A grotto near Naples, in which dogs are suffocated. The deleterious vapour is carbonic acid air, which rises only about eighteen inches. A man, therefore, is not affected; but a dog forcibly-held in, or who cannot rise above it, is soon killed, unless taken out. He is recovered by plunging him in an adjoining lake.

Grotto del serpi. The grotto of the serpents, described by Kircher who visited it. It is near the village of Sassa, not very distant from Braccano, in Italy, filled with warm vapour, from some subterraneous apertures, without any apparent gaseous or other impregnation. Patients affected with lepra, elephantiasis, palsy, or gout, are said to be relieved by these vapours; and the relief is, in part, attributed to some serpents, which are not venomous, but which are numerous in this cavity, particularly in the spring, and are said to lick the diseased parts. The exuviae of serpents abound in the grotto, and are suspended on the trees, apparently to cherish the delusion; but the benefit is wholly derived from the warm water.