Fig. 1. Nineteenth century: searching for the essence of life. Claude Bernard (A ) formulated a unified paradigm of anesthetic action rooted in his vision that susceptibility to anesthesia separated the living from the nonliving worlds. This paradigm had a profound influence on research into anesthetic mechanism for more than a century. Albert Dastre (B , a contemporary cartoon) emphasized the philosophical importance of Bernard's life-defining vision for anesthetic susceptibility. He authored numerous works, among them a textbook of anesthesia (Les Anesthésiques ) published in 1891 in which he described anesthesia as ‘the reagent of life’ (reactif de la vie ). (C ) Course of physiology taught by Dastre at the Sorbonne (a college of the University of Paris), where Claude Bernard became Professor and chaired the Department of Physiology from 1854 to 1868 when he left it for the newly established professorship in general physiology at the Museum of Natural History. Albert Dastre became chair of physiology at the Sorbonne in 1887. The image of Claude Bernard is courtesy of the Wood Library-Museum of Anesthesiology, Park Ridge, Illinois. Albert Dastre's cartoon is copyright Bibliothèque de l'Académie nationale de médecine. The image of Dastre lecturing at the Sorbonne is courtesy of the Bibliothèque Interuniversitaire (BIU) Santé, Paris, France.