When Poussin depicted epidemic disease in his Plague of Ashdod (1630–31), medical theories linking the imagination to health considered such disturbing subjects dangerous, even as objects of thought. Poussin's image, however, was fashioned to immunize the viewer against the very disease it depicts, through application of Aristotle's tragic catharsis. This hypothesis is developed through comparisons with Raphael's Morbetto and Boccaccio's account of plague. Other paintings by Poussin, The Empire of Flora, Landscape with a Man Killed by a Snake, two self-portraits, and The Vision of Saint Francesco Romana, are also discussed in terms of art's impact on health.