Shulchan Aruch, Orach Chayim 4: "The following things require washing the hands in water [after them]: One who rises from bed, goes out of the bathroom, or of the bath house, one who cuts his nails, takes off his shoes, touches his feet, or washes his head, some say: also one who goes among the dead, or touched the dead, one who cleanses his clothes of lice, has sexual intercourse, touches a louse, or touches his body with his hand. Anyone doing any of these and not washing his hands, if he is a scholar, his studies are forgotten, and if he is not a scholar, he goes out of his mind."

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