3. De Incarnationis Dominicæ Sacramento. The book on the Mystery of the Lord’s Incarnation owed its origin to a challenge to dispute publicly given to St. Ambrose by two Arian chamberlains of Gratian. On the day appointed they were, as Paulinus relates in his life of St. Ambrose, thrown out of the chariot which was conveying them and killed. On the next day, that the people might not be disappointed, this discourse was delivered, but the reference made to the absence of the challengers hardly suits the story of Paulinus. The treatise is a very valuable argument in defence of our Lord’s Divinity and Eternity, and that He is perfect God and perfect Man. In rewriting the address the Bishop added a refutation of the argument that the Begotten and the Unbegotten could not be of one nature and substance. The treatise may be considered as a supplement to that concerning the Faith.