In 1885, Toppan began training to be a nurse at Cambridge Hospital. Unlike her early years, where she was described as brilliant and terrible, at the hospital she was well-liked, bright and friendly, evoking the nickname "Jolly Jane". Once Toppan became close with the patients, she picked her favorite ones. The patients were normally elderly and very sick. During her residency, Toppan used her patients as guinea pigs in experiments with morphine and atropine; she altered their prescribed dosages to see what it did to their nervous systems. However, she spent considerable time alone with patients, making up fake charts and medicating them to drift in and out of consciousness and even getting into bed with them.