How about a visit to a place where dogs once fainted for tourists? This is the Grotta del Cane. It is also known as the Cave of Dogs. We are standing near Naples, Italy at this infamous site.
Grotta del Cane is a small cave. It is only about ten meters deep. The cave sits on the eastern side of the Phlegraean Fields. The cave’s name comes from a macabre practice. Guides once demonstrated the cave’s toxicity on dogs.
Let’s step back in time. Imagine wealthy travelers on the Grand Tour in the 17th and 18th centuries. They would visit the Grotta del Cane. Local guides would show off the cave’s carbon dioxide. They forced dogs into the cave. The dogs would suffocate in the fumes. Guides hoped to revive them in nearby Lake Agnano.
Carbon dioxide seeps into the cave from volcanic activity. It creates a high concentration of the gas. The gas is heavier than air. It accumulates in the lower parts of the cave. Dogs held inside would faint from carbon dioxide poisoning. Humans standing upright were generally unaffected.
The earliest mention of Grotta del Cane is from Pliny the Elder. He wrote about it in his Naturalis Historia around 77 AD. But the cave’s popularity soared during the Grand Tour era. Famous visitors included Goethe Alexandre Dumas and Mark Twain.
Mark Twain was eager to see the cave. He even wanted to suffocate a dog himself. He wrote about it in his book The Innocents Abroad. He said he wanted to time the dog’s suffering but he had no dog.
Athanasius Kircher a German scholar studied the cave in 1638. He described an experiment. A dog’s head was lowered into the cave. The dog tried to escape. Tied down it seemingly died. When thrown into the lake it revived.
Cornelis de Bruijn a Dutch traveler visited in 1677. He noted that a dog standing was unharmed. But if pressed down it would quickly weaken. He saw dogs revive in the nearby lake. He also noted the venom was only one foot high from the ground.
In 1877 a scientist examined the cave’s gas. Smoke from a torch fell to a layer of gas. The gas’s surface resembled water with undulations. Holding his head below the gas caused a prickling sensation on his eyes. He also noted the dogs got into such a nervous state that they had to be killed after three months.
Thankfully such cruelty ended in the 1870s. The nearby Lake Agnano became polluted. It was then drained. Tourism to the cave declined. The cave was even blocked to prevent access by children.
In 2001 Italian speleologists investigated the cave. Nine meters from the entrance the temperature was 52 degrees Celsius. The carbon dioxide concentration was 80 percent. Oxygen was negligible.
The Grotta del Cane was often described in science textbooks. It showed the density and toxicity of carbon dioxide. Today local groups have improved access to the cave. They offer guided tours but no dogs are allowed.