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The History of Diving: Why you owe Paul Bert and Dog DXXVIII a debt of gratitude for your deco stop

FROM the beginning of our scuba diving journey we are taught about the sport's forefathers whose early efforts defined decompression theory and made it possible for us to venture beneath the waves. Today I'm going to make a case for us to remember Paul Bert and, more precisely, the sacrifice made by his Dog DXXVIII.

I came across the unfortunate fate of canine subject DXXVIII when given chance to read a copy of Bert's classical work La Pression Barometrique while researching the book Between the Devil and the Deep. While not condoning animal testing, I think it is a worthy story for us to remember.

That nitrogen is known to be the culprit for so much that goes wrong with diving is thanks, in no small part to Canine DXXVIII. Slumped inside a cylindrical steel pressure cylinder, the small dog whimpered its last breath on June 18, 1875. Observing impassively through a small, 18mm thick glass porthole, notebook in hand, was French zoologist and physiologist, Paul Bert.

Born in Auxerre in 1833, Bert had become interested in the problems that low air pressure caused for mountain climbers and the new adventurers - balloonists. As a result of his research he began to look at the problems of dealing with increased pressure associated with deep sea diving and bridge-building caisson workers.

In order to build the footings for bridges, these men were working in pressurised boxes sunk onto river beds known as plenum pneumatic, or caissons. These boxes were an engineering triumph as they allowed workers easy access from the surface and the increased pressure inside kept the area dry. However, as the use grew, workers began to report a number of physical ailments upon returning to the surface, dizzy spells, shortness of breath, acute pain in their joints. These were similar to the symptoms reported by hard-hat divers of the day. This became known as maladie du caisson, or Caisson's Disease. During the construction of the Brooklyn Bridge between 1870 and 1883, three workers died and one in six of those who suffered were left with some form of permanent paralysis.

By the time the bridge was completed, Bert had discovered the cause of the sickness was nitrogen which had been absorbed into the body by the men while they were working under pressure. As part of his investigations, Bert exposed dogs to increased pressures and then rapidly decompressed them to see what happened. Dog DXXVIII was one of them.

In his classical work La Pression Barometrique (1878) he wrote: "Small dog. Taken in one hour to 10 atmospheres; stays there about 1 hour; decompressed in 3 minutes. The animal cannot get out of the apparatus; there are no other movements than those of respiration; constant cries of pain."

The dog later died. During a post-mortem examination, Bert found the heart full of frothy blood. A sample of the gas inside the blood found it was almost four-fifths nitrogen. Bert went on to explain that it was the increase in pressure which caused nitrogen to become dissolved in the bodies tissues and then the subsequent reduction in pressure caused the nitrogen to come out of solution and form bubbles.

Bert concluded that divers and caisson workers decompress slowly and at a constant rate “for they must not only allow time for the nitrogen of the blood to escape but also to allow the nitrogen of the tissues time to pass into the blood”. He also went on to suggest stopping divers halfway to the surface during decompression after a deep dive and as such was the first to suggest what are now known as deep stops.

So it is thanks to the research conducting by Paul Bert using dogs like DXXVIII that paved the way for the understanding we now have about decompression theory. I think it is time we remembered the canine for the enforced sacrifice it made.

If your French is any good, I strongly recommend you find a copy of La Pression Barometrique as it makes interesting reading. There will be more on Dog DXXVIII, Bert and other animals in the book.

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