Today, let's swim like fish. The
University of Houston's College of Engineering presents this series about the
machines that make our civilization run, and the people whose ingenuity created them.
So why can't you and I breath indefinitely under water the way
fish do. They need oxygen just as surely as we. And the waters of our lakes and oceans
contain plenty of it. I don't mean the oxygen that's bound up with hydrogen to make
H2O; I mean the free oxygen that's dissolved into water.
If you want to kill a fish, just put him in water that's been boiled for some time,
then cooled without exposing it to air. All the gases will've been driven out of
solution and carried away by steam bubbles. Cool that water, put a fish in it, and
(since fish are oxygen breathers) it'll suffocate.
So why is it that fish can breathe in water and we can't? And might that situation be
remedied for us? Well, let's look at fish gills. They include a feathery structure of
membranes that offer a large surface area to a great deal of water. As water passes
through them, dissolved oxygen flows into the membranes just as it flows into the
membranes of our lungs.
Now writer Michael LePage describes recent work in which experimenters have been building
artificial gills. And it's easier than we might think. A watertight box made from an
appropriate membrane is all we need. The gas inside the box will come into equilibrium
with the gas content of the water outside.
Unfortunately, while the mixture in the box will be life-sustaining, it has more carbon
dioxide and less oxygen than the air around us. It'll leave us woozy. Therefore, people
working on artificial gills are developing techniques for processing the gas that crosses
the membrane to make it more oxygen-rich. But, so far, their systems are much clumsier
than scuba gear.
A diver is still better off carrying an air tank. And another problem: Very little nitrogen
dissolves in water. Without it, pure oxygen becomes toxic at pressures thirty feet below the
surface. Even with an artificial gill, a diver would still need nitrogen.
So, is this a fool's game? Well, no, it isn't. Think about submarines. Gill membranes
not only acquire new oxygen; they also scrub out CO2. In the closed environment of a submarine,
nitrogen is preserved. Artificial gills, not for the passengers but for the submarine itself,
might be the wave of the future -- providing oxygen, not only to breathe, but to supply power
fuel cells as well.
We humans have always looked at animals and wondered why we're denied what they have. We finally
solved the problem of getting ourselves into the air a century ago. We did so, not by growing
wings, but by finally despairing of growing wings. We do not fly like birds; rather we build
machines that carry us beyond birds.
And we've always wanted to swim like fish. That goal has been more elusive. Perhaps we've just
come one step closer, now that we're thinking of taking our needed oxygen from the water, just
as fish themselves have long been able to do.
I'm John Lienhard, at the University of Houston,
where we're interested in the way inventive minds
work.
(Theme music)
M. LePage, Oceans of air. New Scientist, January 7-13, 2006, pp. 28-31.
For more on artificial gills, see:
http://www.crabbsac.org.uk/articles/A001.htm
or http://www.drtomorrow.com/lessons/lessons9/42.html
The gills of a prawn (see b).
(From A. Buckley, Life and Her Children. 1892.)
The Engines of Our Ingenuity is
Copyright © 1988-2005 by John H.
Lienhard.
