, it turns out, wasn't a healthy subject: He showed signs of behavioral and neurological impairment, never learned to talk or walk, and only lived to age six, dying from hydrocephalus (water on the brain). He also suffered from a bacterial meningitis infection he may have acquired accidentally during treatments for his hydrocephalus, or, as some theorize, may have been -- horrifyingly -- intentionally infected as part of another experiment.
In the end, Merritte was never deconditioned, and because he died at such a young age no one knows if he continued to fear small furry things post-experiment.