What actually takes place may be thus briefly described: in a silver reliquary, which in form and size somewhat suggests a small carriage lamp, two phials are enclosed. The lesser of these contains only traces of blood and need not concern us here. The larger, which is a little flagon-shaped flask four inches in height and about two and a quarter inches in diameter, is normally rather more than half full of a dark and solid mass, absolutely opaque when held up to the light, and showing no displacment when the reliquary is turned upside down. Both flasks seem to be so fixed in the lantern cavity of the reliquary by means of some hard gummy substance that they are hermetically sealed. Moreover, owing to the fact that the dark mass in the flask is protected by two thicknesses of glass it is presumably but little affected by the temperature of the surrounding air.
Eighteen times in each year, i.e. (1) on the Saturday before the first Sunday in May and the eight following days, (2) on the feast of St. Januarius (19 Sept.) and during the octave, and (3) on 16 December, a silver bust believed to contain the head of St. Januarius is exposed upon the altar, and the reliquary just described is brought out and held by the officiant in view of the assembly. Prayers are said by the people, begging that the miracle may take place, while a group of poor women, known as the "zie di San Gennaro" (aunts of St. Januarius), make themselves specially conspicuous by the fervour, and sometimes, when the miracle is delayed, by the extravagance, of their supplications.
The officiant usually holds the reliquary by its extremities, without touching the glass, and from time to time turns it upside down to note whether any movement is perceptible in the dark mass enclosed in the phial. After an interval of varying duration, usually not less than two minutes or more than an hour, the mass is gradually seen to detach itself from the sides of the phial, to become liquid and of a more or less ruby tint, and in some instances to froth and bubble up, increasing in volume. The officiant then announces, "Il miracolo é fatto", a Te Deum is sung, and the reliquary containing the liquefied blood is brought to the altar rail that the faithful may venerate it by kissing the containing vessel. Rarely has the liquefaction failed to take place in the expositions of May or September, but in that of 16 December the mass remains solid more frequently than not.
It is of course natural that those who are reluctant to admit the supernatural character of the phenomenon should regard the liquefaction as simply due to the effects of heat. There are, they urge, certain substances (e.g. a mixture of spermaceti and ether) which have a very low boiling point. The heat produced by the hands of the officiant, the pressing throng of spectators, the lights on the altar, and in particular the candle formerly held close to the reliquary to enable the people to see that the mass is opaque, combine to raise the temperature of the air sufficiently to melt the substance in the phial--a substance which is assumed to be blood, but which no one has ever analysed.
Further, ever since the early years of the eighteenth century, sceptical scientists, by using certain chemical preparations, have reconstructed the miracle with more or less of success; that is to say, they have been able to exhibit some red substance which, though at first apparently solid, melted after an interval without any direct application of heat. None the less, it may be said with absolute confidence that the theory of heat affords no adequate explanation of the phenomena observed.
For more than a century careful observations of the temperature of the air in the neighbourhood of the relic have been made on these occasions and the records have been kept. It is certain from the scientific memoirs of Professors Fergola, Punzo, and Sperindeo that there is no direct relation between the temperature, and the time and manner of the liquefaction. Often when the thermometer has stood at 77° Fahrenheit or even higher, liquefaction has been delayed for as much as twenty or even forty minutes, while on the other hand the contents of the phial have sometimes liquefied in considerably less time than this when the thermometer remained as low as 60 or 65 degrees.
Moreover, the heat theory by no means accounts for another more remarkable fact observed for quite two hundred years past. The mass in melting commonly increased in volume, but when it solidifies again it does not necessarily return to its original bulk. Sometimes the whole phial is seen to be occupied, at other times hardly more than half. This has led a Neapolitan scientist of modern times, Professor Albini, to suggest a new physical theory derived from observing the behaviour of a viscous fluid such as partly congealed honey. He conjectures that the unknown substance in the phial consists of some highly divided solid matter which is partly held in suspension by a disproportionately small quantity of liquid. When at rest, the liquid sinks to the bottom of the phial, while the solid particles form a sort of crust not easily displaced when the vessel is turned upside down. This cohesion is however overcome by repeated movements, such as those that the reliquary experiences when the moment of liquefaction is impatiently waited for. Further, such a viscous fluid easily cakes upon the walls of the containing vessel, and admits large air bubbles which cause the deceptive appearance of a change of volume.
Professor Albini claims to have reproduced all the phenomena with a compound made of powdered chocolate and the serum of milk. On the other hand, those who have studied closely the process of liquefaction of the contents of the phial declare that such an explanation is absolutely impossible. Moreover, there seem to be well-attested instances of liquefaction taking place both in the case of this and other similar relics of blood, when the reliquary has been standing by itself without any movement whatsoever.
Accordingly, the suggestion has also been made (see Di Pace, "Ipotesi scientifica sulla Liquefazione", etc., Naples, 1905) that the phenomenon is due to some form of psychic force. The concentration of thought and will of the expectant crowd and specially of the "aunts of St. Januarius" are held to be capable of producing a physical effect. Against this, however, must be set the fact that the liquefaction has sometimes taken place quite unexpectedly and in the presence of very few spectators.