Encyclical Letter of His Holiness Pope Pius XI: Mens Nostra, Closed Retreats, Spiritual Exercises; Published by National Catholic Laymen's Retreat Conference, PGEN 131/5833. General Collection, GEN. University of Notre Dame Archives. https://archivesspace.library.nd.edu/repositories/2/archival_objects/1097499 Accessed November 29, 2024.