The Gospel accounts of Jesus' Passion highlight the pouring out of his blood on the cross. This is found in particular in the Gospel of John:
[W]hen they came to Jesus and saw that he was already dead, they did not break his legs, but one soldier thrust his lance into his side, and immediately blood and water flowed out. (John 19:33-34)
Ever since that moment the Catholic Church has been devoted to Jesus' Precious Blood, and Catholics have developed various traditions that have endured over time.
While it is not the most popular devotion in the modern history of the Church, historically it has received widespread practice.
The Directory on popular piety lists four specific devotions that are approved by the Church and are practiced by Christians throughout the world:
1Chaplet of the Most Precious Blood
The Chaplet of the Most Precious Blood, in which the seven "effusions of the Blood of Christ," implicitly or explicitly mentioned in the Gospels, are recalled in a series of biblical meditations and devotional prayers: the Blood of the Circumcision, the Blood of the Garden of Gethsemane, the Blood of the Flagellation, the Blood of the Crowning of Thorns, the Blood of the Ascent to Calvary, the Blood flowing from Christ's side pierced by the lance;
2Litany of the Blood of Christ
The Litany of the Blood of Christ, which clearly traces the line of salvation history through a series of biblical references and passages. In its present form it was approved by the Blessed John XXIII on 24 February 1960(195);
3Adoration of the Most Precious Blood of Christ
Adoration of the Most Precious Blood of Christ takes a great variety of forms, all of which have a common end: adoration and praise of the Precious Blood of Christ in the Eucharist, thanksgiving for the gift of Redemption, intercession for mercy and pardon; and offering of the Precious Blood of Christ for the good of the Church;
4Via Sanguinis
The Via Sanguinis: a recently instituted pious devotion, practiced in many Christian communities whose anthropological and cultural roots are African. In this devotion, the faithful move from place to place, as in the Via Crucis, reliving the various moments in which Christ shed his blood for our salvation.
Read here the story of St. Maria de Mattias, who founded the Sisters Adorers of the Blood of Christ, a teaching order active in the United States, South Korea, and other places.