Per Quem
The "Per Christum Dominum nostrum" at the end of the Second Intercession is not followed by the usual "Amen." What follows instead is the short prayer (reserved to the principal celebrant in a concelebrated Mass): "Per quem haec omnia, Domine, semper bona creas, santificas, vivificas, benedicis, et praestas nobis." (Through whom you continue to make all these good things, O Lord, you sanctify them, fill them with life, bless them and bestow them upon us.)
It is unclear what is referred to by the phrase "all these good things". One theory is that it refers to fruits of the earth and prepared food brought up to be blessed at this point of the Canon, which is when the bishop blesses the oil of the sick with a special formula at the Chrism Mass on Holy Thursday.
The Tridentine Missal requires the priest to make three signs of the cross over the host and chalice together during this prayer.
Read more about this topic: Text And Rubrics Of The Roman Canon