18 And it seems important to determine special days on which, with the august sacrament of the altar exposed for adoration, the works of the sacred missions are commended in appropriate sermons. And We desire that this be done annually in each parish, in the colleges, and in the seminaries. May the youth especially approach the Eucharistic table to receive the bread of the strong and "the corn of the elect." Then perhaps not a few among them will experience with the greatest joy of soul, the divine call to this kind of vocation.
Source: Saeculo Exeunte Octavo (Vatican.va)