The text and melody below were already in existence before the time of Thomas Aquinas in Monday of the Octave of Pentecost. See (among many) Codex Bodmer 74, p.106v, http://www.e-codices.unifr.ch/de/cb/0074/001r
See the following 12th century Ms Clm 2541, from Bayerische StaatsBibliothek, p. 199, http://daten.digitale-sammlungen.de/~db/ausgaben/thumbnailseite.html:
|Contra, O per omnia laudabilem virum, de sancto Nicholao.|
After looking at innumerable manuscripts, I did not find this Introitus/Officium for St. Nicholas. They refer rather to "Statuit" or "Sacerdotes Dei" from the Commons. But the text is that of the 5th antiphon for Lauds of his feast:
Here is an attempt to follow Thomas' instruction, adding the final two (8th tone) Alleluias from Pentecost:
He fed them with the best wheat,
and replenished them with honey from the rock.
[Note: This trope was not composed by Thomas Aquinas, but was in circulation in his time. It fits the following "Roman" Kyrie fons bonitatis, which is not among Dominican Mass chants.]
Deus qui nobis sub sacramento mirabili passionis tuae memoriam reliquisti, tribue, quaesumus, ita nos corporis et sanguinis tui sacra mysteria venerari, ut redemptionis tuae fructum in nobis iugiter sentiamus. Qui vivis et regnas cum Deo patre in unitate spiritus sancti Deus per omnia saecula saeculorum. Amen.
God, in this wonderful sacrament you left us a memorial of your Passion. Enable us, we ask, so to venerate the sacred mysteries of your Body and Blood, that we may always fell the fruit of your redemption in us. You live and reign with God the Father in the unity of the Holy Spirit, forever and ever. Amen.
|Lectio epistolae beati Pauli apostoli ad Corinthios (11:23-29)
Fratres, ego enim accepi a domino quod et tradidi vobis; quoniam dominus Iesus in qua nocte tradebatur, accepit panem, et gratias agens fregit et dixit: accipite et manducate: hoc est corpus meum, quod pro vobis tradetur; hoc facite in meam commemorationem. Similiter et calicem, postquam cenavit, dicens: hic calix novum testamentum est in meo sanguine; hoc facite, quotiescumque sumitis, in meam commemorationem. Quotiescumque enim manducabitis panem hunc et calicem bibetis, mortem domini annuntiabitis donec veniat. Itaque quicumque manducaverit panem vel biberit calicem domini indigne, reus erit corporis et sanguinis domini. Probet autem seipsum homo; et sic de pane illo edat, et de calice bibat. Qui enim manducat et bibit indigne, iudicium sibi manducat et bibit, non diiudicans corpus domini.
For I received from the Lord what I also handed on to you, that the Lord Jesus, on the night he was handed over, took bread, and, after he had given thanks, broke it and said, "This is my body that is for you. Do this in remembrance of me." In the same way also the cup, after supper, saying, "This cup is the new covenant in my blood. Do this, as often as you drink it, in remembrance of me." For as often as you eat this bread and drink the cup, you proclaim the death of the Lord until he comes. Therefore whoever eats the bread or drinks the cup of the Lord unworthily will have to answer for the body and blood of the Lord. A person should examine himself, and so eat the bread and drink the cup. For anyone who eats and drinks without discerning the body, eats and drinks judgment on himself.
|Gradualis (Borrowed from Thursday, third week of Lent)
℟. The eyes of all hope in you, Lord, and you give them their food in due time.
℣. You open your hand, and fill every living thing with blessing.
My flesh is really food, and my blood is really drink. He who eats my flesh and drinks my blood dwells in me, and I in him.
|Contra, Nativitas gloriosa, de sancta Maria.
The contra text —Numbers correspond in melody, with minor variants, to those of Lauda Sion.
I provisionally offer the translation of "Msgr. Henry" (slightly modified):
|Contra, Laudes crucis attolamus, de sancta Cruce (below, at border).|
Exaltatio S. Crucis f. 327v-330v, Universittsbibliotek, Graz, 15th c. http://220.127.116.11/digbib/handschriften/Ms.0001-0199/Ms.0017/index21.html & Ms. 0017
Inventio S. Crucis, ibid., f. 290v-291v.
|Secundum Ioannem (6:56-58)
In illo tempore dixit Iesus discipulis suis et turbis Iudaeorum: Caro mea vere est cibus, et sanguis meus vere est potus. Qui manducat meam carnem et bibit meum sanguinem, in me manet et ego in illo. Sicut misit me vivens pater, et ego vivo propter patrem; et qui manducat me, et ipse vivet propter me. Hic est panis qui de caelo descendit. Non sicut manducaverunt patres vestri manna, et mortui sunt: qui manducat hunc panem, vivet in aeternum.
Whoever eats my flesh and drinks my blood remains in me and I in him. Just as the living Father sent me and I have life because of the Father, so also the one who feeds on me will have life because of me. This is the bread that came down from heaven. Unlike your ancestors who ate and still died, whoever eats this bread will live forever."
The priests of the Lord will offer incense and bread to God, and therefore they shall be holy for their God, and shall not pollute his name. Halleluia. (Cf. Lev 21:6)
Ecclesiae tuae, quaesumus, domine, unitatis et pacis propitius dona concede, quae sub oblatis muneribus mystice designantur.
To your Church, we ask O Lord, kindly give the gifts of unity and peace, which the gifts we offer mystically signify.
|Praefatium (de Nativitate domini)
I will sing to the Lord who bestowed good things on me, and I will sing to the name of the Lord Most High.
Fac nos, quaesumus, domine, divinitatis tuae sempiterna fruitione repleri, quam pretiosi corporis et sanguinis tui temporalis perceptio praefigurat. Qui vivis et regnas cum Deo patre in unitate spiritus sancti Deus per omnia saecula saeculorum. Amen.
We ask, O Lord, always to be filled with the enjoyment of your divinity, which this temporal reception of your body and blood prefigures.