From Aleteia:
One particular devotion in the Catholic Church connected to the Passion of Jesus Christ is the honoring of his Precious Blood. It is a recognition of Jesus’ sacrifice and how he spilled his blood for the salvation of humanity. Furthermore, this blood is made present through the gift of the Eucharist and is something we can consume at Mass, along with the body of Christ, under the appearance of bread and wine.
Over time the Church developed various feasts of the Precious Blood, but it wasn’t until the 19th century when a universal feast was established. During the First Italian War for Independence in 1849, Pope Pius IX went into exile to Gaeta. He went there with Don Giovanni Merlini, third superior general of the Fathers of the Most Precious Blood.