Cave of Dogs

[1] It may have been known to Pliny the Elder, who, in his Natural History Chapter 95[4] (written 77–79 AD), mentions a location near Pozzuoli where animals die from poisonous fumes.

As a result, small animals such as dogs held inside the cave suffered carbon dioxide poisoning, while a standing human was not affected.

[6] Tourists who came to see this attraction included Sir Thomas Browne,[7] Richard Mead,[8] Goethe, John Evelyn, Montesquieu,[9] Alexandre Dumas père, and Mark Twain.

He wrote: Next, one comes close to the road by a small cave called Grotta del Cani, which is very venomous, to the extent that if a dog is kept inside, it dies very quickly.

However, if one forcibly presses it down, it quickly loses its strength after great struggling and desperate resistance, and would undoubtedly die in an instant if not promptly picked up and thrown into a nearby water or lake, where it immediately recovers but with some dizziness, walking like a human who is completely drunk.

[11] Some tourists including Washington Irving (1804),[12] Percy Bysshe and Mary Shelley (1818)[13] and Ralph Waldo Emerson (1833),[14] objecting to the cruelty, refused to pay for the experiment to be performed on the dog.

While in the cave, also, the dog was able to stand, but when carried and set on its feet outside in the fresh air, it fell, and lay struggling as if in paroxysms of suffocation, but recovered in two or three minutes.

Illustration of the cave from a 1865 science book. A guide shows a suffocated dog to a man and woman tourist.
Lake Agnano and the Cave of Dogs depicted in an etching by the Sieur de Rogissart , 1706
The principle of the Cave of Dogs sketched by Alfred Swaine Taylor , 1832. The carbon dioxide (marked with a darker color) gathers in the lower part of the cave.