July 1st is the Feast of the Most Precious Blood of Our Lord. This is a very appropriate devotion for an altar server, who serves at the Holy Mass; where the True Blood of Jesus Christ becomes really present under the appearances of Bread and Wine; where the Blood of Christ, the price of our redemption, is applied to our souls for our sanctification and salvation.
The entire month of July is devoted to the Most Precious Blood of our Lord, so this is an especially good prayer to use throughout this month.
I don't know how old this Litany is, who authored it. It was certainly included in early 20th century prayer books, and has the feel of being older, thought it was only approved for Public recitation by Pope John XXIII in 1960 (the pope had a special devotion to the precious blood).
The devotion to Jesus specifically in His most Precious Blood was popularized by St. Gaspar del Bufalo (1786-1837, feast Dec. 28) who founded the Missioners of the Most Precious Blood.
Litany of the Most Precious Blood of Our Lord Jesus Christ
Lord, have mercy.
Christ, have mercy.
Lord, have mercy.
Christ, hear us.
Christ, graciously hear us.
God the Father of Heaven, have mercy on us.
God the Son, Redeemer of the world, have mercy on us.
God, the Holy Spirit, have mercy on us.
Holy Trinity, One God, have mercy on us.
Blood of Christ, only-begotten Son of the eternal Father, save us.
Blood of Christ, Incarnate Word of God, save us.
Blood of Christ, of the New and Eternal Testament, save us.
Blood of Christ, falling upon the earth in Agony, save us.
Blood of Christ, shed profusely in the Scourging, save us.
Blood of Christ, flowing forth in the Crowning with Thorns, save us.
Blood of Christ, poured out on the Cross, save us.
Blood of Christ, price of our salvation, save us.
Blood of Christ, without which there is no forgiveness, save us.
Blood of Christ, Eucharistic drink and refreshment of souls, save us.
Blood of Christ, stream of mercy, save us.
Blood of Christ, victor over demons, save us.
Blood of Christ, courage of Martyrs, save us.
Blood of Christ, strength of Confessors, save us.
Blood of Christ, bringing forth Virgins, save us.
Blood of Christ, help of those in peril, save us.
Blood of Christ, relief of the burdened, save us.
Blood of Christ, solace in sorrow, save us.
Blood of Christ, hope of the penitent, save us.
Blood of Christ, consolation of the dying, save us.
Blood of Christ, peace and tenderness of hearts, save us.
Blood of Christ, pledge of eternal life, save us.
Blood of Christ, freeing souls from purgatory, save us.
Blood of Christ, most worthy of all glory and honor, save us.
Lamb of God, who taketh away the sins of the world, spare us, O Lord.
Lamb of God, who taketh away the sins of the world, graciously hear us, O Lord.
Lamb of God, who taketh away the sins of the world, have mercy on us, O Lord.
Thou hast redeemed us, O Lord, in Thy Blood. And made us, for our God, a kingdom.
Let us pray.
Almighty and eternal God, Thou hast appointed Thine only-begotten Son the Redeemer of the world and willed to be appeased by his blood. Grant, we beg of Thee, that we may worthily adore this price of our salvation and through its power be safeguarded from the evils of the present life so that we may rejoice in its fruits forever in heaven. Through the same Christ our Lord. Amen.
The Latin version of this Litany is available from:
http://www.fisheaters.com/litanypreciousblood.html
A partial indulgence is granted to the faithful who recite this litany, which is approved for either private or public use.