It is said that those eyes and tongues of serpents are only found by the Maltese when they dig into the earth, which is whitish throughout the island, or draw up stone, especially about the cave of St. Paul. This stone is so soft, that, like clay, it may be cut through with any sharp instrument, and made to receive easily different figures, for building the walls of their houses and ramparts; but, when it has been imbibed with a sufficient quantity of rain or well water, it changes into a flint that resists the cutting of the sharpest instrument: whence the houses that are built of it in the two cities, appear as hewn out of one solid rock, and become harder, the more they are exposed to the inclemencies of the weather. This hardness may, with good reason, be ascribed to the salt of nitre, which contracts a certain viscidity from the rain wherewith it is mixed, and which easily penetrates into these stones, because their substance is spongy and cretaceous, and adheres to the tongue as hartshorn.
It is in these stones that not only the eyes and tongues of serpents are found, but also their viscera and other parts: as lungs, liver, heart, spleen, ribs, and so resembling life, and with such natural colours, that one may well doubt whether they are the work of nature or art; the figure of the eyes and tongues is very different. Some are elliptic, but, for the greater part round: some represent an hemisphere, others a segment, others an hyperbola. The glossopetrae are naturally of a conic figure, representing acute, obtuse, regular, and irregular cones. They are also of different colours, especially the eyes; for some of them are of an ash-colour, others liver colour, some brown, others blackish; but these, as most rare, are most esteemed. Bracelets are frequently made of them and set in gold: some representing an entire eye with a white pupil, and these are the most beautiful. Several are likewise found of an orange colour.
The virtues attributed by the Maltese to those eyes and tongues, and to the white earth which is found in the island, particularly in St. Paul's cave, and which is kept for use by the apothecaries, as the American bole, are very singular; for they reckon them not only a preservative against all sorts of poison, and an efficacious remedy for those who have taken poison, but also good in a number of diseases. They are taken internally, infused in water, wine, or in any other convenient liquor; or let to lie for some hours in vessels made of the white earth; or the white earth is taken itself dissolved in those liquors. The eyes set as precious stones in rings, and so as to touch immediately the flesh, are worn by the inhabitants on the fingers; but the tongues are fastened about the arm, or suspended from the neck.