Santorio (or Sanctorius) was a graduate of Padua and returned there at the age of fifty to take the chair of medicine. The frontispiece to this work shows him seated in the chair attached to a yard arm by which he recorded his changes of weight after eating, an experiment which showed for the first time that the body suffered weight loss that could not be explained by ordinary excretions. While he realised that this loss occured through the mouth and surface of the skin, he understandably assumed that the lost weight was mainly moisture since nothing was known of the nature of air and gases until Boyle proved that they were material substances. Santorio's work was first published in 1614 and met with astonishing success.