Self-experimentation refers to the very special case of single-subject scientific experimentation in which the experimenter conducts the experiment on her- or himself. Usually this means that the designer, operator, subject, analyst, and user or reporter of the experiment are all the same. It is a special case of single-subject research. Sanctorius of Padua was probably the first documented case of self-experimentation living on a balance for 30 years in the early 17th century, weighing himself, his daily food, liquids, and combined excretions, leading him toward the discovery of metabolism.