In Italy alone there are 190 blood samples of various saints that are venerated by the faithful as important religious relics. In a number of cases, these vials of clotted blood become liquefied in a paranormal manner, especially during religious ceremonies, thus exalting the sample from relic to a supernatural miracle.
Perhaps the most celebrated of such relics is the vial of blood said to be that of St. Januarius (c. 272–305), an early bishop of Benevento, who was beheaded during the persecutions of the Christians by Emperor Diocletian (245–316) in 305. Once or twice a year since 1389, St. Januarius' dried blood has liquefied in full view of the pilgrims who arrive to pay tribute to his memory in Naples.
The blood of St. Lorenzo (d. 258) rests in a small flask in the right wing of the church of St. Maria in Amaseno. Lorenzo was martyred on August 10, 258 under the order of the Emperor Valerian (d. 260), and although he was condemned to be burned to death on a grill, some of his blood was caught and preserved by his fellow Christians. Each year on the anniversary of his martyrdom, the vial is brought near the altar and locked in a glass cabinet. There, in full view of the assembled worshippers at St. Maria, the transformation of the centuries-old clotted blood to liquid occurs.
Psychical researcher Luigi Garlaschelli has proposed that a process called "thixotropy" might explain how the blood of St. Januarius might liquefy each year. Thixotropy "denotes the property of certain gels to liquefy when stirred or vibrated, and to solidify again when left to stand." It is Garlaschelli's theory that the very act of handling the relic during the religious ceremony, the motions of a priest repeatedly checking the progress of the blood in the vial, might well provide the necessary movement to prompt the liquefaction of the saint's blood.
But the investigator is cautious about applying his theory to explain the liquefied blood of St. Lorenzo, which is only moved once on August 10 from its place of safekeeping to the altar, or the large vial containing the blood of St. Panatleone, which becomes liquefied on July 27 and is never moved from its resting place behind a grating.
Garlaschelli speculates that the overall look of the substances in the vials, together with their observed properties of softening and liquefying when near the warming effect of altar candles and human touch, then returning to solid once removed from the warmth, suggest that the relics may consist of fats or waxes and an oil-soluble red dye. While the rational mind insists that the substance in the vials of the saints cannot possibly be blood, until church authorities permit scientists to withdraw actual specimens from the receptacles, the question remains a puzzle to scientists and a miracle of faith to believers.
Garlaschelli, Luigi, Ramacine, F. and S. Della Sala. "Working Bloody Miracles," Nature, Vol. 353, 1991, p. 507.
——. "A Miracle Diagnosis," Chemistry in Britain, Vol. 30, 1994, p. 123.