Why Dogs Can’t Stand ‘The Cave of Dogs’

In the west of Naples, Italy, is a large volcanic area called Phlegraean Fields filled with craters of old, extinguished volcanoes. Lying mostly underwater, the area is still volcanically active as evidenced by the numerous boiling pools of mud and fumaroles from which copious amount of steam can be seen rising at any time of day or night. Centuries ago, travellers who could afford to travel came to Naples to see the famous volcano that buried the Roman towns of Pompeii and Herculaneum under magma and ash. They also made a visit to Phlegraean Fields, where tour guides took them to a small cave called “Cave of Dogs”, or Grotta del Cane , for a gruesome little experiment. A guide shows a suffocated dog to two tourists at the Cave of Dogs near Naples. The cave’s entrance is a narrow opening on the side of a hill, that leads to a short corridor—about ten meters long—that slopes downward ending in a cavity. Inside this cavity is a fumarole that releases carbon dioxide, which being heavier than air settles at the bottom of the cavity forming a shallow lake about 30 centimeters deep. The carbon dioxide lake doesn’t affect people because their heads are well above its surface, but for something much shorter, such as a dog, the condition inside the cave can be fatal. Carbon dioxide is a normal component of air, and the low concentration at which it exists is harmless to humans and other living beings that breathe oxygen for survival. But as the concentration of carbon dioxide in air increases, it leads to serious physiological harm—a condition known as hypercapnia . Initially, carbon dioxide poisoning causes flushed skin, muscle twitches, elevated blood pressure, and reduced neural activity. Severe hypercapnia causes headache, lethargy, increased cardiac output, irregular heart beat, panic, disorientation, convulsions, loss of consciousness and finally death.