"The immaculate body of Mary remained without corruption and was borne up to heaven, before the general resurrection." (Lesson at Matins).
The Council of the Vatican, which had to be adjourned in 1870, was not able to carry out the desire which had been expressed for the definition of this dogma. The task was completed by Pope Pius XII in 1950, in his Apostolic Constitution Munificentissimus Deus, in which he exercised the proper infallibility of the Roman Pontiff - "that they might religiously guard and faithfully expound the revelation or deposit of faith transmitted by the apostles." (Vatican Council 1870)
Previously it was held as doctrinally certain. As the St Andrew Missal reported, "although not defined as a dogma of our faith, this truth is of those no one is permitted to doubt, as Benedict XIV declares."
O Jesu, vivens in Maria, veni et vive in famulis tuis, in Spiritu sanctitatis tuae, in plenitudine virtutis tuae, in veritate virtutum tuarum, in perfectione viarum tuarum, in communione mysteriorum tuorum, dominar omni adversae potestati in Spiritu tuo ad gloriam Patris. Amen.
O Jesus, who dost live in Mary, come and live in Thy servants, in the spirit of Thine own holiness, in the fullness of Thy power, in the reality of Thy virtues, in the perfection of Thy ways, in the communion of Thy mysteries, - have Thou dominion over every adverse power, in Thine own Spirit, to the glory of Thy Father. Amen.