Here are a few brief excerpts from Saint Justin Martyr's "First Apology":

Chapter 1. Address
To the Emperor Titus Elius Adrianus Antoninus Pius Augustus Caesar, and to his son Verissimus the Philosopher,
and to Lucius the Philosopher, the natural son of Cæsar, and the adopted son of Pius, a lover of learning, and to the
sacred Senate, with the whole People of the Romans, I, Justin, the son of Priscus and grandson of Bacchius, natives
of Flavia Neapolis in Palestine, present this address and
petition in behalf of those of all nations who are unjustly
hated and wantonly abused, myself being one of them.

Chapter 65. Administration of the sacraments
But we, after we have thus washed him who has been convinced and has assented to our teaching, bring him to the
place where those who are called brethren are assembled, in order that we may offer hearty prayers in common for
ourselves and for the baptized [illuminated] person, and for all others in every place, that we may be counted worthy,
now that we have learned the truth, by our works also to be found good citizens and keepers of the commandments,
so that we may be saved with an everlasting salvation. Having ended the prayers, we salute one another with a kiss.
There is then brought to the president of the brethren bread and a cup of wine mixed with water; and he taking them,
gives praise and glory to the Father of the universe, through the name of the Son and of the Holy Ghost, and offers
thanks at considerable length for our being counted worthy to receive these things at His hands.
And when he has
concluded the prayers and thanksgivings, all the people present express their assent by saying Amen. This word Amen
answers in the Hebrew language so be it. And when the president has given thanks, and all the people have expressed
their assent, those who are called by us
deacons give to each of those present to partake of the bread and wine mixed
with water over which the thanksgiving was pronounced, and to those who are absent they carry away a portion.

Chapter 66. Of the Eucharist
And this food is called among us the Eucharist, of which no one is allowed to partake but the man who believes that
the things which we teach are true, and who has been washed with the washing that is for the remission of sins, and
unto regeneration, and who is so living as Christ has enjoined. For not as common bread and common drink do we
receive these; but in like manner as Jesus Christ our Saviour, having been made flesh by the Word of God, had both
flesh and blood for our salvation,
so likewise have we been taught that the food which is blessed by the prayer of His
word, and from which our blood and flesh by transmutation are nourished, is the flesh and blood of that Jesus who
was made flesh. For the apostles, in the memoirs composed by them, which are called Gospels, have thus delivered
unto us what was enjoined upon them; that Jesus took bread, and when He had given thanks, said, “This do in
remembrance of Me, Luke 22:19 this is My body;” and that, after the same manner, having taken the cup and given
thanks, He said, “This is My blood;” and gave it to them alone. Which the wicked devils have imitated in the
mysteries of Mithras, commanding the same thing to be done. For, that bread and a cup of water are placed with
certain incantations in the mystic rites of one who is being initiated, you either know or can learn.

Chapter 67. Weekly worship of the Christians
And we afterwards continually remind each other of these things. And the wealthy among us help the needy; and we
always keep together; and for all things wherewith we are supplied, we bless the Maker of all through His Son Jesus
Christ, and through the Holy Ghost.
And on the day called Sunday, all who live in cities or in the country gather
together to one place, and the memoirs of the apostles or the writings of the prophets are read, as long as time
permits; then, when the reader has ceased, the president verbally instructs, and exhorts to the imitation of these good
things. Then we all rise together and pray, and, as we before said, when our prayer is ended, bread and wine and
water are brought, and the president in like manner offers prayers and thanksgivings, according to his ability, and the
people assent, saying Amen; and there is a distribution to each, and a participation of that over which thanks have
been given, and to those who are absent a portion is sent by the deacons.
And they who are well to do, and willing,
give what each thinks fit; and what is collected is deposited with the president, who succours the orphans and widows
and those who, through sickness or any other cause, are in want, and those who are in bonds and the strangers
sojourning among us, and in a word takes care of all who are in need.
But Sunday is the day on which we all hold our
common assembly, because it is the first day on which God, having wrought a change in the darkness and matter,
made the world; and Jesus Christ our Saviour on the same day rose from the dead.
For He was crucified on the day
before that of Saturn (Saturday); and on the day after that of Saturn, which is the day of the Sun, having appeared to
His apostles and disciples, He taught them these things, which we have submitted to you also for your consideration.

Chapter 68. Conclusion
And if these things seem to you to be reasonable and true, honour them; but if they seem nonsensical, despise them as
nonsense, and do not decree death against those who have done no wrong, as you would against enemies. For we
forewarn you, that you shall not escape the coming judgment of God, if you continue in your injustice; and we
ourselves will invite you to do that which is pleasing to God. And though from the letter of the greatest and most
illustrious Emperor Adrian, your father, we could demand that you order judgment to be given as we have desired,
yet we have made this appeal and explanation, not on the ground of Adrian's decision, but because we know that
what we ask is just. And we have subjoined the copy of Adrian's epistle, that you may know that we are speaking
truly about this.

Read the full text here:
Saint Justin Martry's First Apology
Saint Justin Martyr was a Christian apologist, born at Flavia Neapolis,
about A.D. 100.  He converted to Christianity in A.D. 130 and taught and
defended the Christian religion in Asia Minor and at Rome, where he
suffered martyrdom about the year 165.  In his work titled “First Apology”
which was addressed to the Roman Emperor, he defended the beliefs of the
early Church and explained what happened during Christian worship.  
During the Early Church, Christians were persecuted by the Romans and
accused of practicing cannibalism because they ate and drank of the Body
and Blood of Christ.  Saint Justin Martyr, in his “First Apology” explains
to the Roman Emperor the practices of the Church, specifically the Holy
Sacrifice of Mass.  This early church writing gives interesting insight to the
early practices of the Catholic Church.  It’s also important to note that
this early writing clearly shows that the early Church believed that the
Eucharist was the real Body and Blood of Jesus Christ, just as the Catholic
Church teaches and believes today.