This work presents us the surgeon Desplein, teacher of Horace Bianchon, the most recurrent doctor in the Comédie humaine. He is a honest man, an hardened atheist and a fanatical believer in science. When Bianchon sees Desplein attending Mass in the church of Saint-Sulpice, he is so intrigued by the conduct of his teacher that is so contrary to the ideas he professes, that he observes the surgeon. This way he discovers that Desplein assists four Masses a year and he decides to confront Desplein with it...