full-scale computer model,” the researcher said. “It’s a
work of art. The computer model has 1,000 million mesh
elements. Because the dog’s nose is so complicated, if
you didn’t have that level of detail you would not have
the fidelity of the internal surfaces required to get a good
understanding of how it works. The air passages are on
the order of a millimeter wide.”
The team learned that the canine nose has hundreds of
folds. As air is drawn in through the nostrils to the
lungs, some of that air is channeled off to pass over
these surfaces, covered with mucus membranes containing scent receptors.
“The dog’s olfactory surfaces look like scroll work,”
Settles said. “That’s how a dog has so much olfactory
surface area in such a relatively small head.”
He said the number of folds, or “turbinates,” where air
is circulated and olfaction can occur in a human is three,
but in a dog there are hundreds. Where a human may have
5 million scent receptors, a dog may have 200 million.
“Numbers have been used in the literature indicating the dog’s nose is thousands of times more sensitive
than that of a human,” he said.
The canine olfactory system also is more selective.
“Humans cannot detect a weak scent masked by a
strong one, like gasoline, but a dog can,” he said.
Settles’ team included Eric Paterson, a professor from
Penn State’s Applied Physics Laboratory, and Penn State
grad students Brent Craven and Mike Lawson. They ran
the computer model on a supercomputer for several days,
and it was able to show for the first time what the air flow
is doing in the dog’s nose. Lawson created the experimental model to test how well the computational model performed in mimicking and predicting the air flow.
For serious sniffing, dogs alter their breathing to
ensure the airflow uses the most of the olfactory capability. The alar fold, just inside their nostrils, functions
like a valve to move the air through the upper nasal
passages when inhaling, and pushing the air to agitate
odors when exhaling. Mucous-covered scent receptors
within the nose detect chemical changes, which then
are transmitted along olfactory nerves to the olfactory
bulb at the dog’s brain.
Odor molecules emanate from a source and become
more dispersed in the air the farther away from the
source. Dogs can detect a scent and follow it as the
smell becomes stronger, until they reach the source.
By watching the dynamics of the air during sniffing,
Settles and his team could see that dogs smell partly by
blowing, where they exhale and push air from their nostrils to stir up the air surrounding sources of odors and
the surrounding air and environment to find more smells.
Most animals, especially ones with a long nose, can
Master at Arms 1st Class Blake Soller leads Jake, his military
working dog, through training in narcotic detection at Naval
Base Ventura County, Calif., in September 2009.
smell food and pheromones, the scents given off by
other animals. Dogs have evolved to be able to sense a
range of chemicals.
Humans can be fooled by overpowering smells that
mask other odors, but not dogs.
“Dogs can detect a weak scent that humans can’t.
All that surface sensor area inside the dog’s nose acts
like a gas chromatograph, apparently able to separate
different scent components according to their chemical
properties,” Settles said.
With the proverbial fire hydrant, a dog can tell the
difference between the urine smells from multiple dogs.
“It can detect layers, and the subtle nuances of the
dogs that have been there. Dogs read these scent messages with their noses similarly to the way we read text
with our eyes,” Settles said.
With this basic phase of the research complete,
Settles is looking to the future.
“Our next goal, if funding is found, is to study the
intricate processes that occur in the mucus layer of the
dog’s nose as scent molecules absorb it from the air
and cross it in order to be detected by olfactory receptors,” he said. ■