nblinks

A little living gem from Alexander von Humboldt's turn-of-the-19th-century descriptions of what's now northeastern Venezuela:

Of all the productions on the coasts of Araya, that which the people consider as the most extraordinary, or we may say the most marvellous, is 'the stone of the eyes,' (piedra de los ojos.) This calcareous substance is a frequent subject of conversation: being, according to the natural philosophy of the natives, both a stone and an animal. It is found in the sand, where it is motionless; but if placed on a polished surface, for instance on a pewter or earthen plate, it moves when excited by lemon juice. If placed in the eye, the supposed animal turns on itself, and expels every other foreign substance that has been accidentally introduced. At the new salt-works, and at the village of Maniquarez, these stones of the eyes were offered to us by hundreds, and the natives were anxious to show us the experiment of the lemon juice. They even wished to put sand into our eyes, in order that we might ourselves try the efficacy of the remedy. It was easy to see that the stones are thin and porous opercula, which have formed part of small univalve shells. Their diameter varies from one to four lines. One of their two surfaces is plane, and the other convex. These calcareous opercula effervesce with lemon juice, and put themselves in motion in proportion as the carbonic acid is disengaged. By the effect of a similar reaction, loaves placed in an oven move sometimes on a horizontal plane; a phenomenon that has given occasion, in Europe, to the popular prejudice of enchanted ovens.