Plague doctors treated bubonic plague during epidemics in the 16th and 17th centuries, treating patients regardless of income, especially the poor. They were often volunteers, second-rate doctors, or young doctors. They recorded death tolls and infected people for demographic purposes. Plague doctors wore a special costume, including an ankle-length overcoat and a bird-like beak mask, to purify the air they breathe. The mask was filled with herbs and spices, such as lavender.