Venomous Exhalations

Photo of the descending floor of the cave

Photo of the descending floor of the cave

Dr Mead was fascinated by venom from the very start of his career. While at Leiden University, he took an interest in poisons and their anecdotes, and on his Grand Tour of Italy he was especially intrigued by a cave near Naples where he observed what he referred to as ‘venomous exhalations’. His observations caused the development of his thoughts on why air is so necessary to life.

The cave in question was the Grotta del Cane, found on the shore of Lake Agnano – a lake which fills the crater of the extinct Agnano volcano. In actual fact, it is not a cave, but a volcanic feature called a mofetta, or a fumarole – an aperture caused by the discharge of carbon dioxide. The Grotta is like a small corridor which slopes down into the ground, and it is this sloping floor which gives it its name.

Carbon dioxide is heavier than oxygen, so a shallow lake of noxious gas forms at the bottom of the ‘cave’. People walking inside will not notice any difference because their heads will be above the lake of carbon dioxide. However, smaller animals such as dogs will soon suffocate due to the lack of oxygen.

Etching of Lake Agnano. Three men take a dog into the grotto to demonstrate the asphyxiation of the dog. On the left, two local men suspend an asphyxiated dog in the lake in order to revive it: two tourists attend the experiment © Wellcome Library, London

Etching of Lake Agnano. Three men take a dog into the grotto to demonstrate the asphyxiation of the dog. On the left, two local men suspend an asphyxiated dog in the lake in order to revive it: two tourists attend the experiment © Wellcome Library, London

Visits to the Grotta del Cane became extremely popular with the tourists who flooded into Italy in the eighteenth and nineteenth centuries. So-called guides would demonstrate the deadly effects of the cave by walking dogs inside. When the animals keeled over the guides would take them outside to revive them or throw them into the lake to wake them up. Johann Wolfgang von Goethe, in his Italian Journey (Italienische Reise – published 1816–17), writes about the cave, as does Alexandre Dumas (writing in 1841-1843), who notes this gruesome attraction.

Mead visited the cave in 1695 on his tour of Italy and was extremely interested in the effects of these particular ‘venomous exhalations’. He wrote:

from the Ground arises a thin, subtle, warm Fume, visible enough to a discerning Eye, which does not spring up in little parcels here and there, but is one continued Stream, covering the whole Surface of the bottom of the cave; and has this remarkable difference from common Vapours, that it does not, like Smoak, disperse itself into the Air, but quickly after its rise falls back again, and returns to the Earth.

Mead notes that experiments are often made with dogs in order to demonstrate the deadliness of the fumes, but also mentions other more horrible tests:

Charles the Eighth of France prov’d it with an Ass; and two slaves put into it by order of D. Pietro di Toledo, Viceroy of Naples, with their Heads held down to the Earth, were both kill’d.

A couple of tourists are shown a demonstration of the cave's lethal effects

A couple of tourists are shown a demonstration of the cave’s lethal effects. The guide holds up the dog which has already passed out.

In the text, Mead dismisses the possibility of the fumes being a real poison seeing as any animal that comes out in time will quickly recover. He therefore theorises that “the blood may be supplied with something from the air, whatever it be, necessary to life”. Although Mead would not have known about the existence of oxygen, he understood that the air contains something crucial to life which is then transmitted into the blood through the lungs.

What Mead didn’t know was that there was quite a different mystery to be found at the end of the corridor…

Diagram of the sloping corridor © Rosario Varriale

Diagram of the sloping corridor © Rosario Varriale

In 2001 Rosario Varriale, an expert in caves from the Centre for Speleological Research of Naples, cleared out the interior of the corridor (equipped with an oxygen tank) and discovered a chamber measuring thirty-two square metres at the bottom. The chamber was partially blocked-off, with a stepped “walkway” around the sides, and traces of cocciopesto (pottery fragments mixed with lime or sand used to make plaster or mortar) on the floor. Up in one of the corners of the room was an opening that must once have served as a sort of sky-light. The temperature in the chamber reached as high as 60ºC.

The chamber found at the bottom © Rosario Varriale

The chamber found at the bottom © Rosario Varriale

One theory is that the grotto was dug out to be used as a steam room or thermal bath in the 3rd-2nd century BC. There is a complex of Roman baths from the time of Hadrian, (117-138 AD), nearby. Presumably at this time the carbon dioxide had not yet broken into the chamber, or was somehow kept from building up inside it.

If Mead had known it would have been a perfect mix of antiquities and poisons to match his interests. However, the fumes prevented even him from entering.

 

The Foundling Museum’s current exhibition, The Generous Georgian: Dr Richard Mead, reunites key objects from Mead’s life and collection, including a number of his medical treatises on a broad range of subjects from poisons to the plague.

 

The next post will be an interview with Dr Mead, discussing his experiments with poisons.

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2 thoughts on “Venomous Exhalations

  1. Pingback: Poisonous Experiments | the generous georgian: dr richard mead

  2. Pingback: Whewell’s Gazette: Vol. #23 | Whewell's Ghost

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