We might be disposed to regard the sacraments as this medium, because they are the instruments by which grace is conferred, in a manner apprehensible through the senses. Nevertheless, we cannot find the constitutive principle of the Church in the sacraments alone. It is well known that Protestantism has set forth the legitimate administration of the sacraments as a mark of the true Church. A searching glance at the Protestant conception of the Church will hereafter give us a proof that a bare communication in sacraments, at least from the Protestant stand-point, cannot possibly verify itself as making a visible Church. According to the Protestant doctrine of justification, a sacrament is indebted for its grace-giving efficacy solely to the faith of the receiver. In this view, therefore, the connection of the invisible element of the supernatural with the historically manifested reality, and consequently the making visible of the true Church, is dependent on conditions where historical fulfilment is not provable. Who can prove whether the recipient of a sacrament has faith? It is true that, according to the Catholic view, an objective efficacy is ascribed to the sacrament, i.e., the outwardly perceptible completion of the sacramental action of itself permits the invisible element of the supernatural to penetrate into the sphere of the visible. Notwithstanding this, the Catholic sacrament is, by itself alone, no sufficient medium through which the being of the true Church can be brought into visibility. Did she embody herself historically only in so far as a sensible matter and an outward action are endued with a supernatural efficacy, the element of the supernatural would come to a historical manifestation only as the purely objective. A profound view of the essence of the Church would not find this satisfactory. The Church, even on her visible side, is not a purely objective, or merely outward, institution. The ultimate principle of catholicity--and this statement will make our conception intelligible--although implanted in the world as a supernatural leaven from above, has nevertheless its seat in the deepest interior of the human spirit. Thence it penetrates upward into the sphere of historical manifestation, and thus proves itself a church-constitutive principle. Such a connection of the region of the interior and subjective with that of historical and visible reality is caused by the objective efficacy of a sacrament, only in the case where the same is productive of its proper effect. This, however, according to Catholic doctrine, presupposes an inward disposition on the part of the recipient, the presence of which cannot be manifested to outward apprehension. A Church, whose essence consisted merely in the bond established through the sacraments, could either not be verified with certitude, or would have an exclusively exterior character. Accordingly, we have not yet found, in the