The Grotto Del Cane (of the Dog)

A favorite excursion from Naples is to the Grotto del Cane, which is a celebrated cavern at the base of a hill. It is closed by a door and guarded by a keeper. The interest here centres in the fact of the specific gravity of carbonic acid gas. Pliny describes the cave as the "breathing place of Pluto." It constantly exhales volumes of vapor mixed with carbonic acid gas, which latter is so heavy that it accumulates on the floor and runs over the doorstep. The grotto was once used as a place for the execution of Turkish captives, who were shut within its walls and left to perish. It is named from the cruel experiments performed here for the amusement of visitors.

A dog is thrust down upon the floor and expires in a few seconds, but upon being dragged into the open air it can be revived. Very many scientific experiments have been made here, which render the cave celebrated. Addison found that a pistol could not be fired in the bottom of this cave. Of course the gas instantly extinguishes a lighted taper of any kind. The upper part of the grotto is free from gas, so that it is perfectly safe for travellers or scientific explorers to enter, so long as they do not fall to the floor.